Recent Advances in Iga Nephropathy

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RECENT ADVANCES IN

IgA NEPHROPATHY

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RECENT ADVANCES IN

IgA NEPHROPATHY

Editor

Kar Neng Lai University of Hong Kong Hong Kong China

World Scientific NEW JERSEY

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LONDON

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SINGAPORE

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BEIJING

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SHANGHAI

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HONG KONG

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TA I P E I

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CHENNAI

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Published by World Scientific Publishing Co. Pte. Ltd. 5 Toh Tuck Link, Singapore 596224 USA office: 27 Warren Street, Suite 401-402, Hackensack, NJ 07601 UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE

British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library.

RECENT ADVANCES IN IGA NEPHROPATHY Copyright © 2009 by World Scientific Publishing Co. Pte. Ltd. All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the Publisher.

For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher.

ISBN-13 978-981-283-586-4 ISBN-10 981-283-586-5

Typeset by Stallion Press Email: [email protected]

Printed in Singapore.

JQuek - Recent Advances in IGA Nephropathy.pmd 1

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This book is dedicated to my wife Diana and my children Andrew, Christopher and Sarah — the most important people in my life.

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Contents

xi

Contributors

xix

Preface 1

IgA Nephropathy: Discovery of a Distinct Glomerular Disorder

1

Keng Thye Woo, Richard J. Glassock and Kar Neng Lai 2

Epidemiology and Ancestral Difference Francesco P. Schena and Francesco Pesce

3

Genetic Contribution to IgA Nephropathy Patrick H. Maxwell and Yiming Wang

21

4

Histopathology, Immunofluorescence and Ultrastructural Examination Fernand M. Lai

37

5

Tubulointerstitial Injury in IgA Nephropathy Joris J. Roelofs and Sandrine Florquin

55

6

Podocyte Pathology Kar Neng Lai and Joseph C. K. Leung

69

vii

9

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viii ✦ Contents

7

Clinicopathologic Findings Bruce A. Julian and Robert J. Wyatt

83

8

Clinical Course of Primary IgA Nephropathy Franc ois C. Berthoux and Hesham Mohey

107

9

Special Clinical Syndromes Judit Nagy and Tibor Kovács

121

10

IgA Nephropathy in Children Ronald J. Hogg

139

11

Recurrent IgA Nephropathy in Transplant Bo Ying Choy and Kar Neng Lai

149

12

IgA Molecule Jan-Willem Eijgenraam, Mahamed R. Daha and Cees van Kooten

161

13

IgA Immune-Complex Jan Novak and Jiri Mestecky

177

14

B and T Lymphocytes Abdalla Rifai and Ann Chen

193

15

IgA Receptors and Mesangial IgA Deposition Ivan C. Moura and Renato C. Monteiro

211

16

Antigen-Dependent Mechanism of IgA Nephropathy Yasuhiko Tomino and Yoshio Shimizu

225

17

Complement Activation Sydney C. W. Tang and Kar Neng Lai

237

18

Cytokines and Growth Factors Jürgen Floege and Tammo Ostendorf

243

19

Monocytes and Macrophages Yohei Ikezumi and David J. Nikolic-Paterson

267

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Contents ✦ ix

20

Renin-Angiotensin System Kar Neng Lai and Joseph C. K. Leung

289

21

Corticosteroids Claudio Pozzi and Lucia Del Vecchio

309

22

Treatment for IgA Nephropathy: Renin-Angiotensin Blockade Rosanna Coppo and Licia Peruzzi

321

23

Other Immunomodulatory Agents Sydney C. W. Tang and Kar Neng Lai

339

24

Other Non-Immunomodulatory Agents Jonathan Barratt and John Feehally

349

25

Treatment of IgA Nephropathy: Tonsillectomy Osamu Hotta

369

26

Experimental Model of IgA Nephropathy Yusuke Suzuki and Yasuhiko Tomino

387

27

Future Prospects for IgA Nephropathy Richard J. Glassock

403

Index

413

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Contributors

Jonathan Barratt, MD, FRCP John Walls Renal Unit Leicester General Hospital University of Leicester Leicester, LE4 5PW United Kingdom François C. Berthoux, MD Service de Néphrologie Dialyse et Transplantation Rénale CHU de Saint-Etienne 42055 Saint-Etienne Cédex 2 France Ann Chen, MD Department of Pathology Tri-Service General Hospital National Defense Medical Center No. 325, Sec. 2, Cheng-Gung Road Taipei, Taiwan Bo Ying Choy, MBBS, FRCP Department of Medicine University of Hong Kong Queen Mary Hospital Hong Kong xi

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xii ✦ Contributors

Rosanna Coppo, MD Nephrology, Dialysis and Transplantation Unit Regina Margherita Hospital University of Turin 10127 Torino, Italy Mahamed R. Daha, PhD Department of Nephrology Leiden University Medical Center Albinusdreef 2, 2333 ZA Leiden The Netherlands Lucia Del Vecchio, MD Department of Nephrology, Dialysis, and Renal Transplant “A. Manzoni” Hospital Lecco, Italy Jan-Willem Eijgenraam, MD, PhD Department of Nephrology Leiden University Medical Center Albinusdreef 2, 2333 ZA Leiden The Netherlands John Feehally, MD, FRCP John Walls Renal Unit Leicester General Hospital University of Leicester Leicester, LE4 5PW United Kingdom Jürgen Floege, MD Division of Nephrology and Immunology University of Aachen RWTH Aachen Germany

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Contributors ✦ xiii

Sandrine Florquin, MD Department of Pathology Academic Medical Center P. O. Box 22660 NL-1100 DD Amsterdam The Netherlands Richard J. Glassock, MD, MACP Professor Emeritus, Department of Medicine The David Geffen School of Medicine at UCLA Los Angeles, CA 90095, USA Ronald J. Hogg, MD Department of Pediatrics, Division of Pediatric Nephrology Texas A&M Health Science Center College of Medicine The Children’s Hospital at Scott & White 2401 South 31st Street Temple, TX 76508, USA Osamu Hotta, MD Department of Nephrology Sendai Shakaihoken Hospital Sendai, Japan Yohei Ikezumi, MD Department of Pediatrics Niigata University Medical and Dental Hospital Niigata, Japan Bruce A. Julian, MD Division of Nephrology Departments of Medicine, Surgery and Microbiology University of Alabama at Birmingham Birmingham, AL 35924, USA

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xiv ✦ Contributors

Tibor Kovács, MD, PhD Second Department of Medicine and Nephrological Center University of Pécs H-7624 Pécs, Pacsirta u.1 Hungary Fernand M. Lai, MD, FRCPA Department of Anatomical and Cellular Pathology Prince of Wales Hospital Chinese University of Hong Kong Hong Kong Kar Neng Lai, MD, DSc, FRCPath, FRCP, FRACP Department of Medicine University of Hong Kong Queen Mary Hospital Hong Kong Joseph C. K. Leung, PhD Department of Medicine University of Hong Kong Queen Mary Hospital Hong Kong Patrick H. Maxwell, MBBS, DPhil, FRCP Division of Medicine Rayne Institute University College London London, WC1E 6JJ United Kingdom Jiri Mestecky, MD, PhD Department of Microbiology University of Alabama at Birmingham 845 19th Street S, BBRB 757 Birmingham, AL 35294, USA

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Contributors ✦ xv

Ivan C. Moura, PhD Inserm U699 “Renal Immunopathology, Receptors and Inflammation” Bichat Medical School — University of Paris 7 16, rue Henri Huchard 75018 Paris cedex 18 France Hesham Mohey, MD Service de Néphrologie Dialyse et Transplantation Rénale CHU de Saint-Etienne 42055 Saint-Etienne Cédex 2 France Renato C. Monteiro, MD, PhD Inserm U699 “Renal Immunopathology, Receptors and Inflammation” Bichat Medical School — University of Paris 7 16, rue Henri Huchard 75018 Paris cedex 18 France Judit Nagy, MD, DSc Second Department of Medicine and Nephrological Center University of Pécs H-7624 Pécs, Pacsirta u.1 Hungary David J. Nikolic-Paterson, PhD Department of Nephrology Monash Medical Centre Clayton Road, Clayton Victoria 3168, Australia Jan Novak, PhD Department of Microbiology University of Alabama at Birmingham 845 19th Street S, BBRB 734 Birmingham, AL 35294, USA

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xvi ✦ Contributors

Tammo Ostendorf, PhD Division of Nephrology and Immunology University of Aachen RWTH Aachen Germany Licia Peruzzi, MD Nephrology, Dialysis and Transplantation Unit Regina Margherita Hospital University of Turin 10127 Torino, Italy Francesco Pesce, MD Renal, Dialysis and Transplant Unit Department of Emergency and Organ Transplant University of Bari Policlinico Piazza G. Cesare 11 70124 Bari, Italy Claudio Pozzi, MD Department of Nephrology and Dialysis “E. Bassini” Hospital Cinisello Balsamo (MI), Italy Abdalla Rifai, PhD Department of Pathology and Laboratory Medicine Lifespan Academic Medical Center The Warren Alpert Medical School of Brown University Providence, RI 02903, USA Joris J. Roelofs, MD Department of Pathology Academic Medical Center P. O. Box 22660 NL-1100 DD Amsterdam The Netherlands

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Contributors ✦ xvii

Francesco P. Schena, MD Renal, Dialysis and Transplant Unit Department of Emergency and Organ Transplant University of Bari Policlinico Piazza G. Cesare 11 70124 Bari, Italy Yoshio Shimizu, MD Division of Nephrology Department of Internal Medicine Juntendo University School of Medicine Tokyo, Japan Yusuke Suzuki, MD, PhD Division of Nephrology Department of Internal Medicine Juntendo University School of Medicine Tokyo, Japan Sydney C. W. Tang, MD, PhD Department of Medicine University of Hong Kong Queen Mary Hospital Hong Kong Yasuhiko Tomino, MD Division of Nephrology Department of Internal Medicine Juntendo University School of Medicine Tokyo, Japan Cees van Kooten, MD, PhD Department of Nephrology Leiden University Medical Center Albinusdreef 2, 2333 ZA Leiden The Netherlands

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xviii ✦ Contributors

Yiming Wang, MD, PhD Department of Medical Genetics Zhongshan Medical College 74 Zhongshan Road Second Guangzhou 510089, P. R. China Keng Thye Woo, MD, FRACP Department of Renal Medicine Singapore General Hospital Outram Road Singapore 169608 Robert J. Wyatt, MD, MS Department of Pediatrics University of Tennessee Health Science Center Memphis, TN 38105, USA

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Preface

It is almost 40 years since Dr. Jean Berger first described primary IgA nephropathy as a new disease entity. We are now fully aware that IgA nephropathy is one of the most common forms of chronic glomerulonephritis in the world. It is also recognized that this disease is the most frequent cause of end-stage renal failure despite the kidney being an innocent bystander with primary pathogenetic defect in the IgA molecule itself. Dr. Anthony Clarkson had emphasized that IgA nephropathy was a syndrome of uniform morphology, diverse clinical features and uncertain prognosis. The exact pathogenesis of IgA nephropathy is still obscure and specific treatment is not yet available. Efforts by many investigators around the world have gradually elucidated various aspects of the pathogenesis and treatment of this disease. This unique volume provides a comprehensive overview of the advances in this disease over the last ten years. The volume covers the genetics, epidemiology, clinicopathological features, pathogenesis, prognostic mechanisms, and treatment of this unique disease. Twenty-seven chapters are written by 43 contributors from 13 countries. These contributors have been providing forefront scientific findings of this disease to the scientific community in the last 20 years. They have authored 17.5% of all 5535 scientific papers on IgA nephropathy in different languages listed on PubMed at October 2008. Such an expansive wealth of experience is concisely summarized in this unique volume.

xix

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xx ✦ Preface

My sincere thanks go to Professor Richard J. Glassock, who discussed with me the editorial policy of this book. I owe to my many patients whose diseases have provided the most important insights and to the late Dr. Yu Chiu Kwong for his support of my research. Kar Neng LAI, MD, DSc, FRCP, FRACP, FRCPath Yu Chiu Kwong Chair of Medicine University of Hong Kong October 2008

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Chapter 1

IgA Nephropathy: Discovery of a Distinct Glomerular Disorder Keng Thye Woo, Richard J. Glassock and Kar Neng Lai

Introduction IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis in the developed world and it is an important cause of end stage kidney failure.1,2 Epidemiologic studies have shown that IgAN is nearly universally distributed around the world but the frequency with which it is diagnosed varies, mostly according to local policies regarding the indications for renal biopsy. Prevalence appears highest in Asia (Singapore, Japan, and Hong Kong), Australia, Finland, and southern Europe (20% to 40% of cases of primary glomerulonephritis). In the United Kingdom, Canada, and the United States, prevalence rates are much lower (reviewed by Schena3). This chapter will focus on the early events which preceded and surrounded the discovery of IgAN by Berger and Hinglais more than four decades ago.

History of IgA Nephropathy (Berger’s Disease) It was the use of the techniques of immunohistochemistry and renal biopsy which led Berger to discover IgAN. The idea of using fluorescentlabeled specific antibodies to detect proteins in tissue was introduced by Coons and Kaplan4 in 1950 and was first used for evaluation of disease 1

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2 ✦ K. T. Woo, R. J. Glassock & K. N. Lai

renal tissue by Mellors and Ortega5 in 1957. Percutaneous renal biopsy was initially described as a technique to diagnose kidney disease by Iverson and Brun in 1951.6 By 1960, there were still only a relatively few sites where percutaneous renal biopsies were performed and even fewer laboratories skilled in the use of the immunofluorescent technique and the antisera used were of poor specificity. In 1963, antibodies against class specific epitopes of the immunoglobulin light chains became commercially available so IgG, IgA and IgM could be identified separately. Tomasi et al.7 had discovered the IgA immune system in 1965. Thus two techniques, immunofluorescent tagging of antibodies to detect antigens in tissues and percutaneous renal biopsy, along the discovery of an new immunoglobulin present in serum and in tissue secretions (IgA) all collided to prepare the way for the seminal observations, beginning in 1967 of Jean Berger and Nicole Hinglais at the Necker Hospital in Paris, France concerning a new entity they subsequently called mesangial IgA/IgG deposition. They described their novel observations in a brief paper published in 1968 which described predominant IgA mesangial deposition in some renal biopsies where the immunostaining of IgA strongly outshone the IgG reagent. This was the birth of IgA nephropathy, also subsequently called Berger’s disease.8 In the following year in 1969, Berger published another paper “IgA glomerular deposits in renal disease” in the Transplantation Proceedings.9 This was a new journal in its first year. Fifty-five patients with various forms of glomerular morphology were described, mostly “focal glomerulonephritis.” These patients had minor proteinuria, but all had microscopic hematuria, of whom 22 had one or more bouts of gross hematuria. It was also already known then that IgA could also be found in patients with nephritis associated with Henoch-Schonlein purpura as well as lupus nephritis. The nephrology world was still sceptical about the “new disease entity.” In 1972, Levy and colleagues10 used in print for the first time the term “Berger’s Disease.” It was recorded that Jean Berger was somewhat embarrassed, as one knows he is indeed a very modest man, following appearance of this paper in the US, the UK, the Netherlands, Japan and Australia.11 By 1975, “Berger’s Disease” became an established glomerular entity: a condition with moderate proliferative glomerular changes, usually mesangial but often focal or segmental in distribution; associated with microscopic hematuria and about 15% to 20% with macroscopic hematuria. Serum IgA levels were also shown to be elevated in some patients. It was a slowly progressive renal disease with increasing proteinuria, hypertension and renal failure in ~30% of

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IgA Nephropathy: Discovery of a Distinct Glomerular Disorder ✦ 3

Table 1.1

Different nomenclature of IgA nephropathy.

Nephropathy with mesangial IgA-IgG deposits Les glomerulopathies primitives a depots mesangiaux d’IgA et d’IgG Diffuse intra- und extrakapillare Glomerulonephritis mit IgA-Depots IgA-IgG-Nephropathie Glomerulites a depots d’IgA diffuse dan le mesangium IgA-associated glomerulonephritis IgA nephropathy IgA-IgG deposits nephritis Immunoglobulin A glomerulonephritis Primary glomerulonephritis with mesangial deposits of IgA Benign hematuria-loin pain syndrome

patient over 25–30 years. The different nomenclature of “Berger’s Disease” is shown in Table 1.1. When such patients were transplanted, Berger showed that about 50% had a recurrence, though not all grafts failed because of recurrent diease.9

First Description of the Broader Clinical Features of “Berger’s Disease” Clarkson et al.,12 in an impressive collection of cases with “Berger’s Disease” emphasized that “Berger’s Disease” was a syndrome of uniform morphology, diverse clinical features and uncertain prognosis. It is now fully recognized that Berger’s Disease (henceforth called IgA nephropathy) is not always a benign disease. It has a cumulative renal survival of 89% after five years, 81% after ten years and 65% after 20 years.13,14 The data showed that renal deterioration in IgAN is generally slow and progressive over a long period of time (average: 7.7 years). The unfavorable long-term prognostic indices are proteinuria of more than 1 g/day, hypertension, glomerulosclerosis exceeding 20%, presence of crescents, and medial hyperplasia of blood vessels on renal biopsy. A smaller group of patients run a more rapid clinical course progressing to end-stage renal failure within a few years, in which severe uncontrolled hypertension seems to be the major adverse factor. As in the time of Berger, the cause remains unknown in the majority of IgAN. However, cases of familial IgAN and secondary IgAN have been reported and these have provided insights into underlying genetic and environmental triggers for this common glomerular disease.

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Secondary IgAN is seen most commonly in patients with liver disease or mucosal inflammation, in particular affecting the gastrointestinal tract. A number of dietary and microbial antigens have been identified in circulating IgA immune complexes and mesangial IgA deposits, suggesting that environmental factors may play a role in the pathogenesis of IgAN.15 Whether these reports represent chance associations or genuine shared pathophysiology remain to be confirmed.

The Recognition of Disease Progression and Proteinuria At the time of its discovery, IgAN was believed to be a “benign” disorder. We now recognize that the majority of cases will progress to renal failure although at a widely varying rate. A small subset of patients with heavy proteinuria behaves clinically like minimal change disease. Their proteinuria responds to steroid and this subset was recognized as “an overlapping syndrome of IgA nephropathy and lipoid nephrosis.”16 Otherwise, severe nephrotic-range proteinuria is not common in IgAN, but nephrotic-range proteinuria in the absence of minimal change disease is associated with poor prognosis.

Evolution of Beliefs Regarding Treatment of IgAN Initially, IgAN was not thought to require any treatment. However, upon recognition that progression to renal failure was not uncommon, interest in attempting therapy become of significant importance. However, early attempts were reported mainly as anecdotes, small prospective, uncontrolled trials or retrospective observational analyses. This, whether truly beneficial and safe forms of therapy for IgAN existed was quite uncertain. The paucity of controlled clinical trials of therapy for IgAN during the past three decades contrasts with the number of recent reviews, illustrating frustrations in obtaining new, reliable long-term data on treatment for IgAN. Scrutiny and evaluation of other regimens can only be good for patients, but current recommendations are polarized and sometimes changeable, supporting or denying use of corticosteroids when proteinuria exceeds 1 g/24 h. The quality of

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randomized, controlled trials is substantially influenced by design parameters, so retrospective interpretation using a mathematically insufficient approach is a likely source of discrepancy between reviews. Recent commentaries address how disparate opinion may have risen and quantify existing data to balance recommendations.17,18 In sum, the paucity of good clinical trials highlights the remaining uncertainty persisting from the early 1970s concerning what is best treatment and for how long must treatment be continued. History has taught us that good clinical trials are difficult to conduct in IgAN because of the slow progressive nature of the disease, diverse clinical features, different biopsy criteria for determining prognosis, and selection of end-points.

Conclusion It is now four decades since Berger’s observation and description of this distinct clinico-pathological entity first called Berger’s Disease and now called IgA nephropathy. The coalescence of immunohistochemistry, percutaneous renal biopsy and discovery of the IgA molecule in 1950–1965 set the stage for this discovery. We now know that IgAN is characterized immunologically by the presence of IgA immune complexes deposition in the mesangium in the clinical setting of diverse clinical features, but primarily asymptomatic hematuria and proteinuria. Histologically, most patients have a diffuse mesangial proliferative glomerulonephritis, whilst others have focal proliferative lesions and a very small minority develop acute renal failure with crescents as in “malignant” lgAN. We now recognize, not well understood in the initial years following the discovery of IgAN, that in the majority of patients, IgAN is a smouldering disease of a slowly progressive nature. Up to the present, there is no universally agreed-upon definitive therapy for IgAN, though reninangiotensin system blockade can slow the progression to end stage renal failure.19 Ever since Berger, investigators in the field of IgAN have pursued the underlying mechanisms responsible for the disease with a view to seeking a cure, yet the gap between the bench and the patient’s bedside does not seem to be closing very rapidly. Slow progress has been made, particularly in the understanding of the abnormalities of the IgA molecule itself in subjects with IgAN (reviewed in Chapter 12). Seekers of the Holy Grail or the final chapter of the IgAN story which began in

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Paris so many years ago will have to continue to persevere and hopefully one day harness a solution for the commonest form of primary glomerulonephritis worldwide.

References 1. D’Amico G. (2004) Natural history of idiopathic IgA nephropathy and factors mediative of disease outcome. Semin Nephrol 24: 179–196. 2. Woo KT, Lau YK. (2003) Factors associated with progression of IgA nephropathy. Clin Nephrol 59: 481–482. 3. Schena FP. (1990) A retrospective analysis of the natural history of primary IgA nephropathy worldwide. Am J Med 89: 209–215. 4. Coons AH, Kaplan MH. (1950) Localization of antigen in tissue cells; improvements in a method for the detection of antigen by means of fluorescent antibody. J Exp Med 91: 1–13. 5. Mellors RC, Ortega LG, Holman HR. (1957) Role of gamma globulins in the renal lesions of systemic lupus erythematosus and chronic membranous glomerulonephritis, with an observation on the lupus erythematosus cell reaction. J Exp Med 106: 191–201. 6. Iverson P, Brun C. (1951) Aspiration biopsy of the kidney. Am J Med 11: 324–330. 7. Tomasi TB Jr, Tan EM, Solomon A, Prendergast RA. (1965) Characteristics of an immune system common to certain external secretions. J Exp Med 121: 101–124. 8. Berger J, Hinglais N. (1968) Les depots intercapillaires d’IgA-IgG. J Urol Nephrol 74: 694–695. 9. Berger J. (1969) IgA glomerular deposits in renal disease. Transplant Proc 1: 939–944. 10. Levy M, Beaufils H, Gubler MC, Habib R. (1972) Idiopathic recurrent macroscopic hematuria and mesangial IgA-IgG deposits in children (Berger’s disease). Clin Nephrol 1: 63–69. 11. Cameron JS. History of Berger’s Disease Before Berger. The International IgA Nephropathy Network: http://www.iga-world.org/bergercameron.htm. 12. Clarkson AR, Seymour AE, Thompson AJ, et al. (1977) IgA nephropathy: a syndrome of uniform morphology, diverse clinical features and uncertain prognosis. Clin Nephrol 8: 459–471. 13. Woo KT, Edmondson RPS, Wu AYT, et al. (1986) The natural history of IgA nephritis in Singapore. Clin Nephrol 25: 15–21. 14. Woo KT, Lau YK, Choong HL, et al. (2002) IgA nephropathy: effect of clinical indices, ACEI/ATRA therapy and ACE gene polymorphism on disease progression. Nephrology 7: S166–S172.

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15. Pouria S, Baratt J. (2008) Secondary IgA nephropathy. Semin Nephrol 28: 27–37. 16. Lai KN, Lai FM, Chan KW, et al. (1986) An overlapping syndrome of IgA nephropathy and lipoid nephrosis. Am J Clin Pathol 86: 716–723. 17. Ballardie FW. (2007) Quantitative appraisal of treatment options for IgA nephropathy. J Am Soc Nephrol 18: 2806–2809. 18. Tumlin JA, Madaio MP, Hennigar R. (2007) Idiopathic IgA nephropathy: pathogenesis, histopathology, and therapeutic options. Clin Am J Nephrol 2: 1054–1061. 19. Woo KT, Lau YK, Wong KS, Chiang GSC. (2000) ACEI/ATRA therapy decreases proteinuria by improving glomerular permselectivity in IgA nephritis. Kidney Int 58: 2485–2491.

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Chapter 2

Epidemiology and Ancestral Difference Francesco P. Schena and Francesco Pesce

Introduction In 1988 Levy and Berger outlining the “Worldwide perspective of IgA nephropathy” suggested that the apparent geographic variations in the percentage of this glomerulonephritis in kidney biopsy specimens could reflect different clinical policies for diagnostic tests more than a real ancestral difference.1 Later, abnormal deposition of deglycosylated IgA1 was reported in kidneys of the patients and today the disease is called IgA1-Nephropathy (MIM 161950) or more commonly, IgA nephropathy (IgAN). IgA deposits are also present in 4%–16% of normal, healthy adults, living and cadaveric donors. Thus, from the epidemiological perspective, the biopsy-proven IgAN cases represent a very small fraction of the total individuals with disease in the population as a whole.2,3 The systematic screening of urines could have influenced the higher prevalence reported both in Japan and in Singapore, the rare detection of IgAN in blacks either from the United States or from Africa was to be ascribed to the infrequent performance of biopsies in African patients with only microscopic hematuria and the frequent absence of immunofluorescence applied to renal biopsy.4,5 While on one hand they were quite attentive to this primary aspect, they also got the hint that ancestral differences could suggest a possible role of genetic factors in the etiology of IgAN. This field has been widely tracked in the last few years leading to partial answers to the primary question but also setting interesting milestones throughout its course. 9

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10 ✦ F. P. Schena & F. Pesce

The finding of familial aggregation of IgAN has contributed to better define the genetic features of the disease in definite ancestral groups (refer to Chapter 3). The clinical onset of IgAN is usually found in the second and third decade of life but may occur at any age. Males are affected from twofold, in Japan, to six-fold more than females as reported in Europe and in the United States. The disease is more frequent in Whites and Asians than in Blacks from United States and South Africa, but the explanation of this difference is still unknown. Haas6 found no significant difference in renal survival associated with white race, black race or Hispanic origin. The frequency of IgAN in African Americans does not seem to be influenced by the higher prevalence of the IgA2 allotype among this group. Most of the worldwide studies report prevalence rates as a percentage of cases of primary glomerulonephritides or as a percentage of a total series of renal biopsies, while few epidemiologic studies focused on the real incidence of primary IgAN in various populations.7 An interesting study by Geddes et al.8 aimed at examining four IgAN databases from four different countries in three continents to determine if geographic variability in long term outcome is independent of renal function, proteinuria and blood pressure at the time of diagnosis. They included patients from Glasgow (United Kingdom), Helsinki (Finland), Sydney (Australia) and Toronto (Canada). The results supported the hypothesis that the variation in the rate of progression of renal disease was probably due to variability at presentation in both duration (lead-time bias) and severity of disease in different countries. They did not exclude the possibility that true geographic variability exists mainly because of genetic variability, but also because of environmental factors, including dietary differences between countries. There were no differences in renal survival or slope of creatinine clearance between males and females suggesting that the outcome is the same. The geographic variability is responsible for difference in tenyear renal survival in patients with IgAN ranging between 95.7% in Helsinki and 61.6% in Toronto. The role of environmental antigen triggers together with a genetic susceptibility factor determining the onset of the disease is still under debate. The higher prevalence of IgAN in Asian/Pacific Islanders could be supported by the evidence that high intake of rice and n-6 polyunsaturated fatty acids could be associated with an increased risk

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Epidemiology and Ancestral Difference ✦ 11

of the disease as reported by Wakai et al.9 or by the suggested role of Hemophilus parainfluenzae as a causative agent of the disease in Japanese individuals.10–12

Worldwide Distribution Europe The incidence of IgAN in Italy is 8.4 patients/per million population (pmp) per year. According to the Italian Registry of Renal Biopsies (IRRB)13 based on data related to 32,862 renal biopsies collected during the years 1987–2000 from 128 renal units in Italy, IgAN is still the most frequent disease among primary glomerulonephritides (21.5%) and its frequency is higher in males (39.3%) than in females (27.8%). The Italian Registry of Pediatric Renal Biopsy reported the diagnosis of IgAN in 18.8% of children (Figure 2.1).14,15 The disease is also the most common primary glomerulopathy in Germany.16 Simon et al.17 in 2004 considered the annual incidence of the disease in western France for two consecutive ten-year periods: period A (1976 to 1985), period B (1986 to 1995) and for one seven-year period: period C (1996 to 2002). The incidence of the disease was the same throughout the three periods: 28, 28, and 26 pmp per year. The incidence of IgAN was three- to fourfold higher in the adults (20–59 years old) than in the elderly during the periods A (38 vs. 11 pmp per year) and B (37 vs. 12 pmp per year), but it was quite similar whatever age group during the last period C accounting for 25 pmp per year in the 20–59 years old group; 27 pmp per year in the 60 to 79 years old group and 28 pmp per year in the 80 years old and over. The prevalence was 2.4 in 1000 individuals (3.6 in 1000 males and 1.3 in 1000 females). In a study of renal biopsies between 1970 and 1986, with a sample size of 8545 cases in adults and 1364 in children, Rivera et al.18 described the high incidence of IgAN and the decrease of membranoproliferative glomerulonephritis in Spain. The mean annual incidence (pmp) of the disease was 7.9, making the disease the most common nephropathy. In children, the most frequent renal diseases were minimal-change disease (24.2%) and IgAN (19.5%). In adults the most common disease was IgAN (17.2%). In the elderly, among the primary glomerulonephritides the disease (6.2%) was second to membranous glomerulonephritis.

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13519 4514 961 1045 3555 1544 2030

A=Adults; C=Children; RB= Renal Biopsy

Figure 2.1

Frequency of IgA nephropathy worldwide.

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31.2 (A) 17.2 (A); 19.5 (C) Italy 21.5 (A); 18.8 (C) Croatia 18.1 (A); 20.0 (C) Lithuania 35.0 (A) Romania 28.9 (A) Rep. Macedonia 11.8 (A)

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In Portugal, the relative frequency of IgAN increased significantly over time, becoming the most common type of primary glomerular disease (31.2%) found over a period of 27 years.19 In Croatia the most frequent primary glomerulonephritis form in adults is focal segmental glomerulosclerosis (24.6%), followed by mesangial proliferative glomerulonephritis (19.2%) and then IgAN (18.1%). The disease, primary or related to Henoch-Schönlein Purpura (20.0%), is the most common biopsy-proven renal nephritis in Croatian children.20 In Romania, Moldova (North-eastern Romania) and Banat regions (Western Romania) among the different forms of primary glomerulonephritides, IgAN (as part of the group of mesangioproliferative glomerulonephritis) accounting for 28.9%, is second to membranoproliferative glomerulonephritis (29.4%). The Czech Registry of Renal Biopsy (CCRB) reports mesangioproliferative glomerulonephritis as the most frequent accounting for 45.8%.21 IgAN is the most frequent primary glomerulopathy in Lithuania, accounting for 35% of all the biopsies performed in Lithuanian nephrology units from in the period from 2000–2006.22 IgAN is the most frequent renal disease in the Hungarian biopsy registry.23 In the Republic of Macedonia the frequency of the disease is 11.8%, second to membranous nephropathy (13.5%).24 The exceptional rise in the observed frequency of IgAN (31% of all glomerulopathies in 1986) in comparison to the low frequency found in the early 1970s in Manchester, England could be due to a higher detection of the disease rather than true rise in frequency as indicated by Ballardie et al.,25 thus IgAN is the most common primary glomerulopathy in the United Kingdom.

America In Brazil, IgAN (29.4%) is the most frequent disease diagnosed among non-nephrotic patients. An increase in frequency of focal and segmental glomerulosclerosis has been reported in non-nephrotic patients; thus this disease became as common as IgAN (31.6% and 28.0%, respectively), from 1994–1999.26 The most common primary glomerular disease in San Paolo is focal and segmental glomerulosclerosis (29.7%), followed by membranous nephropathy (20.7%) and then IgAN (17.8%), confirming the above data.27

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Hurtado A et al., 28 in a large series of renal biopsies from Peru, showed low frequency of IgAN (0.9%) over a ten-year period from a central reference renal pathology laboratory in Lima. The United States Renal Data System (USRDS)29 reports that 0.8% of incident end stage renal disease patients in the USA have documented or suspected IgAN. In a study by Wyatt et al.30 on the epidemiology of IgAN in central and eastern Kentucky, the incidence of the disease was 5.4 cases pmp per year for the period 1975–1979, increasing to 12.4 cases pmp per year for the period 1990–1994. Males had a 2.7 times higher incidence than females for the period 1975–1984 and 2.2 times higher for the period 1985–1994. While during the period 1975–1984, the highest incidence of IgAN (for any age and gender group) was 24.3 cases pmp per year for males. For the period 1985–1994, the incidence for males was similar for each decade between ages 20 and 59 (approximately 19 cases pmp per year). In the period 1985–1994 incidence for blacks and whites was similar (10.7 and 10.2 cases pmp per year, respectively) contrary to the period 1975–1984 in which no African-American was diagnosed. During the period 1990–1994, the incidence of end-stage renal disease due to IgAN was 5.5 cases pmp per year: 8.4 for males and 2.7 for females. In a 30-year renal biopsy study in Olmsted County (Minnesota), IgAN was present in 22% of biopsy-proven patients, thus representing the most frequent glomerulonephritis.31 Between 1974 and 1983 and from 1994 to 2003, the incidence of any type of glomerulonephritis among Olmsted County residents increased more than two-fold and IgAN by three-fold. Currently (1994 to 2003), the most frequent type of glomerulonephritis is IgAN (25%) with annual incidence rates of 2.1 per 100,000 individuals per year. In 2006, Nair and Walker32 examined if IgAN still remained the most common primary glomerulopathy among young adults in the USA. In their study from a large renal biopsy referral center serving 24 Midwestern and Southern states they grouped the patients in adults (≥ 20 years) and young adults (20–39 years). The disease was the most common primary glomerulopathy in young adult Caucasians (with a ratio IgAN/focal segmental glomerulosclerosis of 2.1:1) and also the most common cause of end-stage renal disease in this race. On the contrary, the disease was rare in African Americans in whom focal segmental glomerulosclerosis remains more common (focal segmental glomerulosclerosis/IgAN 9.7:1).

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Australia In a retrospective review of the pathology reports of all native renal biopsies performed in the state of Victoria, Australia, the most common glomerulonephritis in 1995 and 1997, in children under the age of five years was focal glomerulosclerosis, followed by minimal change disease and IgAN.33 In children of five to 14 years of age, the most common diagnosis was lupus nephritis, followed by IgAN and focal glomerulosclerosis. In adults, the most common glomerulonephritis was IgAN (10.5 per 100,000 individuals). The disease accounted for 34.1% of all biopsyproven glomerulonephritides and was also the most common cause of end-stage renal disease due to glomerulonephritis.

Asia Renal biopsy has been routinely performed in China in the last 20 years and IgAN is the most common primary glomerulonephritis occurring in the largest Asian country, representing 45.3% of the primary glomerulonephritides. The disease is also the leading cause of end stage renal disease, accounting for approximately 18% of patients.34–36 It has also been reported a frequency of 35% in Hong Kong by Lai and 34% in Singapore by Sinniah in the 1980s.37 In Korea, in a study on a total of 4514 cases of renal biopsy collected over a 23-year period between 1973 and 1995 the most common primary glomerulonephritis in adults was minimal change disease (26.6%), followed by IgAN (22.1%).38 In children, the frequencies were 24.8% for minimal change disease and 10.3% for IgAN. The disease is listed as primary cause of end stage renal disease in 28% of new dialysis patients as reported by Koyama et al.39 in a national survey of Japanese patients. It is possible that 40% of newly registered dialysis patients in Japan might have had a chronic kidney disease like IgAN because many biopsies lacked immunofluorescent description in the survey. The Research Group on Progressive Chronic Renal Disease, in their Nationwide and long-term survey of primary glomerulonephritis in Japan, found that 47.4% out of 1045 biopsy specimens examined by immunofluorescence microscopy were IgAN.40 The incidence of pediatric IgAN in Japan is 4.5 cases per 100,000 children under 15 years per year41 while in adults it is 143 cases pmp per year.42

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In a retrospective analysis of 1592 renal biopsies received from various hospitals all over Kerala (India) over a period of two years, Chandrika43 observed that of the 1544 native kidney biopsies, the majority of cases (18.84%) were focal segmental glomerulosclerosis followed in frequency by IgAN (14.26%). In Thailand, the most common primary glomerular disease in a study of 2154 biopsy-proven patients was IgM nephropathy (45.8%) followed by IgAN (17.9%).44

Conclusion IgAN is a renal disease with different frequency throughout the world which is influenced by different causes as: (1) ancestral factors and geographical situations; (2) different social and regional attitude to the management of renal disease in different countries; for example the high incidence of IgAN in Singapore is due to a high selection of patients with asymptomatic microscopic hematuria or occasional mild proteinuria, discovered during the regular medical examination of army recruits. In Japan school children receive a yearly urinalysis, because of the school Health Law of 1973 and the persistence of microhematuria and/or proteinuria leads to a renal biopsy; (3) there are differences in the interest and judgment of clinicians on the diagnostic value of renal biopsy; (4) differences in the indications for and background to renal biopsy.

References 1. Levy M, Berger J. (1988) Worldwide perspective of IgA nephropathy. Am J Kidney Dis 12: 340–347. 2. Sinniah R. (1983) Occurrence of mesangial IgA and IgM deposits in a control necropsy population. J Clin Pathol 36: 276–279. 3. Suzuki K, Honda K, Tanabe K, et al. (2003) Incidence of latent mesangial IgA deposition in renal allograft donors in Japan. Kidney Int 63: 2286–2294. 4. Schena FP. (1990) A retrospective analysis of the natural history of primary IgA nephropathy worldwide. Am J Med 89: 209–215. 5. Yamagata K, Iseki K, Nitta K, et al. (2008) Chronic kidney disease perspectives in Japan and the importance of urinalysis screening. Clin Exp Nephrol 12: 1–8.

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6. Haas M. (1997) Histologic subclassification of IgA nephropathy: a clinicopathologic study of 244 cases. Am J Kidney Dis 29: 829–842. 7. Donadio JV, Grande JP. (2002) IgA nephropathy. N Engl J Med 347: 738–748. 8. Geddes CC, Rauta V, Gronhagen-Riska C, et al. (2003) A tricontinental view of IgA nephropathy. Nephrol Dial Transplant 18: 1541–1548. 9. Wakai K, Nakai S, Matsuo S, et al. (2002) Risk factors for IgA nephropathy: a case-control study with incident cases in Japan. Nephron 90: 16–23. 10. Ogura Y, Suzuki S, Shirakawa T, Masuda M, et al. (2000) Haemophilus parainfluenzae antigen and antibody in children with IgA nephropathy and Henoch-Schonlein nephritis. Am J Kidney Dis 36: 47–52. 11. Suzuki S, Nakatomi Y, Sato H, et al. (1994) Haemophilus parainfluenzae antigen and antibody in kidney biopsy samples and serum of patients with IgA nephropathy. Lancet 343: 12–16. 12. Hall YN, Fuentes EF, Chertow GM, Olson JL. (2004) Race/ethnicity and disease severity in IgA nephropathy. BMC Nephrol 5: 10. 13. http://www.irrb.net. 14. Schena FP and the Italian Group of Renal Immunopathology. (1997) Survey of the Italian registry of renal biopsies. Frequency of the renal disease for 7 consecutive years. Nephrol Dial Transplant 12: 418–426. 15. Gesualdo L, Di Palma AM, Morrone LF, et al. (2004) Italian Immunopathology Group, Italian Society of Nephrology. The Italian experience of the national registry of renal biopsies. Kidney Int 66: 890–894. 16. Floege J, Grone H. (2003) IgA nephropathy: frequent, but rarely diagnosed. Internist (Berlin) 44: 1131–1139. 17. Simon P, Ramee MP, Boulahrouz R, et al. (2004) Epidemiologic data of primary glomerular diseases in western France. Kidney Int 66: 905–908. 18. Rivera F, López-Gómez JM, Pérez-García R. (2002) Spanish Registry of Glomerulonephritis. Frequency of renal pathology in Spain 1994–1999. Nephrol Dial Transplant 17: 1594–1602. 19. Carvalho E, do Sameiro Faria M, Nunes JP, et al. (2006) Renal diseases: a 27-year renal biopsy study. J Nephrol 19: 500–507. 20. Batinic´ D, Sc´ukanec-Spoljar M, Milosevic´ D, et al. (2007) Clinical and histopathological characteristics of biopsy-proven renal diseases in Croatia. Acta Med Croat 61: 361–364. 21. Covic A, Schiller A, Volovat C, et al. (2006) Epidemiology of renal disease in Romania: a 10 year review of two regional renal biopsy databases. Nephrol Dial Transplant 21: 419–424. – nas E, Laurinavicius A. (2007) Primary glomeru22. Beitnaraite S, Kovaliu lopathies in Lithuania: a retrospective analysis of renal biopsy cases (2000–2006). Medicina (Kaunas) 43(Suppl 1): 6–10.

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23. Sipiczki T, Ondrik Z, Abrahám G, et al. (2004) The incidence of renal diseases as diagnosed by biopsy in Hungary. Orv Hetil 145: 1373–1379. 24. Polenakovic MH, Grcevska L, Dzikova S. (2003) The incidence of biopsyproven primary glomerulonephritis in the Republic of Macedonia — long-term follow-up. Nephrol Dial Transplant 18(Suppl 5): 26–27. 25. Ballardie FW, O’Donoghue DJ, Feehally J. (1987) Increasing frequency of adult IgA nephropathy in the UK? Lancet 2(8569): 1205. 26. Bahiense-Oliveira M, Saldanha LB, Mota EL, et al. (2004) Primary glomerular diseases in Brazil (1979–1999): is the frequency of focal and segmental glomerulosclerosis increasing? Clin Nephrol 61: 90–97. 27. Malafronte P, Mastroianni-Kirsztajn G, Betônico GN, et al. (2006) Paulista Registry of Glomerulonephritis: five-year data report. Nephrol Dial Transplant 21: 3098–3105. 28. Hurtado A, Escudero E, Stromquist CS, et al. (2000) Distinct patterns of glomerular disease in Lima, Peru. Clin Nephrol 53: 325–332. 29. http://www.usrds.org. 30. Wyatt RJ, Julian BA, Baehler RW, et al. (1998) Epidemiology of IgA nephropathy in central and eastern Kentucky for the period 1975 through 1994. Central Kentucky Region of the Southeastern United States IgA Nephropathy DATABANK Project. J Am Soc Nephrol 9: 853–858. 31. Swaminathan S, Leung N, Lager DJ, et al. (2006) Changing incidence of glomerular disease in Olmsted County, Minnesota: a 30-year renal biopsy study. Clin J Am Soc Nephrol 1: 483–487. 32. Nair R, Walker PD. (2006) Is IgA nephropathy the commonest primary glomerulopathy among young adults in the USA? Kidney Int 69: 1455–1458. 33. Briganti EM, Dowling J, Finlay M, et al. (2001) The incidence of biopsyproven glomerulonephritis in Australia. Nephrol Dial Transplant 16: 1364–1367. 34. Li LS, Liu ZH. (2004) Epidemiologic data of renal diseases from a single unit in China: analysis based on 13,519 renal biopsies. Kidney Int 66: 920–923. 35. Li L. (1996) End-stage renal disease in China. Kidney Int 49: 287–301. 36. Xie Y, Chen X. (2008) Epidemiology, major outcomes, risk factors, prevention and management of chronic kidney disease in China. Am J Nephrol 28: 1–7. 37. Lai KN, Wang AY. (1994) IgA nephropathy: common nephritis leading to end-stage renal failure. Int J Artif Organs 17: 457–460. 38. Choi IJ, Jeong HJ, Han DS, et al. (2001) An analysis of 4,514 cases of renal biopsy in Korea. Yonsei Med J 42: 247–254. 39. Koyama A, Igarashi M, Kobayashi M. (1997) Natural history and risk factors for immunoglobulin A nephropathy in Japan. Am J Kidney Dis 29: 526–532.

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40. Research Group on Progressive Chronic Renal Disease. (1999) Nationwide and long-term survey of primary glomerulonephritis in Japan as observed in 1,850 biopsied cases. Nephron 82: 205–213. 41. Utsunomiya Y, Koda T, Kado T, et al. (2003) Incidence of pediatric IgA nephropathy. Pediatr Nephrol 18: 511–515. 42. Yamagata K, Takahashi H, Tomida C, et al. (2002) Prognosis of asymptomatic hematuria and/or proteinuria in men. High prevalence of IgA nephropathy among proteinuric patients found in mass screening. Nephron 91: 34–42. 43. Chandrika BK. (2007) Non-neoplastic renal diseases in Kerala, India — analysis of 1592 cases, a two-year retrospective study. Indian J Pathol Microbiol 50: 300–302. 44. Parichatikanond P, Chawanasuntorapoj R, Shayakul C, et al. (2006) An analysis of 3,555 cases of renal biopsy in Thailand. J Med Assoc Thai 89 (Suppl 2): 106–111.

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Chapter 3

Genetic Contribution to IgA Nephropathy Patrick H. Maxwell and Yiming Wang

Introduction Substantial progress has been made towards defining the role of genetic factors in IgA nephropathy (IgAN). Several loci for familial IgAN have been mapped, and some genetic variants which may predispose to sporadic IgAN have been identified. We will briefly describe general approaches to identify genetic contributions1,2 before summarizing recent advances in IgAN, and possible future directions.

Approaches to Identifying Genetic Contributions to IgAN Determining Whether Genetic Factors Contribute to the Disease This is an important first step before attempting to dissect the genetic component(s) of a disease or trait; the approaches used do not differ in principle between IgAN and other diseases. (i) Family studies This includes pedigree analysis, and determination of the recurrence rate of a particular trait in relatives of affected family members compared to the rate in the general population. Higher incidence in relatives

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22 ✦ P. H. Maxwell & Y. Wang

usually indicates genetic involvement, but the shared family environment can also contribute. (ii) Twin and adoption studies Twin studies analyze the concordance rates in monozygotic and dizygotic twins for a particular trait. Adoption studies can separate the genetic and environment components for a particular character. (iii) Population and migration studies Population studies compare disease frequency in different populations. Geographically isolated populations are more likely to have markedly different frequencies of particular alleles, so are useful for this approach. Migration studies can differentiate genetic and environmental factors through comparing disease incidence between migrants and nonmigrants, and the incidence before and after migration. This usually requires data from several generations.

Identifying Disease Genes in Families Once it is determined that there is a genetic component in a disease and there is at least one family of a suitable size, the next step is to map the gene(s) onto particular chromosomal region(s), or directly find the causative gene by a position-independent approach or association study. (i) Mapping of the gene Linkage analysis The main tool to map a gene is linkage analysis. Linkage refers to the tendency of genes or DNA sequences to be transmitted together during meiosis as the consequence of their physical proximity on a single chromosome. By scanning with polymorphic markers (usually microsatellites or single nucleotide polymorphisms — SNPs) spaced on the whole genome or a region of the chromosome, a linkage study searches for genetic markers linked to the gene in the analyzed family. The location of the linked markers on the chromosome indicates the region which confers the causal gene. In linkage analysis the ratio of the likelihood of linkage and the likelihood of non-linkage is calculated at a particular recombination

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Genetic Contribution to IgA Nephropathy ✦ 23

fraction (θ), which gives the odds of linkage. The logarithm of the odds is the lod score. A lod score greater than 3 is considered positive for linkage, and linkage will be excluded if lod score < −2 for autosomal Mendelian characters. There are two types of linkage analyses; parametric and nonparametric. Parametric analysis requires specification of the inheritance model (dominant or recessive), disease gene frequency, penetrance (the proportion in which the genotype results in the phenotype), and sometimes the rate of phenocopy (the trait being due to the environment but resembling the genetic effect). Data for heterogeneity (the same phenotype being caused by different genes) in multiple families may also be required. Parametric linkage analysis is best suited to mapping Mendelian or near Mendelian traits. In contrast, non-parametric linkage analysis is model free and is mostly used in mapping genes in multiple small families in which the disease model is not clear. However, to obtain positive results, causal genes have to have relatively major effects. Affected sib-pair analysis This is a form of linkage analysis. Affected sib pairs are expected to share the same causal gene-bearing chromosomal region on both chromosomes in recessive disorders or the same haplotype (a series of linked alleles on a single chromosome) in dominant diseases. The chromosomal regions/haplotypes shared significantly above the ratio predicted by random sharing are identified. (ii) Cloning of the gene Positional cloning Once the chromosomal position is identified, and the critical region is defined, the next step is to identify the gene responsible for the disease. The most widely used strategy is as follows. First, to obtain contig(s) (a series of ordered and overlapped DNA fragment clones) covering the mapped region. Second, to identify all the genes in the region by their transcripts. Third, to select candidate genes and test their relationship with the disease and sequence these to identify potential mutations. Approaches to showing that a mutation causes a disease include (a) co-segregation analysis (whether the mutation co-segregates

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with the disease phenotype in the family); (b) understanding how the candidate gene’s function would lead to the phenotype; (c) demonstrating that the mutation in the gene is not present in unaffected populations and unaffected family members; and (d) demonstrating that the mutations in the gene causes the same condition in patients/families unrelated to the family. Functional cloning This strategy is also termed “position-independent.” Some prior knowledge regarding the gene, such as the amino acid sequences of the possible protein, are required for the design of probes for library screening.

Identifying Genetic Variants Underlying Sporadic Cases (i) Association studies Association studies are the most suitable for polygenic diseases. Since this approach can use sporadic cases rather than requiring multiply affected kindreds, large collections of cases and controls can be analyzed. This gives the analysis more power to detect genes exerting relatively modest effects. Until recently, association studies usually adopted a candidate gene approach in IgAN. The ability to perform genome-wide association (GWA) studies with dense SNP markers provides a new approach. Most regions of the genome are believed to be divided into block-like structures due to linkage disequilibrium, separated by recombination events. Each block contains several common haplotypes, which can be tagged by a few SNPs (tagSNPs). Therefore by using a relatively small number of tagSNPs one can test the association of most common haplotypes genome-wide. The GWA approach is “hypothesis-free,” and powerful in detecting genes exerting relatively modest effects. (ii) Family-based association studies Population stratification (admixture) refers to differences in allele frequency in population subgroups due to different ancestry. This can yield false positive results in association studies. Family-based association studies are designed to overcome this problem. The Transmission Disequilibrium Test (TDT) is used to analyze parents (regardless of

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their affection status), and their affected offspring. The rates of transmission of the alleles of heterozygous parents to the affected offspring are compared statistically with the rates that would be expected if transmission was random. Over-transmission of a particular allele is evidence that it is associated with disease susceptibility. The test is not affected by population stratification. A final point about association studies is that variants that are genuinely associated with disease may not actually be involved in causation, but may be linked to a causal variant by linkage disequilibrium. It can be a daunting task to identify the truly causative variant from the associated alleles/haplotypes.

Genetic Studies of IgAN The trait that has been investigated in genetic studies of IgAN is the presence of mesangial IgA on a renal biopsy that has been performed for overt nephropathy. Investigating the genetic contribution to subclinical IgAN (see Chapter 11) would be interesting, but is not feasible since ascertainment would require renal biopsy, and the risk of this procedure substantially outweighs any benefit in subclinical disease.

Genes Responsible for, or Predisposing to, IgAN Several lines of evidence support a contribution by genetic factors to the development of, or susceptibility to, overt IgAN. (1) Many pedigrees have been described in which more than one individual is affected by IgAN. In some of these, genetic loci have been identified by linkage analyses.3–5 (2) There are differences in prevalence in ethnically different populations which are unlikely to be fully accounted for by differences in environment and ascertainment.6 (3) First and second degree relatives of IgAN patients have higher relative risks of developing this disease compared to the general population.7 Most cases of IgAN are “sporadic” rather than familial. IgAN is therefore generally considered to be a complex disorder, i.e. it is a multifactorial disease with both genetic and environmental factors likely

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contributing in the majority of IgAN cases. However, in some families the disease segregates in an obviously autosomal dominant fashion. It therefore seems likely that the genetic contribution to the disease is heterogeneous, and can lie anywhere in the spectrum from monogenic, through oligogenic to polygenic, differing in individual cases and families. This is the case for many other diseases; for example in diabetes, there are Mendelian disorders (neonatal and MODY types) but more commonly type II diabetes is truly polygenic. (i) Familial IgAN and linked loci The strongest evidence for a genetic component in IgAN comes from familial IgAN (OMIM %161950).a This was first reported in 1973, and a number of multiply affected IgAN families have been reported subsequently. While there have been no criteria to precisely define familial IgAN, families with two or more affected members are reported to account for as many of 15% of all IgAN cases in a geographic region in Italy.6 This provides strong evidence for a genetic contribution. Furthermore, the segregation of disease in an apparently Mendelian fashion in some families argues for a major causal gene effect, at least in these cases. Using linkage analysis several loci have been implicated in IgAN in different pedigrees, as follows. (1) 2q36 locus The most clearcut report of familial IgAN and linkage is a study of a four-generation Canadian family of German-Austrian origin with 14 affected and 11 unaffected members. The pedigree is consistent with autosomal dominant inheritance. Parametric and non-parametric linkage analysis produced significant lod scores according to standard

a

OMIM refers to the web resource On-Line Mendelian Inheritance in Man. Symbols preceding the entry number have the following meanings. (*) indicates a gene of known sequence. (#) indicates a descriptive entry, usually of a phenotype, and does not represent a unique locus. (+) indicates that the entry contains the description of a gene of known sequence and a phenotype. (%) indicates that the entry describes a confirmed mendelian phenotype or phenotypic locus for which the underlying molecular basis is not known. No symbol before an entry indicates a description of a phenotype for which the Mendelian basis, although suspected, has not been clearly established or that the separateness of this phenotype from that in another entry is unclear.

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criteria for Mendelian disease. The evidence for a genetic basis for disease in this family is compelling.5 (2) 6q22-q23 (IGAN1) and 3p24-p23 loci These were the first loci identified in linkage analysis of IgAN. The study analyzed 24 Italian and six American families. Under an autosomal dominant model with reduced penetrance, linkage analysis produced a maximum lod score of 5.6 to 6q22-q23, which was named IGAN1. This study also reported a suggestive locus at 3p24-p23 in the collection with maximum lod score of 2.8.3 (3) 4q26-q31 (IGAN2) and 17q12-q22 (IGAN3) loci In 2006 the European IgAN consortium identified suggestive loci at 4q26-q31 and 17q12-q22, in 22 Italian families with 59 affected and 127 unaffected members. The loci were named IGAN2 and IGAN3. The lod scores were relatively modest.4 If each of these loci truly harbors a causative gene for IgA nephropathy in these families, then at least five genes are expected to be responsible for IgAN in these kindreds. To date no gene responsible has been cloned from the linked loci. (ii) IgAN in other Mendelian disorders Although not widely recognized, IgAN is considered part of the phenotype in some rare Mendelian diseases; Fabry disease (OMIM #301500),8 Wiskott-Aldrich syndrome (OMIM #301000)/ X-linked thrombocytopenia (OMIM #313900),9 familial spastic paraplegia (OMIM 182690), hereditary C1q deficiency (OMIM + 120550). The mechanisms for IgAN in these diseases are largely unknown, however this provides support for a genetic contribution to IgAN and the elucidation of the pathogenesis may provide insight into the pathways and mechanisms underlying the disease. (For references also see the OMIM database at http://www.ncbi. nlm.nih.gov/sites/entrez?db=OMIM&itool=toolbar.) (iii) Susceptibility genes in non-familial IgAN While the genes responsible for familial IgAN have been the subject of intense investigation, the great majority of cases are non-familial (sporadic). The contribution to sporadic IgAN is considered to be polygenic,

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i.e. a number of causative genes each contribute a moderate risk in an additive fashion. The evidence for a genetic contribution mainly comes from the increased recurrence risk in relatives of IgAN patients, and association studies implicating particular genetic variants. Schena et al. reported that the relative risk of IgAN is 16 times higher in first degree relatives (parents and siblings), and more than two-fold increased in second degree relatives (grandparents, grant children) of index cases compared to the general population.7 This rapid fall off in more distant relatives is consistent with a polygenic model. Numerous association studies have reported different frequencies of genetic variants in patients with IgAN compared to controls (Table 3.1). To date, most have employed a candidate gene-based approach, sample size has been small, and replication is not reported in ethnically similar or different populations. It is therefore unclear which of the reported genes may truly confer susceptibility. Table 3.1 Genes in which variants have been reportedly associated with susceptibility to IgA nephropathy. Immune system genes: PIGR (Polymeric immunoglobulin receptor)13 IGHMBP2 (Immunoglobulin mu binding protein 2)14 TRAC (T cell receptor alpha constant; T-cell receptor constant alpha chain)15 FCAR (Fc fragment of IgA, receptor for; CD89; FcalphaR, Fcalpha receptor)16 HLA-DRA (Major histocompatibility complex, class II, DR α)17 FCGR3B (Fc fragment of IgG, low affinity IIIb, receptor; CD16b; FcgRIIIb)18 Cytokine coding genes: TNF α (Tumor necrosis factor alpha)19 IFNG (Interferon gamma)20 TGFB1 (Transforming growth factor, beta1; TGF-beta1)21,22 IL10 (Interleukin 10)23 IL5RA (Interleukin 5 receptor, alpha; IL5RA)24 TNFRSF6B (Tumor necrosis factor receptor superfamily, member 6b, decoy)24 (Continued )

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Table 3.1

(Continued )

Adhesion molecule genes: SELE (Selectin E; Endothelial adhesion molecule 1)25 SELL (Selectin L; Lymphocyte adhesion molecule 1)25 Renin-angiotensin system genes: ACE (Angiotensin I converting enzyme 1)26–28 Glycosylation-related gene: ST6GALNAC2 (ST6 alpha-N-acetyl-neuraminyl-2,3-beta-galactosyl-1, 3-N-acetylgalactosaminide alpha-2,6-sialyltransferase 2)29 C1GALT1(Core 1 synthase, glycoprotein-N-acetylgalactosamine 3-beta-galactosyltransferase, 1)30 Others: EDN1 (Endothelin 1; ET-1)31 NPHS2 (Nephrosis 2, idiopathic, steroid-resistant; Podocin)32 GNB3 (G protein beta polypeptide 3; G protein beta 3 subunit)33 SERPINB7 (Serpin peptidase inhibitor, clade B, member 7; MEGSIN)34,35 SCGB1A1(Secretoglobin, family 1A, member 1; Uteroglobin; UG)36

Genetic Variants Associated with Progression of IgAN A substantial number of studies have compared the incidence of particular genetic variants in a group of patients in whom the disease has progressed more rapidly with those in whom it has not (Table 3.2). This suggests some genetic variations may contribute to more rapid progression of the disease. Again, these studies have tended to be relatively small.

Genetic Variants Associated with Response to Treatment There is increasing interest in the notion that genetic variants influence the response to drug treatments (pharmacogenomics). In IgAN there is some evidence that variants in ACE (Angiotensin I converting enzyme I)10 and AGT (Angiotensinogen)11 alter response to ACE inhibitors and/or angiotensin receptor blocker.

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Table 3.2 Genes in which variants have been reportedly associated with progression of IgA nephropathy. Immune system genes: FCGR3B (Fc fragment of IgG, low affinity IIIb, receptor; CD16b; FcgRIIIb)18 FCGR2A (Fc fragment of IgG, low affinity IIa, receptor; CD32; FcgammaRIIa)37 CD14 (CD14 molecule)38 Cytokine coding genes: TNF α (Tumor necrosis factor alpha)39 IL10 (Interleukin 10)40 IL4 (Interleukin 4)20 TGFB1 (Transforming growth factor beta 1; TGF-beta1)21 CCL2 (Chemokine C-C motif ligand 2; Monocyte chemoattractant protein -1; MCP-1)41 CCR5 (Chemokine C-C motif receptor 5; CC-chemokine receptor five; Chemokine receptor 5)42,43 Adhesion molecules: SELE (Selectin E; Endothelial adhesion molecule 1, E-selectin)44 SELL (Selectin L; Lymphocyte adhesion molecule 1, L-selectin)44 Renin-angiotensin system genes: ACE (Angiotensin I converting enzyme 1)26,45 AGT (Angiotensinogen; Serpin peptidase inhibitor, clade A, member 8)46 Others: SCGB1A1(Secretoglobin, family 1A, member 1; Uteroglobin; Clara cell secretory protein; CC16)47,48 PON1 (Paraoxonase 1)49 NPHS1 (Nephrosis 1, congenital, Finnish type; Nephrin)50 NPHS2 (Nephrosis 2, idiopathic, steroid-resistant; Podocin)32 VEGFA (Vascular endothelial growth factor A; VEGF )51 SERPINE1 (Serpin peptidase inhibitor, clade E, member 1; Plasminogen activator inhibitor-1; PAI-1)52 SERPINB7 (Serpin peptidase inhibitor, clade B, member 7; MEGSIN)53 PPARG (Peroxisome proliferator-activated receptor gamma)54 ACSM3 (Acyl-CoA synthetase medium-chain family member 3; SA)55 MUC20 (Mucin 20, cell surface associated)56

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Determining How Genetic Variants Influence IgAN Susceptibility and Progression Ultimately, it will be important to understand how genetic variants influence gene function, and how altered gene function results in altered susceptibility to IgAN. The variants that have been reported to be associated with IgAN are mostly located in non-coding regions of genes. Functional tests of these variants and the mechanism by which they would have functional consequences have generally not been explored. Clearly coding sequence variations may alter the function of the encoded protein, whereas non-coding variations in regulatory sequence could alter the expression level.

Novel Aspects of Genetic Variation That May Be Relevant in IgA Nephropathy The roles of submicroscopic structural variations (including copy number variation), epistasis (interactions between non-allelic genes for disease phenotypes), epigenetics (changes in gene expression that are not due to differences in nucleotide sequences and can be transmitted at meiosis or mitosis), and microRNAs to IgAN remain to be investigated.

Current Priorities in Genetic Studies of Sporadic IgAN A problem with studies of sporadic IgAN has been small sample size. Since individual groups do not have large enough collections, excellent organization of collection efforts is required and collaborations between groups are needed. The European IgAN consortium provides a good example of this,12 and some large collections already exist in China, including Hong Kong, Japan, and Canada. A second problem has been lack of replication. It is likely that many reported associations are false positives, arising at least in part through publication bias towards positive results, and others may be population-specific. A sensible approach is to have pre-specified replication strategies, which require careful study design and well-organized collaborations. Results in one ethnic

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population may not apply to another ethnic group, since allele frequency differs and interacting genetic and environmental factors may also differ. Therefore a logical approach is first to replicate findings in an ethnically similar population. There are encouraging signs that the IgAN community is organizing large-scale collections and effective collaborations. This is opportune, because of the feasibility of GWA studies which are eagerly awaited for IgAN.

Summary and Future Directions Genetically IgAN is a heterogeneous disease. The genetic contribution likely lies along the whole spectrum from monogenic to polygenic, differing in each case or family. In sporadic IgAN it is likely that a combination of genetic variants predispose individuals to the disease, and that these act together with environmental factors. Additional genetic variants probably influence disease progression and response to therapy. We expect that the next decade will see the successful cloning of the genes for familial IgAN and the identification of variants for sporadic IgAN. This may allow personalized medicine for sporadic cases, and identification of carrier status and counseling for IgAN families. It could also provide new therapeutic targets.

References 1. Strachan T, Read AP. (2003) Part 3: Mapping and identifying disease genes and mutations. In: Human Molecular Genetics, 3rd ed. Garland Science Taylor & Francis Group, London and New York, pp. 395–483. 2. Turnpenny PD, Ellard S. (2007) Polygenic and multifactorial inheritance. In: Emery’s Elements of Medical Genetics, 13th ed. (eds.) Dimock K, McCormick H. Churchill Livingstone Elsevier, Edinburgh, pp. 73–75, 136–143. 3. Gharavi AG, Yan Y, Scolari F, et al. (2000) IgA nephropathy, the most common cause of glomerulonephritis, is linked to 6q22-23. Nat Genet 26: 354–357. 4. Bisceglia L, Cerullo G, Forabosco P, et al. (2006) Genetic heterogeneity in Italian families with IgA nephropathy: suggestive linkage for two novel IgA nephropathy loci. Am J Hum Genet 79: 1130–1134.

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5. Paterson AD, Liu X-Q, Wang K, et al. (2007) Genome-wide linkage scan of a large family with IgA nephropathy localizes a novel susceptibility locus to chromosome 2q36. J Am Soc Nephrol 18: 2408–2415. 6. Beerman I, Novak J, Wyatt RJ, et al. (2007) The genetics of IgA nephropathy. Nat Clin Pract Nephrol 3: 325–338. 7. Schena FP, Cerullo G, Rossini M, et al. (2002) Increased risk of end-stage renal disease in familial IgA nephropathy. J Am Soc Nephrol 13: 453–460. 8. Whybra C, Schwarting A, Kriegsmann J, et al. (2006) IgA nephropathy in two adolescent sisters heterozygous for Fabry disease. Pediatr Nephrol 21: 1251–1256. 9. Matsukura H, Kanegane H, Miya K, et al. (2004) IgA nephropathy associated with X-linked thrombocytopenia. Am J Kidney Dis 43: e7–e12. 10. Woo KT, Lau YK, Zhao Y, et al. (2007) Disease progression, response to ACEI/ATRA therapy and influence of ACE gene in IgA nephritis. Cell Mol Immunol 4: 227–232. 11. Narita I, Goto S, Saito N, et al. (2003) Angiotensinogen gene variation and renoprotective efficacy of renin-angiotensin system blockade in IgA nephropathy. Kidney Int 64: 1050–1058. 12. Schena FP, Cerullo G, Torres DD, et al. (2005) The IgA nephropathy Biobank. An important starting point for the genetic dissection of a complex trait. BMC Nephrol 6: 14. 13. Obara W, Iida A, Suzuki Y, et al. (2003) Association of single-nucleotide polymorphisms in the polymeric immunoglobulin receptor gene with immunoglobulin A nephropathy (IgAN) in Japanese patients. J Hum Genet 8: 293–299. 14. Ohtsubo S, Iida A, Nitta K, et al. (2005) Association of a single-nucleotide polymorphism in the immunoglobulin mu-binding protein 2 gene with immunoglobulin A nephropathy. J Hum Genet 50: 30–35. 15. Li PK, Poon P, Phil M, et al. (1997) Association of IgA nephropathy with T-cell receptor constant alpha chain gene polymorphism. Am J Kidney Dis 30: 260–264. 16. Tsuge T, Shimokawa T, Horikoshi S, et al. (2001) Polymorphism in promoter region of Fcalpha receptor gene in patients with IgA nephropathy. Hum Genet 108: 128–133. 17. Akiyama F, Tanaka T, Yamada R, et al. (2002) Single-nucleotide polymorphisms in the class II region of the major histocompatibility complex in Japanese patients with immunoglobulin A nephropathy. J Hum Genet 47: 532–538. 18. Xu G, He Q, Shou Z, Wang H, et al. (2007) NA1/NA2 heterozygote of Fcgr3b is a risk factor for progression of IgA nephropathy in Chinese. J Clin Lab Anal 21: 298–302.

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19. Tuglular S, Berthoux P, Berthoux F. (2003) Polymorphisms of the tumour necrosis factor a gene at position -308 and TNFd microsatellite in primary IgA nephropathy. Nephrol Dial Transplant 18: 724–731. 20. Masutani K, Miyake K, Nakashima H, et al. (2003) Impact of interferongamma and interleukin-4 gene polymorphisms on development and progression of IgA nephropathy in Japanese patients. Am J Kidney Dis 41: 371–379. 21. Lim CS, Kim YS, Chae DW, et al. (2005) Association of C-509T and T869C polymorphisms of transforming growth factor-beta 1 gene with susceptibility to and progression of IgA nephropathy. Clin Nephrol 63: 61–67. 22. Carturan S, Roccatello D, Menegatti E, et al. (2004) Association between transforming growth factor beta 1 gene polymorphisms and IgA nephropathy. J Nephrol 17: 786–793. 23. Chin HJ, Na KY, Kim SJ, et al. (2005) Interleukin-10 promoter polymorphism is associated with the predisposition to the development of IgA nephropathy and focal segmental glomerulosclerosis in Korea. J Korean Med Sci 20: 989–993. 24. Liu XQ, Paterson AD, He N, et al. (2008) IL5RA and TNFRSF6B gene variants are associated with sporadic IgA nephropathy. J Am Soc Nephrol 19: 1025–1033. 25. Takei T, Iida A, Nitta K, et al. (2002) Association between single-nucleotide polymorphisms in selectin genes and immunoglobulin A nephropathy. Am J Hum Genet 70: 781–786. 26. Yong D, Qing WQ, Hua L, et al. (2006) Association of angiotensin I-converting enzyme gene insertion/deletion polymorphism and IgA nephropathy: a meta-analysis. Am J Nephrol 26: 511–518. 27. Woo KT, Lau YK, Choong LH, et al. (2004) Polymorphism of renin-angiotensin system genes in IgA nephropathy. Nephrology (Carlton) 9: 304–309. 28. Lau YK, Woo KT, Choong HL, et al. (2004) Renin-angiotensin system gene polymorphisms: its impact on IgAN and its progression to endstage renal failure among Chinese in Singapore. Nephron Physiol 97: p1–p8. 29. Li GS, Zhu L, Zhang H, et al. (2007) Variants of the ST6GALNAC2 promoter influence transcriptional activity and contribute to genetic susceptibility to IgA nephropathy. Hum Mutat 28: 950–957. 30. Li GS, Zhang H, Lü JC, et al. (2007) Variants of C1GALT1 gene are associated with the genetic susceptibility to IgA nephropathy. Kidney Int 71: 448–453. 31. Maixnerová D, Merta M, Reiterová J, et al. (2007) The influence of three endothelin-1 polymorphisms on the progression of IgA nephropathy. Folia Biol (Praha) 53: 27–32.

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32. Di Duca M, Oleggini R, Sanna-Cherchi S, et al. (2006) Cis and trans regulatory elements in NPHS2 promoter: implications in proteinuria and progression of renal diseases. Kidney Int 70: 1332–1341. 33. Thibaudin L, Berthoux P, Thibaudin D, et al. (2004) G protein beta 3 subunit C825T polymorphism in primary IgA nephropathy. Kidney Int 66: 322–328. 34. Wang ZH, Chen N, Pan XX, et al. (2006) Association of single nucleotide polymorphism of MEGSIN gene with IgA nephropathy. Zhonghua Yi Xue Za Zhi 86: 1337–1341. 35. Li YJ, Du Y, Li CX, Guo H, et al. (2004) Family-based association study showing that immunoglobulin A nephropathy is associated with the polymorphisms 2093C and 2180T in the 3′ untranslated region of the Megsin gene. J Am Soc Nephrol 15: 1739–1743. 36. Matsunaga A, Numakura C, Kawakami T, et al. (2002) Association of the uteroglobin gene polymorphism with IgA nephropathy. Am J Kidney Dis 39: 36–41. 37. Tanaka Y, Suzuki Y, Tsuge T, et al. (2005) FcgammaRIIa-131R allele and FcgammaRIIIa-176V/V genotype are risk factors for progression of IgA nephropathy. Nephrol Dial Transplant 20: 2439–2445. 38. Yoon HJ, Shin JH, Yang SH, et al. (2003) Association of the CD14 gene — 159C polymorphism with progression of IgA nephropathy. J Med Genet 40: 104–108. 39. Tuglular S, Berthoux P, Berthoux F. (2003) Polymorphisms of the tumour necrosis factor alpha gene at position -308 and TNFd microsatellite in primary IgA nephropathy. Nephrol Dial Transplant 18: 724–731. 40. Bantis C, Heering PJ, Aker S, et al. (2004) Association of interleukin-10 gene G-1082A polymorphism with the progression of primary glomerulonephritis. Kidney Int 66: 288–294. 41. Mori H, Kaneko Y, Narita I, et al. (2005) Monocyte chemoattractant protein-1 A-2518G gene polymorphism and renal survival of Japanese patients with immunoglobulin A nephropathy. Clin Exp Nephrol 9: 297–303. 42. Berthoux FC, Berthoux P, Mariat C, et al. (2006) CC-chemokine receptor five gene polymorphism in primary IgA nephropathy: the 32 bp deletion allele is associated with late progression to end-stage renal failure with dialysis. Kidney Int 69: 565–572. 43. Panzer U, Schneider A, Steinmetz OM, et al. (2005) The chemokine receptor 5 Delta32 mutation is associated with increased renal survival in patients with IgA nephropathy. Kidney Int 67: 75–81. 44. Watanabe Y, Inoue T, Okada H, et al. (2006) Impact of selectin gene polymorphisms on rapid progression to end-stage renal disease in patients with IgA nephropathy. Intern Med 45: 947–951.

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45. Wiwanitkit V. (2006) Angiotensin-converting enzyme gene polymorphism is correlated to the progression of disease in patients with IgA nephropathy: a meta-analysis. Ren Fail 28: 697–699. 46. Bantis C, Ivens K, Kreusser W, et al. (2004) Influence of genetic polymorphisms of the renin-angiotensin system on IgA nephropathy. Am J Nephrol 24: 258–267. 47. Lim CS, Kim SM, Oh YK, et al. (2007) Association between the clara cell secretory protein (CC16) G38A polymorphism and the progression of IgA nephropathy. Clin Nephrol 67: 73–80. 48. Lü JC, Zhang H, Chen YQ, et al. (2004) Uteroglobin G38A polymorphism is associated with the progression of IgA nephropathy in Chinese patients. Zhonghua Nei Ke Za Zhi 43: 37–40. 49. Kovács TJ, Harris S, Vas TK, et al. (2006) Paraoxonase gene polymorphism and serum activity in progressive IgA nephropathy. J Nephrol 19: 732–738. 50. Narita I, Goto S, Saito N, et al. (2003) Genetic polymorphism of NPHS1 modifies the clinical manifestations of IgA nephropathy. Lab Invest 83: 1193–1200. 51. Chow KM, Szeto CC, Lai FM, et al. (2006) Genetic polymorphism of vascular endothelial growth factor: impact on progression of IgA nephropathy. Ren Fail 28: 15–20. 52. Suzuki H, Sakuma Y, Kanesaki Y, et al. (2004) Close relationship of plasminogen activator inhibitor-1 4G/5G polymorphism and progression of IgA nephropathy. Clin Nephrol 62: 173–179. 53. Xia Y, Li Y, Du Y, et al. (2006) Association of MEGSIN 2093C-2180T haplotype at the 3′ untranslated region with disease severity and progression of IgA nephropathy. Nephrol Dial Transplant 21: 1570–1574. 54. Song J, Sakatsume M, Narita I, et al. (2003) Peroxisome proliferatoractivated receptor gamma C161T polymorphisms and survival of Japanese patients with immunoglobulin A nephropathy. Clin Genet 64: 398–403. 55. Narita I, Saito N, Goto S, et al. (2002) Role of genetic polymorphism in the SA gene on the blood pressure and prognosis of renal function in patients with immunoglobulin A nephropathy. Hypertens Res 25: 831–836. 56. Li G, Zhang H, Lü J, et al. (2006) Tandem repeats polymorphism of MUC20 is an independent factor for the progression of immunoglobulin A nephropathy. Am J Nephrol 26: 43–49.

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Chapter 4

Histopathology, Immunofluorescence and Ultrastructural Examination Fernand M. Lai

Introduction Berger and Hinglais first described IgA nephropathy (IgAN) as a distinct entity in 1968, based on the study of a cohort of 25 patients, and is recognized today as the most common primary glomerulonephritis worldwide.1–7 Most observations Berger and Hinglais made then remain accurate, and constitute the fundamentals of IgAN: “The duration of the nephropathy from the first symptom to the biopsy varied from several months to 12 years. Thus, it appears that in the majority of cases of chronic focal glomerulonephritis, there are diffuse intercapillary deposits associated with the focal lesions. This observation, in addition to its theoretical interest, has some practical implications: immunofluorescence microscopy allows an easy diagnosis of this syndrome in cases in which the kidney is either normal or shows other lesions.”1,2 Primary IgAN is a chronic glomerulonephritis defined by the presence or deposition in the mesangium of predominant IgA-C3 immune complexes, within which antigenic moiety remains elusive (Figure 4.1).6,8–10 IgAN has conventionally been subdivided into primary and secondary IgA nephropathy, depending upon whether there is absence or presence of recognizable systemic conditions, respectively.3,6,10 These systemic diseases refer to Henoch-Schonlein purpura, dermatitis

37

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Figure 4.1 (a) Glomerular deposition of IgA-containing immune complexes, in a diffuse global mesangial distribution (FITC-labeled anti-human IgA, original magnification ×360). (b) Mesangial deposition of IgA-containing immune complexes, in a diffuse global mesangial distribution (Gold-labeled anti-human IgA, lead citrate and uranyl acetate, ×9400).

herpetiformis, liver cirrhosis, chronic hepatitis, coeliac disease, ankylosing spondylitis, rheumatoid arthritis, Reiter’s syndrome, human immunodeficiency virus infection, mycosis fungoides, and lung cancer. Such a subdivision relies on the diagnostic clinical features, since the renal lesions are relatively similar to all these distinct conditions. However, Henoch-Schonlein purpura has been most often regarded as a variant of primary idiopathic IgAN, with common systemic and vasculitic manifestations, while their renal lesions are indistinguishable.4,11–13 Renal biopsy is necessary to establish the diagnosis of IgAN, however this is often withheld in patients with isolated microscopic hematuria or mild urinary abnormalities, and thus indications for renal biopsy may vary between institutions and countries.5,10,14–16 This partly explain the geographic differences in the prevalence of renal lesions, or even in the gender preponderance, though should not affect the spectrum

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Histopathology, Immunofluorescence and Ultrastructural Examination ✦ 39

of renal lesions observed in IgAN.4,6,14,15,17,18 The interplay between complex genetic traits and environmental factors is also contributing to the geographic and ethnic differences in the prevalence and clinical manifestations of IgAN.10,19–21 However, the importance of renal biopsy does not only reside in diagnosis, but also in the useful prognostic information it may provide for the management of patient, clinical trials, and for assessing renal survival.14–18,22–25 The value of a uniform clinical and pathological classification of IgAN is now being tested in a large international collaborative effort through the International IgA Nephropathy Network with the Renal Pathology Society, under the auspices of the International Society of Nephrology.10,25 One must keep in mind that the application of a classification in an individual patient requires a discerning correlation of both morphological parameters and clinical features, for the prognostication to be useful or effective.

Histopathology of IgA Nephropathy The spectrum of glomerular lesions observed in IgAN is relatively broad, though it is far from the diversity encountered in lupus nephritis.17,18,26,27 There have been many proposed classifications of renal lesions, but none of these is widely adopted. Difficulties in reaching a consensus in classification may be explained by the divergent approaches between the “splitters” and the “lumpers” of renal lesions, and by some geographic difference in their prevalence.17,18,22,24,28 Perhaps, a basic reason for the lack of agreement owes to the poor understanding of mechanisms of the renal lesions.10,17,19 As an example, mesangial sclerosis and hypercellularity are observed in both immune complex IgAN and pauciimmune glomerulonephritis, indicating that such lesions depend mostly on less specific inflammatory response and on ubiquitous mediators such as transforming growth factor-β (TGF-β), plasminogen activatorinhibitor-1 (PAI-1), and platelet-derived growth factors (PDGFs).10,29,30 These same inflammatory processes are likely to play an important role in the maintenance and progression of glomerulosclerosis or other renal lesions. Despite the diversity of lesions and the apparent lack of a consensus in classification in IgAN, the glomerulus in fact shows limited morphological response to various insults, so that most studies agree on the importance of glomerular sclerosis and of tubulo-interstitial fibrosis in the assessment of renal survival, and in correlation with the clinical predictors.5,6,13–18,22–25,31

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The separation of renal lesions into active and chronic is somewhat arbitrary, in that the pathogenesis of these lesions is poorly understood. However, the evolution of many renal lesions can be appreciated from their various appearances or stages within the same biopsy. The unfolding histological changes permit to distinguish the more transient acute injuries from the more durable and cumulative chronic lesions.13,17,22 The subdivision into acute and chronic renal lesions can be useful in assessing prognosis, and to make treatment decision.

Acute Renal Lesions in IgA Nephropathy 1. Mesangial hypercellularity is defined when the mesangial cells exceed three per segmental area to as much as ten or 20 mesangial cells. This lesion is common, with characteristic focal and segmental distribution, particularly in early disease. These may be accompanied by expansion of mesangial matrix or sclerosis. Short of repeat biopsy, it is unclear whether mesangial hypercellularity is reversible or cumulative. On our hands, mesangial hypercellularity is not correlated with disease progression or renal survival.13,16,22 2. Necrotizing lesion can be defined when any three of the following features are identified in glomeruli, including disruption of capillary wall, mesangiolysis, leucocytic infiltration, nuclear fragments, fibrinous deposits, and cellular crescent. Necrotizing lesion can be viewed as an intra-glomerular vasculitis, seen in about 10% of patients with IgAN, and up to 50% in the nephritis of Henoch-Schonlein purpura. While this lesion may not affect actuarial renal survival, immunosuppression is beneficial to prevent flare-ups and progression to end-stage renal failure in some of the patients.13,22,32–34 3. Epithelial hypercellularity forming three or more solid layers constitute a cellular crescent, usually with a focal and segmental distribution, often closely associated with necrotizing lesion, both accounting for 5% to 15% of cases. Severe examples are rare, with full blown diffuse and circumferential crescentic lesions, and distinctive rapidly progressive renal failure with poor renal survival, though some cases may respond to cytotoxic drugs and plasma exchange.13,22,32–34 4. In contrast to lupus nephritis, global endocapillary hypercellularity with or without leucocytic infiltration, and interstitial inflammatory

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cells infiltrates unrelated to tubulo-interstitial fibrosis are all uncommon. When present, these consist generally of modest focal and segmental lesions in IgAN. A good periodic acid-Schiff (PAS) stain is useful to distinguished mesangial hypercellularity associated with sclerosis from endocapillary lesion. Due to their relatively low prevalence, these glomerular lesions have not been correlated with disease progression or renal survival.13,17,18,22–24

Chronic Renal Lesions in IgA Nephropathy 1. Glomerular sclerosis refers to accumulation of mesangial or basement membrane matrix. Its pathogenesis is incompletely understood, but inflammatory mediators such as TGF-β, PAI-1, and PDGFs play an important role in their development and their progression.10,30,35,36 The morphological changes associated with sclerosis are clinically important, as they relate to the impairment of renal function. These composite sclerosing lesions include capillary collapse resulting in luminal obliteration in some loops or luminal dilation in some others, the latter may further accumulate proteinaceous hyaline or degenerative foam cells. These segmental luminal collapse and hyalinosis may further be complicated by capsular adhesion, distortion of capillary tufts, and coalescence of segmental sclerosis to evolve finally global sclerosis or glomerular obsolescence (Figure 4.2).5,14,16–18,22,23 Such a sequence of events is sometimes observed within a single biopsy, which allows to conclude with relative certainty that sclerosis is irreversible and cumulative. The clinical correlation between extent of glomerular sclerosis and loss of renal function supports the notion that sclerosing process is cumulative and parallels the progressive decrease in functional nephrons.5,14,16–18,22,23,35 2. Tubular atrophy and interstitial fibrosis. The mechanisms leading to tubular atrophy and interstitial fibrosis are also incompletely understood, but in part they result from glomerular sclerosis, and are regarded as secondary to primary glomerular injury. There is no evidence of a immune mediated tubular insult as in lupus nephritis, however activated inflammatory mediators and inflammatory cells induced by chronic proteinuria are contributory.5,14,22,23,30 While there may be a delay for the tubulo-interstitial fibrosis to appear from the occurrence of glomerulosclerosis, in most biopsies however, the extent of tubular atrophy and interstitial fibrosis matches that of glomerulosclerosis, and correlated by semi-quantitative analysis.22,23

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Figure 4.2 (a) IgA nephropathy at an early stage with minimal mesangial expansion and preserved glomerular capillary tufts architecture (periodic acidsilver methenamine, H&E counterstain, ×360). (b) Small segmental sclerosis at six o’clock with partial capillary collapse, and capsular adhesion (periodic acidsilver methenamine, H&E counterstain, ×360). (c) Segmental sclerosis involving at least 50% of the glomerulus, with hyalinosis, capsular adhesion, marked consolidation and distortion of capillary tufts architecture (periodic acid-silver methenamine, H&E counterstain, ×360). (d) IgA nephropathy with advanced glomerulosclerosis, paralleled by extensive tubular atrophy and interstitial fibrosis (periodic acid-silver methenamine, H&E counterstain, ×180).

Three patterns of chronic tubulo-interstitial lesions can be recognized in IgAN, which may reflect different mechanism of injury. Most commonly, tubular atrophy and interstitial fibrosis appear diffuse and parallel the extent of glomerular sclerosis or obsolescence, and the difference among patients only relates to their severity (Figure 4.2d). The second pattern of tubulo-interstitial scarring refers to the so-called “striped fibrosis” distribution, which consists of groups of atrophic tubules and advanced glomerular sclerosis, alternating with groups of intact nephrons. The morphology of “striped fibrosis” is attributed to

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cyclosporin A toxicity in allografts, and reflects the glomerular arteriopathy induced by the drug. In fact, the same “striped fibrosis” distribution of tubulo-interstitial fibrosis also results from hypertensive hyaline arteriosclerosis, and in IgAN patients with such “striped fibrosis,” hypertensive injury prevails.22,23 The third pattern is uncommon, and may be recognized when tubular injury appears more pronounced than the extent of glomerular sclerosis. Notably, when tubular injury is accompanied by many eosinophils and histiocytes, this raises the possibility of a superimposed drug-induced interstitial nephritis, which is potentially reversible. When these patterns co-exist in a biopsy, it may be difficult to make their distinction or to assess their respective contribution to the tubulointerstitial injury. The acute tubular injury associated with bouts of gross hematuria and reversible acute renal failure can be overlooked, unless prominent and clinically correlated.37,38 Such injury is attributed to altered glomerular hemodynamics, and tubular obstruction by red blood cells, though oxidative stress imposed by the heme oxidase systems has also been implicated.37,38 When these patterns and insults co-exist in a biopsy, it may be difficult to make their distinction or to assess their respective contribution to the tubulointerstitial injury, but it remains very important to identify them. 3. Hyaline arteriosclerosis is identified in at least a third of the patients with IgAN at the time biopsy, and attributed to hypertension. The other features of hypertension such as arteriolar wall thickening, luminal narrowing and “onion skin” layering of myocytes are less often detected, except in advanced renal disease or poor control of hypertension.

Grading of IgA Nephropathy Due to the relative diversity of renal lesions in IgAN, the “splitters” approach to classification would stress on the comprehensive inclusion of all morphological spectrums, and on the semantic. In contrast, classification that stresses on the clinical impact would focus on clinically significant morphologies, and incline to adopt the “lumpers” approach. For the latter, it is perhaps appropriate to apply the term “grading” to emphasize on the prognostic character of the classification. IgAN is well recognized as a chronic condition with a protracted course, related to the persistence of mesangial immune complexes, and to the ensuing inflammatory response. These observations argue for the

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sustained glomerular and tubulo-interstitial injuries, leading to cumulative glomerular sclerosis and tubulo-interstitial fibrosis, which are the most prevalent renal lesions seen in IgAN, and appear the most accountable for the chronic course and disease progression (Figure 4.2).5,16,17,22,23 We thus use a chronicity-based histological grading, comprising the assessment of glomerular sclerosis, tubular atrophy and interstitial fibrosis, and hyaline arteriosclerosis as previously reported.13,22,23,37,38 Glomerular sclerosis is semi-quantitatively assessed in two steps: in the first, each glomerulus of a biopsy is rounded off as 0%, 25%, 50%, 75% and 100% for the extent of sclerosis. In a second step, the mean sclerosis per glomerulus expressed in percentage (%) is obtained from the sum of sclerosis of all glomeruli in % divided by the number of glomeruli, and this mean sclerosis determined the glomerular grade.22,23 The tubulointerstitial grade is defined by the extent of tubular atrophy and interstitial fibrosis in the cortex estimated in %, and glomerular hyaline arteriolosclerosis is assessed as present or absent, irrespective of arteriolar smooth muscle hypertrophy or luminal narrowing. This chronicity-based histological grading has correlated morphological and clinical parameters that have been widely recognized by others for their predictive values in disease progression and renal survival, and these include the glomerular grade, tubulo-interstitial fibrosis, hyaline arteriosclerosis, with serum creatinine, level of proteinuria and hypertension at the time of biopsy.5,7,14–18,22–24 The application of this grading is relatively simple, requiring one extra minute in the appraisal of a renal biopsy. It can be argued whether a morphological classification of IgAN based on subdivision of histological lesions is useful in such case, the diagnosis label reported can be redundant, since histological findings are already described in the microscopy, and such subcategories may hinder the prognostic information. The diagnosis of IgAN, established by immunofluorescence microscopy, can simply be stated as such, followed by the semi-quantitative grading, that provides an informative report for prognosis, management, and even segregated groups for therapeutic trials.22,23,37 In renal allograft, the diagnosis of IgAN is also straightforward, except sometimes for the distinction between de novo and recurrent IgAN, due to the lack of previous records. There are no demonstrable histological features that may distinguish a primary IgAN from IgAN in an allograft.22,23,38–40 IgAN in an allograft usually runs an indolent course, except for the rare crescentic form and perhaps in the allograft late

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course.38–40 While IgAN may contribute to chronic allograft nephropathy and to graft failure, the diagnosis of IgAN in allograft should not preclude the more common possibilities of graft rejection, drug toxicity or hypersensitivity, or simply uncontrolled hypertension.

Immunofluorescence Examination of IgA Nephropathy The diagnosis of IgAN is usually straightforward, and based on the mesangial deposition of predominant IgA-C3 immune complexes, a rather distinctive pattern which defines the disease.1,2 As in Berger’s original description, immune depositions are global and “diffuse intercapillary” irrespective of whether or not the light microscopic lesions are focal and segmental.1,2 In the article entitled “IgA nephropathy: a syndrome of uniform morphology, diverse clinical features and uncertain prognosis,”4 Clarkson referred to the distinctive mesangial distribution and composition of IgA-containing immune deposits as “uniform morphology” (Figure 4.1). Perhaps, it was also a reference to the most prevalent glomerular sclerosis, which after 40 years observation stands as the most tangible lesion associated with disease chronicity and progression.4 The immunofluorescence microscopy in the nephritis of HenochSchonlein purpura is indistinguishable from that of IgAN.2,13,41 IgAcontaining immune depositions in mesangium for both nephritis are similar, and consists mostly of polymeric IgA1 with the absence of secretory component and presence of J chain, regarded as the result of abnormal glycosylation of the IgA1 molecule.41–43 While glomerular depositions of IgA1, secretory component, J chain, and light chains are important in understanding the pathogenesis of IgAN, antibodies to detect them are not used in routine diagnosis. Predominance of IgA-C3 complexes relates to the dominance or co-dominance of IgA-containing immune complexes when other immunoglobulins such as IgG or IgM are also present in the mesangium, and with similar intensity. This is rarely a diagnostic problem, but when such a co-dominance occurs, the possibility of lupus nephritis, in particular the class II mesangiopathic nephritis needs to be considered. In lupus nephritis, the so-called “full house” composition of immunoreactants in glomeruli is rather distinctive, in marked contrast to lupus nephritis, complements of the classical pathway C1q and C4 as well as

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the capillary wall distribution of immunoreactants are rarely seen in IgAN. Finally, clinical and serological features are helpful to exclude systemic lupus erythematosus. In some instances, predominant mesangial IgA-C3 complexes are unequivocally positive, but of weak intensity of + on a scale of 3+, with a diffuse and global distribution, the diagnostic label of early IgAN may be used. In contrast, when glomerulosclerosis is advanced and extensive, where capillary tufts distortion and consolidation is marked, the mesangial distribution of a predominant IgA-C3 may not be clear-cut, and yet the case may be an example of IgAN presenting at a late stage, thus only a presumptive diagnosis can be issued. In biopsies with typical IgAN fluorescence microscopy, associated with atypical features that are not those of a distinct superimposed glomerular lesion, for example a membranous nephropathy, it may be a diagnostic dilemma to determine whether or not one is dealing with a variant form of IgAN, though these are uncommon situation.47,48

Ultrastructural Examination of IgA Nephropathy In a majority of patients with IgAN, the findings of electron microscopy only confirm or recapitulate the observations made in light and immunofluorescence microscopies, and do not add to the diagnosis. The salient feature consists of mesangial electron dense deposits (EDDs), which are per se not diagnostic, unless using immuno-electron microscopy labeling with anti-human IgA and C3 reagents (Figure 4.1).44 A particular globular distribution of mesangial or paramesangial EDDs protruding into the urinary space is common in IgAN, but rarely seen in other glomerulonephritis (Figure 4.3). The glomerular capillary basement membrane (GCBM) shows no abnormality in early or low-grade IgAN, but as sclerosing process accumulates, capillary wall irregularities appear, often in the form of segmental thinning, wrinkling and even disruption.45 Some of these peripheral capillary wall irregularities have been attributed to active lesions such as necrosis or epithelial crescents.46 The GCBM usually does not demonstrate presence of EDDs, unless one considers subendothelial EDDs small extension from paramesangial immune deposits. However, truly isolated subendothelial or subepithelial EDDs are observed, but they are generally small and segmental, accounting from 10% to 20% of the cases in the literature.44,47

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Figure 4.3 IgA nephropathy with a rather distinctive globular paramesangial electron dense deposits, protruding into the urinary space, equivalent to the paramesangial hyaline “nipple” seen in light microscopy (lead citrate and uranyl acetate, ×3800).

Any major deviation from the above ultrastructural observations of IgAN should raise the possibility of a superimposed glomerular lesion. A few entities have been identified and deserve some discussion here as they support the notion that two or more primary glomerular diseases may co-exist or be overlapping, requiring electron microscopy for diagnosis. The diagnosis of minimal change nephropathy overlapping on IgAN must be considered when visceral epithelial cells are activated with prominent microvillous cell membrane, and extensive effacement or fusion of the foot processes. These patients often present with a nephrotic range proteinuria and may show response to steroids treatment.34 Co-existing membranous nephropathy and IgAN are recognized, when ultrastructure global subepithelial EDDs are related to the immunofluorescent granular IgG-C3 complexes, and distinct from the mesangial IgA-C3 complexes or EDDs.48,49 Membranous nephropathy in

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such overlap syndrome can be idiopathic, but some cases are associated with hepatitis B viral antigen, which may pathogenetically link the two nephropathies.48,49 The differential diagnosis with lupus nephritis should not be difficult, as “full house” immunoreactants in lupus nephritis are distributed in both the mesangium and GCBM. Only a minority of patients with diabetes may undergo renal biopsy for atypical clinical manifestation such as hematuria, and IgAN can be diagnosed with detectable mesangial IgA-C3 immune complexes, superimposed on classical diabetic mesangial nodular sclerosis.50,51 Such an overlapping may not alter significantly both the renal prognosis of diabetic glomerulosclerosis or its management, but the occurrence in patients with diabetic glomerulosclerosis of other forms of glomerular diseases support the notion that in double or triple nephropathies, the cross of pathogenetic pathway appears to be coincidental.50–52 In adult IgAN patients with low-grade glomerular lesions, the GCBM thickness can be appraised by ultrastructural morphometry, and two groups can be identified: one group with a mean GCBM thickness within the normal range established in our adult controls, ranging from 346 to 396 nm, and the other group with a global uniformly thick GCBM with a mean thickness ranging from 400 to over 600 nm. The latter group represents patients with IgAN with superimposed isolated thick GCBM renal lesion.53,54 Isolated thick GCBM renal lesion is described in proteinuric patients, who may demonstrate composite clinical manifestations that include obesity, elevated fasting blood glucose, impaired glucose tolerance, hypertension, hyperuricemia, hyperlipidemia and hyperinsulinemia, in keeping with the metabolic syndrome. The GCBM has been ascribed as the renal lesion associated with hyperinsulinemia, pre-diabetes or possibly the metabolic syndrome.54,55 It appears that the isolated uniformly thick GCBM represent a relatively early renal lesion associated with the metabolic syndrome, and the increasing number of observations parallel the worldwide epidemic of obesity and diabetes.54–56 The evolution and prognosis of the isolated thick GCBM renal lesion are still unknown and need to be clarified, however obesity and insulin resistance have been attributed a major role in end-stage renal failure, in the controversy of “hypertensive nephrosclerosis.”56 The finding of a thick GCBM in patients with IgAN should not be regarded as a variant of IgAN, but rather a patient with a superimposed renal lesion, significant for its propensity to develop

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metabolic syndrome or associated complication, including a full blown diabetic glomerulosclerosis or even end-stage renal failure.54–56 Similarly, GCBM thinning is a fairly common observation, as a focal segmental finding, more often associated with prevalent chronic lesions, such as sclerosis, aneurysmal changes and hyalinosis, as well as disease progression.45,46 In contrast, diffuse global thinning of the GCBM can also be observed, but rare, and displays a uniform quality in the thinning with a mean thickness in the range of thin membrane nephropathy.57–60 These examples should be regarded as a superimposed thin membrane nephropathy rather than a variant of IgAN, as many may be indolent or do not alter the course of IgAN.58–60

References 1. Berger J, Hinglais N. (1968) Les dépots intercapillaires d’IgA-IgG. J Urol Nephrol 74: 694–695. 2. Berger J, Hinglais N, Striker L. (2000) Intercapillary deposits of IgA-IgG. J Am Soc Nephrol 11: 1957–1959. 3. D’Amico G. (1987) The commonest glomerulonephritis in the world: IgA nephropathy. Q J Med 245: 964–965. 4. Clarkson AR, Seymour AE, Thompson AJ, et al. (1977) IgA nephropathy: a syndrome of uniform morphology, diverse clinical features and uncertain prognosis. Clin Nephrol 8: 459–471. 5. Ibels LS, Gyory AZ. (1994) IgA nephropathy: analysis of the natural history, important factors in the progression of renal disease and review of the literature. Medicine 73: 79–100. 6. Galla JH. (1995) IgA nephropathy. Kidney Int 47: 377–387. 7. Li L. (1996) End-stage renal disease in China. Kidney Int 49: 287–301. 8. Tomino Y, Sakai H, Miura M, et al. (1985) Specific binding of circulating IgA antibodies in patients with IgA nephropathy. Am J Kidney Dis 6: 149–153. 9. Coppo R, Amore A, Hogg R, Emancipator S. (2000) Idiopathic nephropathy with IgA deposits. Pediatr Nephrol 15: 139–150. 10. Barratt J, Feehally J. (2005) IgA nephropathy. J Am Soc Nephrol 16: 2088–2097. 11. Meadow SR, Scott DG. (1985) Berger disease: Henoch-Schönlein syndrome without the rash. J Pediatr 106: 27–32. 12. Davin JC, Ten Berge IJ, Weening JJ. (2001) What is the difference between IgA nephropathy and Henoch-Schönlein purpura nephritis? Kidney Int 59: 823–834.

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13. Szeto CC, Choi PC, To KF, et al. (2001) Grading of acute and chronic renal lesions in Henoch-Schönlein purpura. Mod Pathol 14: 635–640. 14. D’Amico G. (2004) Natural history of idiopathic IgA nephropathy and factors predictive of disease outcome. Semin Nephrol 24: 179–196. 15. Alamartine E, Sabatier JC, Berthoux FC. (1990) Comparison of pathological lesions on repeated renal biopsies in 73 patients with primary IgA glomerulonephritis: value of quantitative scoring and approach to final prognosis. Clin Nephrol 34: 45–51. 16. Li PK, Ho KK, Szeto CC, et al. (2002) Prognostic indicators of IgA nephropathy in the Chinese — clinical and pathological perspectives. Nephrol Dial Transplant 17: 64–69. 17. Haas M. (1997) Histologic subclassification of IgA nephropathy: a clinicopathologic study of 244 cases. Am J Kidney Dis 29: 829–842. 18. Lee HS, Lee MS, Lee SM, et al. (2005) Histological grading of IgA nephropathy predicting renal outcome: revisiting H. S. Lee’s glomerular grading system. Nephrol Dial Transplant 20: 342–348. 19. Wyatt RJ, Julian BA, Baehler RW, et al. (1998) Epidemiology of IgA nephropathy in central and eastern Kentucky for the period 1975 through 1994. Central Kentucky Region of the Southeastern United States IgA Nephropathy DATABANK Project. J Am Soc Nephrol 9: 853–858. 20. Beerman I, Novak J, Wyatt RJ, et al. (2007) The genetics of IgA nephropathy. Nat Clin Pract Nephrol 3: 325–338. 21. Hsu SI. (2008) Racial and genetic factors in IgA nephropathy. Semin Nephrol 28: 48–57. 22. To KF, Choi PC, Szeto CC, et al. (2000) Outcome of IgA nephropathy in adults graded by chronic histological lesions. Am J Kidney Dis 35:392–400. 23. Lai FM, Szeto CC, Choi PCL, et al. (2002) Primary IgA nephropathy with low histologic grade and disease progression: is there a “point of no return”? Am J Kidney Dis 39: 401–406. 24. Manno C, Strippoli GF, D’Altri C, et al. (2007) A novel simpler histological classification for renal survival in IgA nephropathy: a retrospective study. Am J Kidney Dis 49: 763–775. 25. Feehally J, Barratt J, Coppo R, et al. (2007) International IgA Nephropathy Network. International IgA nephropathy network clinico-pathological classification of IgA nephropathy. Contrib Nephrol 157: 13–18. 26. Markowitz GS, D’Agati VD. (2007) The ISN/RPS 2003 classification of lupus nephritis: an assessment at 3 years. Kidney Int 71: 491–495. 27. Schwartz MM. (2007) The pathology of lupus nephritis. Semin Nephrol 27: 22–34.

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28. D’Amico G. (2000) Natural history of idiopathic IgA nephropathy: role of clinical and histological prognostic factors. Am J Kidney Dis 36: 227–237. 29. Fogo A. (1999) Mesangial matrix modulation and glomerulosclerosis. Exp Nephrol 7: 147–159. 30. Lai KN, Chan LY, Leung JC. (2005) Mechanisms of tubulointerstitial injury in IgA nephropathy. Kidney Int Suppl 94: S110–S115. 31. Wyatt RJ, Emancipator SN, Kon V, et al. (1997) IgA nephropathy databank: development of a system for management of renal biopsy acquired data. Am J Kidney Dis 29: 817–828. 32. D’Amico G, Napodano P, Ferrario F, et al. (2001) Idiopathic IgA nephropathy with segmental necrotizing lesions of the capillary wall. Kidney Int 59: 682–692. 33. Tumlin JA, Lohavichan V, Hennigar R. (2003) Crescentic, proliferative IgA nephropathy: clinical and histological response to methylprednisolone and intravenous cyclophosphamide. Nephrol Dial Transplant 18: 1321–1329. 34. Lai KN, Lai FM, Ho CP, et al. (1986) Corticosteroid therapy in IgA nephropathy with nephrotic syndrome: a long-term controlled trial. Clin Nephrol 26: 174–180. 35. Suzuki J, Yoshikawa N, Nakamura H. (1990) A quantitative analysis of the mesangium in children with IgA nephropathy: sequential study. J Pathol 161: 57–64. 36. Fogo AB. (2006) Progression versus regression of chronic kidney disease. Nephrol Dial Transplant 21: 281–284. 37. Szeto CC, Lai FM, To KF, et al. (2001) The natural history of immunoglobulin A nephropathy among patients with hematuria and minimal proteinuria. Am J Med 110: 434–437. 38. Wang AY, Lai FM, Yu AW, et al. (2001) Recurrent IgA nephropathy in renal transplant allografts. Am J Kidney Dis 38: 588–596. 39. Choy BY, Chan TM, Lo SK, et al. (2003) Renal transplantation in patients with primary immunoglobulin A nephropathy. Nephrol Dial Transplant 18: 2399–2404. 40. Floege J. (2004) Recurrent IgA nephropathy after renal transplantation. Semin Nephrol 24: 287–291. 41. Conley ME, Cooper MD, Michael AF. (1980) Selective deposition of immunoglobulin A1 in immunoglobulin A nephropathy, anaphylactoid purpura nephritis, and systemic lupus erythematosus. J Clin Invest 66: 1432–1436. 42. Lomax-Smith JD, Zabrowarny LA, Howarth GS, et al. (1983) The immunochemical characterization of mesangial IgA deposits. Am J Pathol 113: 359–364.

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43. Novak J, Moldoveanu Z, Renfrow MB, et al. (2007) IgA nephropathy and Henoch-Schoenlein purpura nephritis: aberrant glycosylation of IgA1, formation of IgA1-containing immune complexes, and activation of mesangial cells. Contrib Nephrol 157: 134–138. 44. Woodrow DF, Shore I, Moss J, et al. (1989) Immunoelectron microscopic studies of immune complex deposits and basement membrane components in IgA nephropathy. J Pathol 157: 47–57. 45. Morita M, Sakaguchi H. (1988) A quantitative study of glomerular basement membrane changes in IgA nephropathy. J Pathol 154: 7–18. 46. Ng WL, Chan KW, Yeung CK, Kwan S. (1984) Peripheral glomerular capillary wall lesions in IgA nephropathy and their implications. Pathology 16: 324–330. 47. Lee HS, Choi Y, Lee JS, et al. (1989) Ultrastructural changes in IgA nephropathy in relation to histologic and clinical data. Kidney Int 35: 880–886. 48. Magil A, Webber D, Chan V. (1986) Glomerulonephritis associated with hepatitis B surface antigenemia. Report of a case with features of both membranous and IgA nephropathy. Nephron 42: 335–339. 49. Lai FM, Lai KN, Tam JS, et al. (1994) Primary glomerulonephritis with detectable glomerular hepatitis B virus antigens. Am J Surg Pathol 18: 175–186. 50. Lai FM, Li PK, Pang SW, et al. (1993) Diabetic patients with IgA nephropathy and diabetic glomerulosclerosis. Mod Pathol 6: 684–690. 51. Mak SK, Wong PN, Lo KY, et al. (2001) Prospective study on renal outcome of IgA nephropathy superimposed on diabetic glomerulosclerosis in type 2 diabetic patients. Nephrol Dial Transplant 16: 1183–1188. 52. Ainsworth SK, Hirsch HZ, Brackett NC, et al. (1982) Diabetic glomerulonephropathy: histopathologic, immunofluorescent, and ultrastructural studies of 16 cases. Hum Pathol 13: 470–478. 53. Cusumano AM, Bodkin NL, Hansen BC, et al. (2002) Glomerular hypertrophy is associated with hyperinsulinemia and precedes overt diabetes in aging rhesus monkeys. Am J Kidney Dis 40: 1075–1085. 54. Lai FM, Szeto CC, Choi PC, et al. (2004) Isolate diffuse thickening of glomerular capillary basement membrane: a renal lesion in prediabetes? Mod Pathol 17: 1506–1512. 55. Ko GT, Cockram CS, Chow CC, et al. (2006) Metabolic syndrome by the international diabetes federation definition in Hong Kong Chinese. Diabetes Res Clin Pract 73: 58–64. 56. Kincaid-Smith P. (2004) Hypothesis: obesity and the insulin resistance syndrome play a major role in end-stage renal failure attributed to hypertension and labelled “hypertensive nephrosclerosis”. J Hypertens 22: 1051–1055.

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57. Berthoux FC, Laurent B, Alamartine E, Diab N. (1996) New subgroup of primary IgA nephritis with thin glomerular basement membrane (GBM): syndrome or association. Nephrol Dial Transplant 11: 558–559. 58. Liapis H, Gökden N, Hmiel P, Miner JH. (2002) Histopathology, ultrastructure, and clinical phenotypes in thin glomerular basement membrane disease variants. Hum Pathol 33: 836–845. 59. Frascá GM, Soverini L, Gharavi AG, et al. (2004) Thin basement membrane disease in patients with familial IgA nephropathy. J Nephrol 17: 778–785. 60. Foster K, Markowitz GS, D’Agati VD. (2005) Pathology of thin basement membrane nephropathy. Semin Nephrol 25: 149–158.

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Chapter 5

Tubulointerstitial Injury in IgA Nephropathy Joris J. Roelofs and Sandrine Florquin

Introduction Although the majority of progressive renal diseases are glomerular and vascular in origin, clinicopathological studies have revealed that renal outcome is largely determined by the extent of secondary tubulointerstitial damage.1 In particular in IgA nephropathy, several studies have shown that the degree of tubular atrophy and interstitial fibrosis correlates better with deterioration of renal function than the extent of glomerular injury.

Clinicopathological Correlations Several early studies noted the importance of chronic lesions and in particular tubulointerstitial damage in the appraisal of IgA nephropathy.2–5 In a study including 55 cases of IgA nephropathy, elevated glomerulosclerosis index, tubulointerstitial injury index, serum creatinine, presence of nephritic syndrome, elevated crescent index, and elevated total cholesterol were found to be negative predictors for renal outcome in descending order of odds ratio in a univariate analysis. After multivariate analysis of the data, however, only tubulointerstitial index independently predicted unfavorable outcome.6 In a larger study including 194 patients with a mean follow-up of ten years, tubular grade 2 defined as ≥ 25% but < 50% tubular damage (relative risk: 5.5) and grade 3 defined as > 50% tubular damage (relative risk: 28.8) were the best 55

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factors to predict chronic renal failure in multivariate analysis.7 To et al.8 examined separately the degree of glomerulosclerosis, tubulointerstitial damage, and hyaline arteriosclerosis in 126 renal biopsies of IgA nephropathy. In this study global glomerulosclerosis represented the only independent prognostic factor for renal survival. Both glomerulosclerosis and tubulointerstitial damage, however, were significantly correlated with the degree of proteinuria, hypertension and serum creatinine level. More recently, Myllymaki et al.9 analyzed 204 renal biopsies of IgA nephropathy and concluded from a multivariate analysis that interstitial fibrosis and tubulointerstitial inflammation were independently associated with progressive diseases. In the evidence-based Oxford classification 2008 for IgA nephropathy, tubular atrophy/interstitial fibrosis was significantly associated with renal outcome independently of glomerular filtration rate, proteinuria, and blood pressure at presentation (manuscript in preparation). Altogether these independent clinicopathological studies reveal that the degree of tubulointerstitial damage correlates with deterioration of renal function in IgA nephropathy. Irrespective of the primary insult, the histological characteristics of kidneys with chronic renal failure are remarkably similar and characterized by simplification of tubular epithelial cells (TECs), thickening of the tubular basement membrane, mild to moderate interstitial infiltrate of mononuclear cells and scattered neutrophils with focal tubulitis, degeneration of the peritubular capillary network, accumulation of (myo)fibroblasts and ultimately deposition of extracellular matrix. It is beyond the scope of this chapter to review in detail the different steps of this cascade. Instead, we shall focus on some crucial pathophysiological mechanisms that have particularly been investigated in the progression of IgA nephropathy. The principal mechanisms implicated in the progression of tubulointerstitial injury in IgA nephropathy are summarized in Table 5.1.

Glomerulo-Tubular Communication Although glomerular deposition of IgA is the main pathophysiological driving force in the initiation of IgA nephropathy, progression of interstitial damage is probably not directly caused by tubular and/ or interstitial deposition of IgA. Indeed, IgA deposits are only seldom encountered in the tubulointerstitial compartment.10 In recent years,

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Tubulointerstitial Injury in IgA Nephropathy ✦ 57

Table 5.1 Potential mechanisms involved in tubulointerstitial damage in IgA nephropathy. Factors

Mechanisms

IgA (↑)

TECs activation No TEC activation TECs activation Inflammation Inflammation Inflammation Inflammation Inflammation Tubular damage Tubular damage Tubular damage Tubular damage TECs activation Fibrosis TEC protection Inflammation TEC proliferation TEC apoptosis Fibrosis Fibrosis Fibrosis Capillary protection Fibrosis Inflammation TEC protection Capillary degeneration Pro-fibrotic

Proteinuria (↑) IL-6 (↑) TNF-α (↑) PDGFR-β (↑) ICAM-1 (↑) CD80 and CD86 (↑) CD3+ cells (↑) CD20+ cells (↑) Cytotoxic T cells (↑) CD68 (↑) TGF-β (↑) HGF (↑) Angiotensin-2 (↑)

Caldesmon (↑) α-SMA (↑) FSP-1 (↑) VEGF (↑) Capillary network (↓) CD44 (↑)

References 10 13 17 59 13 21 24, 60 23 9, 26 25, 26 26 9 31 61 and others 29 47 49 48 40 37 41 35 35 58 56 57

glomerulotubular crosstalk has been proposed as one of the mechanisms involved.11 Upon deposition of IgA, mesangial cells start to proliferate and release cytokines/chemokines, among which TNF-α and IL-6.12,13 These inflammatory mediators are filtered by damaged glomeruli and stimulate downstream TECs, which subsequently produce pro-inflammatory mediators including IL-1, TNF-α, MIF, IL-8, MCP-1, RANTES, and sICAM-1.13,14 This glomerulotubular communication has been implicated in the pathogenesis and aggravation of

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tubulointerstitial damage in IgA nephropathy. Interestingly, despite in vitro binding of isolated IgA to TECs, the exposure of TECs to IgA did not result in either proliferation or enhanced synthesis of inflammatory mediators by TECs.13 Proteinuria is recognized as a poor prognostic marker for renal outcome in IgA nephropathy.15 In vitro and in vivo studies have demonstrated that proteinuria leads to activation of the nuclear NF-κB transcription factor in TECs16,17 that, in turn, induces the up-regulation of pro-inflammatory cytokines/chemokines including MCP-1, RANTES, and osteopontin but also of the profibrogenic cytokine TGF-β.17

Leukocytes Chemokines play pivotal roles in the recruitment of inflammatory cells into the kidney. The chemokine receptors CXCR3 and CCR5 are expressed on activated T cells. Expression of both chemokine receptors parallels infiltration of CD3+ cells into the interstitium in IgA nephropathy, suggesting that interstitial CXCR3, as well as CCR5-positive T cells may play a role in the progression of renal diseases.18,19 Supporting this hypothesis, it has been shown recently that a mutation in the CCR5 gene is associated with an increased renal survival in IgA nephropathy.20 PDGF is a potent chemoattractant for macrophages. In addition, it causes the release of other cytokines among which TGF-β. Interstitial PDGFR-β is significantly increased in IgA nephropathy and associated with monocyte/macrophage infiltration21 (refer also to Chapter 18). The secretion of cytokines by TECs not only leads to up-regulation of adhesion molecules including ICAM-1 and CD4422 but also of MHC class II and the co-stimulatory signals CD80 and CD86,23 which support infiltration and activation of inflammatory cells. In a study comprising 33 cases of IgA nephropathy, CD80/CD86 expression correlated with renal function at the time of renal biopsy and with monocyte/macrophage infiltration. These data support the hypothesis that TECs in IgA nephropathy may act as antigen presenting cells and activate T cells.23 The inflammatory infiltrate, mainly composed of monocytes/macrophages and T lymphocytes, contributes to a positive feedback of inflammation, among other things by facilitating the up-regulation of tubular ICAM-1 expression.24 Similar results have been obtained in a study comprising 204 renal biopsies in which tubulointerstitial CD45+ cells, CD3+ cells

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and CD68+ cell infiltrates correlate with progression of renal disease. CD3+ score displayed the strongest correlation and remained significant in multivariate analysis.9 In contrast, little has been published about B-cell infiltration and IgA nephropathy. Heller et al.25 characterized B-cell infiltrates and the factors involved in B-cell recruitment in 18 cases of IgA nephropathy. They concluded that CD20-positive B cells form a prominent part of the interstitial inflammatory infiltrate and that B-cell infiltrates are associated with increased local expression of the chemokine CXCL13 and the corresponding receptor CXCR5 on B cells. However, no correlation could be established between B cell infiltration and the Haas classification of IgA nephropathy. Correlations with clinical features were not reported. In a recent study by van Es et al.26 the tubulointerstitial inflammatory infiltrate is characterized in detail and correlated to renal outcome in IgA nephropathy. In patients with an estimated GFR > 60 ml/min at time of biopsy, the amounts of CD45, CD3, CD4, CD20, and GMP-17-positive cytotoxic T cells in the interstitium and/or tubules correlate with progression of disease. In a multivariate analysis, only GMP17-cytotoxic T cell-induced tubulitis and interstitial B-cell infiltrate remained significant. Quite surprisingly, the presence of macrophages (marker: CD68) was not associated with progression. Macrophages and their products are implicated in various deleterious processes in the course of renal damage such as direct cell toxicity, basement membrane damage and interstitial fibrosis. On the other hand, macrophages are also involved in tissue repair by phagocytosing apoptotic bodies, removing immune complexes and fibrin and secreting protecting mediators such as HGF.27

Growth Factors Hepatocyte growth factor (HGF) has recently emerged as a potent antifibrotic and reno-protective factor that counteracts the pro-fibrotic actions of TGF-β.28 In a series of 35 renal biopsies from patients with IgA nephropathy, 14 biopsies showed positive immunoreactivity for HGF in damaged tubules.29 This may represent an endogenous mechanism of repair. The expression of TGF-β is increased in tubules and tubulointerstitial areas in IgA nephropathy and correlates significantly with the severity of histological damage.30 TGF-β has also been shown

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to induce the activation of the transcription factor c-Jun in TECs that in turn regulates the expression of genes involved in proliferation and inflammation.31 The expression of activated c-Jun in tubules also correlates with the degree of interstitial fibrosis in IgA nephropathy.31 Progression of renal disease correlates with rarefaction of the peritubular capillary network which results from an increase in the expression of the anti-angiogenic factor thrombospondin-1 (TSP-1) and decrease of the pro-angiogenic factor vascular endothelial growth factor (VEGF) by tubular epithelial cells.32–34 In IgA nephropathy, VEGF immunoreactivity has been shown to increase with the degree of tubulointerstitial injury. Despite this up-regulation of VEGF but in accordance with other progressive renal diseases, the numbers of peritubular capillaries diminishes with progression of the disease.35 In this study, the expression of the anti-angiogenic TSP-1 was not investigated. It is possible that a misbalance between TSP-1 and VEGF occurred and led to the rarefaction of peritubular capillaries.

Myofibroblast Influx Accumulation of myofibroblasts in the interstitium is a key event in the development of fibrosis. These cells are characterized by the expression of α-smooth muscle actin (α-SMA) and fibroblastic-specific protein-1 (FSP-1).36 In a series of 38 patients with IgA nephropathy, the intensity of the interstitial α-SMA staining correlated with renal functional outcome.37 In contrast, no correlation could be established between interstitial α-SMA expression and renal outcome in other studies.38,39 Caldesmon is a major calmodulin- and actin-binding protein found in smooth muscles and is a marker for smooth muscle cells. In 38 cases of IgA nephropathy, caldesmon expression was enhanced where interstitial fibrosis was found and caldesmon staining co-localizes with α-SMA expression.40 FSP-1 is a S100A4 protein constitutively expressed in the cytoplasm of tissue fibroblasts. In a series of 142 renal biopsies with IgA nephropathy, the numbers of FSP-1 positive fibroblasts directly correlated with serum creatinine and inversely with estimated creatinine clearance. In the multivariate analysis ≥ 20 FSP-1 positive fibroblasts per high power field correlated with renal outcome. Interestingly, staining for FSP-1 was largely non-overlapping with α-SMA positive cells in the interstitium.41

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Matrix Metalloproteinases Accumulation of extracellular matrix (ECM) results from an imbalance between synthesis by myofibroblasts and degradation by matrix metalloproteinases (MMP).42 MMP activity has been implicated in a broad variety of inflammatory and remodeling renal diseases, such as lupus nephritis, membranous glomerulopathy, and diabetic nephropathy.42 Surprisingly, very few studies address the issue of MMP activity in IgA nephropathy. Brisk glomerular activity of MMP-9 and, to a lesser extent, MMP-2 has been reported in IgA nephropathy.43 In patients with IgA nephropathy and lupus nephritis, increased serum levels of MMP-3 and TIMP-2 have been described.44 Furthermore, PBMCs from patients with IgA nephropathy have been shown to express higher level of MMP9 mRNA than those from patients with other forms of glomerulonephritis or from healthy controls.45 Also, MMP-9 mRNA production by PBMCs correlated significantly with the severity of histopathologic grading for IgA according to Haas. In addition, MMP-9 mRNA levels from patients with IgA nephropathy showed a strong correlation with the severity of proteinuria in these patients.45 Although these data suggest that PBMC-derived MMP are of importance during disease progression in IgA nephropathy, solid data on MMP activity in the tubulointerstitial compartment in IgA nephropathy are currently lacking. MMP-9 activity can lead to destruction of the tubular basement membrane which in turn results in myofibroblastic transition of TECs via epithelial-mesenchymal transition.

The Renin-Angiotensin System The Renin-Angiotensin system (RAS) has been shown to play a key role in the development of renal fibrosis. While several components of the RAS exert profibrotic activity, Angiotensin II (Ang II), produced by activated macrophages and fibroblasts has been shown to be the key hormone responsible for renal fibrosis.46 Besides being a vasoactive peptide, Ang II induces expression of several cytokines/chemokines, including TGF-β, TNF-α, IL-6, MCP-1 and RANTES, through interaction with the Ang II receptors type 1 and 2 (ATR1 and ATR2).47 Furthermore, Ang II influences renal tissue turnover by mediating TEC apoptosis (via interaction with ATR2),48 while at the same time mediating TEC proliferation

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(via ATR1).49 Pharmacologic blockade of the RAS effectively slows down the progression of interstitial fibrosis.50 In IgA nephropathy, the intrarenal RAS is activated.51 In a study of 20 renal biopsies from IgA nephropathy patients, mRNA levels of angiotensinogen, renin, ACE and AT1R and AT2R were significantly enhanced in both microdissected glomerular and tubulointerstitial tissue samples.51 In addition, by immunostainings Chan et al.52 have shown significant up-regulation of ATR1 and ATR2 protein in proximal TECs in biopsies from patients with IgA nephropathy. In the same study, it was shown that the expression of ATR1 and ATR2 was not a direct result of interaction between patient-derived IgA and TECs. Instead, significant expression of ATR1 and ATR2 by TECs was generated after incubation of TECs with conditioned medium from mesangial cells that

Figure 5.1 Immunostainings for CD44 in normal kidney (A) and in IgA nephropathy (B–D) showing minimal CD44 expression upon normal conditions. In IgA nephropathy, a strong basolateral expression for CD44 is observed in damaged tubules (C and D). The inflammatory infiltrate is also positive for CD44 (B and C). Magnification ×4 (A and B) and ×10 (C and D).

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were activated by patient-derived IgA,52 providing further evidence for the importance of glomerulotubular crosstalk in IgA nephropathy.

CD44 One molecule that may orchestrate the different mechanisms that lead to tubulointerstitial damage and ultimately chronic renal failure in IgA nephropathy is CD44. The shortest form of CD44, CD44 standard (CD44s), is able to bind hyaluronan and osteopontin, two major components of the extracellular matrix. The CD44-variant containing variable-exon 3 (CD44v3) is capable of binding growth factors at its attached heparan sulfate-chain and presents these factors to their high affinity receptors. CD44 comprises a family of type I transmembrane glycoproteins with a wide tissue distribution that are involved in cellcell and cell-matrix interactions.53,54 Using murine models of renal diseases, we have shown that CD44 plays a crucial role in the cascade of renal inflammation, tubular atrophy, rarefaction of the peritubular capillary network and ultimately fibrosis.55–57 In addition, CD44 regulates the balance between HGF and TGF-β during renal fibrogenesis.56 Under normal conditions, CD44 is undetectable in the kidney except in passenger leukocytes. In IgA nephropathy, a strong basolateral expression of CD44 was observed in damaged tubules as well as in the interstitium (Figure 5.1). CD44 expression paralleled the degree of tubular atrophy and interstitial fibrosis and correlated significantly with the degree of proteinuria.58 We hypothesize that CD44 may exert a pivotal role in the cascade of renal inflammation and fibrosis in IgA nephropathy.

References 1. D’Amico G, Ferrario F, Rastaldi MP. (1995) Tubulointerstitial damage in glomerular diseases: its role in the progression of renal damage. Am J Kidney Dis 26: 124–132. 2. Bogenschütz O, Bohle A, Wehrmann M, et al. (1990) IgA nephritis: on the importance of morphological and clinical parapeters in the long-term prognosis of 239 patients. Am J Nephrol 10: 137–147. 3. Haas M. (1997) Histologic subclassification of IgA nephropathy: a clinicopathologic study of 244 cases. Am J Kidney Dis 29: 829–842. 4. Lee SM. (1997) Prognostic indicators of progressive renal disease in IgA nephropathy: emergence of a new histologic grading system. Am J Kidney Dis 29: 953–958.

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5. Wyatt RJ, Emancipator SN, Kon V, et al. (1997) IgA nephropathy databank: development of a system for management of renal biopsy acquired data. Am J Kidney Dis 29: 817–828. 6. Mera J, Uchida S, Nagase M. (2000) Clinicopathologic study on prognostic markers in IgA nephropathy. Nephron 84: 148–157. 7. Daniel L, Saingra Y, Giorgi R, et al. (2000) Tubular lesions determine prognosis of IgA nephropathy. Am J Kidney Dis 35: 13–20. 8. To KF, Choi PC, Szeto CC, et al. (2000) Outcome of IgA nephropathy in adults graded by chronic histological lesions. Am J Kidney Dis 35: 392–400. 9. Myllymaki JM, Honkanen TT, Syrjanen JT, et al. (2007) Severity of tubulointerstitial inflammation and prognosis in immunoglobulin A nephropathy. Kidney Int 71: 343–348. 10. Frasca GM, Vangelista A, Biagini G, Bonomini V. (1982) Immunological tubulointerstitial deposits in IgA nephropathy. Kidney Int 22: 184–191. 11. Lai KN, Chan LY, Leung JC. (2005) Mechanisms of tubulointerstitial injury in IgA nephropathy. Kidney Int Suppl 94: S110–S115. 12. Gomez-Guerrero C, Lopez-Armada MJ, Gonzalez E, Egido J. (1994) Soluble IgA and IgG aggregates are catabolized by cultured rat mesangial cells and induce production of TNF-alpha and IL-6, and proliferation. J Immunol 153: 5247–5255. 13. Chan LY, Leung JC, Tsang AW, et al. (2005) Activation of tubular epithelial cells by mesangial-derived TNF-alpha: glomerulotubular communication in IgA nephropathy. Kidney Int 67: 602–612. 14. van Kooten C, Daha MR. (2001) Cytokine cross-talk between tubular epithelial cells and interstitial immunocompetent cells. Curr Opin Nephrol Hypertens 10: 55–59. 15. Reich HN, Troyanov S, Scholey JW, Cattran DC. (2007) Remission of proteinuria improves prognosis in IgA nephropathy. J Am Soc Nephrol 18: 3177–3183. 16. Gomez-Garre D, Largo R, Tejera N, et al. (2001) Activation of NF-kappaB in tubular epithelial cells of rats with intense proteinuria: role of angiotensin II and endothelin-1. Hypertension 37: 1171–1178. 17. Mezzano SA, Barria M, Droguett MA, et al. (2001) Tubular NF-kappaB and AP-1 activation in human proteinuric renal disease. Kidney Int 60: 1366–1377. 18. Segerer S, Banas B, Wornle M, et al. (2004) CXCR3 is involved in tubulointerstitial injury in human glomerulonephritis. Am J Pathol 164: 635–649. 19. Segerer S, Mac KM, Regele H, et al. (1999) Expression of the C-C chemokine receptor 5 in human kidney diseases. Kidney Int 56: 52–64.

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20. Panzer U, Schneider A, Steinmetz OM, et al. (2005) The chemokine receptor 5 Delta32 mutation is associated with increased renal survival in patients with IgA nephropathy. Kidney Int 67: 75–81. 21. Stein-Oakley AN, Maguire JA, Dowling J, et al. (1997) Altered expression of fibrogenic growth factors in IgA nephropathy and focal and segmental glomerulosclerosis. Kidney Int 51: 195–204. 22. Shappell SB, Mendoza LH, Gurpinar T, et al. (2000) Expression of adhesion molecules in kidney with experimental chronic obstructive uropathy: the pathogenic role of ICAM-1 and VCAM-1. Nephron 85: 156–166. 23. Wu Q, Jinde K, Endoh M, Sakai H. (2004) Clinical significance of costimulatory molecules CD80/CD86 expression in IgA nephropathy. Kidney Int 65: 888–896. 24. Arrizabalaga P, Sole M, Abellana R, et al. (2003) Tubular and interstitial expression of ICAM-1 as a marker of renal injury in IgA nephropathy. Am J Nephrol 23: 121–128. 25. Heller F, Lindenmeyer MT, Cohen CD, et al. (2007) The contribution of B cells to renal interstitial inflammation. Am J Pathol 170: 457–468. 26. van Es LA, de Heer E, Vleming LJ, et al. (2008) GMP-17-positive T-lymphocytes in renal tubules predict progression in early stages of IgA nephropathy. Kidney Int 73: 1426–1433. 27. Nikolic-Paterson DJ, Atkins RC. (2001) The role of macrophages in glomerulonephritis. Nephrol Dial Transplant 16(Suppl 5): 3–7. 28. Matsumoto K, Nakamura T. (2001) Hepatocyte growth factor: renotropic role and potential therapeutics for renal diseases. Kidney Int 59: 2023–2038. 29. Taniguchi Y, Yorioka N, Yamashita K, et al. (1997) Localization of hepatocyte growth factor and tubulointerstitial lesions in IgA nephropathy. Am J Nephrol 17: 413–416. 30. Taniguchi Y, Yorioka N, Masaki T, et al. (1999) Localization of transforming growth factors beta1 and beta2 and epidermal growth factor in IgA nephropathy. Scand J Urol Nephrol 33: 243–247. 31. De Borst MH, Prakash J, Melenhorst WB, et al. (2007) Glomerular and tubular induction of the transcription factor c-Jun in human renal disease. J Pathol 213: 219–228. 32. Kang DH, Hughes J, Mazzali M, et al. (2001) Impaired angiogenesis in the remnant kidney model: II. Vascular endothelial growth factor administration reduces renal fibrosis and stabilizes renal function. J Am Soc Nephrol 12: 1448–1457. 33. Kang DH, Joly AH, Oh SW, et al. (2001) Impaired angiogenesis in the remnant kidney model: I. Potential role of vascular endothelial growth factor and thrombospondin-1. J Am Soc Nephrol 12: 1434–1447.

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34. Kang DH, Nakagawa T, Feng L, Johnson RJ. (2002) Nitric oxide modulates vascular disease in the remnant kidney model. Am J Pathol 161: 239–248. 35. Namikoshi T, Satoh M, Horike H, et al. (2006) Implication of peritubular capillary loss and altered expression of vascular endothelial growth factor in IgA nephropathy. Nephron Physiol 102: 9–16. 36. Strutz F, Okada H, Lo CW, et al. (1995) Identification and characterization of a fibroblast marker: FSP1. J Cell Biol 130: 393–405. 37. Goumenos DS, Brown CB, Shortland J, El Nahas AM. (1994) Myofibroblasts, predictors of progression of mesangial IgA nephropathy? Nephrol Dial Transplant 9: 1418–1425. 38. Utsunomiya Y, Kawamura T, Abe A, et al. (1999) Significance of mesangial expression of alpha-smooth muscle actin in the progression of IgA nephropathy. Am J Kidney Dis 34: 902–910. 39. Pastorello MT, Costa RS, Ravinal RC, et al. (2005) Alpha-SM actin expression as prognostic indicator in IgA nephropathy (Berger’s disease). Dis Markers 21: 21–27. 40. Ando Y, Moriyama T, Oka K, et al. (1999) Enhanced interstitial expression of caldesmon in IgA nephropathy and its suppression by glucocorticoidheparin therapy. Nephrol Dial Transplant 14: 1408–1417. 41. Nishitani Y, Iwano M, Yamaguchi Y, et al. (2005) Fibroblast-specific protein 1 is a specific prognostic marker for renal survival in patients with IgAN. Kidney Int 68: 1078–1085. 42. Lenz O, Elliot SJ, Stetler-Stevenson WG. (2000) Matrix metalloproteinases in renal development and disease. J Am Soc Nephrol 11: 574–581. 43. Urushihara M, Kagami S, Kuhara T, et al. (2002) Glomerular distribution and gelatinolytic activity of matrix metalloproteinases in human glomerulonephritis. Nephrol Dial Transplant 17: 1189–1196. 44. Akiyama K, Shikata K, Sugimoto H, et al. (1997) Changes in serum concentrations of matrix metalloproteinases, tissue inhibitors of metalloproteinases and type IV collagen in patients with various types of glomerulonephritis. Res Commun Mol Pathol Pharmacol 95: 115–128. 45. Koide H, Nakamura T, Ebihara I, Tomino Y. (1996) Increased mRNA expression of metalloproteinase-9 in peripheral blood monocytes from patients with immunoglobulin A nephropathy. Am J Kidney Dis 28: 32–39. 46. Mezzano SA, Ruiz-Ortega M, Egido J. (2001) Angiotensin II and renal fibrosis. Hypertension 38: 635–638. 47. Suzuki Y, Ruiz-Ortega M, Lorenzo O, et al. (2003) Inflammation and angiotensin II. Int J Biochem Cell Biol 35: 881–900. 48. Bhaskaran M, Reddy K, Radhakrishanan N, et al. (2003) Angiotensin II induces apoptosis in renal proximal tubular cells. Am J Physiol Renal Physiol 284: F955–965.

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49. Wolf G. (2002) Angiotensin II and tubular development. Nephrol Dial Transplant 17(Suppl 9): 48–51. 50. Iwano M, Neilson EG. (2004) Mechanisms of tubulointerstitial fibrosis. Curr Opin Nephrol Hypertens 13: 279–284. 51. Del Prete D, Gambaro G, Lupo A, et al. (2003) Precocious activation of genes of the renin-angiotensin system and the fibrogenic cascade in IgA glomerulonephritis. Kidney Int 64: 149–159. 52. Chan LY, Leung JC, Tang SC, et al. (2005) Tubular expression of angiotensin II receptors and their regulation in IgA nephropathy. J Am Soc Nephrol 16: 2306–2317. 53. Gunthert U. (1993) CD44: a multitude of isoforms with diverse functions. Curr Top Microbiol Immunol 184: 47–63. 54. Lesley J, Hyman R, Kincade PW. (1993) CD44 and its interaction with extracellular matrix. Adv Immunol 54: 271–335. 55. Rouschop KM, Roelofs JJ, Claessen N, et al. (2005) Protection against renal ischemia reperfusion injury by CD44 disruption. J Am Soc Nephrol 16: 2034–2043. 56. Rouschop KM, Sewnath ME, Claessen N, et al. (2004) CD44 deficiency increases tubular damage but reduces renal fibrosis in obstructive nephropathy. J Am Soc Nephrol 15: 674–686. 57. Rouschop KM, Claessen N, Pals ST, et al. (2006) CD44 disruption prevents degeneration of the capillary network in obstructive nephropathy via reduction of TGF-beta1-induced apoptosis. J Am Soc Nephrol 17: 746–753. 58. Florquin S, Nunziata R, Claessen N, et al. (2002) CD44 expression in IgA nephropathy. Am J Kidney Dis 39: 407–414. 59. Ranieri E, Gesualdo L, Petrarulo F, Schena FP. (1996) Urinary IL-6/EGF ratio: a useful prognostic marker for the progression of renal damage in IgA nephropathy. Kidney Int 50: 1990–2001. 60. Arrizabalaga P, Sole M, Quinto IL, Ascaso C. (1997) Intercellular adhesion molecule-1 mediated interactions and leucocyte infiltration in IgA nephropathy. Nephrol Dial Transplant 12: 2258–2262. 61. Bottinger EP. (2007) TGF-beta in renal injury and disease. Semin Nephrol 27: 309–320.

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Chapter 6

Podocyte Pathology Kar Neng Lai and Joseph C. K. Leung

Introduction The glomerular filter has a remarkable and well-described selectivity for macromolecules based on both charge and size. High molecular weight proteins are nearly excluded from the glomerular filtrate. Smaller proteins are partially filtered before passing into the raw filtrate, where they can be reabsorbed in the proximal tubule. Structurally, the glomerular filter is composed of three parts: a layer of negativelycharged endothelial cells separated by large fenestrations of 50–100 nm, the glomerular basement membrane (GBM) also negatively-charged that is about 250–300 nm thick, and the podocytes (or glomerular visceral epithelial cells) that are also negatively-charged (Figure 6.1). Altered glomerular filter due to the charge-selectivity has recently been challenged by the hypothesis that urinary albumin loss is a sequel of defective endocytotic and processing function of proximal tubular epithelial cells.1 More confirmatory evidence is needed to support this debate. Podocytes are unique epithelial cells necessary for maintaining the selectivity and integrity of the glomerular filtration barrier. Healthy differentiated podocytes comprised of a cell body that gives off primary processes. These foot processes further divide to provide numerous interdigitating foot processes that surround glomerular capillary walls and that form a specialized intercellular junction often called the slit diaphragm that spans roughly 40 nm between interdigitating tertiary foot processes of adjacent podocytes. Their interdigitating foot processes

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70 ✦ K. N. Lai & J. C. K. Leung

Figure 6.1 The podocyte and slit diaphragm. (A) The glomerular filter viewed perpendicular to podocyte foot processes. Filtrate passes from within the glomerular capillary lumen (at bottom) through fenestrae between endothelial cells, across the glomerular basement membrane, and through the slit diaphragm between podocyte foot processes into the Bowman’s space. Inset: slit diaphragm components are localized to lipid rafts. Podocin serves as a scaffolding molecule to localize nephrin and Neph1 to lipid rafts, which bring multiple proteins together in a small area of membrane to create a signaling platform. GBM, glomerular basement membrane. (B) Scanning electron micrograph of podocytes. Podocytes branch into progressively smaller primary, secondary, and

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Podocyte Pathology ✦ 71

cover the exterior surface of the glomerular basement membrane and, in turn, stabilize the glomerular architecture. The morphology of the mature podocyte is fashioned by a complex cytoskeleton. Microtubules and intermediate filaments provide the scaffold of podocyte major process. Foot process architecture is defined by two populations of actin that include actin filament bundles running longitudinally above the level of the intercellular junction and a subcortical actin web that extends to the foot process intercellular junction and the apical and basal plasma membranes. Numerous molecules constituting the slit diaphragm have been identified. Among them, nephrin, podocin, CD2AP, FAT and NEPH1 are accepted to be essential in maintaining the barrier function of the slit diaphragm. Nature of these molecules is well summarized in reviews by Kawachi et al.2 and Kwoh et al.3 The slit diaphragm is a highly developed cell–cell junction. It is now widely accepted that these cell–cell junctions play a critical role in maintaining the balance of water and ions, and in the intake of nutrition to enable survival. Functional and structural disturbance of cell–cell junctions of the slit diaphragm is associated with proteinuria and hence, a contributory factor for the progress of renal failure. Proteins identified at the podocyte intercellular junction and their known interacting partners are summarized in Table 6.1.4–9 Podocytes hold a strategic position regulating the trafficking between two compartments of the nephron: (i) glomerular mesangial and endothelial cells and (ii) tubular epithelial cells. Defects in podocyte proteins or injury to podocytes lead to podocyte apoptosis, detachment and disorganization of the slit pore membrane and thereby resulting in heavy proteinuria, glomerulosclerosis, and loss of kidney function. A large number of podocyte proteins have been identified and genetic mutations of these podocyte proteins are associated with congenital and post-natal forms of nephrotic syndrome. These genetic breakthroughs have Figure 6.1 (Continued ) tertiary foot processes, which interdigitate with tertiary foot processes from a neighboring podocyte. CB, podocyte cell body; P, primary foot process; S, secondary foot process; T, tertiary foot process. (C) The slit diaphragm model of Karnovsky and colleagues. Podocyte foot processes (left and right) with a central filament running in parallel. Perpendicular cross strands form a regular lattice, with rectangular pores between the strands. [Used with permission from Ref. 35.]

Known interactions

Nephrin

Slit diaphragm

FP effacement/proteinuria

Neph1 Podocin Fyn

Slit diaphragm Slit diaphragm Slit diaphragm

FAT1 ZO-1 IQGAP1 TRPC6 MAGI2 PLCE1 JAM4 Myosin heavy chain P-cadherin α-actinin-4 Synaptopodin CD2AP

Slit diaphragm Near slit diaphragm Slit diaphragm/podocyte Podocyte Podocyte Podocyte Podocyte foot process Podocyte foot process

FP effacement/proteinuria FP effacement/proteinuria Variable FP effacement/ proteinuria FP effacement/proteinuria Unknown Unknown FP effacement/proteinuria Unknown FP effacement/proteinuria Unknown Unknown

Neph1, podocin, CD2AP, Nck, β-arrestin, PI3 kinase, Fyn, nWASP, IQGAP1, CASK, Crk Grb2, podocin, ZO-1 Neph1, nephrin, CD2AP, TRPC6 Neph1, nephrin, CD2AP, TRPC6

Developing podocytes Foot process Associates with actin Cytoplasm

None FP effacement/proteinuria Impaired recovery from injury FP effacement/proteinuria

Source: Adopted from Refs. 4–9.

Ena/VASP Neph1, JAM2, JAM3 Nephrin, PLCE1 Nephrin, Fyn, podocin α-actinin-4, megalin, cortactin H-Ras, IQGAP1

Actin, MAGI, synaptopodin Actin, α-actinin-4 Nephrin, Arp2/3, cortactin, Fyn

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Protein

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Proteins at the podocyte intercellular junction and their functioning properties.


Table 6.1

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stimulated renewed interest in podocyte biology, both in normal, congenital and acquired disease states. While recent studies have looked at congenital nephrosis, studies of podocytes in other acquired glomerular disease are scarce due to difficulties experienced in culturing podocytes.

Podocytes Demonstrate Proliferative Activities The inability of highly differentiated native podocytes to proliferate and repopulate the damaged glomerulus has been taken as a key factor in the progression of glomerular scarring.10 It is well believed that the disappearance of cell cycle promoters and a reciprocal up-regulation of the cell cycle inhibitors, cyclin-dependent kinase (CDK) inhibitors, such as p21, p27 and p57, coincide with the proliferation arrest and terminal differentiation of podocytes in the mature glomerulus. Podocytes have also been shown to fully express most or all the elements of the renin-angiotensin system (RAS).11 Recently, in vitro studies of podocytes cultured with either supernatant from mesangial cells cultured with polymeric IgA isolated from patients with IgA nephropathy (IgAN) or recombinant tumor necrosis factor-α (TNF-α) reveal enhanced proinflammatory changes with increased synthesis of TNF-α and interleukin-6 (IL-6).12 These pro-inflammatory responses are both dose- and time-related. These new findings together previous observations that the RAS and vascular endothelial growth factor (VEGF) are expressed in podocytes suggest podocytes can play a pro-inflammatory role and may not be totally proliferation arrested.11,13

The Morphological Abnormality of Podocytes in IgAN There are scarce reports of podocyte abnormalities in IgAN and their role in the pathogenesis of IgAN has rarely been studied. Necrosis and detachment of the podocytes from the glomerular basement membrane was observed in IgAN.14 The degree of podocytopenia was related with the severity of glomerular dysfunction.15 Complementing the histological findings of podocytopenia, patients with IgAN had increased urinary excretion of podocytes.16 Treatment with angiotensin-converting enzyme inhibitor or angiotensin II receptor antagonists reduced the urinary excretion of podocyte in IgAN.17

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Abnormality of Podocyte Proteins in IgAN Although other proteins are involved in the structure of the epithelial podocyte and specifically the slit diaphragm, nephrin seems to play a pivotal role in preventing passage of protein through the glomerular barrier.18 Two available studies on the expression of nephrin in IgAN revealed conflicting data. Gagliardini et al.19 detected a marked reduction of nephrin mRNA and extracellular nephrin in IgAN but not in minimal change nephropathy or focal segmental glomerulosclerosis. In contrast, Doublier et al.20 found a reduction in nephrin and a shift of podocyte-staining pattern only in IgAN patients with nephrotic syndrome but not in non-nephrotic IgAN patients. Lately, Lai et al.21 examined the expression of two podocyte markers (nephrin and ezrin) in renal biopsy from patients with IgAN with mild histological grading. A reduction in nephrin and ezrin was clearly evident in these patients with mild IgAN. These markers were examined as nephrin has a crucial role in the filtration barrier of the glomerular podocyte and ezrin is a glomerular epithelial cell marker of podocyte injury (podocytopathy). The increased permeability of the filtration barrier in steroid-resistant and proteinuric glomerulopathies may be a consequence of subcellular changes in podocyteassociated proteins following decreased expression of ezrin.22 These findings on nephrin and ezrin are in accordance with a separate report of reduced glomerular epithelial protein 1 (GLEPP1) expression in IgAN.23 GLEPP1, a podocyte receptor membrane protein tyrosine phosphatase located on the apical cell membrane of visceral glomerular epithelial cell and foot processes, is a marker of acute podocyte injury previously reported in puromycin aminonucleoside nephrosis. Lai et al.21 did not find any alteration of secreted protein acidic and rich in cysteine (SPARC) in IgAN. SPARC has a putative role for wound repair. In chronic allograft nephropathy, SPARC is speculated to function as an accessory molecule in chronic PDGFmediated sclerosing interstitial and vascular injury.24 Neither repair process nor PDGF-mediated podocyte injury is evident in most cases of IgAN. Nestin is an intermediate filament protein present in the cell body and primary process within the podocyte but not detected in other structures of the adult human kidney. Su et al.25 demonstrated the glomerular nestin expression in IgAN without proteinuria was not

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different from normal kidney; although its expression was significantly reduced in kidneys of patients with IgAN and proteinuria, suggesting that nestin may play an important role in maintaining normal podocyte function in the human kidney.

Abnormality in Proto-Oncogene and Growth Factors of Podocytes in IgAN Using immunocytochemical and in situ hybridization techniques, a reduced expression of the PP-44 antigen and ability to produce interleukin-1/interleukin-1 related peptides was observed in podocytes in IgAN.26 With similar histochemical techniques, Qiu et al.27 demonstrated that podocyte expression of proto-oncogene, Bcl-2, varied with the disease activity. An over-expression of Bcl-2 (death suppressor) protein observed in the early stages of IgAN may confer protection against apoptotic injury to glomerular cells by counteracting the opposing activities of Bax (death promoter) protein. Down-regulation of Bcl-2, associated with an increased ratio of Bax/Bcl-2 by glomerular epithelial cells correlated with the severity of glomerulosclerosis. Hence, Bcl-2 expression by podocytes may exert modulatory effects on cellular processes that contribute to progressive glomerular injury and outcome in IgAN. The onset and magnitude of mesangial proliferation and sclerosis was also associated with the down-regulation of CDK inhibitors, p27 and p57.28 Although IgA isolated from patients with IgAN exerted no apoptotic effect on podocytes, in vitro studies revealed TNF-α released from glomerular mesangial cells after IgA deposition modulates the expression of Bcl-2 by podocyte through auto-amplification of TNF-α.29 The initial up-regulation followed by the down-regulation of Bcl-2 expression upon prolonged exposure to mesangial-derived TNF-α after IgA deposition suggests an apoptotic effect of mesangial derived-TNF-α on podocytes in chronic IgAN. This may have bearing on the progressive glomerular injury that determines the renal outcome in human IgAN.

No Binding of IgA to Podocytes in IgAN Most recently, Wang et al.30 reported serum IgA1 from IgAN patients directly induced apoptosis in podocytes. The findings are most intriguing as no known IgA receptor has ever been documented in podocytes.

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Lai et al.12 studied the mRNA expression of the FcαR, H1 and H2 chains of ASGPR, pIgR, Fcα/µR and the transferrin receptors in podocytes. Podocytes did not express mRNA for any known IgA receptors except the transferrin receptor. The IgA binding to podocyte was not blocked by pre-incubation with proteins that competitively blocked individual known IgA receptors including IgM, anti-secretory component, ASOR, orosomucoid, anti-FcαR1 (clone My43), and transferrin. In cell culture experiments using an immortalized podocyte cell line, they observed binding of pIgA to podocytes but the quantity of IgA bound to podocytes was less than one-tenth that bound to mesangial cells in IgAN. The lack of difference between binding capacities of IgA isolated from patients with IgAN and healthy controls and the failure to up-regulate the synthesis of TNF-α suggested such binding observed in the cell culture experiments was not specific. Finally, histological demonstration of distinctly separate immunostaining of IgA and nephrin with no co-localization further confirms no direct binding of IgA to podocytes.21

Mechanisms of Podocyte Injury in IgAN The most intriguing question is how podocyte injury occurs when there is no podocytic binding of IgA in IgAN. It is well demonstrated that a glomerulo-tubular cross-talk involving TNF-α exists in IgAN.31 Lai et al.12 hypothesized that a similar glomerulo-podocytic cross-talk existed in IgAN. They conducted podocyte culture experiments using conditioned medium from mesangial cells pre-incubated with different IgA preparations. This medium transfer setting allowed no direct cell-cell communication but simulated the in vivo glomerulo-podocytic communication via humoral factors. Conditioned medium from mesangial cells incubated with IgA from patients with IgAN, but not with IgA from disease or healthy controls, up-regulated the synthesis of TNF-α. From the measured concentration of the TNF-α, the increased synthesis of TNF-α after culturing with the medium was not due to the “leftover” from the mesangial cell conditioned medium. Activated mesangial cells produce different cytokines and chemokines. It was postulated that these humoral factors/mediators from mesangial cells first activated the podocytes before reaching the tubulointerstitium either by glomerular filtration or by transportation via the post-glomerular capillaries. Upon reaching the tubular compartment, these mediators could stimulate tubular epithelial cells to

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produce other pro-inflammatory cytokines and chemokines that eventually led to tubular damage, interstitial mononuclear cells infiltration and fibrosis.31 They showed that TNF-α produced by mesangial cells following stimulation by polymeric IgA from IgAN patients led to increased synthesis of TNF-α by podocytes in an autocrine fashion. Moreover, the result from culture experiments using different neutralizing antibodies suggested that TNF-α plays a unique and crucial role in mediating the inflammatory injury along the glomerulo-podocytic-tubular axis in IgAN. TNF-α receptor-1 (TNF-R1) and receptor-2 (TNF-R2) are constitutively present in normal podocytes. These receptors appear to play a distinct role in different disease entities. In an anti-GBM nephritis model, TNF-R1 promotes systemic immune response and renal T cell apoptosis while intrinsic cell TNF-R2 regulates complement-dependent tissue injury.32 Moreover, both receptors are significantly up-regulated in podocytes of IgAN patients.12 Despite these receptors are not inducible with polymeric IgA isolated from patients with IgAN in vitro, their expression is readily up-regulated by IgA-mesangial cell conditioned medium from patients with IgAN or exogenous TNF-α. In vitro study suggests two functional roles played by the TNF-R1 in podocytes following stimulation by IgA-mesangial cell conditioned medium from patients with IgAN: IL-6 synthesis and apoptosis. Interleukin-6 regulates the tubular angiotensin II receptor subtype-1 (ATR1) expression and enhances tubular angiotensin II production in IgAN.33 Interaction of angiotensin II and early expressed ATR1 will activate the protein kinase C and MAPK pathways, leading to inflammatory responses in tubular epithelial cells. Up-regulation of TNF-R1 in podocytes incubated with IgA-mesangial cell conditioned medium may favor apoptotic cell death. The up-regulation of TNF-R2 observed in in vitro study by Lai et al.12 suggests podocytes are in a chronic pro-inflammatory state in IgAN. On the basis of recent published data,12,31,33 a hypothetical schema outlining the roles of podocytes in IgA-induced tubulointerstitial injury in IgAN is depicted in Figure 6.2. It is now recognized that C3 increases the glomerular filtration barrier’s susceptibility to injury and ultrafiltered C3 contributes more to tubulointerstitial damage induced by protein overload than locally synthesized C3 in animal model of proteinuric nephropathies.34 Local C3 synthesis is irrelevant to the development of proteinuria. However, podocytic injury induced by complement has not been observed in IgAN.

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glomerulo-tubular cross-talk via TNF-α, IL-6 and angiotensin II

humoral factors (TNF-α)

ATR1

x

Y

Y Y

Y

ATR2

ATR1

HMC

x

Y

Podocyte

tubulo-glomerular cross-talk favoring glomerulosclerosis

TEC

proteinuria

apoptosis Bcl-2 Bax

TNF-α IL-6

tubular atrophy

pro-inflammatory cellular response

x

Y IgA no IgA Y binding

TNF-R1

TNF-α

TNF-R2

Figure 6.2 A schema of various mechanisms operating between the glomerular mesangial cells (HMC), podocytes, and tubular epithelial cells (TEC) following mesangial IgA deposition in the development of tubulointerstitial injury in progressive IgAN. TNF-α released from the glomerular mesangium following IgA deposition induced TNF-α synthesis by the podocytes. Podocytederived TNF-α further up-regulated the TNF-α production in an autocrine manner. TNF-α derived from mesangial cells and podocytes up-regulated the expression of TNF receptors. The binding to TNF-R1 leads to IL-6 synthesis and apoptosis while binding to TNF-R2 maintains pro-inflammatory cellular responses. Podocytes played a contributory role in the development of interstitial damage in IgAN by amplifying the TEC activation with enhanced TNF-α synthesis following inflammatory changes of HMC after IgA deposition. ATR1 and ATR2 denote angiotensin II receptor subtype-1 and subtype-2, respectively. [Used with permission from Ref. 12.]

Concluding Remarks Recent studies suggest podocytes may play a contributory role in the development of interstitial damage in IgAN possibly by amplifying the tubular epithelial cell activation with enhanced TNF-α synthesis

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following inflammatory changes of glomerular mesangial cells. In vitro study implicates humoral factors (predominantly TNF-α) released from glomerular mesangium are likely to maintain a glomerulo-podocytic cross-talk in the event of tubulointerstitial injury in IgAN.

Acknowledgments The study was supported by the Research Grant Committee (Hong Kong) [HKU 7678/07M].

References 1. Russo LM, Sandoval RM, McKee M, et al. (2007) The normal kidney filters nephrotic levels of albumin retrieved by proximal tubule cells: retrieval is disrupted in nephrotic states. Kidney Int 71: 504–513. 2. Kawachi H, Miyauchi N, Suzuki K, et al. (2006) Role of podocyte slit diaphragm as a filtration barrier. Nephrology 11: 274–281. 3. Kwoh C, Shannon MB, Miner JH, Shaw A. (2006) Pathogenesis of nonimmune glomerulopathies. Annu Rev Pathol 1: 349–374. 4. Liu G, Kaw B, Kurfis J, et al. (2003) Neph1 and nephrin interaction in the slit diaphragm is an important determinant of glomerular permeability. J Clin Invest 112: 209–221. 5. Huber TB, Schmidts M, Gerke P, et al. (2003) The carboxyl terminus of Neph family members binds to the PDZ domain protein zonula occludens-1. J Biol Chem 278: 13417–13421. 6. Lehtonen S, Ryan JJ, Kudlicka K, et al. (2005) Cell junction-associated proteins IQGAP1, MAGI-2, CASK, spectrins, and alpha-actinin are components of the nephrin multiprotein complex. Proc Natl Acad Sci USA 102: 9814–9819. 7. Asanuma K, Kim K, Oh J, et al. (2005) Synaptopodin regulates the actinbundling activity of alpha-actinin in an isoform-specific manner. J Clin Invest 115: 1188–1198. 8. Huber TB, Kwoh C, Wu H, et al. (2006) Bigenic mouse models of focal segmental glomerulosclerosis involving pairwise interaction of CD2AP, Fyn, and synaptopodin. J Clin Invest 116: 1337–1345. 9. Quack I, Rump LC, Gerke P, et al. (2006) Beta-Arrestin2 mediates nephrin endocytosis and impairs slit diaphragm integrity. Proc Natl Acad Sci USA 103: 14110–14115. 10. Kriz W. (2003) Progression of chronic renal failure in focal segmental glomerulosclerosis: consequence of podocyte damage or of tubulointerstitial fibrosis? Pediatr Nephrol 18: 617–622.

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11. Liebau MC, Lang D, Bohm J, et al. (2006) Functional expression of the renin-angiotensin system in human podocytes. Am J Physiol Renal Physiol 290: F710–F719. 12. Lai KN, Leung JC, Chan LY, et al. (2008) Activation of podocytes by mesangial-derived TNF-α: glomerulo-podocytic communication in IgA nephropathy. Am J Physiol Renal Physiol 294: F945–F955. 13. Cui TG, Foster RR, Saleem M, et al. (2004) Differentiated human podocytes endogenously express an inhibitory isoform of vascular endothelial growth factor (VEGF165b) mRNA and protein. Am J Physiol Renal Physiol 286: F767–F773. 14. Ng WL, Chan KW, Yeung CK, Kwan S. (1984) Peripheral glomerular capillary wall lesions in IgA nephropathy and their implications. Pathology 16: 324–330. 15. Lemley KV, Lafayette RA, Safai M, et al. (2002) Podocytopenia and disease severity in IgA nephropathy. Kidney Int 61: 1475–1485. 16. Hara M, Yanagihara T, Kihara I. (2007) Cumulative excretion of urinary podocytes reflects disease progression in IgA nephropathy and SchonleinHenoch purpura nephritis. Clin J Am Soc Nephrol 2: 231–238. 17. Nakamura T, Ushiyama C, Suzuki S, et al. (2000) Effects of angiotensinconverting enzyme inhibitor, angiotensin II receptor antagonist and calcium antagonist on urinary podocytes in patients with IgA nephropathy. Am J Nephrol 20: 373–379. 18. Cooper ME, Mundel P, Boner G. (2002) Role of nephrin in renal disease including diabetic nephropathy. Semin Nephrol 22: 393–398. 19. Gagliardini E, Benigni A, Tomasoni S, et al. (2003) Targeted downregulation of extracellular nephrin in human IgA nephropathy. Am J Nephrol 23: 277–286. 20. Doublier S, Ruotsalainen V, Salvidio G, et al. (2001) Nephrin redistribution on podocytes is a potential mechanism for proteinuria in patients with primary acquired nephrotic syndrome. Am J Pathol 158: 1723–1731. 21. Lai KN, Leung JC, Chan LY, et al. (2008) Podocyte injury induced by mesangial-derived cytokines in IgA nephropathy. Nephrol Dial Transplant Aug 6 [Epub ahead of print] PMID: 18685143. 22. Ostalska-Nowicka D, Zachwieja J, Nowicki M, et al. (2006) Ezrin — a useful factor in the prognosis of nephrotic syndrome in children: an immunohistochemical approach. J Clin Pathol 59: 916–920. 23. Tian J, Wang HP, Mao YY, et al. (2007) Reduced glomerular epithelial protein 1 expression and podocyte injury in immunoglobulin A nephropathy. J Int Med Res 35: 338–345. 24. Alpers CE, Hudkins KL, Segerer S, et al. (2002) Localization of SPARC in developing, mature, and chronically injured human allograft kidneys. Kidney Int 62: 2073–2086.

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25. Su W, Chen J, Yang H, et al. (2007) Expression of nestin in the podocytes of normal and diseased human kidneys. Am J Physiol Regul Integr Comp Physiol 292: R1761–R1767. 26. Niemir ZI, Stein H, Dworacki G, et al. (1997) Podocytes are the major source of IL-1 alpha and IL-1 beta in human glomerulonephritides. Kidney Int 52: 393–403. 27. Qiu L-Q, Sinniah R, Hsu SI. (2004) Coupled induction of iNOS and p53 upregulation in renal resident cells may be linked with apoptotic activity in the pathogenesis of progressive IgA nephropathy. J Am Soc Nephrol 15: 2066–2078. 28. Qiu L-Q, Sinniah R, Hsu SI. (2004) Role of differential and cell type-specific expression of cell cycle regulatory proteins in mediating progressive glomerular injury in human IgA nephropathy. Lab Invest 84: 1112–1125. 29. Lai KN, Chan L, Saleem M, et al. (2006) Regulation of Bcl-2 expression in podocytes by mesangial cells derived TNF-α in IgA nephropathy. J Am Soc Nephrol 17: 265A. 30. Wang C, Peng H, Tang H, et al. (2007) Serum IgA1 from IgA nephropathy patients induces apoptosis in podocytes through direct and indirect pathways. Clin Invest Med 30: E240–E249. 31. Chan LY, Leung JC, Tsang AW, et al. (2005) Activation of tubular epithelial cells by mesangial-derived TNF-α: glomerulo-tubular communication in IgA nephropathy. Kidney Int 67: 602–612. 32. Vielhauer V, Stavrakis G, Mayadas TN. (2005) Renal cell-expressed TNF receptor 2, not receptor 1, is essential for the development of glomerulonephritis. J Clin Invest 115: 1199–1209. 33. Chan LY, Leung JC, Tang SC, et al. (2005) Tubular expression of angiotensin II receptors and their regulation in IgA nephropathy. J Am Soc Nephrol 16: 2306–2317. 34. Abbate M, Zoja C, Corna C, et al. (2008) Complement-mediated dysfunction of glomerular filtration barrier accelerates progressive renal injury. J Am Soc Nephrol 19: 1158–1167. 35. Johnstone DB, Holzman LB. (2006) Clinical impact of research on the podocyte slit diaphragm. Nat Clin Pract Nephrol 2: 271–282.

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Chapter 7

Clinicopathologic Findings Bruce A. Julian and Robert J. Wyatt

Introduction In the early years after its seminal description by Berger and Hinglais in 1968,1 IgA nephropathy (IgAN) was frequently termed “benign hematuria.” However, longer observation in many countries has shown that this form of glomerulonephritis commonly causes chronic kidney disease, with end-stage renal failure in as many as 40% of patients within 20 years after diagnostic biopsy. Discernment of clinical or laboratory features that predict the clinical course has been difficult. As the pathogenesis of IgAN has been unraveled, novel laboratory findings have been tested for their prognostic merit. In this chapter, we review clinical and pathologic features that may be useful in predicting the clinical course.

Pathogenesis IgAN arises as a consequence of circulating IgA1-containing immune complexes binding to mesangial cells. The IgA1 in these complexes has a reduced content of galactose in hinge-region O-glycans to constitute a neoantigen2,3 that is recognized by circulating IgG or IgA1.4,5 The galactose deficiency accentuates binding of the IgA1 to mesangial cells. The resulting stimulation of mesangial cells leads not only to their proliferation6 as the light-microscopic hallmark of this renal disease, but also to synthesis of extracellular matrix and secretion of a host of cytokines/ chemokines that may culminate in inflammation and scarring in the glomerular and tubulointerstitial compartments. Some of the glomerular 83

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inflammation may be due to more than simply the activation of mesangial cells: cytokines from mesangial cells induce podocytes to secrete TNF-α and IL-6,7 and also attract circulating monocytes, macrophages and T cells8 to augment the inflammatory process. As a result of the glomerular damage, the filtration barrier is compromised and red blood cells and proteins enter the urinary space. These components may mediate additional injury, especially through interactions with podocytes and proximal tubular cells. Absorption of filtered proteins by proximal tubular cells induces cellular activation and synthesis of inflammatory signaling compounds. This sequence of biological reactions leads to transcription of genes encoding vasoactive and chemoattractant peptides and growth factors such as endothelin-1, monocyte chemoattractant protein-1 (MCP-1) and TGF-β.9–12 The release of such peptides causes an influx of monocytes. Proximal tubular epithelial cells may also undergo transformation to mesenchymal cells and secrete extracellular matrix proteins to initiate interstitial scarring. Subsequent stimulation of fibroblasts/myofibroblasts in the renal interstitium augments the fibrosis.10

Selection of Prognostic Markers In the assessment of prognosis, most studies have examined features present at the time of renal biopsy. However, the gauge by which to measure outcome has differed greatly between centers. While endstage renal failure is a definitive endpoint, the indolent course of disease for most patients requires many years for this development, often beyond the scope of prospective studies. Alternatives commonly used include doubling of serum creatinine concentration or halving of estimated glomerular filtration rate (eGFR), and slope of decline in creatinine clearance (or eGFR) over a multi-year interval. A few centers have used more modest rises in serum creatinine concentration (e.g., 20%). Marker(s) that predict outcome when clearance function is relatively normal are desirable, but not widely available currently. Patients with significantly reduced GFR almost always lose renal clearance function. In fact, most studies of prognostic factors exclude patients whose renal insufficiency has passed “the point of no return,” GFR < 30–35 ml/min/1.73 m2.13,14 Analyses have sometimes used improvement in quantitative proteinuria as a surrogate endpoint. Not only does proteinuria indicate glomerular injury and mediate tubulointerstitial

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Clinicopathologic Findings ✦ 85

damage, but a substantial decrease in protein excretion conveys a better clinical outcome.15

Prognostic Factors Demographic Characteristics Among demographic features, male gender16,17 and older age,18 and perhaps obesity,19 portend a worse long-term outcome for patients with IgAN. The gender effect may be mediated by an influence of androgen on apoptosis of proximal tubular cells by triggering pathways that involve Fas upregulation, FasL expression and capase(s) activation.20 An age-associated poor outcome may stem from several factors. It is certainly plausible that diagnosis later in adulthood simply represents belated discovery of an indolent disease process that has progressed over many years. As a person ages, other factors may accentuate renal injury, including higher blood pressure, age-related vascular damage, and increased body mass. Some investigators have shown that obesity, a component of metabolic syndrome, adversely affects patients with various renal diseases, including IgAN.19,21,22 Independent of body mass, insulin resistance has been associated with progressive disease,23 but may relate to an adverse influence on vascular disease. Clinical outcome differs between geographically separated centers. In a retrospective, tri-continental study of patients from Europe, Australia, and Canada, the wide variability in clinical course was largely explained by lead-time bias: centers with better outcomes performed renal biopsy in patients with milder disease.18 However, some disparity was likely due to genetics, diet, or treatment. Ethnicity has shown little value as a prognostic factor. In San Francisco, outcome was not associated with ethnicity in a cohort of Caucasian, Asian, and Hispanic patients.24 However, most of these patients had already lost significant clearance function. In Memphis, TN, clinical outcome was similar in African-American and white children.25 A report from India indicated a disturbingly poor renal survival rate, only 33% at ten years after diagnosis.26

Clinical Features Synpharyngitic macroscopic hematuria is a clinical hallmark for IgAN, and the presenting sign in many younger patients. For reasons not yet

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clear, but independent of age, patients with a least one episode fared better than those who had never experienced this degree of glomerular bleeding.27 On occasion, macroscopic hematuria is associated with acute renal dysfunction accompanied by crescentic glomerulonephritis and acute tubular injury. Many patients in this setting spontaneously recover, presumably after resolution of hemoglobin-induced injury of tubular epithelial cells. Although 15%–50% of patients with microscopic hematuria without albuminuria or proteinuria enter prolonged clinical remission, immunohistologic disease persists. Long-standing isolated microscopic hematuria does not have the benign connotation assumed previously. In a study from China, 20% of normotensive patients without renal insufficiency with microscopic hematuria (> 5 RBC/hpf ) on at least three occasions over a month’s surveillance developed renal insufficiency (eGFR < 60 ml/min/1.73 m2) in less than eight years.28 There is nearly universal agreement that hypertensive patients fare less well than normotensive patients. However, the definition of hypertension has not been uniform between studies. Some groups have used systolic values, whereas others preferred mean arterial pressure or 24hour monitoring.13 The National Kidney Foundation in the United States recommends blood pressure < 130/80 mm Hg for patients excreting < 200 mg protein per g creatinine per day and a lower target for patients excreting > 1000 mg protein per g creatinine per day. These goals are below the definition of hypertension in many studies in the era between 1980 and 2000. As many as 12%–15% of IgAN patients have relatives with clinical and urinary findings suggestive of IgAN. Only a minority of these families includes more than one individual with biopsy-proven disease. Multiplex pedigrees have shown linkage of IgAN to chromosome 6q22–23 (IgAN1) in Italy and southeastern Kentucky29 or chromosome 2q36 in Canada.30 In a separate area in Italy, suggestive linkage was found for chromosomes 4q26–31 and 17q12–22.31 The function of the genes at these loci has not been defined. Compared with patients with sporadic IgAN, patients with a familial disease have neither distinctive clinical manifestations nor a worse prognosis.31 The prognostic effect of several other demographic factors is uncertain. Although some case reports have suggested that pregnancy accelerates decline in GFR, its impact has not been prospectively evaluated in a large cohort. The prognostic value of tonsillectomy is quite controversial. Some centers contend that the procedure removes a source of

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some of the circulatory galactose-deficient IgA1, reduces microscopic hematuria and proteinuria, and leads to a better outcome,32–34 but other investigators disagree.35 To date, no prospective, randomized, controlled clinical trial that evaluated the effect of tonsillectomy has been published.

Laboratory Findings For years, serum creatinine concentration has been the standard clinical measure of renal function. As discussed below, in formulas to predict prognosis in patients with IgAN, serum creatinine is a continuous variable. As such, patients with even mildly impaired eGFR (45–60 ml/min/ 1.73 m2) at the time of diagnostic biopsy have outcomes worse than those with normal clearance function. However, whether the decline in GFR is more rapid in patients with renal insufficiency than in those with preserved GFR at biopsy, remains uncertain. Nevertheless, some patients with mildly/moderately compromised renal function may remain stable for years, especially if treated with agents to attenuate the impact of angiotensin II. In an effort to better compare studies from different centers, estimates of GFR calculated with the Modified-Diet-in-RenalDisease formula have been used for measurement of renal function. Proteinuria has generally correlated with prognosis, although the threshold for a deleterious effect has been less clear. Quantitative measurements better assess this finding than do urinary dipstick values. Most studies have measured 24-hour excretion, although some reports prefer the spot urinary protein/creatinine ratio. While early studies suggested that the cut-off for poor prognosis was 2 g/day, later analyses found a continuous-variable effect, with an adverse influence starting at 500 mg/day. More importantly, rather than one measurement at the time of biopsy, change in proteinuria over several years is a better gauge.15,36 A study in Toronto showed that the cut-off was a timeaveraged value of 1 g/day, calculated as the average of six-month-interval means after diagnosis.15 The decrement in GFR in patients with proteinuria persistently > 3 g/day was 25-fold worse than in patients maintaining excretion rates < 1 g/day. Furthermore, patients who excreted > 3 g/day at presentation but later improved to < 1 g/day had a similar course as those with proteinuria persistently ≤ 1 g/day. These studies support the current emphasis on treatment to reduce proteinuria. Some investigators favor measurement of albuminuria over proteinuria to predict clinical outcome. Microalbuminuria (excretion of 30–299 albumin mg/day)

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is usually found in patients with normal protein excretion. In one study, patients with microalbuminuria at biopsy were more likely to develop proteinuria, hypertension, and renal insufficiency (eGFR < 60 ml/min/m2) 7.5 years later than were patients with normal albuminuria at biopsy.28 Other laboratory features associated with worse outcome include hyperlipidemia and hyperuricemia. Hypertriglyceridemia is a risk factor for progressive disease21 and hypercholesterolemia accentuates glomerular injury in patients with various forms of glomerulonephritis. Treatment with statins has shown beneficial effects on proteinuria and GFR.37 In Finland, serum uric acid levels correlated with degree of tubular atrophy, and interstitial fibrosis and inflammation;38 treatment to reduce the level has not been evaluated.

Light-Microscopy Histology IgAN exhibits a wide spectrum of light-microscopic glomerular changes. Classical features are proliferation of mesangial cells (> 3 mesangial cells/mesangial area) and increased mesangial matrix. These features are frequently segmental (affecting only a portion of a glomerulus) and focal (affecting only some glomeruli), but other patients exhibit a diffuse pattern of changes, with involvement of all glomeruli. Magnitude of mesangial cell proliferation has been associated with upregulation of E2F1 by mesangial cells and downregulation of p27kip1 and p57kip2 by podocytes.39 Cell-type specific, coordinated regulation of proliferative and proapoptotic activities of cell cycle regulatory proteins may play an important role in mediating glomerular injury. Podocyte expression of Bcl-2, a class of proto-oncogenes that blocks apoptosis without promoting cell proliferation, is more pronounced in IgAN patients with a poor prognosis.40 A low number of podocytes per glomerulus has been associated with worse proteinuria and a decrement in renal clearance function.41 In a study with follow-up renal biopsies, decreased numbers of podocytes in the second specimen was associated with poor prognosis.42,43 Other glomerular features signifying an unfavorable outcome include endothelial cellular proliferation, focal necrosis, focal segmental scars, extracapillary cellular proliferation (a crescent if involved area exceeds 10% of the circumference of Bowman’s capsule) and global sclerosis. Some investigators consider any evidence of capillaritis with compromise of the glomerular basement membrane

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(focal necrosis or glomerular crescent) as sufficient basis for aggressive immunomodulatory treatment.13,44,45 Another vascular feature associated with poor prognosis is thrombotic microangiopathy.46 Many centers have shown that degree of interstitial damage is a better prognostic indicator than degree of injury within glomeruli.28 This interstitial feature has usually been assessed as the area affected by tubular atrophy and fibrosis, rather than inflammation. While several centers have incorporated these interstitial findings in chronicity indices, others have shown that this measurement had merit as a component of an activity index. Estimates of the affected interstitial area have been relatively crude, such as < 10%, 10%–25%, 26%–50% or > 50%. This fact has led to attempts to quantitate factors important for interstitial scarring. Enumeration of fibroblasts after staining for fibroblastic-specific protein 1 (FSP1) has been correlated with extent of glomerulosclerosis and interstitial fibrosis, and was a better prognostic marker than was area of interstitial fibrosis or extent of glomerulosclerosis.47 Intensity of staining for CD3+ lymphocytes in patients with normal clearance function has been correlated with progressive disease (20% increase in serum creatinine concentration).48 Increased numbers of Mac387+ monocytes/macrophages and 27E10+ (activated) macrophages have been associated with poor outcome.49 Also, intensity of interstitial staining for CD44, a family of type I transmembrane glycoproteins involved in cell-cell interaction and cell-matrix interactions, has been correlated with proteinuria and interstitial scarring.50 Furthermore, increased interstitial expression of iNOS was associated with clinical indicators of poor prognosis.51 A recent study found that granule membrane protein of 17 kDa (GMP-17)-positive T-lymphocytes within renal tubules and B-lymphocytes in the interstitium were associated with progressive disease in patients with normal or near-normal eGFR.52 In contrast, for patients with impaired GFR, the presence of the intraepithelial lymphocytes was no longer a marker for a poor prognosis, suggesting that these cells exert their harmful effects early in the course of disease. Histological evaluation for several cytokines participating in the genesis of interstitial fibrosis has uncovered some apparent prognostic indicators. Interleukin-1β stimulates synthesis of vascular endothelial growth factor (VGEF) in proximal tubular cells. Tumor growth factorβ and angiotensin II induce VEGF production in vitro.53,54 Expression of

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VEGF in cytoplasm of tubular epithelial cells, perhaps due to local tissue hypoxia, was increased in more advanced interstitial lesions.55 Endothelin-1, a mitogen for renal cells that promotes synthesis of extracellular matrix, has been implicated in development of renal scarring. Activated tubular epithelial cells increase production of vasoactive agents and inflammatory mediators such as endothelin-1 and MCP-1, as well as growth factors, including transforming growth factor-β. The result is the attraction of inflammatory cells and activation of myofibroblasts that contribute to interstitial scarring. Magnitude of proteinuria has been correlated with urinary excretion of endothelin-110 and the extent of staining for endothelin-B receptors. Urinary endothelin-1 excretion significantly decreased after remission of proteinuria after immunosuppressive therapy. Transglutaminase is a calcium-dependent enzyme involved in cross-linking proteins through formation of ε-(γglutamyl)lysine bonds that resist proteolytic degradation. As such, transglutaminase may enhance resistance of extracellular matrix to metalloproteinases. Staining for this enzyme in glomeruli has been correlated with serum creatinine concentration, proteinuria, degree of glomerular sclerosis and mesangial cell proliferation.56 Staining in the tubulointerstitial compartment correlated with serum creatinine concentration, urinary β2-microglobulin, and tubulointerstitial scarring.

Beyond Light Microscopy While IgA in the mesangium shown by immunofluorescence microscopy is the cornerstone for the diagnosis of IgAN, the intensity of its staining has not been found to be a prognostic factor. However, two other immunofluorescence features have been associated with a worse clinical outcome. Impact of the first, IgG in the mesangial immune deposits,57 may reflect the ability of this immunoglobulin to activate complement and induce greater inflammation. IgG may be deposited as antibody in circulating immune complexes directed against galactosedeficient IgA1.4,5,58 The second finding, shown by confocal laser scanning microscopy, is that in children the amount of anionic sites in glomerular basement membranes was lower in patients with proteinuria than in those without proteinuria.59 Electron-microscopy-defined features portending a poor outcome include immune deposits in the capillary loops. In contrast, patients with thin glomerular basement membranes have a better prognosis than patients with normal-thickness membranes.60

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Potential New Prognostic Markers Related to Pathogenetic Factors As the biochemical basis for the inflammatory response to deposition of IgA1-containing immune complexes and resultant injury has been more recently clarified, new markers of prognosis have been proposed. It is plausible that one or more of these measures may prove more useful than our current indicators. Most of the markers discussed below have been reported from single-center studies and require confirmation.

Serum Markers About half of the patients with IgAN have increased serum IgA levels, but this measurement has not correlated with clinical outcome. As discussed above, a small fraction of circulatory IgA is central to the pathogenesis of IgAN: galactose-deficient IgA1 molecules in circulating immune complexes. Serum levels of this aberrant IgA1 are increased in most patients with IgAN61 and display a pattern in families consistent with a genetically influenced trait.62 However, the prognostic value of this measurement is uncertain.61,63 Upon deposition in the kidney, IgA-containing immune complexes activate complement through the alternative and lectin binding pathways.64 C3 activation fragments may be found in the plasma of more than 50% of adult patients.65 A high serum IgA/C3 ratio was correlated with worse histological lesions in non-nephrotic patients and a ratio above 4.5 indicated a worse renal survival.66 Increased plasma levels of advanced oxidation protein products, derived from oxidative stress, have been associated with poor clinical outcome.67

Urinary Markers Activation of mesangial cells and infiltration of inflammatory cells into glomeruli and the interstitium leads to secretion of a diverse array of cytokines and chemokines that play important roles in renal injury. To assess their role in IgAN, measurement of urinary levels is probably more relevant than measurement of serum levels. Excretion of IL-6, IL-8, MCP-1, and TGF-β,68 is increased in patients with IgAN compared to normal individuals. For these factors, urinary IL-669 or the IL-6/ epidermal growth factor ratio and greater amounts of IL-8,70 TGF-β, and transforming growth factor-α1 have been proposed as markers of

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poor prognosis. An increased ratio of urinary epidermal growth factor (EGF) to MCP-1 was associated with development of end-stage renal disease.71 Urinary excretion of IL-11 was correlated with proteinuria and creatinine clearance.72 Excretion of collagen type IV was increased in patients with a poor outcome.73 In contrast, excretion of α1-microglobulin (a major serum protein) was lower in proteinuric IgAN patients than in normal controls.74

Genetic Markers In addition to the study of multiplex families, the search for genetic prognostic markers has included association studies of alleles of many cytokines/chemokines in immunomodulatory or inflammatory pathways. Several centers have evaluated ACE genotype because pharmacological inhibition of the enzyme improves clinical course and allelic variations influence blood levels of angiotensin. The findings have been discordant. Only some studies found an association between poor prognosis and DD genotype;75 one center showed an association also with susceptibility to IgAN.76 Prognostic value of this polymorphism was sometimes associated with variants of other genes, including those encoding α-adducin77 or platelet-activating factor acetylhydrolase.78 Other genes with polymorphisms associated with outcome include those encoding angiotensinogen79 and CC-chemokine receptor 5 in whites,80 and plasminogen activator inhibitor-1,81 selectin,82 FcγRIIa and FcγRIIIa,83 angiotensinogen,84 peroxisome proliferators-activated receptor γ,85 T-cell receptor,86 transforming growth factor-β1,87 and paraoxonase88 in Japanese. While there has been little consensus about these markers to date, in part due to the limited number of studies, failure to detect an association of IgAN with a marker in one ethnic group does not preclude discovery of an association with the same marker in another ethnic group.89 Most of these association studies have examined the frequencies of polymorphisms of proteins selected for their hypothesized roles in the development or course of IgAN. The findings are certainly subject to an ascertainment bias and may also exhibit a substantial influence by geography or ethnicity.

New Directions Emerging technologies assessing the urinary proteome may reveal new markers or patterns of markers that are not necessarily deducible based

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on current knowledge of the pathogenesis of IgAN. In these approaches, proteins/peptides in urine samples are generally first separated by charge, size, or other physicochemical property before analysis of mass spectrometry spectra based on mass/charge ratio.90,91 As one example, capillary electrophoresis coupled on line with mass spectrometry has shown that patterns of peptides distinguished patients with IgAN from patients with other forms of renal disease, even without overt proteinuria.92,93 Some peptides were fragments of collagen and albumin that apparently had been degraded by enzymes, either in glomeruli or tubular lumens. Differential expression of proteases may alter protein excretion in various clinical presentations. Thus, it may soon be possible to non-invasively define prognostic markers for IgAN by proteomic analysis of urine without having fully defined the intricate details of the pathogenesis of the disease.

Predicting Clinical Outcome Predicting clinical outcome for patients with IgAN remains an imprecise process. Table 7.1 lists the clinicopathological features that are generally, but not universally, accepted as indicating a less favorable prognosis in patients with preserved clearance function at diagnosis. Clearly, patients with an increased serum creatinine concentration at diagnosis are likely to have progressive loss of renal function. The mechanism for some of the markers is not understood (e.g. the apparent benefit of a history of macroscopic hematuria). Other markers, such as obesity and hyperuricemia, may exert some of their adverse effects outside of the glomerulus. Several investigators contend that the threshold for the adverse impact of proteinuria on prognosis is significantly lower, as little as 500 mg/day. Light microscopic findings of the renal biopsy are the basis for several classifications that have correlated specific features with a progressively worse prognosis. Table 7.2 summarizes six currently applied pathology-based grading systems using features of the diagnostic renal biopsy.94–99 These classifications have favored injury in glomeruli over that in the interstitium and vasculature. In a separate study with iterative renal biopsy, histological features often showed worse damage even in patients with a stable clinical course.100 This finding suggests that long-term observation is needed to assess prognostic factors for patients with a disease that often exhibits an indolent course.

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Table 7.1 Commonly Accepted Markers of a Worse Prognosis for Patients with IgAN. Demographic Male sex Older age at diagnosis Obesity Clinical No history of macroscopic hematuria Persistent microscopic hematuria Hypertension, persistent Laboratory Proteinuria persistently > 1000 mg/day Albuminuria > 30 mg/day Hyperuricemia Hypertriglyceridemia Histological Light microscopy Mesangial hypercellularity Focal segmental glomerular sclerosis Endocapillary cellular proliferation Capillaritis Interstitial fibrosis Thrombotic microangiopathy Loss of podocytes Immunofluorescence microscopy IgG in mesangial deposits Electron microscopy Electron-dense deposits in capillary loops

In the last two decades, several individual centers have derived formulas to predict the risk of end-stage renal disease or rate of loss of renal clearance function for an individual patient, using commonly measured laboratory and/or histological features.97,101–106 Unfortunately, there has been no consensus as to the components of the formula or even the endpoint, as shown in Table 7.3. Some components are unique to the regional populations. Furthermore, the relative weights of shared components

Classification Author/Year

Grade 1

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Table 7.2

Pathology-based grading systems for IgAN.

Grade 2

Grade 3

Grade 4

Grade 5

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Haas/1997107

Minimal or no mesangial hypercellularity; without sclerosis or crescents.

Focal segmental glomerulosclerosis; minimal increase in mesangial hypercellularity; no crescents.

Focal proliferative: changes, < 50% of glomeruli are hypercellular.

To/200099

Mean glomerular sclerosis < 25%. Tubular atrophy and interstitial fibrosis < 5%.

Mean glomerular sclerosis 25%–49%. Tubular atrophy and interstitial fibrosis 5%–49%.

Mean glomerular sclerosis ≥ 50%. Tubular atrophy and interstitial fibrosis ≥ 50%.

Lee/200596

Normal or focal mesangial cellular proliferation.

Diffuse mesangial cellular proliferation, or < 25% of glomeruli with crescents, segmental/global sclerosis.

25%–49% of glomeruli 50%–75% of with crescents, glomeruli with segmental or crescents, global sclerosis. segmental or global sclerosis.

Diffuse proliferative: > 50% of glomeruli are hypercellular.

Advanced sclerotic changes: ≥ 40% of glomeruli are globally sclerotic and/or ≥ 40% tubular atrophy or loss of cortex.

> 75% of glomeruli with crescents, segmental or global sclerosis.

(Continued )

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Any focal or sclerotic lesion.

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Minimal glomerular Mesangial changes. proliferation only.


SPNSG/198294

Grade 2

Manno/200798

Normal glomeruli Moderate or diffuse or slight increase mesangial in mesangial proliferation matrix and/or and/or focal cellularity. segmental sclerosis and/or endocapillary proliferative and/or cellular crescents ≤ 50% of glomeruli.

Slight mesangial cell Moderate diffuse Severe diffuse proliferation and mesangial cell mesangial cell increased matrix. proliferation and proliferation and Glomerulosclerosis, increased matrix. increased matrix. crescent formation or Glomerulosclerosis, Glomerulosclerosis, adhesion to Bowman’s crescent formation crescent formation capsule in < 10% of or adhesion to or adhesion to glomeruli. Bowman’s capsule Bowman’s capsule in 10%–30% of in > 30% of glomeruli. glomeruli.

SPNSG, Southwest Pediatric Nephrology Study Group.

Cellular crescents in > 50% of glomeruli and/or global sclerosis and fibrous crescents involving > 1/3 of glomeruli and/or diffuse segmental sclerosis.

Grade 5

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Slight mesangial cell proliferation and increased matrix.

Grade 4

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Wakai/200697

Grade 3

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Grade 1

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Classification Author/Year

(Continued )


Table 7.2

Author/Year

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Table 7.3

Approaches to predict clinical outcome of an individual patient with IgAN.

Component of score Clinical factors Histology

Proteinuria, hypertension, Global optical and HLA B35. score (mesangial, tubular, interstitial, and vascular components).

ESRD at 5 yr.

Requires control of hypertension.

No

Renal insufficiency (serum creatinine ≥ 1.5 mg/dL [135 µmol/L]) at 10 and 20 yr.

Proteinuria was strongest factor.

No

Total glomerular score. ESRD at 5 and 10 yr. Serum creatinine dominates. Older age confers better score. No accounting for treatment.

No

Bartosik/2001103 298 patients, Toronto

None.

No

Time-averaged MAP and proteinuria.

Slope of GFR (C-G) after 2–3 yr.

No demographic, clinical, laboratory or histological parameter at biopsy significantly predicted progressive

(Continued )


Radford/1997104 Serum creatinine 206 patients, Midwest and age. USA

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Alamartine/1991105 282 patients, France

None.

Validated

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History of macroscopic hematuria, microscopic hematuria, creatinine clearance, and 24-hr proteinuria.

Comment

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Beukhof/1986106 75 patients, The Netherlands

End-point measurement

End-point measurement

Comment

Validated

Microscopic hematuria, and hypertension.

Arteriosclerosis and glomerular score > 2.

ESRD at 10 yr.

Starting GFR (C-G) > 85 ml/min. Some patients had been treated.

No

Magistroni/2006101 310 patients, Italy

Serum creatinine > 1.4 mg/dL, proteinuria > 1g/d, hypertension and age > 30 yr.

None.

ESRD at 10 yr.

Serum creatinine was strongest risk factor.

Yes

Wakai/200697 1754 patients, Japan

Sex, age, systolic BP, proteinuria (dipstick), hematuria (microscopic), serum total protein, and serum creatinine.

Total histological grade ESRD at 7 yr. (glomerular + interstitial/vascular).

Serum creatinine dominates, better score with older age; no accounting for treatment.

No

BP, blood pressure; C-G, Cockcroft-Gault formula; ESRD, end-stage renal disease; GFR, glomerular filtration rate; MAP, mean arterial pressure.

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Rauta/2002102 161 patients, Finland

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loss of GFR. MAP and proteinuria accounted for only one third of the variability in loss of renal function.

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Component of score Clinical factors Histology

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Author/Year

(Continued )


Table 7.3

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(e.g. serum creatinine) differ between formulas. It is disappointing that these calculations often yield disparate estimates for commonly encountered clinical circumstances. Only one formula101 has been validated in a second cohort of patients. The details of the formulas and their derivation are beyond the scope of this chapter and the reader should review the publications for the precise methods.97,102–106 Because of these disparities and the consequent difficulties in comparing the findings reported from centers using different methods to assess prognosis, the International IgA Nephropathy Network is drafting the Oxford Classification of IgAN based on review of biopsy specimens and five-year clinical data from about 300 patients from around the world.

Concluding Remarks At present, features such as male sex, obesity, poorly controlled hypertension, persistent proteinuria, mesangial-cell proliferation, glomerular extracapillary proliferation and focal necrosis, and extent of interstitial scarring portend an unfavorable clinical outcome. Some recently described, untested, prognostic markers may correlate so closely with currently acceptors indicators, such as proteinuria or interstitial fibrosis, as to have little independent value. Additional studies are needed to define the merit of these newly proposed markers discussed above. Definition of more precise, perhaps molecularly based, prognostic indicators will lead to more appropriate treatment regimens, better selection of participants for clinical trials, and improved monitoring of the response to therapy.

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79.

80.

81.

82.

83.

84.

85.

86.

87.

88.

89. 90. 91. 92.

polymorphisms on the progression of immunoglobulin A nephropathy. Clin Genet 62: 128–134. Bantis C, Ivens K, Kreusser W, et al. (2004) Influence of genetic polymorphisms of the renin-angiotensin system on IgA nephropathy. Am J Nephrol 24: 258–267. Berthoux FC, Berthoux P, Mariat C, et al. (2006) CC-chemokine receptor five gene polymorphism in primary IgA nephropathy: the 32 bp deletion allele is associated with late progression to end-stage renal failure with dialysis. Kidney Int 69: 565–572. Suzuki H, Sakuma Y, Kanesaki Y, et al. (2004) Close relationship of plasminogen activator inhibitor-1 4G/5G polymorphism and progression of IgA nephropathy. Clin Nephrol 62: 173–179. Watanabe Y, Inoue T, Okada H, et al. (2006) Impact of selectin gene polymorphisms on rapid progression to end-stage renal disease in patients with IgA nephropathy. Intern Med 45: 947–951. Tanaka Y, Suzuki Y, Tsuge T, et al. (2005) FcgammaRIIa-131R allele and FcgammaRIIIa-176V/V genotype are risk factors for progression of IgA nephropathy. Nephrol Dial Transplant 20: 2439–2445. Goto S, Narita I, Saito N, et al. (2002) A(-20)C polymorphism of the angiotensinogen gene and progression of IgA nephropathy. Kidney Int 62: 980–985. Song J, Sakatsume M, Narita I, et al. (2003) Peroxisome proliferator-activated receptor gamma C161T polymorphisms and survival of Japanese patients with immunoglobulin A nephropathy. Clin Genet 64: 398–403. Deenitchina SS, Shinozaki M, Hirano T, et al. (1999) Association of a T-cell receptor constant alpha chain gene polymorphism with progression of IgA nephropathy in Japanese patients. Am J Kidney Dis 34: 279–288. Sato F, Narita I, Goto S, et al. (2004) Transforming growth factor-beta1 gene polymorphism modifies the histological and clinical manifestations in Japanese patients with IgA nephropathy. Tissue Antigens 64: 35–42. Kovacs TJ, Harris S, Vas TK, et al. (2006) Paraoxonase gene polymorphism and serum activity in progressive IgA nephropathy. J Nephrol 19: 732–738. Hsu SI. (2008) Racial and genetic factors in IgA nephropathy. Semin Nephrol 28: 48–57. Barratt J, Topham P. (2007) Urine proteomics: the present and future of measuring urinary protein components in disease. CMAJ 177: 361–368. Fliser D, Novak J, Thongboonkerd V, et al. (2007) Advances in urinary proteome analysis and biomarker discovery. J Am Soc Nephrol 18: 1057–1071. Haubitz M, Wittke S, Weissinger EM, et al. (2005) Urine protein patterns can serve as diagnostic tools in patients with IgA nephropathy. Kidney Int 67: 2313–2320.

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93. Julian BA, Wittke S, Novak J, et al. (2007) Electrophoretic methods for analysis of urinary polypeptides in IgA-associated renal diseases. Electrophoresis 28: 4469–4483. 94. A multicenter study of IgA nephropathy in children. (1982) A report of the Southwest Pediatric Nephrology Study Group. Kidney Int 22: 643–652. 95. Haas M. (2005) Histology and immunohistology of IgA nephropathy. J Nephrol 18: 676–680. 96. Lee HS, Lee MS, Lee SM, et al. (2005) Histological grading of IgA nephropathy predicting renal outcome: revisiting H. S. Lee’s glomerular grading system. Nephrol Dial Transplant 20: 342–348. 97. Wakai K, Kawamura T, Endoh M, et al. (2006) A scoring system to predict renal outcome in IgA nephropathy: from a nationwide prospective study. Nephrol Dial Transplant 21: 2800–2808. 98. Manno C, Strippoli GF, D’Altri C, et al. (2007) A novel simpler histological classification for renal survival in IgA nephropathy: a retrospective study. Am J Kidney Dis 49: 763–775. 99. To KF, Choi PC, Szeto CC, et al. (2000) Outcome of IgA nephropathy in adults graded by chronic histological lesions. Am J Kidney Dis 35: 392–400. 100. Alamartine E, Sabatier JC, Berthoux FC. (1990) Comparison of pathological lesions on repeated renal biopsies in 73 patients with primary IgA glomerulonephritis: value of quantitative scoring and approach to final prognosis. Clin Nephrol 34: 45–51. 101. Magistroni R, Furci L, Leonelli M, et al. (2006) A validated model of disease progression in IgA nephropathy. J Nephrol 19: 32–40. 102. Rauta V, Finne P, Fagerudd J, et al. (2002) Factors associated with progression of IgA nephropathy are related to renal function — a model for estimating risk of progression in mild disease. Clin Nephrol 58: 85–94. 103. Bartosik LP, Lajoie G, Sugar L, Cattran DC. (2001) Predicting progression in IgA nephropathy. Am J Kidney Dis 38: 728–735. 104. Radford MG, Jr, Donadio JV, Jr, Bergstralh EJ, Grande JP. (1997) Predicting renal outcome in IgA nephropathy. J Am Soc Nephrol 8: 199–207. 105. Alamartine E, Sabatier JC, Guerin C, et al. (1991) Prognostic factors in mesangial IgA glomerulonephritis: an extensive study with univariate and multivariate analyses. Am J Kidney Dis 18: 12–19. 106. Beukhof JR, Kardaun O, Schaafsma W, et al. (1986) Toward individual prognosis of IgA nephropathy. Kidney Int 29: 549–556. 107. Haas M. (1997) Histologic subclassification of IgA nephropathy: a clinicopathologic study of 244 cases. Am J Kidney Dis 29: 829–842.

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Chapter 8

Clinical Course of Primary IgA Nephropathy Franc ois C. Berthoux and Hesham Mohey

Introduction IgA nephropathy (IgAN) remains the most frequent type of primary glomerulonephritides in the developed world. The initial description was reported 40 years ago by Jean Berger and Nicole Hinglais1 and we refer to the most recent reviews on the subject.2–5 The definition of IgAN is still pathological and needs a renal biopsy with material to be examined by light and immunofluorescent microscopy. The agreed definition is the deposition of at least 1+ (on a semi-quantitative scale: 0 = no deposits; +/− = traces; 1+, 2+ and 3+) immunoglobulin A (IgA) in the mesangial area of glomeruli. The characteristics of these IgA deposits are the followings: granular, coarse with the “en mottes” aspect, predominantly mesangial, dominant or codominant with other immunoglobulins such as IgG and/or IgM, associated with C3 deposits at the same location, and global and diffuse in contrast to the light microscopy lesions which are often segmental and focal. Once the diagnosis of IgAN is made, the clinician has to differentiate the primary form, also called Berger’s disease, which represents about 80% of all cases from the secondary forms observed in SchönleinHenoch purpura, alcoholic liver cirrhosis, and more rarely in systemic lupus erythematosus (ISN/RPS class II), in ankylosing spondylarthritis

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and the rare superimposed cases (overlapping syndrome of IgAN and lipoid nephrosis). In this chapter, we will focus on clinical presentation and long-term clinical course of primary/idiopathic IgAN with a comparison between males and females.6

Clinical Presentation at Onset of the Disease (Table 8.1) The data, we are presenting below, is based on our prospective IgAN cohort from the Saint-Etienne region (IGAN-STET-CO) collected from 1990 to 1999 (date of initial diagnosis) and including 356 patients diagnosed at our institution. In this cohort, the male predominance was 72% and the classical onset with acute infection associated gross (macroscopic) hematuria was seen in only 20% of the patients. By contrast, 26% of the patients had only isolated microscopic hematuria at presentation, and would have not been biopsied in many centers. It should also be noted that arterial hypertension (HT) was present at onset/discovery of IgAN in about 22% of the patients (and sometimes longstanding before occurrence of any renal signs). Presentation at onset was similar between male and female patients except for isolated microscopic (chance) hematuria which was more frequent in females (40% versus 21%; P = 0.003). It should be pointed out that the male:female ratio in Asian patients with IgAN is lower with values between 1 to 1.5.7,8

Clinical Presentation at Diagnosis of the Disease (Table 8.2) The interval time between first renal biopsy (informative) and onset of the disease was a mean (SD) = 5.5 (8.2) year with a median of 2.3 years. Note that the number of patients with severe clinical presentation at diagnosis were as follows: 103 with proteinuria over 1 g/day (28.9%); 126 with HT treated or not (35.4%); already 85 (23.9%) with significant chronic renal failure (defined as glomerular filtration rate (GFR) below 60 ml/mn/1.73 m2 and according to abbreviated MDRD formula), and 123 patients (34.6%) with high global optical score (GOS)9 considered as severe lesions (≥ 8 on a scale from 0 to 20).

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Table 8.1 Characteristics at onset of primary IgA nephropathy and according to gender (IGAN-STET-CO: prospective cohort diagnosed from 1990 to 1999).

•

Number

356

255 (71.6%)

101 (28.4%)

•

Ethnics (all Caucasians): N(%) Regional origin From Maghreb

332 24 (6.7)

238 17 (6.7%)

94 7 (6.9%)

Age at onset: years Mean (SD) Median (range)

35.6 (15.3) 34.5 (2.7–76.6)

35.2 (15.4) 34.4 (5.1–76.6)

Renal signs at onset: N(%) MicroHematuria (microH) Proteinuria (with nephrotic syndrome) MacroHematuria (macroH) Hypertension Renal failure (acute/chronic)

254 (71.3%) 201 (56.5%) 10 (5.0%) 71 (19.9%) 78 (21.9%) 39 (11.0%)

175 (68.6%) 157 (61.6%) 8 (5.1%) 52 (20.4%) 61 (23.9%) 30 (11.8%)

79 (78.2%) 44 (43.6%) 2 (4.5%) 19 (18.8%) 17 (16.8%) 9 (8.9%)

NS (P = 0.09) P = 0.003 NS NS NS NS

94 (26.4%) 35 (9.8%) 43 (12.1%) 93 (26.1%) 52 (14.6%) 39 (11.0%)

54 (21.2%) 24 (9.4%) 34 (13.3%) 73 (28.6%) 40 (15.7%) 30 (11.8%)

40 (39.6%) 11 (10.9%) 9 (8.9%) 20 (19.8%) 12 (11.9%) 9 (8.9%)

P = 0.003 NS NS NS NS NS

•

Modalities of onset: N(%) Isolated microH MacroH +/− microH Isolated Prot Prot +/− (microH/macroH) HT +/− (Prot/microH/macroH) RF (acute/chronic) +/− (HT/Prot/microH/macroH)

36.5 (15.2) 36.2 (2.7–71.6)

P

NS NS NS

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Items

Overall

Male

Female

P

255

101

•

Interval time onset/diagnosis: years Mean (SD) Median (range)

5.5 (8.2) 2.3 (0–46.9)

5.5 (7.8) 2.4 (0–46.9)

5.3 (9.2) 2.2 (0–44.5)

NS NS

Age at diagnosis: years Mean (SD) Median (range)

41.1 (15.0) 41.1 (13.3–78.5)

40.8 (15.1) 41.1 (13.3–71.1)

41.9 (14.9) 41.1 (15.9–78.5)

NS NS

Proteinuria: g/day Mean (SD) Median (range) 0 — null or 8 for presence of cellular crescents a/o segmental/focal hyalinosis). In our cohort, the final number of patients reached 170 with HT (47.8%), 100 with CRF (28.1%) and 46 (12.9%) with the combined primary end-point ESRF/dialysis (N = 32) or death before ESRF (N = 14). Comparisons between males and females showed mild differences but not significant: less proteinuria (P = 0.04), fewer patients with HT (P = 0.06, not significant) and with primary end-point (P = 0.08, not significant). It is important to note that overall proteinuria decreased significantly between diagnosis and last follow-up (paired t test: P < 0.0001) mainly due to ACEI and/or ARBs utilization. Survival without dialysis/death was respectively at time 0, 5, 10, 15 and 20 years for males 100% (N = 255), 97% (N = 209), 91% (N = 140), 86% (N = 78) and 75% (N = 31) versus 100% (N = 100), 99% (N = 84), 96% (N = 54), 91% (N = 31) and 91% (N = 14) in females (log rank test: P = 0.03). So the gender-based differences are minor, only 5% until 15 years and became greater on the very long term. In the literature, the cumulative incidence at 20 years of ESRF/dialysis varies from 10% to 40% depending on the policy of renal biopsy (extended versus restricted to proteinuria over 1 g/d a/o to renal dysfunction).

Overall

Male

Female

P

356

255

101

•

Age/FU: years Mean (SD) Median (range)

48.1 (15.6) 48.9 (16.9–84.1)

47.6 (15.5) 47.8 (16.9–80.8)

41.9 (14.9) 50.9 (17.9–84.1)

NS NS

Time interval (onset/FU): years Mean (SD) Median (range)

12.5 (9.4) 10.8 (0–56.1)

12.3 (8.9) 10.9 (0–47.5)

13.1 (10.6) 10.5 (0.4–56.1)

NS NS

Proteinuria*: g/day Mean (SD) Median (range) Class 0 — null or < 0.30 g/d Class 1 — 0.30–0.99 g/d Class 2 — 1.00–2.99 g/d Class 3 — over 3.00 g/d

N = 322 0.39 (0.83) 0.14 (0–8.1) 222 (68.9%) 67 (20.8%) 28 (8.7%) 5 (1.6%)

N = 227 0.44 (0.81) 0.17 (0–6.0) 144 (63.4%) 54 (23.8%) 25 (11.0%) 4 (1.8%)

N = 95 0.28 (0.87) 0.09 (0–8.1) 78 (82.1%) 13 (13.7%) 3 (3.2%) 1 (1.1%)

•

•

P = 0.04 P = 0.009

}

P = 0.009

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Clinical data at last follow-up or at end-point of IgA nephropathy patients (IGAN-STET-CO) and according to


Table 8.3 gender.

GFR (aMDRD): ml/mn/1.73 m2 S Mean (SD) Median (range) Stages: 1 — > 90 2 — 60–89 3 — 30–59 4 — 15–29 5 — < 15

•

Chronic renal failure: N(%) (GFR < 60 ml/mn)

•

ESRF/dialysis or death: N(%)

* After exclusion of patients with GFR stage 5.

Female

170 (47.8%)

130 (51.0%)

40 (39.6%)

NS (P = 0.06)

69.2 (30.6) 73.6 (5–185)

68.8 (32.0) 75.1 (6–185)

70.2 (27.1) 71.0 (5–169)

NS NS

90 (25.3%) 166 (46.6%) 53 (14.9%) 13 (3.7%) 34 (9.6%)

68 (26.7%) 111 (43.5%) 40 (15.7%) 8 (3.1%) 28 (11.0%)

22 (21.8%) 55 (54.5%) 13 (12.9%) 5 (5.0%) 6 (5.9%)

100 (28.1%)

76 (29.8%)

24 (23.8%)

46 (12.9%)

38 (14.9%)

8 (7.9%)

P

}

NS

NS NS (P = 0.08)

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Overall


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Risk Factors Predicting Progression There are many factors predicting progression towards CRF and then to ESRF/dialysis (CKD stage 5). They can be classified as major/ consensual or minor. The major factors present at diagnosis2,9,11–15 and predictive are: (i) arterial HT (absence or presence and of course treated); (ii) proteinuria as a continuous variable (g/day) or as a categorical variable (proteinuria ≥ 1 g/d; yes or no); and (iii) the severity of renal lesions appreciated in our group by the global optical scoring (GOS)9,10 which is the sum of glomerular, vascular, interstitial and tubular indices, both as a continuous variable from 0 to 20 or as a categorical variable (GOS ≥ 8; yes or no). The minor factors are not consensual such as age at disease onset,15 patients with gross hematuria, body mass index;16 serum triglycerides and uric acid17 all at diagnosis, and some more controversial genetic factors, like polymorphism of chemokine receptor 5 (CCR5).18,19 Serum creatinine is a poor marker because of the influence of physical characteristics (muscle mass) on its value and consequently the great difference between males and females. It should only be used to calculate GFR with either the Cockcroft-Gault formula corrected for body surface area (BSA) or preferably with the abbreviated MDRD formula. For the Cockcroft-Gault formula, the weight of the patient is used two times, one for the formula itself and the other for BSA; the aMDRD does not utilize weight, but only age, gender, ethnics and of course serum creatinine. Multivariate Cox regression analysis with dialysis/death as endpoint confirmed that proteinuria > 1 g/d, GOS ≥ 8 and HT were independent predictors, but not gender (data not shown). The presence of CRF (GFR below 60) at diagnosis (probable continuum between CKD stage 3 to CKD stage 5) was also a predictor for ESRF-dialysis/death, but then substituting to hypertension and proteinuria. It is interesting to note that these three major risk factors (Table 8.4) are present in 61% of patients reaching the primary end-point (28/46) as compared to 6.1% in patients who did not (19/310). In addition, the cumulative incidence rate of dialysis/death, at 20 years according to Kaplan-Meier method, was respectively 4%, 9%, 18% or 63% with the presence at diagnosis of zero, one, two or three of these risk factors (log rank test: P < 0.0001). So at the time of first renal biopsy (diagnosis), the individual final prognosis at 20 years could be estimated and used for individual

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Table 8.4 Distribution of risk factors (RF) at diagnosis and according to gender in IgA nephropathy patients (IGAN-STET-CO). RF number

Overall N (%)

0 1 2 3

167 74 68 47

N=

356

(46.9%) (20.8%) (19.1%) (13.2%)

Males N (%) 108 56 51 40 255

(42.4%) (22.0%) (20.0%) (15.7%)

Females N (%) 59 18 17 7

(58.4%) (17.8%) (16.8%) (6.9%)

P

X 2 = 9.16 P = 0.03

101

management/treatment. The treatment protocol should be individualized based on these risks factors and the rapidity of disease progression.

Conclusion There is a great disparity in the ultimate prognosis of primary IgA nephropathy, with presence of CRF (GFR < 60 ml/mn/1.73 m2) in 25% to 60% of the patients, and with ESRF in 10% to 40%. This variability depends mainly on renal biopsy policy (restricted like in the US or extended like our group and some Asian countries). The independent risk factors present at time of diagnosis (first renal biopsy) and predictive of ESRF/dialysis or death at 20 years from onset are arterial hypertension (presence versus absence), proteinuria ≥ 1 g/day (presence versus absence) and a severe pathological score ≥ 8 (presence or absence) indicating severe renal lesions. Comparison between males and females demonstrated that females have less severe clinical presentation, less risk factors which ended up in a slightly better survival without dialysis/death on the very long term. However at similar risk factor, there is no prognostic role for gender. There might be some differences in the pathogenic mechanisms of the disease between females and males.20

References 1. Berger J, Hinglais N. (1968) Intercapillary deposits of IgA-IgG. J Urol Nephrol 74: 694–695. 2. D’Amico G. (2000) Natural history of idiopathic IgA nephropathy: role of clinical and histological prognostic factors. Am J Kidney Dis 36: 227–237.

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3. Donadio JV, Grande JP. (2002) IgA nephropathy. N Engl J Med 347: 738–748. 4. Barratt J, Feehally J. (2005) IgA nephropathy. J Am Soc Nephrol 16: 2088–2097. 5. Berthoux F, Mohey H, Afiani A. (2008) Natural history of primary IgA nephropathy. Semin Nephrol 28: 4–9. 6. Cattran DC, Reich HN, Beanlands HJ, et al. (2008) The impact of sex in primary glomerulonephritis. Nephrol Dial Transplant 23: 2247–2253. 7. Lai KN, Ho CP, Chan KW, et al. (1985) Nephrotic range proteinuria — a good predictive index of disease in IgA nephropathy? Q J Med 57: 677–688. 8. Yoshikawa N, Nakamura H, Ito H. (1994) IgA nephropathy in children and adult. Springer Semin Immunopathol 16: 105–120. 9. Alamartine E, Sabatier JC, Guerin C, et al. (1991) Prognostic factors in mesangial IgA glomerulonephritis: an extensive study with univariate and multivariate analyses. Am J Kidney Dis 18: 12–19. 10. Alamartine E, Sabatier JC, Berthoux FC. (1990) Comparison of pathological lesions on repeated renal biopsies in 73 patients with primary IgA glomerulonephritis: value of quantitative scoring and approach to final prognosis. Clin Nephrol 34: 45–51. 11. Schena FP. (1990) A retrospective analysis of the natural history of primary IgA nephropathy worldwide. Am J Med 89: 209–215. 12. Koyama A, Igarashi M, Kobayashi M. (1997) Natural history and risk factors for immunoglobulin A nephropathy in Japan. Research Group on Progressive Renal Diseases. Am J Kidney Dis 29: 526–532. 13. Li PK, Ho KK, Szeto CC, et al. (2002) Prognostic indicators of IgA nephropathy in the Chinese — clinical and pathological perspectives. Nephrol Dial Transplant 17: 64–69. 14. Wakai K, Kawamura T, Endoh M, et al. (2006) A scoring system to predict renal outcome in IgA nephropathy: from a nationwide prospective study. Nephrol Dial Transplant 21: 2800–2808. 15. Radford MG, Donadio JV, Bergstralh EJ, Grande JP. (1997) Predicting renal outcome in IgA nephropathy. J Am Soc Nephrol 8: 199–207. 16. Bonnet F, Deprele C, Sassolas A, et al. (2001) Excessive body weight as a new independent risk factor for clinical and pathological progression in primary IgA nephritis. Am J Kidney Dis 37: 720–727. 17. Syrjänen J, Mustonen J, Pasternack A. (2000) Hypertriglyceridaemia and hyperuricaemia are risk factors for progression of IgA nephropathy. Nephrol Dial Transplant 15: 34–42. 18. Panzer U, Schneider A, Steinmetz OM, et al. (2005) The chemokine receptor 5 Delta32 mutation is associated with increased renal survival in patients with IgA nephropathy. Kidney Int 67: 75–81.

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19. Berthoux FC, Berthoux P, Mariat C, et al. (2006) CC-chemokine receptor five gene polymorphism in primary IgA nephropathy: the 32 bp deletion allele is associated with late progression to end-stage renal failure with dialysis. Kidney Int 69: 565–572. 20. Nakamura I, Iwase H, Arai K, et al. (2004) Detection of gender difference and epitope specificity of IgG antibody activity against IgA1 hinge portion in IgA nephropathy patients by using synthetic hinge peptide and glycopeptide probes. Nephrology (Carlton) 9: 26–30.

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Chapter 9

Special Clinical Syndromes Judit Nagy and Tibor Kovács

Introduction IgA nephropathy (IgAN) has been reported to occur in association with a wide range of possible etiologic factors and diseases and this has been called secondary IgAN.1–4 In these diseases the renal lesion appears to be the consequence of a significant extrarenal disease. The great majority of patients with IgAN however are not associated with any known specific etiological agents and are called primary IgAN. IgA mesangial deposition may sometimes be associated with an IgAmediated small vessel vasculitis usually known as Henoch-Schönlein purpura which is differentiated from IgAN only by extrarenal manifestations.5 Most of the cases of Henoch-Schönlein nephritis have also unknown etiology. Very little is known about the incidence and prevalence of secondary IgAN. Similarly to primary IgAN it may be underdiagnosed because of the rare urine examinations of non-renal patients and because of the renal biopsy practice in olygosymptomatic patients. Furthermore, there are many apparently normal subjects with clinically inapparent IgA glomerular deposits (latent IgAN). Their number may be as high as 16% in Asia6,7 (see also Chapters 2 and 11). Evidence from the studies suggests that several pathogenetic mechanisms as well as the combination of these mechanisms can produce IgAN. The real secondary IgAN should be the cases where IgAN is associated with a disease and/or a pathogenic agent fitting into the proved or supposed pathogenetic mechanisms of IgAN (Table 9.1). The other part

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Table 9.1

Diseases with probable pathogenetic association with IgAN.

Diseases

Common

Rare

Gastrointestinal

Celiac disease

Hepatic

Alcoholic liver disease Non-alcoholic liver cirrhosis

Infections

HIV Hepatitis B Schistosomiasis

Brucellosis Leprosy

Malignancies

Renal cell carcinoma

Monoclonal Lymphoproliferative diseases Laryngeal carcinoma Bronchial carcinoma

Rheumatic diseases

Ankylosing spondylitis Rheumatoid arthritis

Autoimmune diseases

Others

Crohn’s disease Ulcerative colitis

Systemic lupus erythematosis Wegener’s granulomatosis Sjögren’s disease Hashimoto’s thyroiditis Diabetes mellitus/ metabolic syndrome

of publications (mainly single case reports) may reflect only a chance association between the disease and/or pathogen agent and IgAN. In this chapter we deal with the special clinical syndromes of IgAN focusing on those diseases which have a probability for a genuine shared pathogenesis with IgAN (Tables 9.1 and 9.2). We only briefly discuss the different dietary and microbial agents which were identified in the circulating IgA immune complexes and mesangial IgA deposits and their presumed role in the pathogenesis of secondary IgAN.

Mucocutaneous and Other Infections The interaction between the mucosal immune system as well as the environmental antigens and pathogens affecting the integrity of

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Special Clinical Syndromes ✦ 123

Table 9.2 Main elements of dysregulation in IgA immune system and the diseases associated with the development of secondary IgAN. Major abnormalities of IgA biology in IgAN 1. Chronic exposure to environmental (food, pathogen agents, etc.) antigens partly because of the permanent or intermittent loss of integrity of mucocutaneous barriers 2. Shift in the site of production of polymeric IgA1 from mucosa to bone marrow with abnormal systemic responses to mucosally encountered antigens 3. Structural abnormality (altered glycolysation) in some part of circulating polymeric IgA1 4. Decreased systemic IgA clearance because of reduced hepatocyte ASGP-R expression and Kupffer cell FcαR1 expression as well as changes in FcαR1 expression by circulating monocytes, neutrophils 5. Persistence of excessive amount of pathogenic IgA1, IgA1 immune complexes and IgA1 aggregates in the circulation 6. Mesangial deposition of pathogenic IgA1 7. Glomerular response to deposited IgA1

Diseases with probable pathogenetic association with IgAN e.g. Inflammatory diseases in gastrointestinal, respiratory and genitourinary tract, skin diseases (psoriasis, etc.)

e.g. Malignancies of the lymphoid system and bone marrow (IgA myeloma, Hodgkin’s and nonHodgkin’s lymphoma, etc.)

e.g. Liver diseases with reduction in liver mass, ankylosing spondylitis, HIV infection

e.g. Diabetes mellitus, hypertension, obesity

mucosa is likely to play an important role in driving the pathogenic processes in IgAN. Furthermore, all of the data about the infect and environmental antigens have been found to drive IgAN in individual patients may be important, even if the studies have failed to identify a single antigen which is responsible for the development of IgAN in all patients.

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Hepatitis Virus Infections A number of case reports have associated IgAN with hepatitis B virus (HBV) infections.8,9 In China, which is an endemic area of HBV infection, the association is common and HBV may play a role in the pathogenesis of IgAN.10,11 In a small study, in seven of 25 hepatitis C virus (HCV)-infected patients with end-stage cirrhosis mainly subclinical IgAN was detected.12 In these cases, however the IgA deposition may be the consequence of impaired clearance of IgA because of the chronic liver disease.

Human Immunodeficiency Virus (HIV) Infections IgAN has been seen in several HIV-infected patients.13,14 An European biopsy study demonstrated a 7.75% prevalence of IgAN in patients who died of AIDS.15 The clinical picture showed asymptomatic urinary abnormalities; few of the patients had massive proteinuria and renal insufficiency. Immunofluorescence in the eluates of glomerular tissues revealed HIV antigens; PCR confirmed the presence of gag genome in the biopsy.14 Circulating immune complexes and the renal eluates contained IgA idiotypic antibodies and anti-HIV IgG or IgM antibodies. These idiotypic immune reactions suggest an immunoregulatory dysfunction associated with HIV infection, culminating in the deposition of circulating IgA-anti-HIV antibody complexes in the glomeruli.

Staphylococcus Infection The association of methicillin-resistant Staphylococcus aureus (MRSA) infections with IgA immune complex GN has been well documented in Japan and only several cases were reported in the US and Europe.16–18 With the increasing prevalence of MRSA and methicillin-resistant Staphylococcus epidermidis (MRSE) infections, one should keep in mind that the incidence of the glomerulonephritis with IgA predominant glomerular immune complex deposits in co-localization with SA cell envelope antigen may also increase. The clinical picture of these patients is different. The disease is quite severe, usually present with acute renal failure, frequently with heavy proteinuria and active sediment.16–18 Koyama et al.19 have shown polyclonal activation of serum antibodies of IgA subclasses against SA in these patients. These authors

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have induced IgA-type glomerulonephritis with SA antigens in Balb/ c mice.20 Furthermore, they identified SA cell envelope antigen in the renal biopsy of 79 from 116 (68%) IgAN patients.21 The Koyama group suggests that, at least at that region in Japan, SA cell envelope antigen is a new candidate for the induction of IgAN.21 Furthermore, papers call attention to the difficulties of the correct diagnosis and the treatment of these cases.

Other Infections A large number of other pathogens associated with chronic infections have been reported to trigger the development of IgAN.4 These include bacteria (Hemophilus parainfluenzae, Helicobacter pylori, Mycoplasma pneumoniae, Mycobacterium tuberculosis, Staphylococcus aureus), viruses (hepatitis B virus, cytomegalic virus, enterovirus, mumps virus) and parasites (Plasmodium malariae, Schistosoma hematobium, Toxoplasma gondii). Any of them may drive the production and release of pathogenic IgA into the circulation and mesangial deposition of IgA. However, it seems more probable that it occurs mainly in individuals who have an inherited dysregulation of IgA immune system.

Liver Diseases The association of IgAN with liver disease is the most common form of secondary IgAN. The information is based on autopsy and biopsy studies. Glomerular lesions were reported in more than 50% of cirrhotics and this rose to 100% in end-stage liver disease. With immunofluorescence IgA mesangial deposition was observed in 30%–90% of cirrhotic patients.22 Clinically most of the patients were asymptomatic. In cirrhotic patients 9.6% had microscopic hematuria and/or mild proteinuria and 1.6% were nephrotic.23 The disease is often static and only rarely progress to end-stage renal failure. There was no correlation between the severity of the cirrhosis and the risk of IgAN. Pathologically, the light microscopic alterations are similar to primary IgAN and generally are mild.24,25 Moreover, mesangial IgA may be seen in the absence of light microscopic change. In the deposits predominantly polymeric IgA1 was detected.26

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There is no established treatment for hepatic IgAN and the prognosis depends on the progression of the liver disease. There is no evidence, that improvement in the liver disease or alcohol abstinence improves the course of IgAN. IgAN usually remains morphologically stable over a number of years.27 The pathogenetic link between the two diseases is not clear. Several mechanisms or combination of mechanisms can produce IgAN in hepatic diseases. Diminished intestinal mucosal integrity may cause persistent antigenemia with increased chronic IgA and circulating IgA immune complex production.28 High level of circulating serum IgA antibodies against different food and microbiological antigens were demonstrated. The mucosal damage may be due to a direct toxic effect of alcohol. Marked changes in IgA1 O-glycosylation were also reported but these were distinct from those previously published in primary IgAN.29 Comparing with healthy subjects a mild increase of IgA1 O-galactosylation with reduced O-sialylation and reduced presentation of N-acetylgalactosamine residues were demonstrated. Furthermore, all hepatic removal routes for IgA immune complexes are impaired in these patients.

Gastrointestinal Diseases The association between IgAN and inflammatory bowel diseases is infrequent. However, the systemic examination for IgAN in these patients is very rare. At a recent screening examination of our group six of 55 patients (10.9%) with Crohn’s disease and two of 57 (3.5%) patients with ulcerative colitis had microscopic hematuria. Furthermore, three of 55 (5.4%) patients with Crohn’s disease and four of 57 (7.0%) patients with ulcerative colitis had microalbuminuria. None of the patients had diabetes mellitus or hypertension. Further examination of the patients with positive urine findings are in progress. At the same time, there are several possible pathophysiological links between IgAN and bowel diseases associated at least in part with loss of mucosal antigen exclusion, with excessive IgA antibody response to musocal antigen exposure and increased IgA immune complex production.

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Coeliac Disease Coeliac disease is an autoimmune disorder triggered by gliadin in genetically predisposed individuals.30 The diagnosis is based on a T-cell mediated chronic mucosal inflammation and villous atrophy of small intestine. Approximately 90% of affected individuals share the human leucocyte antigen (HLA) DR3 DR5/7–DQ2 haplotype and all of the others have HLA DR4-DQ8. The contributory effect from non-HLA genes was also demonstrated.31 The association between coeliac disease and IgAN is frequent. The prevalence of IgAN in coeliac patients is quite rare. In 25 patients with a new diagnosis of coeliac disease but without clinical signs of a renal disease renal biopsy was performed before the start of the specific gluten-free diet. Eight of 25 patients showed mesangial IgA deposition without C3 suggesting that mesangial IgA deposition may be common in coeliac disease, but does not usually cause clinically manifest glomerulonephritis.32 In another study, IgAN was demonstrated with IgA immune complexes and anti-gliadin antibodies in three patients with coeliac disease.33 Two of the patients also had dermatitis herpetiformis. In all of these patients IgA deposits were found not only in the glomeruli but also in the skin either in a papillary pattern typical of dermatitis herpetiformis or within the dermal vessel walls. Because celiac disease and dermatitis herpetiformis are characterized by gluten-sensitive enteropathy the hypothesis is that circulating IgA immune complexes originated from the gut deposit not only in the skin but also in the glomeruli. Much more studies focused on the prevalence of coeliac disease are IgAN patients. High levels of IgA against different food antigens including gliadin have been reported.34,35 IgA-antigliadin antibodies were demonstrated in 3%–70% of IgAN patients.34,36 The presence of circulating IgA and/or mainly IgG1-antiendomysial antibodies was proved in 16 of 36 patients with IgAN.37 Rostocker et al., however, did not find IgA antiendomysium and antireticulin antibodies in IgAN.38 The frequent IgG1, but very rare IgA-antiendomysium antibody positivity in IgAN, suggests that IgG1-antiendomysial antibody positive patients with coeliac disease belong to a subgroup with the same clinical characteristics as IgA-antiendomysium antibody positive patients. Without

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IgG1-antiendomysial antibody examination we might miss the identification of coeliac disease in some IgAN patients. Antibody positivity in IgAN, however, does not mean that these patients have coeliac disease, because the histological examination of duodenal or jejunal biopsies rarely proved coeliac disease. There are conflicting data about the relation between coeliac disease, increased intestinal permeability and IgAN.39–41 Chronically increased intestinal permeability was demonstrated quite frequently in IgAN.39 There was a significant correlation between serum IgA level and the degree of the intestinal permeability. A reduction in IgA immune complexes, proteinuria and microhematuria after introducing a gluten-free diet was described in 29 IgAN patients.42 Improvement in renal function was also found in an isolated case.43 However, only a little correlation was between IgA-antigliadin, IgA-antireticulin and IgA-antiendomysial antibodies or jejunal mucosal atrophy after gluten free diet.40,41 In 223 IgAN patients eight (3.6%) were found to have coeliac disease and all had the HLA DQ2 or DQ8 haplotype.44 There was, however, no increase in the frequency of HLA DQ2 or DQ8 haplotype in the other IgAN patients. For this reason, the association between IgAN and coeliac disease cannot be explained by a similar accumulation of HLA DQ haplotypes. However, even in the absence of villous atrophy enhanced epithelial HLA DR expression and an increased density of γδ-T cell receptor-bearing intraepithelial lymphocytes, both typical for coeliac disease, was observed.45 The pathophysiological link between coeliac disease and IgAN is not clear. It is supposed that impaired mucosal antigen exclusion and systemic hyperresponsiveness cause the production of IgA-antigliadin, IgA-antireticulin and IgA and/or IgG1-endomysial antibodies more likely in IgAN patients susceptible to coeliac disease. The resultant chronic mucosal inflammation and villous atrophy may cause the loss of mucosal antigen exclusion, further driving the production of pathogenic IgA and its mesangial deposition. If this theory is correct than coeliac disease acts more as a disease modifier rather than a true cause of secondary IgAN.4

Crohn’s Disease Crohn’s disease, a chronic inflammation of the gastrointestinal tract and IgAN has several features in common but the association of IgAN

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with Crohn’s disease is rare. Clinical manifestations vary, ranging from macroscopic hematuria, nephrotic syndrome, oligosymptomatic disease to acute renal failure.46–49 The treatment of the bowel disease resulted in the clinical improvement of the Crohn’s disease, in the remission of the nephropathy and in decrease or normalization of serum IgA concentration suggesting a causal relationship between severity of intestinal inflammation and IgA immune response. One of the pathogenetic mechanisms that relate IgAN to Crohn disease may be that in Crohn’s disease, mucosal inflammation results in the loss of mucosal antigen exclusion with systemic absorption of antigens and bacteria, which provokes a rise in IgA and IgG levels. An altered T-cell activation with increased IgA production also occurs in both diseases. Both diseases have a genetic basis with HLA associations.50,51

Ulcerative Colitis The association between IgAN and ulcerative colitis is infrequent. The clinical picture of the published single cases was oligosymptomatic with normal renal function except one.52–55 In two cases ankylosing spondylitis was also present. The pathophysiological link between the two diseases is not clear.

Malignancies Tumor associated IgAN have been documented in a wide variety of human neoplasms. Post-mortem examinations demonstrated eight IgAN in 11 mucin secreting adenocarcinomas.56 Out of 184 IgAN patients six neoplasms (four affected mucosal membranes) were found.57 The prevalence of malignant diseases was five times higher in IgAN than in the normal Finnish population. Glomerular IgA deposition was detected in nine of 27 cases of lung cancer at a post-mortem examination.58

Renal Cell Carcinoma Examining the resected kidneys Magyarlaki et al.59 detected IgAN in 11 of 60 patients and Beaufilis et al.60 in one of 40 patients with renal cell carcinoma. Beaufils et al.60 examined the kidney tissue as far from the tumor tissue as it was possible but Magyarlaki did the study on the renal tissue adjacent to the tumor. Simultaneous glomerular and tumor

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staining for IgA and von Hippel-Lindau protein (a highly specific tumor antigen) was demonstrated in three of 11 patients and the clinical symptoms disappeared after nephrectomy.59 They speculate that renal cell carcinoma induces a tumor antigen-IgA antibody immune complex production and mesangial deposition in some of the patients (with special genetic background).

Monoclonal Lymphoproliferative Diseases Patients with IgA secreting myeloma have elevated serum IgA levels. However, high IgA levels alone are insufficient to cause IgAN except the cases when the monoclonal IgA has specific physicochemical characteristics.61,62 IgAN was infrequently associated with Hodgkin lymphoma and T-cell lymphomas, including mycosis fungoides. The mechanism underlying this association may be a disturbed cooperation between B and T lymphocytes and the loss of precise regulation of the lymphocytic microenvironment at IgA synthesis.

Type 2 Diabetes/ Metabolic Syndrome The abnormalities of the IgA immune system are common in type 2 diabetes. Increased serum and salivary IgA and IgA1 levels were detected and 80%–87% of serum IgA was polymeric.63,64 The association of IgAN with type 2 diabetes was unusually high in Hong Kong; IgAN was diagnosed in 59% of non-diabetic renal diseases of diabetics.65 Sometimes IgAN superimposed on diabetic nephropathy, in others it was the only renal alteration.65–68 Most of the diabetic IgAN patients had also hypertension, dyslipidemia and were obese. The association between IgAN and diabetes/metabolic syndrome may be not coincidental because the intraglomerular hypertension and hyperfiltration and biochemical alterations in glomeruli of diabetic patients may facilitate the deposition of IgA1 immune complexes or aggregates.

Autoimmune Diseases IgAN has been described in many systemic autoimmune diseases (systemic lupus erythematosus, Wegener’s granulomatosis, Sjögren’s disease, Bechet’s disease). Recently, high incidence of Hashimoto’s thyroiditis

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(eight of 65, 12.3%) was demonstrated in IgAN patients.69 The interrelationship between IgAN, autoimmune diseases and regulation of IgA synthesis is not clear yet.

Rheumatic Diseases Several studies demonstrated association between IgAN and seronegative spondylarthropathies, mainly ankylosing spondylitis (Bechterew’s disease), psoriatic arthritis and enteropathic arthritis (associated with Crohn’s disease and ulcerative colitis). In psoriasis vulgaris IgAN was also published without evidence of psoriatic arthropathy.70 The clinical picture varied from oligosymtomatic to extremely severe.71,72 Elevated circulating serum IgA levels and long time persistence of elevated IgA antibodies against enteric organism including Yersinia enterocolica were detected. IgAN is the most common type of nephropathy in Japanese patients with rheumatoid arthritis (RA).73,74 The prevalence of IgAN in the Finnish RA patients was 8%.75 The intensity of mesangial IgA and serum IgA levels correlated with the duration and severity of RA. More frequent occurrence and higher titers of serum rheumatoid factors were also detected in IgAN with RA.75 May be that the rheumatoid factors are involved in the pathogenesis of IgAN. It is also suggested that newer immunomodulating drugs may facilitate IgA immune complex production and the development of IgAN.76

Henoch-Schönlein Purpura and Other Vasculitides Henoch-Schönlein purpura is a small-vessel vasculitis involving skin, gut and renal glomeruli characterized by vascular wall deposits of predominantly IgA1 in target organs. The diagnosis is based mainly on the clinical picture with purpura, intestinal colic, hematuria and arthralgia/ arthritis. The renal histological features are indistinguishable from those of IgAN. Many abnormalities of IgA production and handling reported in IgAN are also detected in Henoch-Schönlein purpura. Both diseases have galactose-deficient IgA1 in the circulation and in the mesangium, and circulating IgG and IgA autoantibodies were detected against the abnormal IgA1 with circulating immune complex formation and mesangial deposition (reviewed recently by Sanders and Wyatt).5

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To differentiate Henoch-Schönlein purpura nephritis from IgAN the demonstration of circulating IgA anti-neutrophil cytoplasmic antibody (IgA-ANCA) has been proposed as a marker of HenochSchönlein purpura nephritis. The findings from these publications are not consistent. The overlap syndrome between ANCA-related small vessel and large vessel vasculitis and IgAN was also described.77–82 In some cases this was manifested in the presence of crescentic IgAN with antimyeloperoxidase or anti-proteinase 3 antibodies, whereas in others, a lesion of ANCA-associated pauci-immune crescentic GN followed the diagnosis of IgAN or vice versa.83,84 The glomerular and vasculitic damage may result from a common immunologic mechanism. Another theory is that the inflammatory response to IgA1 or IgA1 immune complexes in IgAN may predispose some patients to develop ANCA and the presence of ANCA will trigger the development of a more severe crescentic form.77

Conclusion In secondary IgAN the renal lesion appears to be a consequence of a significant extrarenal disease, most commonly liver diseases and gastrointestinal mucosal inflammations. Several pathogenetic mechanisms can produce IgAN. In a variety of associated diseases the mucocutaneous antigen exclusion is impaired with marked systemic antigenemia and systemic IgA immune activation. Diseases with significant loss of hepatic tissue associate with reduced hepatic IgA immune complex clearance. The IgA immune regulation is changed in many autoimmune diseases. It is suggested that the increased intraglomerular pressure and hyperfiltration of diabetic/metabolic patients helps the mesangial IgA1 deposition. Progress in understanding the key pathogenetic features of IgAN will help to clarify the contribution of other diseases to the development of secondary IgAN.

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36. Fornasieri A, Sinico RA, Maldifassi P, et al. (1987) IgA-antigliadin antibodies in IgA meseangial nephropathy (Berger’s disease). Br Med J 295: 78–80. 37. Pierucci A, Fofi C, Bartoli B, et al. (2002) Antiendomysial antibodies in Berger’s disease. Am J Kidney Dis 39: 1176–1182. 38. Rostoker G, André C, Bourhala S, et al. (1988) Lack of antireticulin and IgA antiendomysium antibodies in sera of patients with primary IgA nephropathy associated with circulating IgA antibodies to gliadin. Nephron 48: 81. 39. Kovacs T, Kun L, Schmelczer M, et al. (1996) Do intestinal hyperpermeability and the related food antigens play a role in the progression of IgA nephropathy? I. Study of intestinal permeability. Am J Nephrol 16: 500–505. 40. Sategna-Guidetti C, Ferfoglia G, Bruno M, et al. (1992) Do IgA antigliadin and IgA antiendomysium antibodies show there is latent coeliac disease in primary IgA nephropathy? Gut 33: 476–478. 41. Rostoker G, Laurent J, Andre C, et al. (1988) High levels of IgA antigliadin antibodies in patients who have IgA mesangial glomerulonephritis but not coeliac disease. Lancet 1: 356–357. 42. Coppo R, Roccatello D, Amore A, et al. (1990) Effects of a gluten-free diet in primary IgA nephropathy. Clin Nephrol 33: 72–86. 43. Woodrow G, Innes A, Boyd SM, et al. (1993) A case of IgA nephropathy with coeliac disease responding to a gluten-free diet. Nephrol Dial Transplant 8: 1382–1383. 44. Collin P, Syrjanen J, Partanen J, et al. (2002) Celiac disease and HLA DQ in patients with IgA nephropathy. Am J Gastroenterol 97: 2572–2576. 45. Rantala J, Collin P, Holm K, et al. (1999) Small bowel T cells, HLA class II antigen DR and GroEL stress protein in IgA nephropathy. Kidney Int 55: 2274–2280. 46. Forshaw MJ, Guirguis O, Hennigan TW. (2005) IgA nephropathy in association with Crohn’s disease. Int J Colorectal Dis 20: 463–465. 47. Takemura T, Okada M, Yagi K, et al. (2002) An adolescent with IgA nephropathy and Crohn disease: pathogenetic implications. Pediatr Nephrol 17: 863–866. 48. Hirsch DJ, Jindal KK, Trillo A, et al. (1992) Acute renal failure in Crohn’s disease due to IgA nephropathy. Am J Kidney Dis 2: 189–190. 49. McCallum D, Smith L, Harley F, et al. (1997) IgA nephropathy and thin basement membrane disease in association with Crohn disease. Pediatr Nephrol 11: 637–640. 50. Toyoda H, Wang SJ, Yang HJ. (1993) Distinct associations of HLA class II genes with inflammatory bowel disease. Gastroenterology 104: 741–748.

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51. Friedman BI, Spray BJ, Heise ER. (1994) HLA associations in IgA nephropathy and focal and segmental glomerulosclerosis. Am J Kidney Dis 23: 352–357. 52. Hubert D, Beaufils M, Meyrier A. (1984) Immunoglobulin A glomerular nephropathy associated with inflammatory colitis. Apropos of 2 cases. Presse Med 13: 1083–1085. 53. Iida H, Asaka M, Izumino K, et al. (1989) IgA nephropathy complicated by ulcerative colitis. Nephron 53: 285–286. 54. Trimarchi HM, Freixas EAR, Peters R, et al. (2001) Immunoglobulin A nephropathy and ulcerative colitis. Am J Nephrol 21: 400–405. 55. Onime A, Agaba EI, Sun Y, et al. (2006) Immunoglobulin A nephropathy complicating ulcerative colitis. Int Urol Nephrol 38: 349–353. 56. Sinniah R. (1982) Mucin secreting cancer with mesangial IgA deposits. Pathology 14: 303–308. 57. Mustonen J, Pasternack A, Helin H. (1984) IgA mesangial nephropathy in neoplastic diseases. Contr Nephrol 40: 283–291. 58. Endo Y, Hara M. (1986) Glomerulat IgA deposition in pulmonary diseases. Kidney Int 29: 557–562. 59. Magyarlaki T, Kiss B, Buzogány I, et al. (1999) Renal cell carcinoma and paraneoplastic IgA nephropathy. Nephron 82: 127–130. 60. Beaufils H, Patte R, Aubert Ph, et al. (1984) Renal immunopathology in renal cell carcinoma. Virchows Arch (Pathol Anat) 404: 87–97. 61. Zickerman AM, Allen AC, Talwar V, et al. (2000) IgA myeloma presenting as Henoch-Schönlein purpura with nephritis. Am J Kidney Dis 36: E19. 62. Bianchini G, Festuccia F, Laverde G, Cinotti GA. (1999) IgA myeloma: a potential outcome of IgA nephropathy. Nephrol Dial Transplant 14: 2780–2781. 63. Triolo G, Giardina E, Rinaldi A, Bompiani G. (1987) Serum hyper-IgA in diabetes. I. Increase in the proportion of the polymeric to the monomeric form. Boll Ist Sieroter Milan 63: 173–174. 64. Yavuzyilmaz E, Yumak O, Akdoganil T, et al. (1996) The alterations of whole saliva constituents in patients with diabetes mellitus. Aust Dent J 41: 193–197. 65. Mak SK, Wong PN, Lo KY, Tong G, Wong A. (2001) Prospective study on renal outcome of IgA nephropathy superimposed on diabetic glomerulosclerosis on type 2 diabetic patients. Nephrol Dial Transplant 16: 1183–1188. 66. Lai FM, Li PK, Pang SW, et al. (1993) Diabetic patients with IgA nephropathy and diabetic glomerulosclerosis. Mod Pathol 6: 684–690. 67. Sessa A, Meroni M, Battini G, et al. (1998) IgA nephropathy complicating diabetic glomerulosclerosis. Nephron 80: 488–489.

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68. Orfila C, Lepert JC, Modesto A, Pipy B, Suc JM. (1998) IgA nephropathy complicating diabetic glomerulosclerosis. Nephron 79: 279–287. 69. Pasquariello A, Innocenti M, Sami N, et al. (2008) Hashimoto’s thyreoiditis and IgA nephropathy an underestimated association? Nephrol Dial Transplant Plus 1(Suppl 2): ii298 (Abstract). 70. Zadrazil J, Tichy T, Horák P, et al. (2006) IgA nephropathy associated with psoriasis vulgaris: a contribution to the entity of “psoriatic nephropathy.” J Nephrol 19: 382–386. 71. Shu KH, Lian JD, Yang YF, et al. (1986) Glomerulonephritis in ankylosing spondylitis. Clin Nephrol 25(4): 169–174. 72. Bailey RR, Burry AF, McGiven AR, et al. (1980) A renal lesion in ankylosing spondylitis. Nephron 26: 171–173. 73. Nakano M, Ueno M, Nishi S, et al. (1996) Determination of IgA- and IgMrheumatoid factors in patients with rheumatoid arthritis with or without nephropathy. Ann Rheum Dis 55: 520–524. 74. Sato M, Kojima H, Koshikawa S. (1998) IgA nephropathy in rheumatoid arthritis. Nephron 48: 169–170. 75. Korpela M, Mustonen J, Teppo AM, et al. (1997) Mesangial glomerulonephritis as an extra-articular manifestation of rheumatoid arthritis. Br J Rheumatol 36: 1189–1195. 76. Kemp E, Nielsen H, Petersen LJ, et al. (2001) Newer immunomodulating drugs in rheumatoid arthritis may precipitate glomerulonephritis. Clin Nephrol 55: 87–88. 77. Haas M, Jafri J, Bartosh SM, et al. (2000) ANCA-associated crescentic glomerulonephritis with mesangial IgA deposits. Am J Kidney Dis 36(4): 709–718. 78. Winters MJ, Hurley RM, Lirenman DS. (2002) ANCA-positive glomerulonephritis and IgA nephropathy in a patient on propylthiouracil. Pediatr Nephrol 17: 257–260. 79. Amir ARA, Sheikh SS. (2002) ANCA-associated crescentic IgA glomerulonephritis in pregnancy. J Nephrol 25: 716–719. 80. Allmaras E, Nowack R, Andrassy K, et al. (1997) Rapidly progressive IgA nephropathy with anti-myeloperoxidase antibodies benefits from immunosuppression. Clin Nephrol 48: 269–273. 81. Martin SJ, Audrain MA, Baranger T, et al. (1997) Recurrence of immunoglobulin A nephropathy with immunoglobulin A antineutrophil cytoplasmic antibodies following renal transplantation. Am J Kidney Dis 29: 125–131. 82. Cavatorta F, Campisi S, Trabassi E, Zollo A, Salvidio G. (1995) IgA nephropathy associated with Takayasu’s arteritis: report of a case and review of the literature. Am J Nephrol 15: 165–167.

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83. Ramirez SB, Rosen S, Niles J, Somers MJ. (1998) IgG antineutrophil cytoplasmic antibodies in IgA nephropathy: a clinical variant? Am J Kidney Dis 31: 341–344. 84. Andrassy K, Waldherr R, Erb A, Ritz E. (1992) De novo glomerulonephritis in patients during remission from Wegener’s granulomatosis. Clin Nephrol 38: 295–298.

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Chapter 10

IgA Nephropathy in Children Ronald J. Hogg

Introduction This chapter will concentrate on differences between clinical features, prognostic indicators and therapeutic approaches in children with IgA nephropathy (IgAN) compared to adults.

Clinical Presentation The initial clinical features in children with IgAN are quite variable depending on whether the patients are identified during mass screening programs as opposed to developing overt clinical symptoms or signs. For example, many Japanese children present with asymptomatic microscopic hematuria +/− proteinuria after being discovered by the mandatory annual school screening program that has been in place in Japan since 1974.1,2 In 1988, Kitagawa2 provided details about the program and described renal biopsy results in 1023 children with asymptomatic proteinuria and/or hematuria. IgAN was diagnosed in 366 of the children. Two recent clinical trials reported by Yoshikawa et al.3,4 (indicated that 63 (59%) of 106 patients enrolled in the trials were identified by the Japanese school screening program). Annual screening has also resulted in the diagnosis of IgAN being made in many children in Korea.5,6 In 2001, Cho et al.5 described 405 children with abnormal urinalyses who were identified by the Korean program. A diagnosis of IgAN was made in 51 (30%) of 173 of these patients who underwent a kidney biopsy.

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In 2005, Park et al.6 described 113 children who were identified by the Korean school screening program and underwent a renal biopsy. Thirty-four of 51 (66%) children with hematuria/proteinuria were diagnosed with IgAN. The situation in the Western hemisphere is much different. In this part of the world, most children with IgAN present with gross hematuria.7 However, the clinical features in Japanese children often become similar to those seen in children in the US and Europe during follow-up, with up to 60% eventually having at least one episode of gross hematuria.1

Natural History and Prognosis Many papers have been written about the natural history and prognosis of children with IgAN.7–13 Unfortunately, most of the data have been obtained from populations of patients who received one or more courses of treatment during the period of observation. This precludes accurate evaluation of the prognosis based on clinical or pathologic features at the time of presentation, or during follow-up. Despite this caveat, there are a number of reports that provide useful information about the natural history and prognostic indicators in children with IgAN. The prognosis of children with IgAN appears to be more benign than in adults with a number of studies indicating that 30% to 50% of children with IgA nephropathy show no signs of renal disease after periods of follow-up extending up to 30 years.8,9 However, it is possible that the better outcomes observed in children may represent the fact that adults have been afflicted with IgAN for many years before their diagnosis is made. Only when children with IgAN reach the corresponding age of individuals who present as adults are meaningful comparisons be possible. Most children with progressive forms of IgAN do not develop endstage renal disease (ESRD) until adult life.10,11 Whereas some reports have indicated that the risk of progressive renal failure in children with IgAN is very low,7 others have shown that a significant number will progress to ESRD.1,10,11 It has been estimated that as many as 30% will progress to ESRD in the USA,11 but only 11%–20% in Japan.1,10,12 A recent multi-center study by Haas et al.13 compared the natural history and prognostic indicators in 99 children with IgAN and 125 adults with the condition. The biopsy features were scored using a grading system that was based on a previous study of 244 adults.14 The renal

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biopsies showed a spectrum of changes similar to that described by other authors in this monograph. Focal proliferative GN (Haas subclass III) was the most common lesion seen. The outcome of the children described by Haas et al. was relatively good after a median follow-up of 62 months (range 18–201 months).13 The impact of hypertension on prognosis could not be evaluated precisely as this was based on a BP ≥130/85 for all children rather than age and gender specific norms.15 In addition, the estimated GFR was not available in most of the patients because height measurements (which are necessary for GFR estimation equations in patients < 18 years of age) were not obtained.

Treatment Options for Children with IgAN Randomized controlled trials (RCTs) of therapies for children with IgAN are few in number.16 Although the most important outcome indicator for patients with IgAN is deterioration of GFR to the point of ESRD, the period from diagnosis to ESRD in patients with onset in childhood may be over many years, or even decades. Thus, most studies have relied on surrogate markers such as changes in renal biopsy findings,17,18 and/or the amount of proteinuria or hematuria.18–20 Although deterioration of renal function (such as doubling of the baseline serum creatinine concentration) is the surrogate endpoint most commonly associated with progression to ESRD, this occurs infrequently in patients participating in pediatric trials of IgAN since the period of follow-up is usually five years or less.21

Non-Immunosuppressive Therapies It is important to maintain children with IgAN in a normotensive range, utilizing appropriate norms for age for ideal blood pressure15 and to reduce their level of proteinuria as much as possible (as in adults). An angiotensin II antagonist (angiotensin converting enzyme inhibitor or angiotensin subtype-1 receptor blocker) should be the first option for treatment of hypertension and/or proteinuria. In support of this recommendation is the recent study by Coppo et al.22 in 57 children and young adults < 35 years of age, which showed a significant benefit with benazepril (0.2 mg/kg/day) in preventing progression of renal disease (defined as reduction in GFR by 30% or increase in proteinuria to ≥ 3.5 g/1.73 m²/day).

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Tonsillectomy Although there are no RCTs evaluating the role of this procedure as a single mode of therapy in children with IgAN, there are many observational, uncontrolled case series supporting the use of this treatment23–25 (see also Chapter 24 on Tonsillectomy). In 1985, Lozano et al.23 described eight Spanish patients, mean age 18.7 years, who experienced fewer episodes of gross hematuria post-tonsillectomy. In 1996, Tomioka et al.24 reported that 13 of 15 children with IgAN who underwent tonsillectomy had improved urinalyses. Sanai and Kudoh25 reported that proteinuria and hematuria improved in five of eight patients treated with “medication” combined with tonsillectomy whereas this occurred in only one of seven of the children who received “medication only.” There is no “hard” evidence that tonsillectomy improves the long-term prognosis or prevents ESRD. A RCT is underway in Japan.

Omega 3 Fatty Acids Based upon the limited evidence available, it is not possible to recommend the use of omega 3 fatty acids for treatment of IgAN in pediatric patients although data from the North American IgA Nephropathy Trials, which included both children and adults, indicate that such therapy may be efficacious in reducing proteinuria in such patients.21,26

Children with Crescentic (Rapidly Progressive) IgAN The prognosis for children with crescentic IgAN has been dismal in most reports27 and there are no controlled trials of treatment regimens for children with crescentic IgAN. In 1993, Niaudet et al.28 described 12 children aged eight to 14 years with crescentic IgAN, ten of whom had crescents in ≥ 50% of their glomeruli. The patients received 3 doses of intravenous methylprednisolone for over 5 days at a daily dose of 1 g per 1.73 m², followed by one month of daily prednisone (1 mg/kg/day) and then a tapering dose of alternate day prednisone. Three of the patients received a second course of pulse methylprednisolone while three others received cyclophosphamide. The authors described good outcomes after follow-up periods of up to nine years.

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Corticosteroids as Monotherapy In children presenting with the clinical features of nephrotic syndrome and renal biopsy findings consistent with minimal change disease, a trial of high-dose oral corticosteroids should be considered.29–31 The short-term effect of prednisone in 20 children with mild degrees of proteinuria was examined by Welch et al.20 The patients were randomized to either placebo or prednisone (2 mg/kg/day, maximum 80 mg) for two weeks, followed by the same doses on alternate days for ten weeks. No difference in the severity of hematuria was reported in the two groups. However, most of the subjects in this study had mild histologic changes. Waldo et al.19 compared 13 children with IgAN who received alternate day prednisone for two years, with 15 children who received no therapy. None of the 13 treated patients progressed to ESRD as compared to five of 15 of the untreated patients (P = 0.04). At last follow-up, 12 of 13 treated patients had no hematuria and normal protein excretion.

− Corticosteroids Plus Cyclophosphamide +/− Azathioprine The efficacy of a one-year course of prednisone and azathioprine was evaluated by Andreoli et al.32 Prednisone 60 mg/m² (maximum 60 mg) qday was given for eight weeks followed by 60 mg/m² on alternate days for ten months. Azathioprine 2–3 mg/kg/day was given for 12 months. Proteinuria fell from 4.1 to 1.6 g/day (P < 0.01) and the renal biopsy activity score improved (P > 0.01). However, the chronicity score was unchanged. Murakami et al.33 evaluated the efficacy of a six-month course of prednisone 10–15 mg QOD, combined with cyclophosphamide 1 mg/kg qday, and dipyridamole 5 mg/kg qday in 17 pediatric patients (aged 10.4 ± 3.4 years) who had proteinuria > 1 g/m²/day and were followed for two to ten years (mean 4.8 years). These investigators noted significant improvement in proteinuria but post-therapy biopsies showed persistent signs of chronic disease. Follow-up studies revealed rebound deterioration of proteinuria five to six years later. In recent years, Yoshikawa and the Japanese Pediatric IgA Nephropathy Treatment Group4 have conducted a number of clinical trials in children with IgAN. In 1999, a RCT evaluated two groups of

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children: group 1 received prednisone, azathioprine, heparin, warfarin, and dipyridamole for two years; group 2 received heparin, warfarin and didyridamole.18 Group 1 patients had a significant reduction of proteinuria following therapy (1.35 to 0.22 g per day), while group 2 patients did not (0.98 to 0.88 g per day). Follow-up biopsies showed progression of glomerular sclerosis in group 2 patients, but not in those receiving prednisone and azathioprine. In 2006, Yoshikawa et al.3 described a second RCT, which compared prednisone, azathioprine, warfarin and dipyridamole in 40 children for two years versus prednisone alone in 40 children. Both treatment regimens were beneficial, with proteinuria falling to less than 10 mg/m²/day in 92% of the combination therapy group versus 74% of the prednisone group (P difference = 0.007). The percentage of glomeruli showing sclerotic changes was unchanged from baseline in the combination group but increased significantly in those receiving prednisone alone.

Mycophenolate Mofetil (MMF) and Mizoribine in Children with IgAN MMF has not been studied adequately in children to make a treatment recommendation. Mizoribine, an agent that blocks purine synthesis in a manner similar to MMF, has resulted in a significant reduction in proteinuria when given to Japanese children with IgAN in observational trials.4,34,35 Yoshikawa et al.4 described the results of a pilot study in which mizoribine was substituted for azathioprine as part of the combination therapy approach described in the previous section. The study involved 23 children with diffuse mesangial hypercellularity and persistent proteinuria. Proteinuria fell from 1.19 g/m²/day (range 0.74–2.38) to 0.05 g/m²/day (range 0.02–0.23), p < 0.0001. In addition, 18 of 23 children (80.4%) obtained complete remission of their proteinuria. Yoshikawa et al.4 concluded that the mizoribine combination approach was an acceptable alternative to the azathioprine combination and indicated that a new RCT using the new combination is underway in Japanese children. Ikezumi et al.35 reported the response to mizoribine in three children aged nine to 14 years who had steroid resistant IgAN. The patients had also undergone tonsillectomy and received combined angiotensin converting enzyme inhibitor and angiotensin subtype-1 receptor blocker therapy without benefit. Transient improvement in proteinuria was seen following methylprednisolone pulse therapy but

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this was not sustained when the treatment was stopped. Institution of therapy with mizoribine resulted in a significant reduction of proteinuria and hematuria within three months in all three patients. No significant adverse effects were reported.

Conclusion It is apparent from this consideration of IgAN in children that we still have much to learn about the natural history and active management of such children. Until more specific interventions are discovered it is recommended that non-immunosuppressive regimens (angiotensin converting enzyme inhibitor and/or angiotensin subtype-1 receptor blocker) be tried first with subsequent use of immunosuppressive medications in patients who do not show a good response.

References 1. Yoshikawa N, Ito H, Yoshiara S, et al. (1987) Clinical course of immunoglobulin A nephropathy in children. J Pediatr 110: 555–560. 2. Kitagawa T. (1988) Lessons learned from the Japanese nephritis screening study. Pediatr Nephrol 2: 256–263. 3. Yoshikawa N, Honda M, Iijima K, et al. (2006) Steroid treatment for severe childhood IgA nephropathy: a randomized, controlled trial. Clin J Am Soc Nephrol 1: 511–517. 4. Yoshikawa N, Nakanishi K, Ishikura K, et al. (2008) Combination therapy with mizoribine for severe childhood IgA nephropathy: a pilot study. Pediatr Nephrol 23: 757–763. 5. Cho BS, Kim SD, Choi YM, Kang HH. (2001) School urinalysis screening in Korea: prevalence of chronic renal disease. Pediatr Nephrol 16: 1126–1128. 6. Park YH, Choi JY, Chung HS, et al. (2005) Hematuria and proteinuria in a mass school urine screening test. Pediatr Nephrol 20: 116–1130. 7. Hogg RJ, Silva FG, Wyatt RJ, et al. (1984) Prognostic indicators in children with IgA nephropathy — report of the Southwest Pediatric Nephrology Study Group. Pediatr Nephrol 8: 15–20. 8. Nozawa R, Suzuki J, Takahashi A, et al. (2005) Clinicopathological features and the prognosis of IgA nephropathy in Japanese children on long-term observation. Clin Nephrol 64: 171–179. 9. Ronkainen J, Ala-Houhala M, Autio-Harmainen H, et al. (2006) Long-term outcome 19 years after childhood IgA nephritis: a retrospective study. Pediatr Nephrol 21: 1266–1273.

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10. Kusumoto Y, Takebayashi S, Taguchi T, et al. (1987) Long-term prognosis and prognostic indices of IgA nephropathy in juvenile and in adult Japanese. Clin Nephrol 28: 118–124. 11. Wyatt RJ, Kritchevsky SB, Woodford SY, et al. (1995) IgA nephropathy: long-term prognosis for pediatric patients. J Pediatr 127: 913–919. 12. Lau KK, Gaber LW, Delos Santos NM, et al. (2004) Pediatric IgA nephropathy: clinical features at presentation and outcome for African-Americans and Caucasions. Clin Nephrol 62: 162–172. 13. Haas M, Rahman H, Cohn RA, et al. (2008) IgA nephropathy in children and adults: comparison of histologic features and clinical outcomes. Nephrol Dial Transplant 0: 1–9 (advance publication 2/10/2008). 14. Haas M. (1997) Histological subclassification of IgA nephropathy: a clinicopathologic study of 244 cases. Am J Kidney Dis 29: 829–842. 15. Fourth report on the diagnosis, evaluation, and treatment of high blood pressure in children and adolescents. (2004) Pediatrics 114: 555–576. 16. Wyatt RJ, Hogg RJ. (2001) Evidence-based assessment of treatment options for children with IgA nephropathies. Pediatr Nephrol 16: 156–167. 17. Tanaka H, Waga S, Yokoyama M. (1998) Age-related histologic alterations after prednisolone therapy in children with IgA nephropathy. Tohoku J Exp Med 185: 247–252. 18. Yoshikawa N, Ito H, Sakai T, et al. (1999) A controlled trial of combined therapy for newly diagnosed severe childhood IgA nephropathy. The Japanese Pediatric IgA Nephropathy Treatment Study Group. J Am Soc Nephrol 10: 101–109. 19. Waldo FB, Wyatt RJ, Kelly DR, et al. (1993) Treatment of IgA nephropathy in children: efficacy of alternate-day oral prednisone [see comments]. Pediatr Nephrol 7: 529–532. 20. Welch TR, Fryer C, Shely E, et al. (1992) Double-blind, controlled trial of short-term prednisone therapy in immunoglobulin A glomerulonephritis. J Pediatr 121: 474–477. 21. Hogg RJ, Lee J, Nardelli N, et al. (2006) Clinical trial to evaluate omega-3 fatty acids and alternate day prednisone in patients with IgA nephropathy: report from the Southwest Pediatric Nephrology Study Group. Clin J Am Soc Nephrol 1: 467–474. 22. Coppo R, Peruzzi L, Amore A, et al. (2007) A placebo-controlled, randomized trial of angiotensin-converting enzyme inhibitors in children and young people with IgA nephropathy and moderate proteinuria. J Am Soc Nephrol 18: 1880–1888. 23. Lozano L, Garcia-Hoya R, Egido J, et al. (1985) Tonsillectomy decreases the synthesis of polymeric IgA by blood lymphocytes and clinical activity in patients with IgA nephropathy. Proc EDTA-ERA 22: 33–37.

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24. Tomioka S, Miyoshi K, Tabata K, et al. (1996) Clinical study of chronic tonsillitis with IgA nephropathy treated by tonsillectomy. Acta Otolaryngol Suppl 523: 175–177. 25. Sanai A, Kudoh F. (1996) Effects of tonsillectomy in children with IgA nephropathy, purpura nephritis, or other chronic glomerulonephritides. Acta Otolaryngol Suppl 523: 172–174. 26. Hogg RJ, Fitzgibbons L, Atkins C, et al. (2006) Efficacy of omega-3 fatty acids in children and adults with IgA nephropathy is dose- and size-dependent. Clin J Am Soc Nephrol 1: 1167–1172. 27. Welch TR, McAdams AJ, Berry A. (1988) Rapidly progressive IgA nephropathy. Am J Dis Child 142: 789–793. 28. Niaudet P, Murcia I, Beaufils H, et al. (1993) Primary IgA nephropathies in children: prognosis and treatment. Adv Nephrol Necker Hosp 22: 121–140. 29. Saint-Andre JP, Simard C, Spiesser R, Houssin A. (1980) Nephrotic syndrome in a child, with minimal glomerular lesions and mesangial IgA deposits. Nouv Presse Med 9: 531–532. 30. Association of IgA Nephropathy with steroid-responsive nephrotic syndrome. A report of the Southwest Pediatric Nephrology Study Group. (1985) Am J Kidney Dis 5: 157–164. 31. Sinnassamy P, O’Regan S. (1985) Mesangial IgA deposits with steroid responsive nephrotic syndrome: probable minimal lesion nephrosis. Am J Kidney Dis 5: 267–269. 32. Andreoli SP, Bergstein JM. (1989) Treatment of severe IgA nephropathy in children. Pediatr Nephrol 3: 248–253. 33. Murakami K, Yoshioka K, Akano N, et al. (1994) Combined therapy in children and adolescents with IgA nephropathy. Nippon Jinzo Gakkai Shi 36: 38–43. 34. Kawasaki Y, Hosoya M, Suzuki J, et al. (2004) Efficacy of multidrug therapy combined with mizoribine in children with diffuse IgA nephropathy in comparison with multidrug therapy without mizoribine and with methylprednisolone pulse therapy. Am J Nephrol 24: 576–581. 35. Ikezumi Y, Suzuki T, Karasawa T, et al. (2008) Use of mizoribine as a rescue drug for steroid-resistant pediatric IgA nephropathy. Pediatr Nephrol 23: 645–650.

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Chapter 11

Recurrent IgA Nephropathy in Transplant Bo Ying Choy and Kar Neng Lai

Introduction Immunoglobulin A nephropathy (IgAN) is the most common type of glomerulonephritis in the developed world. The clinical course of this disease is originally considered to be benign but on long term follow-up, a significant proportion of patients with IgAN will progress to end stage renal failure. Renal transplantation is the treatment of choice for individuals with end stage renal failure secondary to IgAN. However, recurrent disease is common after transplantation and there is still controversy regarding the risk of recurrence and its impact on graft survival. In this chapter, issues on recurrence rate, clinical course, potential risk factors, and management of patients with recurrent IgAN will be discussed.

Recurrence Rate Recurrence of mesangial IgA deposits in the renal allografts was first described by Berger et al.1 in 1975. Subsequent studies reported a recurrence rate ranging from 13% to 60% of patients.2–18 Great variation in the reported rate can partly be explained by the difference in biopsy policy of different transplant centers. Most centers performed renal biopsy only when patients presented with clinical symptoms. This would potentially underestimate the rate of recurrence as patients who were clinically asymptomatic but with immunohistological 149

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changes in the graft kidneys would remain undiagnosed. For centers where routine protocol biopsies were being carried out in all transplant recipients, histological recurrence with mesangial IgA deposits and mesangial hypercellularity had been reported in 50%–60% of patients after a duration of follow-up of three to 183 months.1,17 The other important factor contributing to the variation is the difference in duration of follow-up in different studies. The longer the duration of follow-up of the patients after transplantation, the more likely the affected patients become symptomatic, the higher the reported incidence of recurrent disease. Details of studies on recurrent IgAN are summarized in Table 11.1. Table 11.1

Reference 3 4 5 6 7 8 9 10 11 12 13c 14 15b 16 17 18

Recurrence rate of IgA nephropathy.

Follow-up duration (mean) (months)

No. of allograft

*62.4 (45.6–114) 67.8 ± 19.9 100.0 ± 5.8 12–120 67.2 ± 54 70.4 ± 50.5 *52 (18–155) 2–164 *67 (11–159) 61 ± 37 54 (7–127) *78 (3–156) 68.1 ± 37.2 45.9 ± 10 3–183 20 ± 13

116 49 75 532 79 106 48 90 104 61 61 53 84 128 51 13

Recurrence ratea No./(%) 36 (31%) 13 (26.5%) 14 (18.7%) NA 17 (21.5%) 37 (35%) 14 (29.2%) 19 (21.1%) 13 (12.5%) 18 (29.5%) 20 (29.9%) 10 (19%) 13 (15.5%) 47 (36.7%) 17 (33.3%) 6 (46.2%)

Graft loss due to recurrence No. (%) NA 5 (10%) 3 (4.0%) 15 (2.8%) 1 (1.3%) 4 (3.8%) 4 (8.3%) 2 (2.2%) 6 (5.8%) 7 (11.5%) 10 (16.4%) 3 (5.7%) 4 (4.8%) 9 (7.0%) 5 (9.8%) 1 (7.6%)

* Median. % = Percentage was calculated from number of graft loss due to recurrent IgAN/total number of patients with primary IgAN. a Recurrence rate in patients with clinical symptoms of proteinuria/hematuria/renal impairment. b Included 13 patients suffered from underlying Henoch-Schönlein purpura. c Included four patients suffered from underlying Henoch-Schönlein purpura.

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Clinical Course Recurrent disease exhibits considerable clinical similarities with primary IgAN. Microscopic hematuria and proteinuria are common presenting symptoms followed by slow decline in renal function. Berger et al.1 reported a relatively favorable clinical course of recurrent IgAN after renal transplantation. However, with increasing long term data, it is apparent that recurrent disease is not as benign as had been reported previously.4,5,8–18 Graft loss from recurrence with histological features of diffuse mesangial proliferative expansion and glomerular sclerosis were reported between 2%–16% depending on duration of follow-up (Table 11.1).4–18 Briganti et al.6 reported an estimated ten-year incidence of graft loss due to recurrent IgAN of 9.7% (CI = 4.7%–19.5%) basing on data from the Australia and New Zealand Dialysis and Transplant Registry (ANZDATA) which contains 532 allograft recipients with primary IgAN, the largest number of IgAN patients of all series. It is important to note that despite of the potential for recurrent disease in patients with primary IgAN, renal allograft survival for the first five years post-transplant is better compared to patients with other primary diseases.5,7,15,19 Lim et al.19 compared the graft survival rates of 374 patients with primary IgAN reported a superior five-year graft survival rate in patients with IgAN as compared to patients with other primary diseases. The proposed mechanism included increased occurrence of allo-reactive IgA anti-HLA antibodies which may block the deleterious effect of IgG and IgM antibodies on the graft, and the immunological dysfunction of patients with IgAN. The superior graft survival of IgAN patients for the early post-transplant period is no longer observed on longer follow-up. Ponticelli et al.8 reported a comparable ten-year graft survival for patient with IgAN. Choy et al.5 reported an inferior graft survival for primary IgAN patients with follow-up beyond 12 years. These observations suggest that impact of other factors including recurrent disease on graft survival becomes more apparent on long term follow-up and recurrent IgA nephropathy runs an indolent course similar to primary IgAN with favorable outcome in initial ten years post-transplant and thereafter its contribution to graft loss becomes more significant.5,8,10

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Potential Risk Factors for Recurrence Donor Type The relationship between the risk of recurrence and the donor type remains controversial. Some studies had reported a higher risk of disease recurrence in related donors,1,9,11,15,18 while others reported no added risk.10,12,14 Pooling all available data from literature that contained information on graft recurrence and graft loss in relation to donor type showed a higher risk of disease recurrence amongst transplant recipients with related donors (common odds ratio 2.29, p < 0.001) (Table 11.2) but the risk of graft loss was not increased (common odds ratio 1.95, p = 0.24) (Table 11.3). Whether this apparent paradox could be a result of insufficient follow-up remains to be investigated.

Table 11.2 Risk of recurrence of IgA nephropathy in related and non-related transplant. No. of allograft Reference 4 5 7 8 9 10 11 12 14 15* 18 1 Pooled data

Recurrence

RD

NRD

RD

NRD

Follow-up duration (months)

44 32 24 21 17 60 47 18 41 3 6 13

5 43 55 85 31 30 57 43 12 25 7 19

12 9 5 9 6 13 11 6 8 2 5 9

1 5 2 25 8 6 2 12 2 11 1 8

67.8 ± 19.9 100.0 ± 5.8 67.2 ± 54 70.4 ± 50.5 52 (18–155) 2–164 67 (11–159) 61 ± 37 78 (3–156) 68.1 ± 37.2 20 ± 13 > 24

326

412

95

83

20–159

RD: Related donor, NRD: non-related donor. * Included five patients suffered from underlying Henoch-Schönlein purpura. Recurrent rate for RD: 29.1%, NRD: 20.1%. Breslow-Day test of homogeneity of odds ratio: χ 2 = 12.18, df = 11, p = 0.351. Mantel-Haenszel estimate of common odds ratio: 2.29 (95% CI = 1.53, 3.41; p < 0.001).

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Table 11.3 Risk of graft loss from recurrent IgA nephropathy according to donor type. Recurrence Reference 4 5 9 12 14 18 Pooled data

Graft loss

RD

NRD

RD

NRD

12 9 6 6 8 5

1 5 8 12 2 1

5 1 3 4 2 1

0 2 1 3 1 0

46

29

16

7

Percentage of graft loss from RD: 34.8%, NRD: 24.1%. Breslow-Day test of homogeneity of odds ratio: χ 2 = 7.37, df = 5, p = 0.194. Mantel-Haenszel estimate of common odds ratio: 1.95 (95% CI = 0.64, 5.97; p = 0.243).

Given the fact that the graft survival of patients with primary IgAN is excellent for the first decade post-transplant, it is inappropriate to refrain from living related donor transplantation even though there may be a slight risk of recurrence. In contrast, familial IgAN should be rigorously excluded in potential living related donors since familial IgAN may be associated with high risk of development of renal failure in affected members. The opinion that that familial IgAN is at no greater risk for progression to end stage renal failure than that in sporadic IgAN remains conflicting. Donor urine microscopy and if necessary, donor kidney biopsy should be performed before proceeding to living related donor transplantation.

Human Leukocyte Antigens (HLA) and Degree of Mismatch No specific type of human leukocyte antigen has been identified to be predictive of recurrence. An association of HLA DR4, B35 or B12 with increased susceptibility to recurrent IgAN had been reported initially in some series7,13 but the finding was not confirmed by other studies.11,14,17,19 Whether the degree of HLA mismatch would affect the rate of recurrence and graft survival is also of interest. McDonald et al.20 studied

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1306 patients with primary IgAN in the ANZDATA reported a higher risk of recurrent disease only in patients who received zero HLA mismatch living donor grafts. Apart from this specific group, number of HLA mismatch did not affect the recurrence rate in both living and deceased donor grafts suggesting degree of HLA matching does not play important role in disease recurrence. Moreover, despite of a potentially higher risk of recurrent disease in patients receiving zero HLA mismatch living donor grafts, the graft survival was not compromised. Thus, there is no reason to refrain patients with primary IgAN from receiving well matched living donor transplantation.

Latent IgA Deposition from Donor Kidney Incidental finding of glomerular mesangial IgA deposits in donor kidneys has been reported in 4%–24% of patients.21,22 These deposits usually disappear within six months post-transplant if recipients do not have primary IgAN. Moriyama et al.4 reported higher risks of recurrence and graft loss in patients with primary IgAN if latent IgA deposition was found in the donor kidneys at time of transplantation. Whether such latent IgA depositions would induce a higher risk of recurrence in susceptible recipients remains speculative and needs confirmation by further studies.

Serological and Genetic Factors High level of aberrantly glycosylated IgA1 and an association with deletion (DD) genotype of angiotensin converting enzyme (ACE) gene have been reported in patients with primary IgAN. Coppo et al.3 investigated whether any of the serological or genetic factors would predict recurrence of IgAN post-transplant could not identify any markers for recurrent disease. High level of aberrantly glycosylated IgA1 in recipients did not predict recurrence and no association of ACE gene [insertion (I)/deletion (D)] polymorphism were detected with recurrence. However, they reported that cytokine gene polymorphisms of TNF-α and IL-10 which down-regulate the Th2 subset of lymphocytes were associated with protection from early recurrence. Prospective studies to verify these putative risk factors are still ongoing.

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Clinical Course of Native IgAN Correlation between the onset time of recurrence and original course of the native disease has been suggested. Bumgardner et al.12 and Freese et al.11 reported an earlier onset of recurrent IgAN in patients who had a shorter duration of the original disease. Similarly, although diffuse crescentic IgAN with rapid deterioration of renal function is uncommon and has only been reported in 3% to 5% of patients, Mousson et al.23 reported recurrence of crescentic IgAN in two patients with crescentic IgAN of the native kidney. Clinical course of patients with primary IgAN is typically indolent and changes in renal function are slow. However, for patients who have aggressive clinical course of original disease with rapid progression to end stage renal failure, they should be informed of the potential risk of early recurrent disease and graft dysfunction after renal transplantation.23,24

Other Risk Factors No correlation has been found between age, gender or race with recurrence.

Markers for Progressive Graft Dysfunction Although no single immunological marker is predictive of progressive disease, non-immunological factors including presence of systemic hypertension, heavy proteinuria greater than 1 g/day and histological findings of cellular crescents, glomerular sclerosis, interstitial fibrosis, tubular atrophy and feature of concomitant chronic allograft nephropathy are associated with progressive deterioration of renal function in patients with recurrent IgAN.25

Prevention and Management Prevention No effective therapy for prevention or treatment of recurrent IgAN is available at the moment. There is no evidence that any particular immunosuppressive regime alters the incidence or clinical course of recurrent disease. Calcineurin inhibitors, in the presence or absence

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of induction therapy, do not influence the recurrent risk. Despite initial enthusiasm, newer immunosuppressive drugs are ineffective in preventing recurrence. Anecdotal reports that mycophenolate mofetil might have averted progression to allograft failure in recurrent IgAN are not substantiated by recent studies by Ponticelli et al.8 and Chandrakantan et al.26 Data on sirolimus is limited. Steroid free or rapid steroid withdrawal regimen does not seem to affect the recurrent risk.27

Management Systemic hypertension, glomerular hyperfiltration and heavy proteinuria secondary to recurrent IgAN are detrimental to the graft function. Angiotensin blockage with angiotensin converting enzyme inhibitor (ACEI) or angiotensin subtype-1 receptor blocker (ARB) is able to alleviate all these factors and theoretically can preserve the renal function of patients with recurrent IgAN.25,28 Courtney et al.29 reported a better graft survival for patients with recurrent IgAN being treated with ACEI or ARB as compared with those without. The finding is in line with earlier studies by Oka et al.25 and Ponticelli et al.8 Thus, for patients with recurrent IgAN, it is recommended to treat the hypertension and proteinuria with ACEI or ARB. Whether a combination of ACEI and ARB has additional beneficial effect on reduction of proteinuria or preservation of renal function as in native IgAN is still unknown and need clarification with further prospective studies. Fish oil has once been considered beneficial for patients with primary IgAN. However, meta-analysis of recent studies did not confirm the favorable effect.30 Effect of fish oil in recurrent IgAN has not been systematically examined but is unlikely to be beneficial.

Retransplant Patients with prior graft loss due to recurrent IgAN has higher risk of recurrence in the second transplant (20%–100%).8,11–13 Ohmacht et al.13 reported a graft loss rate of 60% in their patients with a follow-up duration of 21–51 months while two other series reported good graft function despite of recurrence in their patients up to 92 months of follow-up.8,12 In this regard, living donor transplant should be discouraged if recurrence and graft failure occur within few years after first transplant.

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However, such transplantation would not be a problem if their first graft functions beyond ten years post-transplantation.

Concluding Remarks Recurrence of IgA nephropathy is common after renal transplantation and appears to be a time-dependent phenomenon. Clinical manifestations and course of recurrent IgAN are similar to primary IgAN. Graft survival post-transplant is excellent and the contribution of recurrent disease to graft loss is not apparent until ten years after transplantation. Risk of recurrence appears to be higher in living related donor transplantation but graft survival is not compromised. No effective therapy is available for prevention or treatment of recurrent disease. However, for patients with hypertension or proteinuria, beneficial effect of angiotensin blockage on preservation of graft function has been demonstrated and could potentially prolong the graft survival in patients with recurrent IgAN.

References 1. Berger J, Yaneva H, Nabarra B, Barbanel C. (1975) Recurrence of mesangial deposition of IgA after renal transplantation. Kidney Int 7: 232–241. 2. Choy BY, Chan TM, Lai KN. (2006) Recurrent glomerulonephritis after kidney transplantation. Am J Transplant 6: 2535–2542. 3. Coppo R, Amore A, Chiesa M, et al. (2007) Serological and genetic factors in early recurrence of IgA nephropathy after renal transplantation. Clin Transplant 21(6): 728–737. 4. Moriyama T, Nitta K, Suzuki K, et al. (2005) Latent IgA deposition from donor kidney is the major risk factor for recurrent IgA nephropathy in renal transplantation. Clin Transplant 19(Suppl 14): 41–48. 5. Choy BY, Chan TM, Lo SK, et al. (2003) Renal transplantation in patients with primary immunoglobulin A nephropathy. Nephrol Dial Transplant 18: 2399–2404. 6. Briganti EM, Russ GR, McNeil JJ, et al. (2002) Risk of renal allograft loss from recurrent glomerulonephritis. N Engl J Med 347: 103–109. 7. Andresdottir MB, Hoitsma AJ, Assmann KJ, et al. (2001) Favorable outcome of renal transplantation in patients with IgA nephropathy. Clin Nephrol 56: 279–288. 8. Ponticelli C, Traversi L, Feliciani A, et al. (2001) Kidney transplantation in patients with IgA mesangial glomerulonephritis. Kidney Int 60: 1948–1954.

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9. Wang AYM, Lai FM, Yu AWY, et al. (2001) Recurrent IgA nephropathy in renal transplant allografts. Am J Kidney Dis 38: 588–596. 10. Kim YS, Moon JI, Jeong HJ, et al. (2001) Live donor renal allograft in endstage renal failure patients from immunoglobulin A nephropathy. Transplantation 71: 233–238. 11. Freese P, Svalander C, Norden G, et al. (1999) Clinical risk factors for recurrence of IgA nephropathy. Clin Transplant 13: 313–317. 12. Bumgardner GL, Amend WC, Ascher WL, et al. (1998) Single centre long term results of renal transplantation for IgA nephropathy. Transplantation 65: 1053–1060. 13. Ohmacht C, Kliem V, Burg M, et al. (1997) Recurrent immunoglobulin A nephropathy after renal transplantation: a significant contributor to graft loss. Transplantation 64: 1493–1496. 14. Frohnert PP, Donadio JV, Velosa JA, et al. (1997) The fate of renal transplants in patients with IgA nephropathy. Clin Transplant 11: 127–133. 15. Kessler M, Hiesse C, Hestin D, et al. (1996) Recurrence of immunoglobulin A nephropathy after renal transplantation in the cyclosporin era. Am J Kidney Dis 28: 99–104. 16. Hartung R, Livingston B, Excell L, et al. (1995) Recurrence of IgA deposits/disease in grafts. An Australian Registry Survey 1980–1990. Contrib Nephrol 111: 13–17. 17. Odum J, Peh CA, Clarkson AR, et al. (1994) Recurrent mesangial IgA nephritis following renal transplantation. Nephrol Dial Transplant 9: 309–312. 18. Bachman U, Biava C, Amend W, et al. (1986) The clinical course of IgAnephropathy and Henoch-Schönlein purpura following renal transplantation. Transplantation 42: 511–515. 19. Lim EC, Chia D, Gjertson DW, et al. (1993) In vitro studies to explain high renal allograft survival in IgA nephropathy patients. Transplantation 55: 996–999. 20. McDonald SP, Russ GR. (2006) Recurrence of IgA nephropathy among renal allograft recipients from living donors is greater among those with zero HLA mismatches. Transplantation 82: 759–762. 21. Suzuki K, Honda K, Tanabe K, et al. (2003) Incidence of latent mesangial IgA deposition in renal allograft donors in Japan. Kidney Int 63: 2286–2294. 22. Ji S, Liu M, Chen J, et al. (2004) The fate of glomerular mesangial IgA deposition in the donated kidney after allograft transplantation. Clin Transplant 18: 536–540. 23. Mousson C, Charon-Barra C, Funes de la Vega M, et al. (2007) Recurrence of IgA nephropathy with crescents in kidney transplants. Transplant Proc 39: 2595–2596.

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24. Kowalewska J, Yuan S, Sustento-Reodica N, et al. (2005) IgA nephropathy with crescents in kidney transplant recipients. Am J Kidney Dis 45: 167–175. 25. Oka K, Imai E, Moriyama T, et al. (2000) A clinicopathological study of IgA nephropathy in renal transplant recipients: beneficial effect of angiotensinconverting enzyme inhibitor. Nephrol Dial Transplant 15: 689–695. 26. Chandrakantan A, Ratanapanichkich P, Said M, et al. (2005) Recurrent IgA nephropathy after renal transplantation despite immunosuppressive regimens with mycohenolate mofetil. Nephrol Dial Transplant 20: 1214–1221. 27. Ibrahim H, Rogers T, Casingal V, et al. (2006) Graft loss from recurrent glomerulonephritis is not increased with a rapid steroid discontinuation protocol. Transplantation 81: 214–219. 28. Calvino J, Lens XM, Romero R, et al. (2000) Long-term anti-proteinuric effect of Losartan in renal transplant recipients treated for hypertension. Nephrol Dial Transplant 15(1): 82–86. 29. Courtney AE, McNamee PT, Nelson WE, et al. (2006) Does angiotensin blockade influence graft outcome in renal transplant recipients with IgA nephropathy? Nephrol Dial Transplant 21: 3550–3554. 30. Barratt J, Feehally J. (2005) IgA nephropathy. J Am Soc Nephrol 16: 2088–2097.

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Chapter 12

IgA Molecule Jan-Willem Eijgenraam, Mahamed R. Daha and Cees van Kooten

Introduction IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide and is characterized by mesangial deposits of IgA.1,2 Although a renal disease, IgAN has an important systemic component, as illustrated by the high incidence of recurrence after transplantation.3 Several observations point towards an important role for alterations in IgA biology in the pathogenesis of IgAN. Deposited IgA is predominantly polymeric IgA (pIgA) of the IgA1 subclass and has been shown to be differentially glycosylated. Moreover, vaccination studies have demonstrated alterations in mucosal immunity, whereas in many patients mucosal infections are associated with episodes of macroscopic hematuria. Information outlined above suggests that an important check point is defined by quantitative and qualitative aspects of IgA production. Recent years have witnessed progress in our understanding of this process, including the molecular events of isotype switching in B lymphocytes, as well as cellular events associated with B cell activation. Here we will summarize some basic characteristics of the IgA molecules and concentrate on new developments concerning regulation of IgA production, with a major emphasis on the role of dendritic cells, and their role in the pathogenesis of IgAN.

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Human IgA Immune System Different Molecular Forms of IgA The human IgA system is complex, as human IgA is produced at many different sites in the body and exists in different forms. The majority of IgA is produced by mucosal tissue and secreted as secretory IgA (SIgA). A smaller amount of IgA is produced by plasma cells in the bone marrow and appears in the circulation. These different compartments, the mucosal and the systemic, are linked by the so-called mucosa-bone marrow axis and do not function independent from each other.4 There are two subclasses of human IgA, IgA1 and IgA2, where IgA2 has two different allotypes (IgA2m1 and IgA2m2). The main structural difference between these subclasses is the 18-amino acid hinge region, which is lacking in IgA2.5 This hinge region contains six potential O-linked glycosylation sites, and it has been demonstrated that in IgAN part of the IgA1 molecules are undergalactosylated, resulting in terminal GalNac residues.6 This unique feature of IgA1 has been proposed as one of the explanations for the predominance of IgA1 in renal depositions. Both IgA1 and IgA2 exist in monomeric (mIgA) and in polymeric forms (pIgA). pIgA consists of dimeric IgA (dIgA), but also larger molecules exist. Dimeric IgA consist of two IgA molecules linked with a 21 kD joining protein, the J chain. IgA and J chain are co-synthesized by plasma cells and polymers are assembled before secretion.7,8 The composition of pIgA is variable and may consist of complexes of IgA and the FcαRI/CD89, IgA immune complexes and IgA-fibronectin complexes.9,10 Although mainly produced at the mucosa, IgA is also present in the systemic compartment in a concentration of 2–3 mg/ml. Serum IgA exists mainly as IgA1 (90%) and circulates predominantly in a monomeric form. Like the majority of other immunoglobulins in serum, IgA is produced by plasma cells in the bone marrow. The function of systemic IgA is not well understood. It might be that monomeric IgA is involved in the regulation of immune responses in an anti-inflammatory way.11 In contrast, it is thought that interaction of high MW forms of IgA with the myeloid FcαRI, CD89, has probably pro-inflammatory effects.12 Complexes of IgA have been shown to be present in IgAN patients and in an animal model their presence was associated with IgA deposition and glomerulonephritis.13,14 It is important to note that the IgA system

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in mice is fundamentally different. Murine IgA lacks a hinge region with potential O-glycosylation sites, serum IgA in mice is almost exclusively polymeric in nature, and a homologue of the myeloid FcαRI/CD89 is not present. These differences have certainly hampered the development of appropriate animal models for IgAN (also refer to Chapter 26).

Mucosal IgA Compartment IgA is the major immunoglobulin in mucosal secretions and has an important function in mucosal defence against bacterial and viral infections. IgA at mucosal surfaces is mainly dimeric and secreted as secretory IgA (SIgA). Before secretion dIgA is bound to the polymeric Ig receptor (pIgR), located at the basolateral site of the mucosal epithelium. Then IgA is transported to the mucosal surface, where it is secreted together with a proteolytically cleaved part of the pIgR (secretory component).15 Both subclasses IgA1 and IgA2 are produced at the mucosa. The distribution of the two subclasses varies at different mucosal sites. In the nasal mucosa the relative contribution of IgA1 is 93% and in the bronchial mucosa 75%. In the proximal gastrointestinal tract the relative contribution of IgA1 is high, 83% at the gastric mucosa, and low in the distal part, 36% in the colon.16 Although the major part of SIgA is present in secretions of the gastrointestinal tract and the respiratory tract, small amounts of SIgA are also found in the circulation.17,18 This SIgA might have a role in the pathogenesis in IgAN.17,19,20 There is a cross talk between mucosal sites in the human body. This means that an immune response induced at one mucosal site will result in an immune response with the same antigen specificity at another mucosa and even might induce a clear systemic immune response.21 The different mucosae can be seen as a common mucosal immune system.22 On the other hand in many cases a mucosal immune response will not give rise to a systemic immune response, this phenomenon is called oral tolerance.23

IgA in IgA Nephropathy Levels of plasma IgA1 are elevated in about half of the IgAN patients.24,25 The elevated IgA concentration seems to be the result of

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higher production of IgA by plasma cells in the bone marrow.26–29 Next to the higher concentrations of IgA1, qualitative changes of IgA in IgAN patients have been described. The most important change in IgA is the glycosylation pattern of IgA1 in IgAN patients. IgA of IgAN patients contains a reduced galactosylation of the O-linked glycans in the hinge region.6,30–33 The hinge region consists of 18 amino acids, of which six are O-linked glycosylation sites. Moreover, this undergalactosylated form of the IgA1 hinge region was also over-represented in biopsies of patients with IgAN.34 The same abnormality in glycosylation pattern is found in IgA produced in vitro by tonsillar lymphocytes, suggesting that tonsils might contribute to the abnormally glycosylated IgA in serum.35,36 IgA glycosylation takes place in the golgi apparatus of the B cells. Recently specific glycosyltransferases have been described, but so far no abnormalities in expression or in function were demonstrated in IgAN.37,38 In the urine of IgAN patients immune complexes containing aberrantly glycosylated IgA have been described. These complexes were not present in patients with other glomerular diseases.39 It has been suggested that a lectin-binding assay, based on the detection of undergalactosylated IgA1, might have potential as a non-invasive diagnostic test for IgA nephropathy.40 To have a better view on the development of IgA immune responses, several groups have performed vaccination studies in IgAN patients. Unexpectedly, it could be demonstrated that patients with IgAN have a hampered primary mucosal IgA immune response. Both after nasal immunization with cholera toxin B subunit and after oral immunization with live typhoid vaccine, a clear IgA hyporesponse was present in the IgAN group as compared to control persons.21,41 Although a clear difference in the titers of antigen-specific IgA was present no difference in the size distribution of the antigen-specific IgA was detected.42 However, it should be noted that in both groups most of the antigen-specific IgA was in the high MW fraction of serum IgA. As a result of this mucosal hyporesponse, the clearance of antigens might be less effective leading to a prolonged antigen exposition, which might eventually lead to higher levels of memory and higher IgA serum titers. The fact that other diseases with high serum IgA concentrations, like multiple myeloma or HIV, are not associated with renal IgA depositions supports the idea that the higher IgA1 concentrations are not the only cause of mesangial IgA deposition in IgAN.

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A Pathogenic Role for SIgA Results described above provide a rationale for a connection between induction of mucosal immune responses and IgAN.43 In addition, we demonstrated that SIgA is present in renal biopsies in 15% of the cases.44 The presence of SIgA in renal biopsies correlates with the presence of MBL depositions. Although SIgA is mainly present at mucosal surfaces, in all secretory fluids, low concentrations of SIgA are also present in the circulation. In purified IgA, the relative concentration of SIgA is higher in IgAN patients than in control persons.45 Recently we were able to detect small amounts of antigen-specific SIgA in the circulation of both IgAN patients and controls, after mucosal immunization.42 A pathogenic role for SIgA is suggested by the fact that about 40% of IgAN patients have episodes of macroscopic hematuria, often preceded by upper respiratory tract infections.43 Combining these different findings, it is our hypothesis that the quantitative and qualitative abnormalities of IgA in IgAN patients might be the result of a disturbed regulation of the mucosal IgA immune response. Glycosylation and molecular size of the IgA are determined within the B cells and are most likely dependent on external factors. In the next paragraph we will focus on the regulation of IgA production by B cells and describe some characteristics of the immune response in IgAN patients.

Production of IgA Regulation of IgA Production Production of IgA antibodies is a tightly regulated process, and is controlled at several levels. Naïve B cells express surface IgM/IgD and have to go through a process of clonal expansion, isotype switching, affinity maturation and differentiation before IgA plasma cells have developed. The process of class switch recombination (CSR) occurs by looping out and deletion of segments of DNA46–48 (Figure 12.1). Induction of Ig secretion can be mediated by both T cell-dependent and T cell-independent mechanisms, operating via different mechanisms. The T cell-dependent mechanism is mainly dependent on the CD40CD40-ligand interaction. In the hyper IgM syndrome, a genetic alteration of CD40L results in the absence of IgA and IgG.49,50 For IgA production cytokines like transforming growth factor β (TGF-β), IL-2 and IL-10

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Circulation

Lymphoid organs

Activation Proliferation Affinity Maturation Class switch Differentiation Naïve B

B

Mucosa IgA Plasma cell

Bone marrow Bone marrow Figure 12.1 Schematic representation of the regulation of IgA production. After development in the bone marrow, naïve B cells have to undergo a process of activation, proliferation, somatic hypermutation and affinity maturation, class switch recombination and differentiation, before they become IgA producing plasma cells. These processes are tightly regulated and mostly occur in organized lymphoid structures (germinal centers). Resulting plasma cells can become long lived cells after migration to appropriate sites including mucosa and bone marrow.

have been shown to be involved.51 In addition, also cytokines like IL-4, IL-5, IL-6 and IL-21 have been suggested to play a direct or indirect role, but their contribution is less well established. More recently, it has become clear that IgA production can also be induced in a T cellindependent manner.52 Molecular signals involved in this process are less well characterized, but might involve members of the TNF superfamily expressed at the surface of dendritic cells (DC).53 In view of the central role that DC might have in both T-dependent and T-independent responses, we will first discuss and introduce DC.

General Characteristics of Dendritic Cells Dendritic cells (DC) are professional antigen presenting cells that play a critical role in the initiation and regulation of immune responses.54,55 In humans different subsets of DC can be distinguished, based on different phenotypic characteristics: (i) Langerhans cells and interstitial

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DC, both belonging to the myeloid lineage and (ii) plasmacytoid DC, which are thought to be derived from a lymphoid precursor. An important characteristic of DC is their potency to migrate from blood to tissues and from tissue to draining lymph nodes. DC are abundantly present in lymphoid tissue, skin and in mucosal tissue of the gastrointestinal tract and the respiratory tract.56,57 In fact, immature DC are present in most peripheral organs, including the kidney.58 Immature DC have a high capacity to capture antigens.54 After capturing antigens, DC can migrate to draining lymph nodes. As a consequence of antigen uptake and concomitant activation signals, DC will mature and differentiate in distinctive ways, dependent on the type of stimulus that is given to the DC. After maturation DC express co-stimulatory molecules and adhesion molecules on their cell surface, produce cytokines and are able to present antigens to T cells in the context of major histocompatibility (MHC) molecules. This process then leads to T cell activation, proliferation, development of effector functions and capacity to migrate to sites of inflammation.59,60 DC are actively involved in the immunological response and additionally play a crucial role in maintenance of self-tolerance. In the thymus DC can present self-antigens in the context of MHC and T cells with a too high an affinity are deleted (negative selection).61 So DC are involved and decisive in different immunological processes. On the one hand they induce immune responses directed against bacteria and viruses, on the other hand they are involved in prevention of autoimmunity.

Role of DC and B Cell Activation As mentioned above, regulation of IgA production can occur both in a T cell-dependent and a T cell-independent manner. In both cases, DC are thought to have a critical role (Figure 12.2). DC can induce a humoral immune reaction by presenting antigens to T cells, generating T helper cells, which subsequently can lead to activation of B cells. This interaction between B cells and T cells has been studied extensively and is mainly dependent on MHC and the CD40-CD40-ligand interaction.62 Next to this T cell-dependent effect of DC on B cells, there can also be a direct interaction between B cells and DC (Figure 12.2A). This has been shown in an in vitro model, where DC were co-cultured with B cell in the presence of a CD40L-transfected cell line.63,64 This resulted in a three- to six-fold increase in the recovery of viable B cells within a week.65

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A

Ag Ag

APC

BCR

CD80/86

Mucosal environment

B

MHC-II TCR

CD28

CD40 CD40L

TCR T

T

Cytokines

CD4+

IgA

T-dependent B BAFF

APC

BAFF-R

BCMA

APRIL

Mucosal environment B

TACI Cytokines

IgA

T-independent Figure 12.2 Schematic representation of T cell-dependent and T cellindependent regulation of IgA production. (A) T cell-dependent activation of B cells is initiated by antigen presenting cells (APC), taking up antigen (Ag), processing this and presenting peptides in the context of MHC II to CD4+ T cells. This mechanism is dependent on co-stimulatory molecules like CD80/86 and CD28, and results in polarized T helper cells. Upon subsequent interaction between T cells and B cells, activated T cells secrete a variety of immunostimulatory factors and start to express CD40L. In this model, Ag specificity is determined by the fact that B cells have to take up Ag through surface Ig expression (BCR) and present this in class II in order to recruit T cell help. Expression of CD40L and the local cytokine milieu, including signals from APC and/or the mucosal environment, will together regulate the production of IgA. (B) In the T cell-independent response, specific B cells will be activated through local cytokines, in combination with an Ag-specific activation signal through the B cell receptor. In this case there is an important direct role of APC. Activation of APC, for instance through TLR signaling, increases the expression of TNF family members BAFF and APRIL. These ligands show a complex interaction with

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Moreover, the presence of DC in culture strongly increased isotype switching of naïve B cells towards IgA1 and IgA2 producing plasma cells.64 More recently, it has become clear that under specific circumstances, IgA can also be induced in a T cell-independent, and thereby also CD40L-independent manner (Figure 12.2B).53 It has been suggested that this might be a characteristic of a specific subset of B cells, especially B-1 cells, expressing CD5 in addition to the pan-B cell markers CD19 and CD20.52 Interestingly, also in this case antigen presenting cells, including DC, are thought to play an important role. Activated DC are able to express several members of the TNF/CD40L family including B lymphocyte stimulator protein (BlyS, also called BAFF or TALL-1) and a proliferation inducing ligand (APRIL), interacting with a set of receptors belonging to the TNF-R superfamily (Figure 12.2B). A critical role of these molecules in B cell activation was confirmed in genetically deficient mice and men which showed hampered IgA production.66,67 Efficient activation of these B cells is dependent of co-signals derived from the B cell receptor (surface expressed Ig complex).68 Therefore antigen specificity of the response is determined by the antigen specific BCR, either for antigen uptake and presentation to recruit appropriate T cell help, or through a direct signaling event. Upon activation DC can produce several chemokines, important for recruitment of B cells which might facilitate the processes described above.69

DC in IgA Nephropathy Being professional antigen presenting cells, DC are critically involved in the initiation of immune responses. Besides DC can have a direct effect on B cells and are capable to skew immunoglobulin production by naïve B cells towards IgA1 and IgA2.64 In view of the hampered mucosal IgA response against a neoantigen,21 we postulated that the number of DC present in the nasal mucosa might be reduced in IgAN patients and Figure 12.2 (Continued ) three potential receptors expressed on B cells: TACI, BCMA and BAFF-R. Antigen specificity is determined by cross-linking of B cell receptors, thereby generating signals which are critical for B cell activation, and in combination with the local environment regulates IgA switch and differentiation into antibody producing cells.

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could be responsible for the differences in IgA responses between IgAN patients and controls. To test our hypothesis, nasal biopsies of IgAN patients and control persons were taken and stained for the presence of DC and subsets of DC. In nasal biopsies we found that the number of DC in the nasal mucosa of IgAN patients was not decreased. As a matter of fact there were even higher numbers of CD1a positive DC, a feature of Langerhans cells, in the epithelial layer.70 Similarly, higher numbers of DC-SIGN positive myeloid DC were observed in the lamina propria.70 Numbers of BDCA1 expressing myeloid DC and BDCA2 expressing plasmacytoid DC were not different between the groups. As the number of nasal mucosal DC in IgAN patients was not reduced as compared to controls, it is unlikely that this provides an explanation for the described IgA hyporesponsiveness in vaccination. Therefore, we postulated that DC might be less effective in inducing IgA production by naïve B cells. To test this hypothesis we investigated in an in vitro model the functional capacity of DC to induce IgA production in naïve B cells,71 in a model first described by Fayette et al.64 In this model naïve B cells are cultured in the presence of CD40L-transfected cells, which mimic activated T cells and bypass MHC restriction. We investigated monocyte-derived DC cultured with CD40L-transfected cells and naïve B cells, in the presence of different cytokines, including IL-10 and IL-2. The only variable in the system is the source of the DC, which is either from an IgAN patient or from a control person. In these experiments it appeared that DC derived from IgAN patients showed a reduced capacity to induce IgA production in the presence of IL-10.71 Although the mean IgA production induced by DC from IgAN patients was strongly reduced, DC from some individual patients showed a near normal IgA production, whereas others completely lacked the capacity to enhance IgA production. This might reflect that IgAN is a heterogeneous disease. No differences in IgG or IgM production were observed, independent of the different cytokines that were used. Supernatant of CD40-stimulated DC only showed limiting effects, suggesting that a membrane bound factor might be responsible for the reduced functional capacity of DC from IgAN patients to induce IgA production by naïve B cells. However, so far it not clear which factors are responsible for the disturbed DC function in IgAN patients.

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From these results it can be postulated that the IgA hyporesponse in IgAN patients observed after mucosal immunization can at least partially be explained by a functional defect of DC in the nasal mucosa, which is caused by a molecule present at the cell surface of DC. The increased number of sub-epithelial DC-SIGN positive DC and epithelial CD1a-positive DC in the nasal mucosa of patients with IgAN could be a compensatory increase for the described reduced capacity to induce IgA production. It is important to note that experiments performed with monocytederived DC might not be completely representative for mucosal DC. There are strong indications that mucosal DC have very special characteristics and functions, important for the regulation of mucosal immunity.72 For instance, immune cells in the mucosa, including DC and B cells, seem to be programmed by the presence of retinoic acid. In mice, intestinal DC were shown to be efficient in the induction of T cell-independent expression of IgA and gut-homing receptors on B cells.73 Finally, also nonimmune cells, like epithelial cells, can have an active contribution in the regulation of mucosal IgA production.74

Concluding Remarks IgAN is characterized by mesangial deposition of mainly pIgA1. The glycosylation pattern of the deposited IgA1 is disturbed and the undergalactosylated IgA1 seems to be over-represented in renal biopsy specimen. The regulation of the primary mucosal IgA immune response in IgAN patients is disturbed, leading to an IgA hyporesponse after mucosal challenge. In about 15% of cases SIgA is present in the mesangium and co-localizes with complement factors of the MBL system. In the present chapter we have described the possible contribution of various players of the immune response that might be involved in the pathogenesis of IgAN. The disturbed IgA immune response is partially determined by some so far undetermined dysfunctions of DC. Which specific DC function is disturbed and whether other factors, like local mucosal factors, are involved in the dysregulation of the immune response is not clear and should be subject of further investigations. It would especially be challenging to link alterations in immune regulation to the intrinsic changes such as glycosylation of the IgA molecule.

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References 1. Berger J, Hinglais N. (1968) Intercapillary deposits of IgA-IgG. J Urol Nephrol (Paris) 74: 694–695. 2. Donadio JV, Grande JP. (2002) IgA nephropathy. N Engl J Med 347: 738–748. 3. van der Boog PJ, de Fijter JW, Bruijn JA, van Es LA. (1999) Recurrence of IgA nephropathy after renal transplantation. Ann Med Interne (Paris) 150: 137–142. 4. Suzuki Y, Tomino Y. (2007) The mucosa-bone-marrow axis in IgA nephropathy. Contrib Nephrol 157: 70–79. 5. Kerr MA. (1990) The structure and function of human IgA. Biochem J 271: 285–296. 6. Coppo R, Amore A. (2004) Aberrant glycosylation in IgA nephropathy (IgAN). Kidney Int 65: 1544–1547. 7. Braathen R, Hohman VS, Brandtzaeg P, Johansen FE. (2007) Secretory antibody formation: conserved binding interactions between J chain and polymeric Ig receptor from humans and amphibians. J Immunol 178: 1589–1597. 8. Johansen FE, Braathen R, Brandtzaeg P. (2000) Role of J chain in secretory immunoglobulin formation. Scand J Immunol 52: 240–248. 9. Floege J, Feehally J. (2000) IgA nephropathy: recent developments. J Am Soc Nephrol 11: 2395–2403. 10. van der Boog PJ, van Kooten C, de Fijter JW, Daha MR. (2005) Role of macromolecular IgA in IgA nephropathy. Kidney Int 67: 813–821. 11. Mestecky J, Russell MW, Elson CO. (1999) Intestinal IgA: novel views on its function in the defence of the largest mucosal surface. Gut 44: 2–5. 12. Monteiro RC, van de Winkel JG. (2003) IgA Fc receptors. Annu Rev Immunol 21: 177–204. 13. Launay P, Grossetete B, Arcos-Fajardo M, et al. (2000) Fcalpha receptor (CD89) mediates the development of immunoglobulin A (IgA) nephropathy (Berger’s disease). Evidence for pathogenic soluble receptor-Iga complexes in patients and CD89 transgenic mice. J Exp Med 191: 1999–2009. 14. van Egmond M, Damen CA, van Spriel AB, et al. (2001) IgA and the IgA Fc receptor. Trends Immunol 22: 205–211. 15. Mostov KE. (1994) Transepithelial transport of immunoglobulins. Annu Rev Immunol 12: 63–84. 16. Brandtzaeg P, Johansen FE. (2005) Mucosal B cells: phenotypic characteristics, transcriptional regulation, and homing properties. Immunol Rev 206: 32–63. 17. Oortwijn BD, van der Boog PJ, Roos A, et al. (2006) A pathogenic role for secretory IgA in IgA nephropathy. Kidney Int 69: 1131–1138.

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18. Thompson RA, Asquith P, Cooke WT. (1969) Secretory IgA in the serum. Lancet 2: 517–519. 19. Oortwijn BD, Rastaldi MP, Roos A, et al. (2007) Demonstration of secretory IgA in kidneys of patients with IgA nephropathy. Nephrol Dial Transplant 22: 3191–3195. 20. Oortwijn BD, Eijgenraam JW, Rastaldi MP, et al. (2008) The role of secretory IgA and complement in IgA nephropathy. Semin Nephrol 28: 58–65. 21. de Fijter JW, Eijgenraam JW, Braam CA, et al. (1996) Deficient IgA1 immune response to nasal cholera toxin subunit B in primary IgA nephropathy. Kidney Int 50: 952–961. 22. McGhee JR, Xu-Amano J, Miller CJ, et al. (1994) The common mucosal immune system: from basic principles to enteric vaccines with relevance for the female reproductive tract. Reprod Fertil Dev 6: 369–379. 23. Fujihashi K, Kato H, van Ginkel FW, et al. (1983) A revisit of mucosal IgA immunity and oral tolerance. Acta Odontol Scand 59: 301–308. 24. Delacroix DL, Elkom KB, Geubel AP, et al. (1983) Changes in size, subclass, and metabolic properties of serum immunoglobulin A in liver diseases and in other diseases with high serum immunoglobulin A. J Clin Invest 71: 358–367. 25. van den Wall Bake AW, Daha MR, van der AA, et al. (1988) Serum levels and in vitro production of IgA subclasses in patients with primary IgA nephropathy. Clin Exp Immunol 74: 115–120. 26. Harper SJ, Allen AC, Layward L, et al. (1994) Increased immunoglobulin A and immunoglobulin A1 cells in bone marrow trephine biopsy specimens in immunoglobulin A nephropathy. Am J Kidney Dis 24: 888–892. 27. van den Wall Bake AW, Daha MR, Valentijn RM, van Es LA. (1987) The bone marrow as a possible origin of the IgA1 deposited in the mesangium in IgA nephropathy. Semin Nephrol 7: 329–331. 28. van den Wall Bake AW, Daha MR, Evers-Schouten J, van Es LA. (1988) Serum IgA and the production of IgA by peripheral blood and bone marrow lymphocytes in patients with primary IgA nephropathy: evidence for the bone marrow as the source of mesangial IgA. Am J Kidney Dis 2: 410–414. 29. van den Wall Bake AW, Daha MR, Haaijman JJ, et al. (1989) Elevated production of polymeric and monomeric IgA1 by the bone marrow in IgA nephropathy. Kidney Int 35: 1400–1404. 30. Allen AC, Bailey EM, Barratt J, et al. (1999) Analysis of IgA1 O-glycans in IgA nephropathy by fluorophore-assisted carbohydrate electrophoresis. J Am Soc Nephrol 10: 1763–1771. 31. Allen AC, Feehally J. (2000) IgA1 glycosylation and the pathogenesis of IgA nephropathy. Am J Kidney Dis 35: 551–556.

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32. Allen AC, Bailey EM, Brenchley PE, et al. (2001) Mesangial IgA1 in IgA nephropathy exhibits aberrant O-glycosylation: observations in three patients. Kidney Int 60: 969–973. 33. Barratt J, Smith AC, Feehally J. (2007) The pathogenic role of IgA1 O-linked glycosylation in the pathogenesis of IgA nephropathy (Review Article). Nephrology (Carlton) 12: 275–284. 34. Hiki Y, Odani H, Takahashi M, et al. (2001) Mass spectrometry proves under-O-glycosylation of glomerular IgA1 in IgA nephropathy. Kidney Int 59: 1077–1085. 35. Horie A, Hiki Y, Odani H, et al. (2003) IgA1 molecules produced by tonsillar lymphocytes are under-O-glycosylated in IgA nephropathy. Am J Kidney Dis 42: 486–496. 36. Itoh A, Iwase H, Takatani T, et al. (2003) Tonsillar IgA1 as a possible source of hypoglycosylated IgA1 in the serum of IgA nephropathy patients. Nephrol Dial Transplant 18: 1108–1114. 37. Barratt J, Smith AC, Molyneux K, Feehally J. (2007) Immunopathogenesis of IgAN. Semin Immunopathol 4: 427–443. 38. Buck KS, Smith AC, Molyneux K, et al. (2008) B-cell O-galactosyltransferase activity, and expression of O-glycosylation genes in bone marrow in IgA nephropathy. Kidney Int 73: 1128–1136. 39. Matousovic K, Novak J, Yanagihara T, et al. (2006) IgA-containing immune complexes in the urine of IgA nephropathy patients. Nephrol Dial Transplant 21: 2478–2484. 40. Moldoveanu Z, Wyatt RJ, Lee JY, et al. (2007) Patients with IgA nephropathy have increased serum galactose-deficient IgA1 levels. Kidney Int 71: 1148–1154. 41. Roodnat JI, de Fijter JW, van Kooten C, et al. (1999) Decreased IgA1 response after primary oral immunization with live typhoid vaccine in primary IgA nephropathy. Nephrol Dial Transplant 14: 353–359. 42. Eijgenraam JW, Oortwijn BD, Kamerling SW, et al. (2008) Secretory immunoglobulin A (IgA) responses in IgA nephropathy patients after mucosal immunization, as part of a polymeric IgA response. Clin Exp Immunol 152: 227–232. 43. Nicholls KM, Fairley KF, Dowling JP, Kincaid-Smith P. (1984) The clinical course of mesangial IgA associated nephropathy in adults. Q J Med 53: 227–250. 44. Oortwijn BD, Rastaldi MP, Roos A, et al. (2007) Demonstration of secretory IgA in kidneys of patients with IgA nephropathy. Nephrol Dial Transplant 22: 3191–3195. 45. Oortwijn BD, Roos A, Royle L, et al. (2006) Differential glycosylation of polymeric and monomeric IgA: a possible role in glomerular inflammation in IgA nephropathy. J Am Soc Nephrol 17: 3529–3539.

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46. Cerutti A. (2008) The regulation of IgA class switching. Nat Rev Immunol 8: 421–434. 47. Ballantyne J, Henry DL, Muller JR, et al. (1998) Efficient recombination of a switch substrate retrovector in CD40-activated B lymphocytes: implications for the control of CH gene switch recombination. J Immunol 161: 1336–1347. 48. Banchereau J, Rousset F. (1992) Human B lymphocytes: phenotype, proliferation, and differentiation. Adv Immunol 52: 125–262. 49. Conley ME, Cooper MD. (1998) Genetic basis of abnormal B cell development. Curr Opin Immunol 10: 399–406. 50. Notarangelo LD, Hayward AR. (2000) X-linked immunodeficiency with hyper-IgM (XHIM). Clin Exp Immunol 120: 399–405. 51. Zan H, Cerutti A, Dramitinos P, et al. (1998) CD40 engagement triggers switching to IgA1 and IgA2 in human B cells through induction of endogenous TGF-beta: evidence for TGF-beta but not IL-10-dependent direct S mu → S alpha and sequential S mu → S gamma, S gamma → S alpha DNA recombination. J Immunol 161: 5217–5225. 52. Fagarasan S, Honjo T. (2000) T-Independent immune response: new aspects of B cell biology. Science 290: 89–92. 53. Litinskiy MB, Nardelli B, Hilbert DM, et al. (2002) DCs induce CD40independent immunoglobulin class switching through BLyS and APRIL. Nat Immunol 3: 822–829. 54. Banchereau J, Steinman RM. (1998) Dendritic cells and the control of immunity. Nature 392: 245–252. 55. Steinman RM, Banchereau J. (2007) Taking dendritic cells into medicine. Nature 449: 419–426. 56. Akbari O, DeKruyff RH, Umetsu DT. (2001) Pulmonary dendritic cells producing IL-10 mediate tolerance induced by respiratory exposure to antigen. Nat Immunol 2: 725–731. 57. Banchereau J, Briere F, Caux C, et al. (2000) Immunobiology of dendritic cells. Annu Rev Immunol 18: 767–811. 58. Woltman AM, de Fijter JW, Zuidwijk K, et al. (2007) Quantification of dendritic cell subsets in human renal tissue under normal and pathological conditions. Kidney Int 71: 1001–1008. 59. Kapsenberg ML. (2003) Dendritic-cell control of pathogen-driven T-cell polarization. Nat Rev Immunol 3: 984–993. 60. Reis e Sousa C. (2006) Dendritic cells in a mature age. Nat Rev Immunol 6: 476–483. 61. Brocker T. (1999) The role of dendritic cells in T cell selection and survival. J Leukoc Biol 66: 331–335. 62. van Kooten C, Banchereau J. (2000) CD40-CD40 ligand. J Leukoc Biol 67: 2–17.

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63. Dubois B, Vanbervliet B, Fayette J, et al. (1997) Dendritic cells enhance growth and differentiation of CD40-activated B lymphocytes. J Exp Med 185: 941–951. 64. Fayette J, Dubois B, Vandenabeele S, et al. (1997) Human dendritic cells skew isotype switching of CD40-activated naive B cells towards IgA1 and IgA2. J Exp Med 185: 1909–1918. 65. Dubois B, Bridon JM, Fayette J, et al. (1999) Dendritic cells directly modulate B cell growth and differentiation. J Leukoc Biol 66: 224–230. 66. Castigli E, Scott S, Dedeoglu F, et al. (2004) Impaired IgA class switching in APRIL-deficient mice. Proc Natl Acad Sci USA 101: 3903–3908. 67. Castigli E, Wilson SA, Garibyan L, et al. (2005) TACI is mutant in common variable immunodeficiency and IgA deficiency. Nat Genet 37: 829–834. 68. Craxton A, Magaletti D, Ryan EJ, Clark EA. (2003) Macrophage-and dendritic cell-dependent regulation of human B-cell proliferation requires the TNF family ligand BAFF. Blood 101: 4464–4471. 69. Dubois B, Massacrier C, Caux C. (2001) Selective attraction of naive and memory B cells by dendritic cells. J Leukoc Biol 70: 633–641. 70. Eijgenraam JW, Reinartz SM, Kamerling SW, et al. (2008) Immunohistological analysis of dendritic cells in nasal biopsies of IgA nephropathy patients. Nephrol Dial Transplant 23: 612–620. 71. Eijgenraam JW, Woltman AM, Kamerling SW, et al. (2005) Dendritic cells of IgA nephropathy patients have an impaired capacity to induce IgA production in naive B cells. Kidney Int 68:1604–1612. 72. Coombes JL, Powrie F. (2008) Dendritic cells in intestinal immune regulation. Nat Rev Immunol 8: 435–446. 73. Mora JR, Iwata M, Eksteen B, et al. (2006) Generation of gut-homing IgAsecreting B cells by intestinal dendritic cells. Science 314: 1157–1160. 74. He B, Xu W, Santini PA, et al. (2007) Intestinal bacteria trigger T cellindependent immunoglobulin A(2) class switching by inducing epithelial-cell secretion of the cytokine APRIL. Immunity 26: 812–826.

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Chapter 13

IgA Immune-Complex Jan Novak and Jiri Mestecky

Introduction IgA nephropathy (IgAN) was described in 1968 by Berger and Hinglais based on its unique renal immunohistologic features as IgA-IgG immune-complex renal disease.1 Since that time, the diagnosis of IgA nephropathy has been based on the finding of mesangial deposits of IgA by immunohistochemical analysis of cortical renal tissue obtained by biopsy. IgA is the dominant or co-dominant immunoglobulin, usually with C3 but without significant amounts of C1q (Figure 13.1). Additional studies specified that IgA in the immune deposits is of the IgA1 subclass.2 IgA1 may be the sole immunoglobulin present, or it may be dominant or co-dominant immunoglobulin with co-deposits of IgG, or IgM, or both.3 There is considerable amount of data indicating that the mesangial deposits originate from circulating IgA immune complexes. Evidence that the primary cause of IgA nephropathy is extra-renal includes the recurrence of the disease in approximately 50%–60% of patients who receive a new kidney.4–8 Moreover, in the few cases in which a kidney was transplanted from a donor with subclinical IgA nephropathy into a patient with non-IgA nephropathy renal disease, clearance of the immune deposits from the affected kidney was observed within several weeks.9 It is well established that many patients with IgA nephropathy have elevated levels of IgA and IgA-containing immune complexes in the circulation.10–14 Idiotypic determinants are shared between the circulating complexes and the mesangial deposits;15 however, a disease-specific

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Figure 13.1 IgA1-containing immune deposits in a human glomerulus in a renal biopsy from a patient with IgA nephropathy revealed by immunofluorescence microscopy. (A) Entire glomerulus (40× objective) stained for IgA. (B) Enlarged section from A taken by 100× objective. (C) Confocal microscopic image of a large glomerular immune complex stained for IgG (red), IgA (blue), and complement C3 (green) taken by 100× objective, as an example of immune complex with mixed components. Pictures courtesy of Dr. Lea Novak, University of Alabama at Birmingham, Department of Pathology.

idiotype has not been identified.16 Circulating immune complexes in patients with IgA nephropathy contain IgA1.10,14,17

Circulatory and Mesangial IgA1 Complexes Contain Aberrantly Glycosylated IgA1 Analysis of the glycosylation of IgA1 in patients with IgA nephropathy is yielding novel insights into the mechanisms underlying immunecomplex formation and deposition in the mesangium.12,14,18,19 Specifically, galactose deficiency of IgA1 appears to be a key pathogenetic factor contributing to the development of the disease. Circulating complexes in

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IgA Immune-Complex ✦ 179

IgA nephropathy contain IgA1 with galactose-deficient hinge-region O-linked glycans.12,14,18,19 Notably, galactose-deficient IgA1 is the predominant glycosylation variant of IgA1 in the mesangium.20,21 A relationship between galactose deficiency and nephritis also has been observed in other diseases. Galactose-deficient IgA122 and IgA-IgG circulating complexes23 are found in sera of patients with HenochSchoenlein purpura who develop nephritis but not in sera of patients who do not. Also, patients with IgA1 myeloma have high levels of circulating IgA1, but only those with aberrantly glycosylated IgA1 develop immune-complex glomerulonephritis.24,25

Structure and Origin of Aberrantly Glycosylated IgA1 IgA1 represents one of two structurally and functionally distinct subclasses of IgA.26–29 Unlike IgA2, IgM, and IgG, IgA1 molecules have heavy chains that contain a hinge-region segment between the first and second constant region domains that is unique. This hinge region, with a high content of Pro, Ser, and Thr, is the site of attachment of usually three to six O-linked glycan chains consisting of N-acetylgalactosamine (GalNAc) with a β1,3-linked galactose that may be sialylated.30–36 Sialic acid can also be attached to GalNAc by an α2,6 linkage. The carbohydrate composition of the O-linked glycans in the hinge region of normal human serum IgA1 is variable. The prevailing forms include galactoseGalNAc disaccharide, and its mono- and di-sialylated forms.12,32,37 Galactose-deficient variants with terminal GalNAc or sialylated GalNAc are rarely found in the O-glycans of normal individuals,32 but are much more common in patients with IgA nephropathy, predominantly in the glomerular immunodeposits and in the circulating complexes.12,14,20,21,38–43 Structure of IgA1 and its glycosylation are addressed in detail in Chapter 12. Cultured EBV-immortalized IgA1-producing cells from the circulation of IgA nephropathy patients secrete galactose-deficient IgA1 while IgA1 from the cells originating from healthy or disease controls is predominantly normally glycosylated.44 Serum levels of galactosedeficient IgA1 of the patients correlate with the level of galactose deficiency of IgA1 secreted by their IgA1-producing cells. These findings localized the glycosylation defect to the IgA1-producing cells and subsequent analyses uncovered an inherent defect related to this aberrancy.

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Cells from patients with IgA nephropathy had low expression and activity of the corresponding galactosyltransferase and high expression and activity of sialyltransferase; both enzymes are specific for GalNAc of IgA1. Consequently, the O-glycans on the secreted IgA1 are galactosedeficient with high proportion of GalNAc being sialylated.44 In the view of the fact that sialylation was shown to prevent galactosylation of GalNAc,45 it is quite possible that “premature” sialylation helps to increase the levels of galactose-deficient O-glycans in IgAN.44,46 Thus, this “premature” sialylation may represent the missing factor responsible for galactose deficiency of IgA1 in IgAN cited in a recent publication. Buck et al.47 found using B cells from circulation and bone marrow of IgAN patients that O-galactosylation activity correlated with β-galactosyltransferase expression but not with IgA1 galactosylation in IgAN patients. Based on this observation, the authors suggested that factors other than β-galactosyltransferase or its chaperone, Cosmc, are responsible for altered IgA1 O-glycosylation. That study used mixed B-cell population, while the study by Suzuki et al.44 used purified IgA1-secreting cell lines. EBV-immortalized IgA1-producing cells are thus a convenient model that may advance our understanding of molecular mechanisms associated with aberrant glycosylation of IgA1 in IgAN and may provide new opportunities for development of future disease-specific therapies.

Promotion of IgA1 Immune Complex Formation by Aberrant Glycosylation Alterations in glycan moieties of cell surface or free glycoproteins are now recognized as factors that can cause or contribute to autoimmune disease.48–52 Tn-syndrome, or “permanent mixed-field polyagglutinability,” is a rare autoimmune disease in which subpopulations of blood cells in all lineages carry an incompletely O-glycosylated membrane glycoprotein.53,54 The aberrant glycosylation creates an epitope, known as the Tn antigen. The immunodominant epitope of the Tn antigen is terminal GalNAc, whereas the normal glycan has an additional terminal galactose. The neoepitope on the cell surfaces is recognized by anti-Tn antibodies in the sera,55 leading to thrombocytopenia, leukopenia, and hemolytic anemia.53,54 IgAN is another autoimmune disease arising due to alterations in glycan moieties.14,19,46,56 It has been shown that, after alteration of the glycosylation of the IgA1, neoepitopes represented by IgA1 glycans12,14

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or hinge-region glycopeptides are exposed57,58 and recognized by naturally-occurring antibodies with anti-glycan or anti-glycopeptide specificities.59 IgA1-IgG-containing immune complexes isolated from sera of patients with IgAN are dissociable at acidic pH. Experiments using various compounds as potential inhibitors of re-association of the complexes showed that IgG from the IgA1-IgG complexes binds to GalNAc-containing epitopes.14 Further studies indicated that these anti-GalNAc antibodies are present in sera of IgAN patients as well as healthy individuals, and in cord blood.60–62 However, IgAN patients have elevated levels of such IgG in the circulation.14,59 Clones of EBVtransformed peripheral blood lymphocytes from IgAN patients in culture secrete IgG antibodies specific for galactose-deficient IgA1.59 These IgG anti-glycan antibodies bind to GalNAc in the hinge region of galactose-deficient IgA1. Thus, the presence of glycan-specific anti-IgA1 antibodies promotes formation of immune complexes.62 The resultant IgA1 complexes are relatively large. Because of their size, they are not efficiently cleared from the circulation and thus tend to deposit in the renal mesangium.56,60–63

Effects of Aberrant Glycosylation on Clearance of IgA1 Immune Complexes from the Circulation The relatively short half-life (∼5 days) of normal serum IgA is due to its rapid catabolism by hepatocytes.33,64–67 Hepatocytes express the asialoglycoprotein receptor33,66,67 that binds glycoproteins through terminal galactose or GalNAc residues.33,66–69 Because the structural pre-requisite for binding is a terminal galactose or GalNAc, the absence or enzymatic removal of the otherwise terminal sialic acid is essential for effective binding. Indeed, human IgA1 myeloma proteins and polyclonal human IgA1 are removed promptly from the circulation after enzymatic cleavage of terminal sialic acid.33,70,71 Galactose-deficient IgA1 is retained in the circulation for long periods of time.72 Galactose deficiency in itself should not hinder disposal of IgA1 molecules because the asialoglycoprotein receptor recognizes terminal GalNAc as well as galactose.68 However, if the GalNAc is linked to sialic acid or is covered by an antibody, it cannot be recognized by the hepatic asialoglycoprotein receptor and is not catabolized.18,73 Because

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galactose-deficient IgA1 is present in the form of immune complexes, it is plausible to speculate that this IgA1 does not effectively reach the hepatic asialoglycoprotein receptor. The larger size of such complexes, compared to uncomplexed IgA1, precludes binding to this receptor because the relatively small endothelial fenestrae block entry into the space of Disse. In animals, large-molecular-weight immune complexes induce more severe glomerular lesions than do small complexes.63 Thus, immune complexes containing aberrantly glycosylated IgA1 are not efficiently cleared from the circulation and eventually deposit in the mesangium.46,56,61,74–76 Renal deposits of IgA and IgA-containing immune complexes frequently occur in patients with liver cirrhosis.77,78 However, it appears that the deposits develop due to the reduced IgA clearance79 and/or formation of immune complexes with microbial antigens rather than due to the aberrant glycosylation of IgA1 typical for primary IgAN. For example, patients with alcoholic liver disease have deposits of IgA, mainly monomeric IgA1, in hepatic sinusoidal walls, but without complement components.80 Furthermore, many patients with hepatitis have circulatory IgA immune complexes and are diagnosed with IgAN based on renal biopsy evidence; however, recent studies showed that these patients do not exhibit urinary biomarkers typical of primary IgAN.78,81,82

IgA1 Immune Complexes Activate Cultured Mesangial Cells Cultured human mesangial cells present a convenient model to evaluate biologic activities of IgA1 complexes.18,19,62,83–87 Immune complexes from patients with IgAN containing galactose-deficient IgA1 bind to the cells more efficiently than do uncomplexed IgA1 or immune complexes from healthy controls. On assessing the biological activity of IgA1 complexes, large-molecular-weight IgA1 complexes stimulate cellular proliferation (measured as 3H-thymidine incorporation) and production of cytokines (e.g. IL-6 or TGF-β).88,89 IgA1-depleted fractions are devoid of stimulatory activities.19,62 Additional support for the role of IgA1 complexes has come from supplementation experiments. Addition of small amounts of desialylated polymeric IgA1 to sera of IgAN patients results in formation of new immune complexes; the amount of stimulatory complexes of molecular masses 800–900 kDa increases. ELISA indicated

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that these complexes contain IgG and IgA1.19 In contrast, uncomplexed IgA1 does not alter cellular proliferation. Complexes in the native sera of the patients enhance cellular proliferation more than do complexes of similar mass from healthy volunteers.19 Also, complexes of IgAN patients collected during macroscopic hematuria stimulate cellular proliferation more than do complexes obtained during a later quiescent phase. IgA1 complexes with high levels of galactose-deficient IgA1 induce more proliferation of cultured human mesangial cells compared to complexes with little galactose-deficient IgA1.19,62,90 Cellular mechanisms and receptors involved in binding IgA1 complexes and activation of mesangial cells are addressed in Chapter 15.

IgA1 Immune Complexes and Possible Means to Manipulate Their Properties The presence of immune complexes in body fluids, and their potential for selective tissue distribution and biological activity depend on the properties of antigens(s), the isotypes of antibodies, an ability to activate the complement system, and the relative proportion of antigen to antibodies that dictates the size of such complexes.91 Immune complexes formed either in the antigen- or antibody-excess zones may not be biologically active, as demonstrated for complexes from sera of some IgAN patients.19,60–62 The possibility of immunologically mediated intervention by altering formation of complexes through providing an excess of antibodies and thus converting the “pathogenic” complexes into biologically less active complexes has been considered clinically and experimentally in several studies (Figure 13.2). Intravenous injection of human gamma-globulin in immune-complex diseases, including IgAN, or laminin-derived peptides in experimental model of systemic lupus erythematosus proved to be of benefit. It must be kept in mind, however, that bivalent (two Agbinding sites and therefore cross-linking) antibodies were used. In IgAN, monovalent and therefore non-cross-linking, high-affinity fragments of GalNAc-specific antibodies can be theoretically generated as a means of interference with the formation of nephritogenic high-molecular-mass immune complexes. Consequently, this approach should reduce proliferative activity of mesangial cells due to the diversion of the galactosedeficient IgA1 from the kidney to the liver.

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pIgA1

pIgA1 IgG

2

1 Fv

Fab

Figure 13.2 Two immunologically-mediated strategies for preventing the formation of large, nephritogenic immune complexes in IgA nephropathy. (1) Antigenic determinants in the hinge region glycans will be “covered” with monovalent, high-affinity Fv or Fab fragments that would prevent naturally occurring anti-GalNAc IgG antibodies from cross-linking galactose-deficient polymeric IgA1 molecules. (2) A synthetic glycopeptide with a single GalNAc residue (to prevent cross-linking) is recognized by naturally occurring IgG antiGalNAc antibodies which cannot cross-link galactose-deficient polymeric IgA1. In both cases, small, non-nephritogenic complexes are formed.

Concluding Remarks IgAN is characterized by mesangial immune deposits, likely derived from circulating immune complexes containing aberrantly glycosylated IgA1.14,20,21,40,44,59 These IgA1 molecules have incompletely galactosylated O-linked glycans in the hinge region that are recognized by anti-glycan IgG and IgA1 antibodies.12,14 The resultant complexes deposit in the mesangium and induce mesangial cellular proliferation and matrix expansion. IgAN should be considered as an autoimmune disease in which IgA1 proteins with altered glycans represent an autologous antigen recognized by ubiquitous, naturally occurring antibodies, mostly of the IgG isotype. Because only large complexes

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exhibit a pathogenic potential, it is obvious that the proportion of antigen (IgA1) and antibodies specific for altered hinge-region glycans plays a decisive role in immune-complex tissue distribution and biological activity. Consequently, the immunological interference with and prevention of the formation of biologically active large complexes represents a desirable goal. Immunologically mediated interference with the formation as well as conversion of nephritogenic large complexes into inactive complexes through the competition with monovalent, non-cross-linking Fab or Fv fragments of anti-glycan antibodies may ultimately prove to be of benefit in the targeted treatment of this common disease. In summary, elucidation of the mechanisms of abnormal IgA1 glycosylation and immune complex formation is therefore important for understanding the disease pathogenesis and novel therapeutic approaches.

Acknowledgments The authors appreciate critical reading of the manuscript by Dr. Bruce A. Julian, University of Alabama at Birmingham, AL, USA. This work was supported in part by NIH grants DK078244, DK080301, DK071802, DK061525, DK077279 and DK064400.

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6. Berger J. (1988) Recurrence of IgA nephropathy in renal allografts. Am J Kidney Dis 12: 371–372. 7. Odum J, Peh CA, Clarkson AR, et al. (1994) Recurrent mesangial IgA nephritis following renal transplantation. Nephrol Dial Transplant 9: 309–312. 8. Chandrakantan A, Ratanapanichkich P, Said M, et al. (2005) Recurrent IgA nephropathy after renal transplantation despite immunosuppressive regimens with mycophenolate mofetil. Nephrol Dial Transplant 20: 1214–1221. 9. Silva FG, Chander P, Pirani CL, et al. (1982) Disappearance of glomerular mesangial IgA deposits after renal allograft transplantation. Transplantation 33: 241–246. 10. Czerkinsky C, Koopman WJ, Jackson S, et al. (1986) Circulating immune complexes and immunoglobulin A rheumatoid factor in patients with mesangial immunoglobulin A nephropathies. J Clin Invest 77: 1931–1938. 11. Coppo R, Basolo B, Piccoli G, et al. (1984) IgA1 and IgA2 immune complexes in primary IgA nephropathy and Henoch-Schönlein nephritis. Clin Exp Immunol 57: 583–590. 12. Tomana M, Matousovic K, Julian BA, et al. (1997) Galactose-deficient IgA1 in sera of IgA nephropathy patients is present in complexes with IgG. Kidney Int 52: 509–516. 13. Schena FP, Pastore A, Ludovico N, et al. (1989) Increased serum levels of IgA1-IgG immune complexes and anti-F(ab’)2 antibodies in patients with primary IgA nephropathy. Clin Exp Immunol 77: 15–20. 14. Tomana M, Novak J, Julian BA, et al. (1999) Circulating immune complexes in IgA nephropathy consist of IgA1 with galactose-deficient hinge region and antiglycan antibodies. J Clin Invest 104: 73–81. 15. Gonzales-Cabrero J, Egido J, Mampaso F, et al. (1989) Characterization of circulating idiotypes containing immune complexes and their presence in the glomerular mesangium in patients with IgA nephropathy. Clin Exp Immunol 76: 204–209. 16. van den Wall Bake AWL, Bruijn JA, Accavitti MA, et al. (1993) Shared idiotypes in mesangial deposits in IgA nephropathy are not disease-specific. Kidney Int 44: 65–74. 17. Coppo R, Basolo B, Martina G, et al. (1982) Circulating immune complexes containing IgA, IgG and IgM in patients with primary IgA nephropathy and with Henoch-Schönlein nephritis. Correlation with clinical and histologic signs of activity. Clin Nephrol 18: 230–239. 18. Novak J, Vu HL, Novak L, et al. (2002) Interactions of human mesangial cells with IgA and IgA-containing circulating immune complexes. Kidney Int 62: 465–475.

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19. Novak J, Tomana M, Matousovic K, et al. (2005) IgA1-containing immune complexes in IgA nephropathy differentially affect proliferation of mesangial cells. Kidney Int 67: 504–513. 20. Allen AC, Bailey EM, Brenchley PEC, et al. (2001) Mesangial IgA1 in IgA nephropathy exhibits aberrant O-glycosylation: observations in three patients. Kidney Int 60: 969–973. 21. Hiki Y, Odani H, Takahashi M, et al. (2001) Mass spectrometry proves under-O-glycosylation of glomerular IgA1 in IgA nephropathy. Kidney Int 59: 1077–1085. 22. Allen AC, Willis FR, Beattie TJ, et al. (1998) Abnormal IgA glycosylation in Henoch-Schönlein purpura restricted to patients with clinical nephritis. Nephrol Dial Transplant 13: 930–934. 23. Levinsky RJ, Barratt TM. (1979) IgA immune complexes in HenochSchönlein purpura. Lancet 2: 1100–1103. 24. van der Helm-van Mil AHM, Smith AC, Pouria S, et al. (2003) Immunoglobulin A multiple myeloma presenting with Henoch-Schönlein purpura associated with reduced sialylation of IgA1. Br J Haematol 122: 915–917. 25. Zickerman AM, Allen AC, Talwar V, et al. (2000) IgA myeloma presenting as Henoch-Schönlein purpura with nephritis. Am J Kidney Dis 36: E19. 26. Mestecky J, Moro I, Underdown BJ. (1999) Mucosal immunoglobulins. In: Mucosal Immunology (eds.) Ogra PL, Mestecky J, Lamm ME, Strober W, Bienenstock J, McGhee JR. Academic Press, San Diego, pp. 133–352. 27. Mestecky J. (1988) Immunobiology of IgA. Am J Kidney Dis 12: 378–383. 28. Mestecky J, Lue C, Tarkowski A, et al. (1989) Comparative studies of the biological properties of human IgA subclasses. Protides Biol Fluids 36: 173–182. 29. Mestecky J, Moro I, Kerr MA, et al. (2005) Mucosal immunoglobulins. In: Mucosal Immunology, 3rd ed. (eds.) Mestecky J, Bienenstock J, Lamm ME, Mayer L, McGhee JR, Strober W. Elsevier Academic Press, Amsterdam, pp. 153–181. 30. Baenziger J, Kornfeld S. (1974) Structure of the carbohydrate units of IgA1 immunoglobulin II. Structure of the O-glycosidically linked oligosaccharide units. J Biol Chem 249: 7270–7281. 31. Field MC, Dwek RA, Edge CJ, et al. (1989) O-linked oligosaccharides from human serum immunoglobulin A1. Biochem Soc Trans 17: 1034–1035. 32. Mattu TS, Pleass RJ, Willis AC, et al. (1998) The glycosylation and structure of human serum IgA1, Fab, and Fc regions and the role of N-glycosylation on Fcα receptor interactions. J Biol Chem 273: 2260–2272. 33. Tomana M, Kulhavy R, Mestecky J. (1988) Receptor-mediated binding and uptake of immunoglobulin A by human liver. Gastroenterology 94: 887–892.

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34. Tarelli E, Smith AC, Hendry BM, et al. (2004) Human serum IgA1 is substituted with up to six O-glycans as shown by matrix assisted laser desorption ionisation time-of-flight mass spectrometry. Carbohydr Res 339: 2329–2335. 35. Renfrow MB, Cooper HJ, Tomana M, et al. (2005) Determination of aberrant O-glycosylation in the IgA1 hinge region by electron capture dissociation Fourier transform-ion cyclotron resonance mass spectrometry. J Biol Chem 280: 19136–19145. 36. Renfrow MB, MacKay CL, Chalmers MJ, et al. (2007) Analysis of O-glycan heterogeneity in IgA1 myeloma proteins by Fourier transform ion cyclotron resonance mass spectrometry: implications for IgA nephropathy. Anal Bioanal Chem 389: 1397–1407. 37. Novak J, Tomana M, Kilian M, et al. (2000) Heterogeneity of O-glycosylation in the hinge region of human IgA1. Mol Immunol 37: 1047–1056. 38. Allen AC, Harper SJ, Feehally J. (1995) Galactosylation of N- and O-linked carbohydrate moieties of IgA1 and IgG in IgA nephropathy. Clin Exp Immunol 100: 470–474. 39. Hiki Y, Horii A, Iwase H, et al. (1995) O-linked oligosaccharide on IgA1 hinge region in IgA nephropathy. Fundamental study for precise structure and possible role. Contrib Nephrol 111: 73–84. 40. Mestecky J, Tomana M, Crowley-Nowick PA, et al. (1993) Defective galactosylation and clearance of IgA1 molecules as a possible etiopathogenic factor in IgA nephropathy. Contrib Nephrol 104: 172–182. 41. Leung JC, Tang SC, Chan DT, et al. (2002) Increased sialylation of polymeric lambda-IgA1 in patients with IgA nephropathy. J Clin Lab Anal 16: 11–19. 42. Leung JCK, Poon PYK, Lai KN. (1999) Increased sialylation of polymeric immunoglobulin A1: mechanism of selective glomerular deposition in immunoglobulin A nephropathy? J Lab Clin Med 133: 152–160. 43. Suen KK, Lewis WH, Lai KN. (1997) Analysis of charge distribution of lambda- and kappa-IgA in IgA nephropathy by focused antigen capture immunoassay. Scand J Urol Nephrol 31: 289–293. 44. Suzuki H, Moldoveanu Z, Hall S, et al. (2008) IgA1-secreting cell lines from patients with IgA nephropathy produce aberrantly glycosylated IgA1. J Clin Invest 118: 629–639. 45. Schachter H, McGuire EJ, Roseman S. (1971) Sialic acids. XIII. A uridine diphosphate D-galactose: mucin galactosyltransferase from porcine submaxillary gland. J Biol Chem 246: 5321–5328. 46. Novak J, Julian BA, Tomana M, et al. (2001) Progress in molecular and genetic studies of IgA nephropathy. J Clin Immunol 21: 310–327. 47. Buck KS, Smith AC, Molyneux K, et al. (2008) B-cell O-galactosyltransferase activity, and expression of O-glycosylation genes in bone marrow in IgA nephropathy. Kidney Int 73: 1128–1136.

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48. Rudd PM, Elliott T, Cresswell P, et al. (2001) Glycosylation and the immune system. Science 291: 2370–2376. 49. Yeaman GR, Collins JE, Lang GA. (2002) Autoantibody responses to carbohydrate epitopes in endometriosis. Ann N Y Acad Sci 955: 174–182; discussion 199–200, 396–406. 50. Ju T, Cummings RD. (2005) Protein glycosylation: chaperone mutation in Tn syndrome. Nature 437: 1252. 51. Chui D, Sellakumar G, Green RS, et al. (2001) Genetic remodeling of protein glycosylation in vivo induces autoimmune disease. Proc Natl Acad Sci USA 98: 1142–1147. 52. Kobata A. (1998) A retrospective and prospective view of glycopathology. Glycoconj J 15: 323–331. 53. Vainchenker W, Vinci G, Testa U, et al. (1985) Presence of the Tn antigen on hematopoietic progenitors from patients with the Tn syndrome. J Clin Invest 75: 541–546. 54. Thurnher M, Rusconi S, Berger EG. (1993) Persistent repression of a functional allele can be responsible for galactosyltransferase deficiency in Tn syndrome. J Clin Invest 91: 2103–2110. 55. Berger EG. (1999) Tn-syndrome. Biochim Biophys Acta 1455: 255–268. 56. Julian BA, Novak J. (2004) IgA nephropathy: an update. Curr Opin Nephrol Hypertens 13: 171–179. 57. Kokubo T, Hiki Y, Iwase H, et al. (1999) Exposed peptide core of IgA1 hinge region in IgA nephropathy. Nephrol Dial Transplant 14: 81–85. 58. Kokubo T, Hashizume K, Iwase H, et al. (2000) Humoral immunity against the proline-rich peptide epitope of the IgA1 hinge region in IgA nephropathy. Nephrol Dial Transplant 15: 28–33. 59. Suzuki H, Moldoveanu Z, Hall S, et al. (2007) IgA nephropathy: characterization of IgG antibodies specific for galactose-deficient IgA1. Contrib Nephrol 157: 129–133. 60. Mestecky J, Suzuki H, Yanagihara T, et al. (2007) IgA nephropathy: current views of immune complex formation. Contrib Nephrol 157: 56–63. 61. Mestecky J, Tomana M, Moldoveanu Z, et al. (2008) The role of aberrant glycosylation of IgA1 molecules in the pathogenesis of IgA nephropathy. Kidney Blood Pres Res 31: 29–37. 62. Novak J, Moldoveanu Z, Renfrow MB, et al. (2007) IgA nephropathy and Henoch-Schönlein purpura nephritis: aberrant glycosylation of IgA1, formation of IgA1-containing immune complexes, and activation of mesangial cells. Contrib Nephrol 157: 134–138. 63. Haakenstad AO, Mannik M. (1977) The biology of immune complexes. In: Autoimmunity. Genetic, Immunologic, Virologic, and Clinical Aspects (ed.) Talal N. Academic Press, New York, pp. 277–360. 64. Moldoveanu Z, Epps JM, Thorpe SR, et al. (1988) The sites of catabolism of murine monomeric IgA. J Immunol 141: 208–213.

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65. Moldoveanu Z, Moro I, Radl J, et al. (1990) Site of catabolism of autologous and heterologous IgA in non-human primates. Scand J Immunol 32: 577–583. 66. Stockert RJ, Kressner MS, Collins JD, et al. (1982) IgA interactions with the asialoglycoprotein receptor. Proc Natl Acad Sci USA 79: 6229–6231. 67. Stockert RJ, Haimes HB, Morell AG, et al. (1980) Endocytosis of asialoglycoprotein-enzyme conjugates by hepatocytes. Lab Invest 43: 556–563. 68. Baenziger JU, Fiete D. (1980) Galactose and N-acetylgalactosaminespecific endocytosis of glycopeptides by isolated rat hepatocytes. Cell 22: 611–620. 69. Baenziger JU, Maynard Y. (1980) Human hepatic lectin. Physicochemical properties and specificity. J Biol Chem 255: 4607–4613. 70. Phillips JO, Russell MW, Brown TA, et al. (1984) Selective hepatobiliary transport of human polymeric IgA in mice. Mol Immunol 21: 907–914. 71. Phillips JO, Stohrer R, Russell MW, et al. (1986) Analysis of the hepatobiliary transport of IgA with monoclonal anti-idiotype and anti-allotype antibodies. Mol Immunol 23: 339–346. 72. Mestecky J, Hashim OH, Tomana M. (1995) Alterations in the IgA carbohydrate chains influence the cellular distribution of IgA1. Contrib Nephrol 111: 66–72. 73. Phillips JO, Komiyama K, Epps JM, et al. (1988) Role of hepatocytes in the uptake of IgA and IgA-containing immune complexes in mice. Mol Immunol 25: 873–879. 74. Couser WG. (1999) Glomerulonephritis. Lancet 353: 1509–1515. 75. Coppo R, Amore A. (2004) Aberrant glycosylation in IgA nephropathy (IgAN). Kidney Int 65: 1544–1547. 76. Novak J, Julian BA, Tomana M, et al. (2008) IgA glycosylation and IgA immune complexes in the pathogenesis of IgA nephropathy. Semin Nephrol 28: 78–87. 77. Pouria S, Barratt J. (2008) Secondary IgA nephropathy. Semin Nephrol 28: 27–37. 78. McGuire BM, Julian BA, Bynon JS, Jr, et al. (2006) Glomerulonephritis in patients with hepatitis C cirrhosis undergoing liver transplantation. Ann Intern Med 144: 735–741. 79. Mestecky J, Russell MW. (1986) IgA subclasses. Monogr Allergy 19: 277–301. 80. van de Wiel A, Schuurman HJ, Kater L. (1989) Alcohol and the IgA immune system. Protides Biol Fluids 36: 247–253. 81. Julian BA, Wittke S, Novak J, et al. (2007) Electrophoretic methods for analysis of urinary polypeptides in IgA-associated renal diseases. Electrophoresis 28: 4469–4483. 82. Julian BA, Wittke S, Novak J, et al. (2007) Urinary polypeptide biomarkers of IgA-associated renal diseases. J Am Soc Nephrol 18: 782A.

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83. Amore A, Cirina P, Conti G, et al. (2001) Glycosylation of circulating IgA in patients with IgA nephropathy modulates proliferation and apoptosis of mesangial cells. J Am Soc Nephrol 12: 1862–1871. 84. Chen A, Chen WP, Sheu LF, et al. (1994) Pathogenesis of IgA nephropathy: in vitro activation of human mesangial cells by IgA immune complex leads to cytokine secretion. J Pathol 173: 119–126. 85. Leung JCK, Tsang AWL, Chan DTM, et al. (2000) Absence of CD89, polymeric immunoglobulin receptor, and asialoglycoprotein receptor on human mesangial cells. J Am Soc Nephrol 11: 241–249. 86. Leung JC, Tsang AW, Chan LY, et al. (2002) Size-dependent binding of IgA to HepG2, U937, and human mesangial cells. J Lab Clin Med 140: 398–406. 87. Leung JC, Tang SC, Chan LY, et al. (2003) Polymeric IgA increases the synthesis of macrophage migration inhibitory factor by human mesangial cells in IgA nephropathy. Nephrol Dial Transplant 18: 36–45. 88. Gomez-Guerrero C, Gonzalez E, Hernando P, et al. (1993) Interaction of mesangial cells with IgA and IgG immune complexes: a possible mechanism of glomerular injury in IgA nephropathy. Contrib Nephrol 104: 127–137. 89. Gomez-Guerrero C, Lopez-Armada MJ, Gonzalez E, et al. (1994) Soluble IgA and IgG aggregates are catabolized by cultured rat mesangial cells and induce production of TNF-α and IL-6, and proliferation. J Immunol 153: 5247–5255. 90. Moura IC, Arcos-Fajardo M, Sadaka C, et al. (2004) Glycosylation and size of IgA1 are essential for interaction with mesangial transferrin receptor in IgA nephropathy. J Am Soc Nephrol 15: 622–634. 91. Yancey KB, Lawley TJ (eds.) (2001) Circulating immune complexes and serum sickness. In: Clinical Immunology, 2nd ed. (eds.) Rich RR, Fleisher TA, Shearer WT, Kotzin BL, Schroeder HW. Mosby, London, Vol. 59, pp. 51–100.

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Chapter 14

B and T Lymphocytes Abdalla Rifai and Ann Chen

Introduction A continuum of mucosal and systemic immune responses plays a central role in the pathogenesis of IgA nephropathy (IgAN). Several excellent reviews described numerous immunological abnormalities implicating B and T lymphocytes throughout the clinical course of the disease.1–3 However, we consider immunopathogenesis of IgAN to occur in three phases. In the early primary phase, B cells produce polymeric IgA (pIgA) in response to variety of antigens that initiates glomerular IgA immune deposit formation. In the secondary phase, continuous activation of the mesangial cells, the complement system and the innate immune system by persistent glomerular pIgA immune deposits attract macrophages that produce inflammatory mediators leading to glomerulosclerosis. In the tertiary phase, interstitial infiltration by T cells cause tubular injury and sets in motion irreversible interstitial fibrosis leading to end stage renal failure in 20%–40% of the affected patients. Hence a dynamic constellation of B and T lymphocytes and their soluble mediators participate at all levels in disease pathogenesis: initiation, perpetuation, amplification, regulation, disease relapse, and tissue and organ destruction. They also pose as prime targets for novel interventions. Intense laboratory and clinical investigation over the past decade has brought important insights into lymphocytes cellular subsets, signaling, mediators and regulatory pathways.4–7 This review will highlight the role of B and T lymphocytes and their key immune mechanisms which are clinically implicated in the immunopathogenesis of IgAN.

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Mechanisms of IgA Induction and Production by B Lymphocytes Approximately half of the patients with IgAN have elevated levels of plasma IgA.8 This prompted a number of in vitro clinical investigations into the various aspects of B cell IgA production in these patients. Discordant results have been reported with some studies9–11 finding increased in vitro IgA production by unstimulated peripheral blood mononuclear cells (PBMC), others12 observing an increase only when PBMC were stimulated with pokeweed mitogen (PWM), while some found no abnormality of in vitro immunoglobulin (Ig) synthesis at all.9–14 In a sequential study of IgAN patients in remission and in relapse, the presented results showed no significant differences in PBMC IgA production (PWM-stimulated or unstimulated) between IgAN remission and relapse and controls.15 Although informative, these studies did not account for the critical role of the dendritic cells and the tissue microenvironment on the B cell response. In general the type and amount of antibodies produced by B cells vary according to the nature of the antigen, involvement of T cells, tissue microenvironment and prior history of antigen exposure.16 In the following sections we focus on the updated molecular and cellular mechanisms of IgA induction and production and their clinical relevance to IgAN.

IgA Induction: Class Switching Overview At the core of the mucosal and systemic IgA immune responses is the induction process whereby B cells acquire the expression of IgA. In the antigen-independent phase, B-cell precursors in the bone marrow generate antigen recognition diversity by somatic recombination through selection of one variable (V), diversity (D) and joining (J) gene segments on the immunoglobulin heavy chain (IgH) locus, and rearrangement of these into an “in-frame” VH-D-JH segment. This is followed by generation of primary RNA transcript with the VH-D-JH exon spliced with the closest constant region exon Cµ, that codes IgM heavy chain. A productive assembly of VH-D-JH and VL-JL exons of the light chain locus allows the expression as cell surface IgM by the developing B cells. Differentiated B cells emerge from the bone marrow and migrate to the Peyer’s patches in the mucosa and germinal centers in secondary

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lymphoid organs, where they initiate the antigen-dependent phase of B-cell development. There the antigen-activated B cells receive helper T cell (Th) signals to undergo two additional genetic alterations, somatic hypermutation (SHM) and class switching recombination (CSR), to diversify their antibody repertoire. These two processes require the expression of DNA-editing enzyme known as activation induced cytidine deaminase (AID). SHM introduces point mutations at high rates into VH-D-JH and VL-JL exons whereby high-affinity immunoglobulin variants are selected by the antigen. On the other hand, CSR substitutes the IgH Cµ with Cα which brings the constant regions that encode the exons for the IgA Cα locus close to the VH-D-JH segments that encode the variable region.17 In humans there are two α chain loci giving rise to IgA1 and IgA2. The molecular events underlying preferential IgA1 or IgA2 responses remain unclear. The T-cell-dependent or T-cellindependent nature of the antigen plays an important role in the IgA class switching. Relevance to IgAN. The molecular elements of Sµ and Sα switch regions of the IgH locus, and transcription of Iα1 region are essential in class switching to IgA.18 Their role in the pathophysiology of IgAN is controversial. Increase in frequency of the specific Sα1 allelic forms have been found to be associated with a more severe evolution of IgAN in two studies, but not in a third study.19–21 Expression analysis of Iα1 germline transcripts in PBMC of IgAN patients reported to be absent by Baskin et al.,22 whereas Yano et al.23 reported their increase and their promoter frequently carried specific mutations. It is important to point out the limitations of these studies. First they were reported prior to discovering the critical role of AID in SHM and CSR.24 Second, these studies were performed on PBMC rather than the lymphoid tissue germinal centers, site of SHM and CSR.

IgA Induction and Diversification by Protein Antigens T-cell-dependent IgA class switching. Protein antigens activation of CD4+ Th cells is dependent on their uptake by dendritic cells (DCs) and their peptides presentation to T cell receptor (TCR) on CD4+ Th simultaneously with B7 costimulatory signal. Activated CD4+ Th cells express surface molecule CD40 ligand (CD40L) that engages its cognate

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receptor, CD40, on the B cells inducing their proliferation and early differentiation. The CD40L binding to CD40 lead to the activation and nuclear translocation of transcription factors, including NF-κB that is crucial to the expression of the gene encoding AID. Activated CD4+ Th cells also secrete TGF-β1 that acts in concert with CD40L to stimulate B cell proliferation and IgA CSR. CD40L can also induce IgA class switching in combination with cytokines other than TGF-β1, including interleukin-2 (IL-2), IL-4, IL-5, IL-6, and IL-10. Recent experimental study also showed inducible-nitric-oxide-synthase-deficient (iNOS) regulates the T-cell-dependent IgA CSR through expression of TGF-βRII on B cells.25 Relevance to IgAN. A clinical study by Lai et al.26 demonstrated an increased TGF-β expression in isolated and mitogen-stimulated CD4+ T cells from IgAN patients with elevated plasma IgA. The enhanced level of TGF-β expression correlated with the extent of glomerular injury in these patients.

IgA Induction by Polysaccharide Antigens Bacterial cell wall polysaccharides are T-cell-independent polyvalent antigens that initiate IgA class switching first by cross-linking the B cell receptor complex (BCR) on B cells. DCs also sample T-cellindependent antigens from the environment and present to B cells. In gut associated lymphoid tissues (GALT) DC-derived retinoic acid (RA) alone confers gut tropism on B cells. However, RA potently synergizes with GALT-DC-derived interleukin-6 (IL-6) or IL-5 to provide the milieu for B cell IgA class switching and secretion.27 In the absence of T cells, DCs and macrophages can also produce class-switch-inducing factors related to CD40L, including B-cell activating factor (BAFF; also known as BLyS) and a proliferation-inducing ligand (APRIL). Both factors induce synthesis of AID in antigen-activated B cells.28 This is further enhanced by the innate immune response of Toll-like receptors (TLRs) activation on B cells. Relevance to IgAN. BAFF transgenic mice develop a hyper-IgA syndrome in the intestinal lamina propria concomitant with IgA deposition in the kidneys similar to ddY IgAN mouse model.29 In IgAN patients, tonsillar mononuclear cells stimulated with synthetic oligodeoxynucleotides,

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a surrogate of microbial DNA and TLR-9 activator, responded with enhanced synthesis BAFF and interferon-gamma (IFN-γ) followed by hyper-IgA production.30

IgA Induction and Production by CD5+ B Cell Subset In contrast to the relatively slow process of T-cell-dependent IgA class switching described above, specialized B-cell subsets, such as B-1 (CD5+) cells, can rapidly produce IgM as well as class-switched IgA in a T-cell-independent manner. At mucosal sites B-1 cells contribute to the generation of T-independent IgA responses in experimental animals.31 Without undergoing SHM, B-1 cells express unmutated IgA antibodies that recognize multiple antigen specificities with low affinity. Relevance to IgAN. Magyarlaki et al.32 reported IgAN patients B lymphocytes expressed significantly higher positivity with CD5+ than controls. Independent of T cell, the serum derived from IgAN patients stimulated the immunoglobulin production of IgAN CD5+ B cells in vitro. More recently, Kodama et al.33 reported an increase of B-1 cells in the tonsils germinal centers of IgAN patients that are resistant to Fasmediated apoptosis. These B-1 cells survive in the GC and serve as a source of IgA1. Of interest, in IgAN patients, the raised IgA antitetanus toxoid (but not IgG) produced in response to systemic antigen challenge is of low affinity compared to controls.34 Importantly the same study showed systemic immunization induced in IgAN patients, but not in controls, a hyper IgA response in both the systemic and mucosal systems suggestive of an abnormality overlapping the mucosal and systemic immunity. The low affinity probably renders the pIgA capable of forming intermediate-sized immune complexes that escape the rapid elimination by liver and result in enhanced glomerular IgA deposition.35

B Cell Production of Aberrant pIgA1 — An Autoantigen Numerous reports and excellent reviews36–41 examined the association between the development of IgAN and the production of pIgA1 with aberrant glycosylation in the hinge region. Although it is controversial as to whether the defect is intrinsic or acquired in a later stage of the B cell development, it is well recognized the aberrant glycosylation is

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limited to a small fraction of the total IgA1 and as a corollary originate from a relatively small B cell subset.42,43 Overall, in the hinge region of IgA1 up to six serine (Ser) or threonine (Thr) residues are sites of O-linked glycans structures that may consist of either: (i) Ser/Thr-α1, 3-GalNAc (N-acetylgalactosamine) — a basic unit termed the “Tn antigen”; (ii) Ser/Thr-α1,3-GalNAc-β1,3-Gal (galactose) — termed “T antigen” or the “Core 1 structure”; (iii) Ser/Thr-α1,3-GalNAc-α2, 6-NeuNAc (N-acetylneuraminic acid) — termed “Sialyl-Tn”; (iv) Ser/ Thr-α1,3-GalNAc-β1,3-Gal-α2,3-NeuNAc — termed “Monosialy-T antigen”; or (v) Ser/Thr-[α1,3-GalNAc-α2,6-NeuNAc]/[β1,3-Gal-α2,3NeuNAc] — termed “Disialyl-T antigen”. To elucidate the molecular mechanisms of the aberrant glycosylation of IgA1, Suzuki et al.44 recently established EBV-immortalized IgA1 secreting cells (IgA1SC) from PBMC of IgAN patients. The majority (70%) of the IgA1SC produced galactosedeficient polymeric IgA1 with the O-linked glycan terminal being GalNAc (Tn antigen) or GalNAc-α2,6-NeuNAc (Sialyl Tn antigen), respectively, due to decreased Core 1,3-beta-galactosyltransferase (C1GALT) and increased GalNAc-specific α2,6-sialyltransferase activity. This suggests, in IgAN a subset of IgA1-producing B cells synthesize the aberrant IgA1 with a hinge enriched with Tn and Sialyl-Tn. The polymeric nature of the aberrant IgA1 implicates the tonsils as a potential source, where 90% of the IgA+ immunocytes produce pIgA1. Also a recent report demonstrated similarity of aberrant pIgA1 glycoforms in tonsils and serum IgA1.45 Furthermore, the tonsils are also an organized lymphoid structure that participates as an effector organ of systemic-type as well as mucosal-type of adaptive immunity.46 Importantly such a B cell subset may serve as a unique reservoir of the pIgA1 hingeTn enriched epitopes acting as an autoantigen synthesized and released into the circulation in response to the B cell stimulation (Lai KN, personal communication). In the circulation (as schematized in Figure 14.1), the multivalent-Tn on pIgA1 may form high avidity complex with ubiquitous natural antibody leading to glomerular immune deposition.47 On the other hand, the α2,6-linked sialic acid of the Sialyl-Tn enriched pIgA1 may function as a ligand that is recognized by CD22, a Siglec (sialic-acid-binding immunoglobulin-like lectin) that exert profound effect on B cell signaling.48,49 Of interest, it has been observed that in the absence of BCR ligation by an antigen, CD22 crosslinking with a sialoside ligand results in c-Jun N-terminal kinase (JNK) signaling and proliferation of human tonsillar B cells.50 Based on these observations

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and the findings of sialic acid-enriched pIgA1 in IgAN by Leung et al.51,52 it can be postulated that in IgAN, Sialyl-Tn on pIgA1 upon cis or trans interaction with CD22 stimulates the B cells to proliferate and release more aberrant pIgA1 that perpetuates a vicious cycle of glomerular immune complex deposition and B cells proliferation.

T Cell-Mediated Mechanisms in IgAN Ample early clinical and later experimental published reports implicate T cells in the immunopathogenesis of IgAN.3,53–56 However, these published reports vary in the identity and effector function of the T cells. It is well established that T lymphocytes consist of subsets with distinct phenotypic and function characteristics. The two major T cell subsets are CD4+ Th and CD8+ cytotoxic T lymphocytes (CTL), which express the αβ receptor. Upon antigenic stimulation, naive CD4+ T cells activate, expand and differentiate into different effector subsets termed Th1, Th2 and Th17 and are characterized by the production of distinct cytokines and effector functions. Th1 cells produce interferon-γ (IFNγ) that activates macrophage-mediated immunity that stimulate inflammation and tissue repair. Th2 cells secrete IL-4 and IL-5, which are essential for the generation of appropriate classes of antibodies via promoting B cell CSR. Similar to Th1 and Th2 cells Th17 cells require specific cytokines and transcription factors for their differentiation. Th17 cells are highly pro-inflammatory and may play an important role in host defense as well in mediating damage in autoimmune diseases. CD4+ T cells can also develop into regulatory T cells (Tregs) that have an anti-inflammatory role and maintain tolerance to self components. CD8+ CTLs kill cells that present peptides in association with class I MHC molecules. CTL-mediated killing occurs through release of granzymes and perforin that initiate apoptosis. CD8+ CTLs also express Fas ligand that engages the cognate Fas receptor on target cells triggering apoptosis. Another population of T cells called γδ T cells expresses structurally distinct receptor and display an innate immune response.

T Cell Regulation of IgA Production in IgAN Role of αβ T cells. Only few studies evaluated the CD4+ Th1 and Th2 profiles in IgAN patients. Two separate groups reported similar findings of an increase in both Th1 and Th2 upon in vitro stimulation of

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PBMC from IgAN patients.57,58 In addition, simultaneous analysis of the cytokine phenotype in renal tissue revealed inflammatory profile similar to non-IgA mesangial glomerulonephritis.58 In contrast, one study reported predominance of Th1/Th2 in renal tissue of IgAN patients.59 However, controlled analysis with non-IgA nephropathy was not performed. At the single cell level analysis by flow cytometry, predominance of Th2 (IL-4, IL-10, IL-13) in PBMC of IgAN patients has been reported.60 Other cytokine expression studies of PBMC reported increased levels of TGF-β and IL-10, two cytokines important in IgA class-switch.58,61,62 The potential role of Th17 and CD4+CD25+ Treg in IgAN has not been reported. Role of γ δ T cells. The γδ T cells constitute only a small proportion (1%–5%) of the lymphocytes that circulate in the blood and peripheral organs. Human γδ T cells express one of six Vγ gene segments (Vγ1, Vγ3, Vγ4, Vγ5, Vγ8, and Vγ9) and three functional Vδ genes (Vδ1, Vδ2, and Vδ3). The two major γδ T-cell subsets, defined by TCRs containing Vδ1 or Vδ2 chains, differ in their anatomic localization; Vδ1 T cells predominate within mucosal epithelia and skin whereas Vδ2 T cells are most numerous in peripheral blood. The association of γδ T cells with enhanced IgA production in IgAN has been reported by Fortune et al.63 who examined T and B cell responses following immunization with tetanus toxoid in IgAN patients. They showed dramatic increase in circulating γδ T cells and consequent decrease in CD3+ αβ T cells. Using synthetic peptides of mycobacterial heat shock protein as antigen, Warr et al.64 reported significantly higher γδ T cells proliferation in IgAN than controls. It should be noted, γδ T cells do not require antigen processing and MHC presentation of peptide epitopes. Toyabe et al.65 investigated the role of γδ T cells in the regulation of IgA production by B cells in IgAN patients. Purified γδ T cells from IgAN patients induced surface IgA expression on naïve sIgD+ B cells more effectively than did αβ T cells. Moreover, stimulated γδ T cells from IgAN patients produced a larger amount of TGF-β1, which is the premiere cytokine that induces IgA class switching in B cells.

T Cells as Pathogenic Mediators in IgAN Role of CD4+ Th. Beyond its effect on IgA class switch and production, Th polarization also impacts on other immunoglobulin isotypes switching

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and synthesis, in particular IgG subclasses. Glomerular deposits of IgG co-localized with IgA immune complexes (IgA-IC) are a well-recognized feature of IgA nephropathy. Based on experimental observations66 we recently described a simplified model postulating the linkage between Th1/Th2 polarization and the activation status of glomerular infiltrating macrophages as determinants of IgA glomerulopathy.67 This model may also apply to clinical IgAN. The IgG subclass pathogenic activities can now be explained through selective engagement of their isotypeconstant Fc region with specific cellular receptors.68 The major classes of human Fc-gamma receptors (FcγRs) have been identified with different affinities that vary from high (FcγRI) to low (FcγRIIB and FcγRIIA), with the FcγRIIIA, having selective and intermediate affinity for human IgG1 and IgG3.68 The majority of these receptors (FcγRI, FcγRIIIA, FcγRIIIB) are classified as activating, because they transmit intracellular signaling via immunoreceptor tyrosine-based activation motif (ITAM), whereas FcγRIIB is inhibitory, as it transmits signal via immunoreceptor tyrosine-based inhibition motif (ITIM). Hence a human immune complex (IC) composite of IgA-IC–IgG1 isotype interaction with the paired expression of activating and inhibitory receptors (FcγRIIIA/ FcγRIIB) on macrophages causes a high activation-to-inhibition ratio, triggering generation of mediators that produce injury. In contrast, IC composite of IgA-IC–IgG4 isotype, with higher affinity for the inhibitory FcγRIIB and a lack of interaction with the activating FcγRI and FcγRIIIA receptors, produces a low activation-to-inhibition ratio, keeping the macrophage quiescent with minimal or no injury. Extrarenal pro-inflammatory cytokines such as TNF-α and IFN-γ, a product of Th1, potentiate IgA-IC–IgG1 deposits by up-regulating activating FcγRs and blocking expression of the inhibitory FcγRIIB. Conversely, Th2 cytokines such as IL-4, IL-10, or TGF-β downregulate activating FcγR expression and increase the level of FcγRIIB on macrophages, thereby dampening further the pathogenic potential of IgA-IC–IgG4 complexes. Role of CD8+ T cells. Tubular and interstitial T cell infiltrates are invariable clinical feature associated with tubulointerstitial injury and progression of IgAN.69 The molecular targets of effector CD4+ and CD8+ on tubulointerstitial cells are unknown. Despite vast amount of histopathologic evidence demonstrating that the presence of tubular atrophy is predictive of poor outcome of renal function, the primary role

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of tubular injury has not been explored adequately in IgAN. Recently, van Es et al.70 using immunophenotyping and immunolocalization examined renal biopsies from IgAN progressors and non-progressors. They identified NKG7+/CD8+ intraepithelial lymphocytes (IEL) within renal tubules of IgAN patients as an early marker predicting progression towards renal failure. The NKG7, a transmembrane protein of cytotoxic granules, is highly expressed in activated CD8+ CTL and cytotoxic clones of γδ T cells. Of interest, they also noted paucity of macrophages and CD4+ T lymphocytes infiltrating tubules in the early stage of IgAN progression. This contrasted with the tubulitis pattern of renal allograft which is full of macrophages and mostly of CD4+ and CD8+ T cells that contain cytotoxic granules perforin and granzymes A/B.71 Based on these observations a model postulated dual complementary, adaptive and innate, mechanisms of CD8+ T cell-mediated tubular injury in IgAN.72 The first mechanism postulated the TCR αβ on NKG7+/CD8+ IELs mediate the cytotoxic response to either cross-presented exogenous antigen or an endogenous antigen produced by the tubules. It also suggested the anti-apoptotic action of TGF-β and IL-15 in IgAN, along with the expression of CD103 that binds to E-cadherin on tubular cells, allowing NKG7+/CD8+ IEL to persist and cause disruption of the tubular structure and function. The second mechanism proposed an innate immune response of the NKG7+/CD8+ IELs as contributor to tubulitis whereby the CD8+ IELs express NK lineage activating receptor, NKG2D. Under stress conditions, epithelial cells express MHC class I chain related proteins (MICA or MICB) that serve as ligands of NKG2D hence targeting the cells for cytolysis and elimination. It is relevant to indicate CD8+ IELs dominate the gut where they play pivotal role in the pathogenesis of IgA-related Celiac disease. Overlapping role of T cell subclasses. To determine the relationship between T cell and disease progression, a series of molecular studies examined the TCR repertoire in renal biopsies of IgAN patients.73–75 The αβ T cells were present in stable and progressive disease state with the T cells infiltrating the renal interstitium expressing polyclonal response suggestive of T cell recruitment due to local inflammation process. However, in most patients who progressed to renal failure, the TCR variable Vβ8 gene usage in renal tissue was significantly higher in frequency than the corresponding peripheral blood T cells. By comparison,

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analysis of γδ T cells demonstrated a significant increase in renal tissue associated with disease progression. The renal γδ T cell repertoire also revealed preferential usage of the Vδ1 gene segment suggestive of their mucosal origin. Moreover, sequencing the V-D-J junctional region of TCR indicated Vδ1T cells expanded in response to antigens or ligands. These interesting studies in conjunction with the functional studies described above provide a circumstantial evidence linking the T cellmediated response to the mucosal immune system in IgAN.63–65

Immunopathogenesis of IgA Nephropathy: Clues and a View of B and T Cells Based on the current knowledge of immunologic mechanisms underlying IgA production and the relevant clinical findings in IgAN, a framework of the pathways linking basic and clinical features is presented in Figure 14.1. In this scheme, the critical mechanisms described above are represented. Continuous formation of glomerular pIgA1-immue deposits requires persistent source of pIgA1 and antigens. Continuous sampling of antigens by the M (microfold) cells in the mucosa, as represented in the GALT and tonsils, and the reverse transcytosis of secretory IgA serve as a conduit for antigen access to systemic circulation. Conversely, memory B cells from the GALT that gain access to systemic circulation and secondary lymphoid organs where they differentiate to short-lived IgA plasma cells. In contrast, the recently identified long-lived plasma cells from the tonsils homing to and lodging in the bone marrow may serve as a major reservoir of pIgA1.76 Lastly, aberrant glycosylation of pIgA1 transforms it into a multivalent Tn autoantigen that form complexes with natural antibodies in the circulation leading to immune deposit formation. In addition Sialyl-Tn on aberrantly glycosylated pIgA1 will interact with CD22, a Siglec that modulate B cell signaling and perpetuate aberrant pIgA1 production via long lived plasma cells. This may explain the frequent phenomenon of IgAN recurrence after transplantation. Glomerular macrophage activation may occur via its sialoadhesin (Siglec 1) binding to Sialyl-Tn ligand on pIgA1-IC deposits propagates glomerulonephritis with cytokine spillage and cross-talk to tubulointerstitial compartment that engender the T cell-mediated injury and dictates the final course of progression to end stage renal failure.69

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Figure 14.1 A scheme of postulated mechanisms connecting IgA induction in B cells with T cells in development and progression of IgA nephropathy. From the bone marrow emerge mature B cells expressing surface IgM and chemokine receptors (CXCR4, CXCR5, CCR6, CCR7) that guide their homing to the gut associated lymphoid tissue (GALT) and nasal-associated lymphoid tissue (NALT). In the Peyer’s Patch (PP), T-cell-dependent class-witching recombination (CSR) and somatic hypermutation (SHM) occur in B-2 cells presenting processed antigen to T cell. The antigen presenting

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Figure 14.1 (Continued ) dendritic cell activates T cell via the T-cell receptor (TCR) and co-stimulatory signal relayed by CD28. Expression of CD40L on activated T cells and binding to cognate receptor CD40 on B cells stimulate activation-induced cytidine deaminase (AID) that mediates CSR and SHM. Activated T cells also produce TGF-β that induces AID. Retinoic acid (RA), B-cell activating factor (BAFF), and a proliferation-inducing ligand (APRIL) produced by dendritic cells lead to T-cellindependent CSR. T helper (Th) cells produce IL-5, IL-6 and IL-10 that enhance IgA production. Memory IgA-producing B cells emerging from PP get further imprinting in the mesenteric lymph nodes before homing into the lamina propria where they differentiate into plasma cells. Memory cells may differentiate further in the mucosa into immunocytes producing aberrantly glycosylated IgA1. In the NALT, B-2 cells undergo efficient CSR and SHM in the organized germinal centers under the influence of T cells in the parafollicular areas. T-cell-independent IgA class switching B-1 cells without SMH produce low affinity pIgA1 the dominant subclass in the tonsils. Aberrantly glycosylated pIgA1 producing immunocytes may develop in the tonsils after CSR and differentiate into plasmablasts expressing bone marrow-homing chemokine receptors (CXCR4, CCR7 and CCR10), α4β1 integrin, and L-selectin. The γδ T cells appear to participate in IgA induction in the NALT. B-2 and B-1 may differentiate into long-lived pIgA1 plasma cells that disperse into the systemic circulation and home to the bone marrow. These cells express CXCR4, and CCR10 that bind respectively to CXCL12 and CCL28 produced in the bone marrow. pIgA1 upon encountering antigens, represented as spheres, form immune complexes that get deposited in the glomeruli. Aberrantly glycosylated pIgA1 may form self aggregates (pIgA1-agg), or itself become an autoantigen forming immune complexes (pIgA1IgG) with natural antibodies. Thus glomerular immune deposits are mosaic of complexes composite of pIgA1. Cytokines produced by Th1 and Th2, represented in tabular form, coupled with the engagement of Fc receptors on glomerular macrophages by different human IgG isotypes co-deposits may play a critical role in glomerular injury. Tubulointerstitial stress ensues glomerular injury that usher in CD8+ cytotoxic cells that cause tubulitis by adaptive, TCR-αβ-mediated, and innate responses by NKG2D recognition of MHC-related protein A or B expressed on stressed tubules. The sentinel γδ T cells while maintaining epithelial integrity may contribute to killing of stressed tubular cells. They may also release TGF-β that enhances extracellular matrix accumulation and fibrosis.

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33. Kodama S, Suzuki M, Arita M, et al. (2001) Increase in tonsillar germinal centre B-1 cell numbers in IgA nephropathy (IgAN) patients and reduced susceptibility to Fas-mediated apoptosis. Clin Exp Immunol 123: 301–308. 34. Layward L, Allen AC, Hattersley JM, et al. (1994) Low antibody affinity restricted to the IgA isotype in IgA nephropathy. Clin Exp Immunol 95: 35–41. 35. Rifai A. (1988) Characteristics of nephritogenic IgA immune complexes. Am J Kidney Dis 12: 402–405. 36. Mestecky J, Tomana M, Crowley-Nowick PA, et al. (1993) Defective galactosylation and clearance of IgA1 molecules as a possible etiopathogenic factor in IgA nephropathy. Contrib Nephrol 104: 172–182. 37. Allen AC. (1995) Abnormal glycosylation of IgA: is it related to the pathogenesis of IgA nephropathy? Nephrol Dial Transplant 10: 1121–1124. 38. Hiki Y, Horii A, Iwase H, et al. (1995) O-linked oligosaccharide on IgA1 hinge region in IgA nephropathy. Fundamental study for precise structure and possible role. Contrib Nephrol 111: 73–84. 39. Hiki Y, Odani H, Takahashi M, et al. (2001) Mass spectrometry proves under-O-glycosylation of glomerular IgA1 in IgA nephropathy. Kidney Int 59: 1077–1085. 40. Barratt J, Smith AC, Molyneux K, et al. (2007) Immunopathogenesis of IgAN. Semin Immunopathol 29: 427–443. 41. Novak J, Julian BA, Tomana M, et al. (2008) IgA glycosylation and IgA immune complexes in the pathogenesis of IgA nephropathy. Semin Nephrol 28: 78–87. 42. Smith AC, Molyneux K, Feehally J, et al. (2006) O-glycosylation of serum IgA1 antibodies against mucosal and systemic antigens in IgA nephropathy. J Am Soc Nephrol 17: 3520–3528. 43. Buck KS, Smith AC, Molyneux K, et al. (2008) B-cell O-galactosyltransferase activity, and expression of O-glycosylation genes in bone marrow in IgA nephropathy. Kidney Int 73: 1128–1136. 44. Suzuki H, Moldoveanu Z, Hall S, et al. (2007) IgA1-secreting cell lines from patients with IgA nephropathy produce aberrantly glycosylated IgA1. J Clin Invest 118: 629–639. 45. Iwanami N, Iwase H, Takahashi N, et al. (2008) Similarities between N-glycan glycoform of tonsillar IgA1 and that of aberrant IgA1 abundant in IgA nephropathy patient serum. J Nephrol 21: 118–126. 46. Brandtzaeg P, Johansen FE. (2005) Mucosal B cells: phenotypic characteristics, transcriptional regulation, and homing properties. Immunol Rev 206: 32–63. 47. Mestecky J, Suzuki H, Yanagihara T, et al. (2007) IgA nephropathy: current views of immune complex formation. Contrib Nephrol 157: 56–63.

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48. Walker JA, Smith KG. (2008) CD22: an inhibitory enigma. Immunology 123: 314–325. 49. Crocker PR, Paulson JC, Varki A. (2007) Siglecs and their roles in the immune system. Nat Rev Immunol 7: 255–266. 50. Sato S, Tuscano JM, Inaoki M, et al. (1998) CD22 negatively and positively regulates signal transduction through the B lymphocyte antigen receptor. Semin Immunol 10: 287–297. 51. Leung JC, Poon PY, Lai KN. (1999) Increased sialylation of polymeric immunoglobulin A1: mechanism of selective glomerular deposition in immunoglobulin A nephropathy? J Lab Clin Med 133: 152–160. 52. Leung JC, Tang SC, Chan DT, et al. (2002) Increased sialylation of polymeric lambda-IgA1 in patients with IgA nephropathy. J Clin Lab Anal 16: 11–19. 53. Nomoto Y, Sakai H, Arimori S. (1979) Increase of IgA-bearing lymphocytes in peripheral blood from patients with IgA nephropathy. Am J Clin Pathol 71: 158–160. 54. Sakai H, Nomoto Y, Arimori S. (1979) Decrease of IgA-specific suppressor T cell activity in patients with IgA nephropathy. Clin Exp Immunol 38: 243–248. 55. Sakai H, Endoh M, Tomino Y, et al. (1982) Increase of IgA specific helper T alpha cells in patients with IgA nephropathy. Clin Exp Immunol 50: 77–82. 56. Chao TK, Rifai A, Ka SM, et al. (2006) The endogenous immune response modulates the course of IgA-immune complex mediated nephropathy. Kidney Int 70: 283–297. 57. Lai KN, Ho RT, Lai CK, et al. (1994) Increase of both circulating Th1 and Th2 T lymphocyte subsets in IgA nephropathy. Clin Exp Immunol 96: 116–121. 58. Yano N, Endoh M, Nomoto Y, et al. (1997) Phenotypic characterization of cytokine expression in patients with IgA nephropathy. J Clin Immunol 17: 396–403. 59. Lim CS, Zheng S, Kim YS, et al. (2001) Th1/Th2 predominance and proinflammatory cytokines determine the clinicopathological severity of IgA nephropathy. Nephrol Dial Transplant 16: 269–275. 60. Ebihara I, Hirayama K, Yamamoto S, et al. (2001) Th2 predominance at the single-cell level in patients with IgA nephropathy. Nephrol Dial Transplant 16: 1783–1789. 61. de Caestecker MP, Bottomley M, Telfer BA, et al. (1993) Detection of abnormal peripheral blood mononuclear cell cytokine networks in human IgA nephropathy. Kidney Int 44: 1298–1308. 62. Fayette J, Dubois B, Vandenabeele S, et al. (1997) Human dendritic cells skew isotype switching of CD40-activated naive B cells towards IgA1 and IgA2. J Exp Med 185: 1909–1918.

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63. Fortune F, Courteau M, Williams DG, et al. (1992) T and B cell responses following immunization with tetanus toxoid in IgA nephropathy. Clin Exp Immunol 88: 62–67. 64. Warr K, Fortune F, Namie S, et al. (1997) T-cell epitopes recognized within the 65,000 MW hsp in patients with IgA nephropathy. Immunology 91: 399–405. 65. Toyabe S, Harada W, Uchiyama M. (2001) Oligoclonally expanding gammadelta T lymphocytes induce IgA switching in IgA nephropathy. Clin Exp Immunol 124: 110–117. 66. Suzuki H, Suzuki Y, Aizawa M, et al. (2007) Th1 polarization in murine IgA nephropathy directed by bone marrow-derived cells. Kidney Int 72: 319–327. 67. Rifai A. (2007) IgA nephropathy: immune mechanisms beyond IgA mesangial deposition. Kidney Int 72: 239–241. 68. Nimmerjahn F, Ravetch JV. (2007) Fc-receptors as regulators of immunity. Adv Immunol 96: 179–204. 69. Lai KN, Chan LY, Leung JC. (2005) Mechanisms of tubulointerstitial injury in IgA nephropathy. Kidney Int 94(Suppl): S110–S115. 70. van Es LA, de Heer E, Vleming LJ, et al. (2008) GMP-17-positive T-lymphocytes in renal tubules predict progression in early stages of IgA nephropathy. Kidney Int 73: 1426–1433. 71. Cornell LD, Smith RN, Colvin RB. (2008) Kidney transplantation: mechanisms of rejection and acceptance. Annu Rev Pathol 3: 189–220. 72. Rifai A, Dworkin LD. (2008) IgA nephropathy: markers of progression and clues to pathogenesis. Kidney Int 73: 1338–1340. 73. Falk MC, Ng G, Zhang GY, et al. (1995) Infiltration of the kidney by alpha beta and gamma delta T cells: effect on progression in IgA nephropathy. Kidney Int 47: 177–185. 74. Wu H, Zhang GY, Clarkson AR, et al. (1999) Conserved T-cell receptor beta chain CDR3 sequences in IgA nephropathy biopsies. Kidney Int 55: 109–119. 75. Wu H, Clarkson AR, Knight JF. (2001) Restricted gammadelta T-cell receptor repertoire in IgA nephropathy renal biopsies. Kidney Int 60: 1324–1331. 76. van Laar JM, Melchers M, Teng YK, et al. (2007) Sustained secretion of immunoglobulin by long-lived human tonsil plasma cells. Am J Pathol 171: 917–992.

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Chapter 15

IgA Receptors and Mesangial IgA Deposition Ivan C. Moura and Renato C. Monteiro

Introduction First described by Jean Berger in 1968,1 by a systematic analysis of glomerulonephritides, the presence of mesangial IgA became a major criteria for diagnosis of IgA nephropathy (IgAN) allowing many advances in its epidemiology and in its pathology.2,3 Features of the disease include mesangial cell proliferation, matrix expansion and clinical symptoms of renal injury, such as hematuria and proteinuria.4 Recurrence of IgA1 deposits after transplantation indicates that circulating, rather than kidney abnormalities are crucial to the development of IgAN.5 Abnormalities in the IgA system have been detected in patient’s serum and mesangium. They include formation of IgA1 immune complexes6 and alterations of IgA1 glycans composition.7 In addition, serum IgA levels are two- to three-fold enhanced in one half of the patients associated with increased polymeric:monomeric IgA ratio.8 The mechanisms implicated in IgA deposits formation were overlooked for many years. First considered as a passive phenomenon, IgA deposition became a central field in IgAN research. Several studies showed that stimulation of cultured mesangial cells with complexed IgA from IgAN patients elicit a plethora of cellular consequences such as cell proliferation, cell matrix synthesis but also the secretion of cytokines. Therefore, IgA1-immune complexes (IC) deposition might be in fact the turning point of the disease.

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Composition of Mesangial IgA Deposits In initial studies during the 1980s, many authors used immunofluorescence to characterize the class of IgA and other immunoglobulins or complement components that were deposited in the mesangium. Deposited IgA was mainly of the A1 subclass.9 Light chains of mesangial IgA are predominantly λ although κ chains were also detected.10,11 Recently it has been shown that secretory IgA was also present in the mesangium in a subpopulation of IgAN patients.12 The difficulty to characterize IgA deposits composition by immunohistochemistry prompted some groups to isolate mesangial IgA from renal biopsy specimens. Mesangial IgA isolated by acid elution consists mainly of macromolecular IgA.13,14 We also showed alterations in the biochemical properties of the deposited IgA. Acidic elutions from kidney samples were analyzed under non-dissociating conditions (pH 6.8) and acidic conditions (pH 3.5) by chromatography. Under neutral and acid conditions, 50% or more of the eluted IgA had a molecular weight ≥ 320 kDa. The polymeric nature of these IgA was in agreement with previous indications of their capacity to bind free secretory component. It is noteworthy that J chain detection was not very conclusive in immunohistochemistry because of its difficult accessibility for antibodies due to the intimate intertwining of J chain with the Fc α tails.11,15 By isoelectric focusing we found that eluted mesangial IgA is predominantly anionic suggesting structural abnormalities due to aberrant post-translational modifications of IgA,15 which has been confirmed by others.16 Several authors have proposed that O-glycosylation patterns of the IgA1 hinge region may be involved in the IgAN pathological process. For example, it has been proposed that increased sialylation of IgA1 could contribute to its negative charge.17 Studies using lectins and, more recently, other techniques allowing the direct determination of IgA1 structure, further confirmed this hypothesis. Lectins such as Jacalin (which binds to β1,3 glycosidic residues between galactose and GalNac residues) and Helix aspersa and Vicia villosa (which specifically recognize terminal GalNac residues) revealed that circulating and mesangial IgA1 molecules may possess enhanced amount of truncated O-glycans since they are particularly undergalactosylated.18–21 Abnormally glycosylated IgA molecules undergo self-aggregation in vitro.22 In addition, the

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abnormal IgA glycosylation generates antigenic determinants that can be recognized by naturally occurring IgG and IgA1 antibodies leading to the formation of circulating immune complexes.23 More recent studies characterizing IgA1 from renal biopsies by mass spectrometry, showed altered O-glycosylation pattern of the glomerular IgA.24–27 Some investigators found that the adhesion activity of serum IgA to ECM proteins, such as type IV collagen, fibronectin, and laminin was significantly increased in patients with IgAN.28,29 Since removal of carbohydrates from the IgA1 molecule resulted in a significant increase in adhesion to ECM proteins, underglycosylation of the IgA molecule may play a role in this process. Therefore mesangial, deposits could be both associated to mesangial cells and mesangial matrix components. In IgAN mesangial IgA deposits may be accompanied by IgG and/or IgM and C3, but the C1q component of complement is rarely found.4 It is generally accepted that IgA does not activate the classical pathway of complement. Activation of the alternative complement pathway by IgA is supported by both in vitro and in vivo observations. The complement system can also be activated by human IgA via the lectin pathway, which is mainly driven by mannan-binding lectin (MBL). Activation of the lectin pathway in the renal mesangium is supported by presence of both MBL and MBL associated serine protease (MASP-1) in mesangial areas containing IgA deposits in patient’s biopsies.30 Glomerular co-deposition of MBL with L-ficolin, MBL-associated serine proteases, and C4d was observed in 25% of patients biopsies. In addition, patients with a more severe manifestation of the disease presented with MBL and L-ficolin co-deposits.31 GalNAc and Gal-exposing glycoforms isolated from patients with IgAN showed more alternative complement pathway activation than controls. Furthermore, it was found that abnormally glycosylated IgA was able to modulate human mesangial cell functions such as integrin expression and vascular endothelial growth factor (VEGF) synthesis.32 Therefore, activation of complement in the renal mesangium by IgA may be mediated by both the alternative and lectin pathway. Since activation of both pathways is most prominent for pIgA, deposition of pIgA most likely contributes to the development of renal damage by complement and mesangial cell activation. This mesangial damage may be further enhanced by underglycosylation of deposited IgA.

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Role of IgA Receptors Expressed on Circulating Cells FcαRI (CD89) is the best characterized IgA Fc receptor. The FcαRI is expressed by monocytes/macrophages, neutrophils, eosinophils, Kupffer cells and dendritic cells.33 It can exist in multiple isoforms that are differentially expressed by monocytes, blood-derived macrophages and alveolar macrophages, but it is not expressed by mesangial cells.11 FcαRI can bind both IgA1 and IgA2 antibodies, and has a higher avidity for polymeric IgA than for monomeric IgA.34 The ligand binding chain of the receptor is a transmembrane protein, FcαRI α chain, that lacks obvious signal transduction capability. However, the FcαRI α chain can associate with a dimer of FcRγ chains that have tyrosinebased activation motifs (ITAM) in their cytoplasmic domains. Signal transduction pathways initiated by ligation of this FcαRIα−γ 2 complex engage the protein tyrosine kinases, Lyn, Syk and Btk.35,36 IgA bound to the monomeric FcαRI can be internalized and recycled to the cell surface, whereas the IgA complexes that are bound to the trimeric FcαRIα−γ 2 complex are directed to the lysosomal compartment.37 Ligand-mediated FcαRI-γ 2 aggregation can thus induce endocytosis, phagocytosis and cell activation that is reflected by the release of cytokines such as TNF-α, IL-6, IL-8 and IL-10.38 In recent studies we took advantage of the absence of FcαRI in the mouse and generated human FcαRI transgenic mice that serve as a novel animal model for the spontaneous development of IgAN.39 The human FcαRI interacts with mouse polymeric IgA to form complexes that are deposited in the renal mesangium of the FcαRI Tg mice. Whereas other animal models, such as the ddY, HIGA mice and uterogloblin knockout mice, show only some of the signs of IgAN.11 The human FcαRI transgenic mice develop mesangial IgA deposition, hematuria, mild proteinuria and macrophage infiltration around the renal glomeruli.39 The disease can be transferred to wild-type recipients by infusion of serum IgA/soluble FcαRI complexes from the Tg mice. To examine the contribution of IgA we injected SCID-FcαRI Tg mice with IgA from IgAN patients. Interestingly, IgA from IgAN patients but not from healthy subjects resulted in experimental IgAN in the SCID-FcαRI Tg mice, thereby inferring that abnormally glycosylated IgA and soluble FcαRI may cooperate in the pathogenesis of IgAN. Support for this hypothesis was provided by the demonstration that binding of polymeric IgA to

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monomeric, but not trimeric, CD89 induces shedding of the extracellular domain of the FcαRI,39 and by the detection of soluble FcαRI in the serum of IgAN patients but not in normal serum. In addition, metabolically labeled cells from IgAN patients released a glycosylated FcαRI form of 50–70 kDa with a 24 kDa protein core39 and was mainly mediated by γ-less FcαRI.40 These data indicate that cleavage of the extracellular domain of FcαRI may result in the release IgA/FcαRI complexes into the circulation. The cleavage may be promoted by the aggregation of FcαRI with a cell surface protease, thereby explaining the decreased FcαRI membrane expression observed in patients. The IgA-induced receptor shedding in IgAN patients could amplify the molecular size of immune complexes that may also include IgA-IgG rheumatoid factors or IgA-fibronectin complexes. Recently, we provided evidence that multimeric aggregation of α− γ2trimeric FcαRI induces an inflammatory response that is an integral component of IgAN pathogenesis mediating disease progression.40 The importance of this FcαRI-FcRγ interaction in the promotion of inflammatory damage was revealed through analysis of the differences in disease development in transgenic mice expressing either wild-type FcRγ-associated or mutant FcRγ-less FcαRI. In this study we mimic the IgA immune complex by cross-linking the receptor with anti-FcαRI F(ab′)2 fragments.40 Although both transgenic mice spontaneously develop mesangial IgA deposits only animals expressing wild-type CD89 can develop proteinuria and macrophage infiltration in the glomeruli and periglomerular space. Furthermore, only macrophages expressing wild-type FcαRI, but not those expressing FcRγ-less FcαRI, were able to migrate to the kidney upon adoptive transfer, clearly suggesting the dependency of this recruitment on the association of the receptor with FcRγ. Therefore, binding of pathologic IgA-IC to FcαRI and signaling through FcRγ results in priming of monocytes. Monocytes together with mesangial cell-produced chemokines, promotes the migration of leukocytes into the renal interstitium and periglomerular regions, thereby amplifying glomerular lesions through FcαRI-γ2 activation.40 Although wild-type FcαRI transgenic mice show increased macrophage infiltration they do not develop end-stage disease, suggesting that this model resembles patients with a mild disease course. This may be owing to the low-affinity binding of mouse murine pIgA to human FcαRI with a consequently poor cross-linking of FcαRI by macromolecular IgA or IgA complexes. However, we have been able to show the importance of

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continuous FcαRI cross-linking in the development of renal failure by using a murine model of severe glomerulonephritis induced by the injection of anti-glomerular basement membrane antibodies into wildtype FcαRI transgenic mice. In this model, renal injury was worsened markedly in mice transgenic for FcαRI complexed with FcRγ, whereas no worsening was seen in FcRγ-less FcαRI transgenic mice, highlighting the pathogenic role of FcRγ signaling in disease progression. Consistent with these observations, serum IgA-IC from patients with IgAN induced cell activation and inflammatory cytokine production, indicating that serum IgA can trigger inflammatory signaling through FcαRI in IgAN and that this may be relevant for disease.40 Such inflammatory signaling may be enhanced further in patients who express an increased proportion of signal-competent FcRγ-associated receptors following the shedding of their monomeric FcαRI by IgA-IC. Altogether these data may help explain the well-described heterogeneity in the natural history of IgAN.

Cellular Consequences of Mesangial Deposition Mesangial cells are contractile cells initially described to play a role in regulating capillary hemodynamics.41,42 They are also implicated in glomerular filtration and express receptors for angiotensin II, vasopressin and prostaglandins.43 Mesangial cells actively secrete matrix proteins such as type IV collagen, laminin, fibronectin and heparan sulfate proteoglycans.44–46 The extracellular matrix seems to be implicated in the attachment of mesangial cells to glomerular capillaries, but it also plays a role in controlling mesangial cell growth and differentiation.47–49 Because of their intracapillary location and of their capacity to synthesize cytokines and other inflammatory molecules, mesangial cells are in a critical position to initiate and mediate glomerular damage. Thus, mesangial cell stimulation is an early pathologic alteration characteristic of many forms of immunologically mediated glomerulonephritides such as IgAN, mesangial proliferative glomerulonephritis, and diabetic nephropathy.11 Several studies have shown that IgA complexes are capable of inducing human mesangial cell (HMC) activation. First biochemical evidences were suggested from studies using IgA1 complexes. Mesangial cell activation involves an increase in intracellular Ca2+, PLC-γ1 activation, production of inositol trisphosphate (IP3) and protein tyrosine

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phosphorylation.50 As a consequence, mesangial cells release cytokines, proliferate, and synthesize extracellular matrix. Indeed, IgA-activated HMC secrete pro-inflammatory cytokines such as IL-6, IL-8, IL-1β but also pro-fibrogenic TGF-β.51–54 Mesangial cell proliferation and matrix expansion are characteristics of IgAN physiopathology. This mesangial cell activation process seems thus to rely on IgA-mediated triggering. The first question that several authors asked was whether IgA immune response was altered in IgAN leading to nephrotoxic IgA antibodies. There is however no direct evidence to suggest that the deposited IgA is directed against specific glomerular antigens. These results point to the existence of mesangial IgA receptor that could link IgA and HMC activation. Thus, the cell surface receptor allowing IgA binding and cell activation became the missing link in disease physiopathogenesis.

Mesangial IgA Receptors The IgA receptor family includes five members: the FcαRI (CD89), the polymeric IgA receptor (pIgR), the Fcα/µ receptor, the asialoglycoprotein receptor (ASGP-R) and the transferrin receptor (TfR).33 Among all these members, the only one described so far that binds exclusively IgA is the CD89. All other IgA receptors can bind other immunoglobulins (pIgR and Fcα/µ receptor) or other non-immunoglobulin related ligands. The ASGP-R for example can also bind asialoglycoproteins. The pIgR is expressed on epithelial cells in the mucosa and mediates the transport of polymeric Ig (IgA and IgM) to the intestinal lumen. The Fcα/µR also binds IgA and IgM and is expressed on the majority of B lymphocytes and macrophages.33 Studies from several groups have now excluded the ASPG-R, the FcαRI/CD89 and the pIg receptor as mesangial cell IgA receptors.11 Although mesangial cells express mRNA for the Fcα/µR, IgA1 binding to mesangial cells was not inhibited by IgM or by recombinant Fcα/µR, indicating a non-significant role for this receptor in mesangial activation by IgA and in the formation of deposits.55,56 We identified the transferrin (Tf ) receptor (Tf R or CD71) as an IgA1 receptor expressed on cultured mesangial cells.57 TfR is a multi-ligand receptor that binds transferrin, the hemochromatosis protein, and polymeric IgA1.57 TfR overexpression was detected in the mesangium of patients with IgAN and Henoch-Schönlein purpura. Furthermore, TfR overexpression by mesangial cells was also observed in lupus nephritis

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patients with IgA deposits but not in those without IgA deposits.58 In normal kidney, CD71 was expressed at a very low level in the glomeruli but strongly in proximal tubules. However CD71 expression was not observed in biopsies showing endocapillary proliferation, post-streptococcal acute glomerulonephritis and type I membranoproliferative glomerulonephritis suggesting that in IgAN CD71 is not merely a marker of cell proliferation. In addition, CD71 overexpression was also observed in the glomeruli without any proliferation. All these observations strongly suggest that IgA deposition by itself is associated with an enhancement of CD71 expression and that the level of CD71 expression is correlated with IgA deposition.58 IgA deposits are also found co-localized with CD71 in the mesangium. Interesting, we have recently shown that TfR is also overexpressed on the apical side of enterocytes and mediates a retrotransport of pathogenic IgA-gliadin complexes in celiac disease, another IgA-related disease.59 TfR binds pIgA1 and has a higher avidity for underglycosylated IgA1 and IgA1 complexes than normal IgA1.56 Several authors agree that the Fc portion of IgA1 mediates its binding to mesangial cells, because both intact IgA1 and its Fc portion, but not its Fab fragment, inhibit binding of IgA1 to mesangial cells. We demonstrated that IgA1 binding to TfR was apparently dependent on the IgA1 hinge region and notably by its glycosylation status.56 Indeed, deletion of either N- or O-linked glycosylation sites on IgA1 abrogated its binding to TfR, whereas sialidase and beta-galactosidase treatment of IgA1 significantly enhanced IgA1/TfR interaction. These results indicate that aberrant glycosylation of IgA1, in addition to immune complex formation, is an essential factor favoring mesangial TfR-IgA1 interaction as initial steps in IgAN pathogenesis. To analyze the functional consequences of IgA1 binding to TfR in HMC we produced TfR-specific molecular tools. We characterized a new anti-TfR monoclonal antibody named A2460 that competes with ferrotransferrin (Fe-Tf ) for binding to TfR. Comparison of the binding of A24 and Fe-Tf by Biacore revealed that Fe-Tf has a higher affinity for TfR than A24. Biacore chips were coated with low and high density of TfR. Under high density of TfR, A24 bound better than Fe-Tf itself whereas with low receptor density binding of Fe-Tf was favored. Thus, under physiologic circumstances, such as quiescent mesangial cells, Fe-Tf will bind to TfR but not A24. However, in pathological situations, like in stimulated mesangial cells that express high levels of TfR, A24 binding

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will be favored. With this molecular tool we showed that IgA-induced, but not cytokine-induced, HMC proliferation is dependent on TfR engagement as it is inhibited by mAb A24 and by TfR1 and TfR2 ectodomains.61 In addition, pIgA1-induced IL-6 and TGF-β production from HMC was also inhibited by mAb A24, confirming that pIgA1 triggers a TfR-dependent HMC activation.61 Macromolecular IgA1 is also a major inducer of TfR expression (three- to four-fold increase) in quiescent HMC61 that is dependent on the continued presence of IgA1 rather than on soluble factors released during IgA1-mediated activation. In this study, up-regulation of TfR expression induced by sera from IgAN patients, but not from healthy individuals, was dependent on IgA. We propose that deposited pIgA1 or IgA1 immune complexes could initiate a process of auto-amplification involving hyper-expression of TfR allowing increased IgA1 mesangial deposition.62

Conclusions We propose that two IgA receptors intervene at different steps of IgAN. FcαRI expressed on hematopoietic cells, through its shedding from the cells by abnormal pIgA1, would participate in the formation of pIgA1-IC thus favoring the deposition of pIgA1 in the mesangium. In addition, it would participate in the priming and recruitment of inflammatory cells to the kidney. There, pIgA1 binding to TfR would lead to HMC activation with features (secretion of pro-inflammatory and pro-fibrogenic cytokines and mesangial cell proliferation) which are commonly implicated in the chronicity of mesangial injuries observed in IgAN and that could explain the recurrence of IgA1 deposits in the mesangium after renal allografts.

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6. Coppo R, Basolo B, Martina G, et al. (1982) Circulating immune complexes containing IgA, IgG and IgM in patients with primary IgA nephropathy and with Henoch-Schoenlein nephritis. Correlation with clinical and histologic signs of activity. Clin Nephrol 18: 230–239. 7. Novak J, Julian BA, Tomana M, Mestecky J. (2008) IgA glycosylation and IgA immune complexes in the pathogenesis of IgA nephropathy. Semin Nephrol 28: 78–87. 8. Valentijn RM, Radl J, Haaijman JJ, et al. (1984) Circulating and mesangial secretory component-binding IgA-1 in primary IgA nephropathy. Kidney Int 26: 760–766. 9. Conley ME, Cooper MD, Michael AF. (1980) Selective deposition of immunoglobulin A1 in immunoglobulin A nephropathy, anaphylactoid purpura nephritis, and systemic lupus erythematosus. J Clin Invest 66: 1432–1436. 10. Lai KN, Lai FM, Lo ST, Lam CW. (1988) Light chain composition of IgA in IgA nephropathy. Am J Kidney Dis 11: 425–429. 11. Monteiro RC, Moura IC, Launay P, et al. (2002) Pathogenic significance of IgA receptor interactions in IgA nephropathy. Trends Mol Med 8: 464–468. 12. Oortwijn BD, van der Boog PJ, Roos A, et al. (2006) A pathogenic role for secretory IgA in IgA nephropathy. Kidney Int 69: 1131–1138. 13. Monteiro RC, Halbwachs-Mecarelli L, Berger J, Lesavre P. (1984) Characteristics of eluted IgA in primary IgA nephropathy. Contrib Nephrol 40: 107–111. 14. Tomino Y, Sakai H, Miura M, et al. (1982) Detection of polymeric IgA in glomeruli from patients with IgA nephropathy. Clin Exp Immunol 49: 419–425. 15. Monteiro RC, Halbwachs-Mecarelli L, Roque-Barreira MC, et al. (1985) Charge and size of mesangial IgA in IgA nephropathy. Kidney Int 28: 666–671. 16. Kokubo T, Hiki Y, Iwase H, et al. (1997) Evidence for involvement of IgA1 hinge glycopeptide in the IgA1-IgA1 interaction in IgA nephropathy. J Am Soc Nephrol 8: 915–919. 17. Hiki Y, Horii A, Iwase H, et al. (1995) O-linked oligosaccharide on IgA1 hinge region in IgA nephropathy. Fundamental study for precise structure and possible role. Contrib Nephrol 111: 73–84. 18. Moldoveanu Z, Wyatt RJ, Lee JY, et al. (2007) Patients with IgA nephropathy have increased serum galactose-deficient IgA1 levels. Kidney Int 71: 1148–1154. 19. Lau KK, Wyatt GJ, Moldoveanu Z, et al. (2007) Serum levels of galactosedeficient IgA in children with IgA nephropathy and Henoch-Schönlein purpura. Pediatr Nephrol 22: 2067–2072.

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20. Coppo R, Amore A, Gianoglio B, et al. (1995) Macromolecular IgA and abnormal IgA reactivity in sera from children with IgA nephropathy. Italian Collaborative Paediatric IgA Nephropathy Study. Clin Nephrol 43: 1–13. 21. Hiki Y, Iwase H, Saitoh M, et al. (1996) Reactivity of glomerular and serum IgA1 to jacalin in IgA nephropathy. Nephron 72: 429–435. 22. Hiki Y, Iwase H, Kokubo T, et al. (1996) Association of asialo-galactosyl beta 1-3N-acetylgalactosamine on the hinge with a conformational instability of Jacalin-reactive immunoglobulin A1 in immunoglobulin A nephropathy. J Am Soc Nephrol 7: 955–960. 23. Tomana M, Novak J, Julian BA, et al. (1999) Circulating immune complexes in IgA nephropathy consist of IgA1 with galactose-deficient hinge region and antiglycan antibodies. J Clin Invest 104: 73–81. 24. Hiki Y, Tanaka A, Kokubo TH, et al. (1998) Analyses of IgA1 hinge glycopeptides in IgA nephropathy by matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry. J Am Soc Nephrol 9: 577–582. 25. Iwase H, Tanaka A, Hiki Y, et al. (1998) Application of matrix-assisted laser desorption ionization time-of-flight mass spectrometry to the analysis of glycopeptide-containing multiple O-linked oligosaccharides. J Chromatogr B Biomed Sci Appl 709: 145–149. 26. Hiki Y, Odani H, Takahashi M, et al. (2001) Mass spectrometry proves under-O-glycosylation of glomerular IgA1 in IgA nephropathy. Kidney Int 59: 1077–1085. 27. Renfrow MB, Cooper HJ, Tomana M, et al. (2005) Determination of aberrant O-glycosylation in the IgA1 hinge region by electron capture dissociation fourier transform-ion cyclotron resonance mass spectrometry. J Biol Chem 280: 19136–19145. 28. Coppo R, Amore A, Gianoglio B, et al. (1993) Serum IgA and macromolecular IgA reacting with mesangial matrix components. Contrib Nephrol 104: 162–171. 29. van den Wall Bake AW, Kirk KA, Gay RE, et al. (1992) Binding of serum immunoglobulins to collagens in IgA nephropathy and HIV infection. Kidney Int 42: 374–382. 30. Roos A, Bouwman LH, van Gijlswijk-Janssen DJ, et al. (2001) Human IgA activates the complement system via the mannan-binding lectin pathway. J Immunol 167: 2861–2868. 31. Roos A, Rastaldi MP, Calvaresi N, et al. (2006) Glomerular activation of the lectin pathway of complement in IgA nephropathy is associated with more severe renal disease. J Am Soc Nephrol 17: 1724–1734. 32. Amore A, Conti G, Cirina P, et al. (2000) Aberrantly glycosylated IgA molecules downregulate the synthesis and secretion of vascular endothelial growth factor in human mesangial cells. Am J Kidney Dis 36: 1242–1252.

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33. Monteiro RC, van De Winkel JG. (2003) IgA Fc receptors. Annu Rev Immunol 21: 177–204. 34. Monteiro RC, Kubagawa H, Cooper MD. (1990) Cellular distribution, regulation, and biochemical nature of an Fc alpha receptor in humans. J Exp Med 171: 597–613. 35. Gulle H, Samstag A, Eibl MM, Wolf HM. (1998) Physical and functional association of Fc alpha R with protein tyrosine kinase Lyn. Blood 91: 383–391. 36. Launay P, Lehuen A, Kawakami T, et al. (1998) IgA Fc receptor (CD89) activation enables coupling to syk and Btk tyrosine kinase pathways: differential signaling after IFN-gamma or phorbol ester stimulation. J Leukoc Biol 63: 636–642. 37. Launay P, Patry C, Lehuen A, et al. (1999) Alternative endocytic pathway for immunoglobulin A Fc receptors (CD89) depends on the lack of FcRgamma association and protects against degradation of bound ligand. J Biol Chem 274: 7216–7225. 38. van Egmond M, Damen CA, van Spriel AB, et al. (2001) IgA and the IgA Fc receptor. Trends Immunol 22: 205–211. 39. Launay P, Grossetete B, Arcos-Fajardo M, et al. (2000) Fcalpha receptor (CD89) mediates the development of immunoglobulin A (IgA) nephropathy (Berger’s disease). Evidence for pathogenic soluble receptor-Iga complexes in patients and CD89 transgenic mice. J Exp Med 191: 1999–2009. 40. Kanamaru Y, Arcos-Fajardo M, Moura IC, et al. (2007) Fc alpha receptor I activation induces leukocyte recruitment and promotes aggravation of glomerulonephritis through the FcR gamma adaptor. Eur J Immunol 37: 1116–1128. 41. Zimmermann KW. (1929) Über ben Bau des Glomerulus der menschlichen Niere. Z Mikrosk Anat Forsch 18: 520–552. 42. Latta H. (1960) The centrolobular region of the glomerulus studied by electron microscopy. J Ultrastruct Res 4: 455–472. 43. Ausiello DA, Kreisberg JI, Roy C, Karnovsky MJ. (1980) Contraction of cultured rat glomerular cells of apparent mesangial origin after stimulation with angiotensin II and arginine vasopressin. J Clin Invest 65: 754–760. 44. Couchman JR, Beavan LA, McCarthy KJ. (1994) Glomerular matrix: synthesis, turnover and role in mesangial expansion. Kidney Int 45: 328–335. 45. Ardaillou R, Chansel D, Chatziantoniou C, Dussaule JC. (1999) Mesangial AT1 receptors: expression, signaling, and regulation. J Am Soc Nephrol 10(Suppl 11): S40–S46. 46. Border WA, Ruoslahti E. (1990) Transforming growth factor-beta 1 induces extracellular matrix formation in glomerulonephritis. Cell Differ Dev 32: 425–431.

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47. Rupprecht HD, Schocklmann HO, Sterzel RB. (1996) Cell-matrix interactions in the glomerular mesangium. Kidney Int 49: 1575–1582. 48. Kreisberg JI. (1983) Contractile properties of the glomerular mesangium. Fed Proc 42: 3053–3057. 49. Michael AF, Kim Y. (1988) The glomerular mesangium. Am J Kidney Dis 12: 393–396. 50. Gomez-Guerrero C, Duque N, Egido J. (1996) Stimulation of Fc(alpha) receptors induces tyrosine phosphorylation of phospholipase C-gamma(1), phosphatidylinositol phosphate hydrolysis, and Ca2+ mobilization in rat and human mesangial cells. J Immunol 156: 4369–4376. 51. Kaartinen K, Syrjanen J, Porsti I, et al. (2008) Inflammatory markers and the progression of IgA glomerulonephritis. Nephrol Dial Transplant 23: 1285–1290. 52. Coppo R, Amore A, Chiesa M, et al. (2007) Serological and genetic factors in early recurrence of IgA nephropathy after renal transplantation. Clin Transplant 21: 728–737. 53. Niemir ZI, Stein H, Ciechanowicz A, et al. (2004) The in situ expression of interleukin-8 in the normal human kidney and in different morphological forms of glomerulonephritis. Am J Kidney Dis 43: 983–998. 54. Harada K, Akai Y, Kurumatani N, et al. (2002) Prognostic value of urinary interleukin 6 in patients with IgA nephropathy: an 8-year follow-up study. Nephron 92: 824–826. 55. McDonald KJ, Cameron AJ, Allen JM, Jardine AG. (2002) Expression of Fc alpha/mu receptor by human mesangial cells: a candidate receptor for immune complex deposition in IgA nephropathy. Biochem Biophys Res Commun 290: 438–442. 56. Moura IC, Arcos-Fajardo M, Sadaka C, et al. (2004) Glycosylation and size of IgA1 are essential for interaction with mesangial transferrin receptor in IgA nephropathy. J Am Soc Nephrol 15: 622–634. 57. Moura IC, Centelles MN, Arcos-Fajardo M, et al. (2001) Identification of the transferrin receptor as a novel immunoglobulin (Ig)A1 receptor and its enhanced expression on mesangial cells in IgA nephropathy. J Exp Med 194: 417–425. 58. Haddad E, Moura IC, Arcos-Fajardo M, et al. (2003) Enhanced expression of the CD71 mesangial IgA1 receptor in Berger disease and HenochSchonlein nephritis: association between CD71 expression and IgA deposits. J Am Soc Nephrol 14: 327–337. 59. Matysiak-Budnik T, Moura IC, Arcos-Fajardo M, et al. (2008) Secretory IgA mediates retrotranscytosis of intact gliadin peptides via the transferrin receptor in celiac disease. J Exp Med 205: 143–154. 60. Moura IC, Lepelletier Y, Arnulf B, et al. (2004) A neutralizing monoclonal antibody (mAb A24) directed against the transferrin receptor

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induces apoptosis of tumor T lymphocytes from ATL patients. Blood 103: 1838–1845. 61. Moura IC, Arcos-Fajardo M, Gdoura A, et al. (2005) Engagement of transferrin receptor by polymeric IgA1: evidence for a positive feedback loop involving increased receptor expression and mesangial cell proliferation in IgA nephropathy. J Am Soc Nephrol 16: 2667–2676. 62. Tamouza H, Vende F, Tiwari M, et al. (2007) Transferrin receptor engagement by polymeric IgA1 induces receptor expression and mesangial cell proliferation: role in IgA nephropathy. Contrib Nephrol 157: 144–147.

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Chapter 16

Antigen-Dependent Mechanism of IgA Nephropathy Yasuhiko Tomino and Yoshio Shimizu

Introduction Until now, IgA nephropathy (IgAN) has been considered to be an immune-complex-mediated glomerulonephritis based on the following findings. (i) Depositions of IgA (IgA1), IgG and C3 are observed in the glomerular mesangial areas by immunofluorescence, double immunofluorescence show the co-existence of C3 and IgA, IgG and/or IgM in glomeruli.1 (ii) Electron-dense deposits are observed in the same areas. (iii) IgA and/or C3 are also deposited in the vascular walls of subcutaneous or intramuscular vessels by immunofluorescence.2 (iv) IgA-dominant immune complexes in sera are determined using several different techniques. (v) Percentages of immune complexes included in polymorphonuclear cells (PMN) are significantly increased in patients with IgA nephropathy compared with other glomerular diseases and healthy controls. Since the localization of IgA and C3 in the cytoplasmic inclusion bodies is identical, these inclusion bodies are considered to be immune materials phagocytized by PMN in patients with IgA nephropathy.3 (vi) Recurrence of IgA nephropathy occurs in renal grafts of transplantation patients. It is yet to be determined whether the immune complexes detected in IgA nephropathy are (a) antigen-antibody dependent immune complexes, (b) antigen-antibody independent immune complexes, i.e. self-aggregation of aberrant glycosylated IgA1, (c) complexes formed with soluble IgA Fc receptor I, (d) IgA interacting with other circulating proteins or (e) specific antibodies directed against 225

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glomerular mesangial antigens.4 However, Clarkson et al.5 were not able to detect anti-mesangial antibody activity in sera from patients with IgA nephropathy. There are no data regarding implanted mesangial antigens in IgA nephropathy, i.e. immune complex formation in situ.

Antigen-Antibody Dependent Immune Complex Since IgA is an important immunoglobulin in defense mechanisms against exogenous antigens in the mucosal system, the antigens might be located in the mucosal membranes of patients with IgA nephropathy. Previous studies suggested that immune complexes deposited in the glomeruli were mainly composed of IgA1 dimers or polymers in such patients. However, it is not still known whether antigens are exogenous and/or endogenous in patients with IgA nephropathy. It is speculated that there are many kinds of antigens, i.e. food, virus, bacteria and/or fungus, in patients with IgA nephropathy as follows: (1) dietary antigens, (2) respiratory antigens, (3) intestinal antigens, (4) biliary antigens, and (5) dermal antigens. These antigens might form antigen-antibody dependent immune complexes. In this case, it is necessary to detect antigenic substances including their structural components in glomeruli and/or eluate from the glomeruli. Detection of binding of eluted antigens and IgA(IgA1) antibodies is also warranted.

Food Antigens In 1991, Coppo et al.6 determined IgA antibodies to dietary antigens and lectin-binding IgA in sera from Italian, Australian and Japanese IgA nephropathy patients. They suggested that serum IgA in IgA nephropathy patients may participate in immune complex formation with IgA binding to alimentary antigens and also in formation of non-immune complexes by IgA-lectin interactions. IgA antibodies to other food components such as bovine albumin, ovalbumin and lactoglobulin have also been detected in serum samples of patients with IgA nephropathy.6 They also indicated an increase of macromolecular IgA and abnormal IgA reactivity in sera from children with IgA nephropathy in the Italian Collaborative Pediatric IgA Nephropathy Study.7 On the other hand, IgA antibody titers for against bovine γ-globulin, β-lactoglobulin, chicken γ-globulin, ovalbumin, pig γ-globulin, soy flower extract and

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surface protein of Streptococcus mutans did not differ from those of healthy controls.8 Depositions of soybean and casein could not be demonstrated in glomeruli of Japanese patients.9 Patients with IgA nephropathy who had elevated IgA-antibodies to gliadin showed elevated total serum IgA more frequently than patients who had not.10

Viral Antigens Takeuchi et al.11 reported that depositions of murine retroviral envelope glycoprotein (gp 70) and IgA/IgG were observed in the glomerular mesangial areas of ddY mice, a spontaneous human IgA nephropathy model. Murine retroviral gp 70 was also found in various lymphoid tissues. Thus, they suggested that gp 70 derived from lymphoid tissues circulates in the form of immune complexes and is deposited in the glomerular mesangial areas. Clinically, IgA nephropathy is frequently preceded by episodes of upper respiratory tract infection that is presumed to have some viral etiology.12 The cytopathic effects (CPE) of extracts of pharyngeal cells from patients with IgA nephropathy was examined on fibroblasts such as Vero cells (renal fibroblasts of the African green monkey, FDA Vero, FV-233) or Hel cells (fibroblasts of the human embryonic lung, local strain). CPE of extracts of pharyngeal cells from patients with IgA nephropathy on Vero or Hel cells were significantly increased compared with those from patients with other glomerular diseases or healthy controls. CPE of such fibroblasts were not inhibited by Millipore filtration of extracts of pharyngeal cells obtained from patients with IgA nephropathy. Supernatant of fibroblasts previously cultured with freeze-thawed extracts of pharyngeal cells from patients with IgA nephropathy showed CPE on newly prepared fibroblasts. Weak pathogenic changes might occur in the upper respiratory tracts of patients with IgA nephropathy.13 Virus-like particles and/or microtubular structures were occasionally observed in the glomerular mesangial areas by electron microscopy. Slight deposition of adenovirus, herpes simplex, varicella zoster or parainfluenza 3 virus was observed by immunofluorescence14 not only in renal sections but also in nuclear regions and/or cytoplasm of Hel cells after incubation of extract of pharyngeal cells with or without IUDR from patients with IgA nephropathy. It appears that antigenic stimulation in the upper respiratory tract may be due to several different types of DNA and/or RNA viruses in patients with IgA nephropathy.

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Thus, some antigens such as viruses may exist in the upper respiratory tract that provides continuous antigenic stimulation in some patients with IgA nephropathy. Nagy et al.15 found herpes antigens and antibodies in renal tissues and sera from patients with IgA nephropathy. They also demonstrated that IgA antibodies reacting with Epstein-Barr virus (EBV) capsid antigen (EBVCA) in sera were significantly increased in patients with IgA nephropathy.16 However, they could not detect virus antigens or virus DNA in the glomeruli of IgA nephropathy patients either with immunohistology using a monoclonal antibody or with DNA in situ hybridization.16 Iwama et al.17 reported that EBV may damage the glomerular mesangium in patients with various chronic glomerulonephritides including IgA nephropathy. In brief, they determined the relationship between the detection of EBV-specific DNA and glomerular injury using PCR with subsequent non-radioactive Southern blotting. EBV was detected in seven out of 12 patients with IgA nephropathy (58%), three out of six with membranous nephropathy (50%), one out of nine with minor glomerular abnormalities (11%) and all three with focal/segmental lesions. It appears possible that EBV is an agent damaging the glomerular mesangium in patients with chronic glomerulonephritides including IgA nephropathy. However, Sinniah et al.18 indicated that some patients with IgA nephropathy may have a coincidental rather than causal persistent infection by EB and herpes simplex viruses. Cytomegalovirus (CMV) DNA in various types of glomerulonephritis as well as in IgA nephropathy suggest that CMV is not specifically associated with the pathogenesis of IgA nephropathy seen in endemic areas of CMV infection.19 Lai et al.20 first detected hepatitis B virus (HBV) DNA and RNA in kidneys of HBV related glomerulonephritis including IgA nephropathy. Wang et al.21 also detected HBV DNA in 72% and 82% cases in tubular epithelia and glomeruli, respectively, by in situ hybridization. These findings indicate the presence of viral transcription in glomerular cells and renal tubular epithelia, supporting an etiological role of HBV in some chronic HBV carriers who develop co-existing glomerulonephritides.

Bacterial Antigens In 1980, Woodroffe et al.22 observed a significant temporal rise in antibody titers to specific infectious antigens, i.e. gut flora or food antigens.

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IgA nephropathy has been described as a complication of infections with Yersinia enterocolitica, Campylobactor jejuni, and Mycoplasma pneumoniae. Suzuki et al.23 observed glomerular deposition of Hemophilus parainfluenzae antigens by immunofluorescence and the presence of IgA antibody against H. parainfluenzae in sera by enzyme-linked immunosorbent assay (ELISA) in patients with IgA nephropathy. In immunoblotting, rabbit antiserum recognized four components of H. parainfluenzae with molecular weights of 19.5, 30, 33 and 40.5kD. All 44 patients with IgA nephropathy and two out of the 39 patients with other glomerular diseases showed mesangial deposition of H. parainfluenzae antigens. Patients with IgA nephropathy had significantly more IgA antibody in sera against H. parainfluenzae than patients with other glomerular diseases. Thus, they suggested that H. parainfluenzae has a role in the etiology of IgA nephropathy.23 Yamamoto et al.24 reported that administration of outer membrane antigens of H. parainfluenzae (OMHP) antigens to C3H/HeN mice may induce glomerular deposition of IgA and mesangial proliferation, resembling the changes seen in human IgA nephropathy, with increases in IgA antibodies against OMHP antigen. On the other hand, Ogawa et al.25 reported that the reactivity of IgA eluted from kidney tissues against the Hemophilus influenzae 34 kD antigen was evident in three out of five IgA nephropathy patients. Lamm et al.26 reported a bacterial IgA protease, isolated from Hemophilus influenzae, which exhibits substrate specificity for the hinge region of human IgA1. This protease cleaved human IgA1 and IgA1-containing immune complexes in vitro. In the study, healthy BALB/c mice first received an intravenous injection of immune complexes, consisting of human IgA1 and goat-anti-F(ab′)2, which resulted in mesangial positivity for human IgA. Administration of IgA protease one hour after the injection of the immune complexes significantly reduced the degree of mesangial IgA intensity within the next hour when compared to mice not treated with a protease. They concluded that IgA protease may have potential as a therapeutic agent for human IgA nephropathy.26 Koyama et al.27 reported that the serum IgA and IgG levels in patients with methicillin-resistant Staphylococcus aureus (S. aureus) (MRSA) infections and nephritis was significantly higher than that in patients without nephritis. Furthermore, they demonstrated significant S. aureus antigen deposition in glomeruli of IgA nephropathy

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patients.27 Sharmin et al.28 have extended their work to the murine system to establish an active IgA nephropathy model using an S. aureus membrane protein as an antigen. Mesangial proliferative glomerulonephritis with IgA, IgG and C3 depositions were observed in all BALB/c mice (Th2 dominant type). S. aureus antigens were detected in glomeruli using affinity-purified human anti-S. aureus antibodies, but there was no staining in C57BL/6 mice (Th1 dominant). It is suggested that S. aureus antigens may play an important role in pathogenesis of IgA nephropathy. Shimizu et al.29 reported that IgA class titers of antiS. aureus antibodies in patients with IgA nephropathy were significantly higher than those in healthy controls, and IgG class titers of anti-S. aureus antibodies in patients with post-MRSA infection glomerulonephritis (GN) were significantly higher than those in IgA nephropathy patients and healthy controls. They also reported that the avidity of anti-S. aureus IgA from patients with IgA nephropathy was significantly lower than that from post-MRSA GN patients and healthy controls. It appears that patients with IgA nephropathy have a strong response through production of IgA with low avidity against S. aureus.29 These investigations first indicated that IgA and the Staphylococcal membrane antigen that was identified at the molecular level were co-localized in glomeruli and a high level of IgA that recognized this antigen was produced in patients with this glomerulonephritis. This phenomenon was also mimicked in the mouse model. Thus, post-MRSA infection GN may possibly be a model for IgA nephropathy induced by the exogenous antigen-endogenous IgA immune complex.

Antigen-Antibody Independent Immune Complex T Cell-Independent Antigen While T cell-dependent antigens trigger CD40-dependent class switch recombination (CSR) in B cells located within the germinal center (GC) of secondary lymphoid follicles,30 T cell-independent antigens, such as viral glycoproteins and bacterial polysaccharides, elicit CD40-independent CSR and antibody production in the extrafollicular marginal zone and intestinal B cells.31 This process requires B cell-activating factor of the tumor necrosis factor (TNF) family (BAFF; also known as B-lymphocyte stimulator: BLYS) and proliferation-inducing ligand (APRIL).32 These CD40L-related molecules are produced by myeloid cells. BAFF binds to

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three receptors specifically expressed on B cells, including transmembrane activator, calcium modulator and cyclophylin ligand interactor (TACI), B cell maturation antigen (BCMA), and BAFF receptor (BAFF-R).33,34 In addition to favoring antibody production, BAFF-R delivers survival signals that are crucial for the conservation of the peripheral B cell repertoire. APRIL binds to TACI and BCMA, but not to BAFF-R. In the same way as to CD40, TACI, BCMA and BAFF-R recruit TNFR-associated factors (TRAFs) to their cytoplasmic tails.35 TRAFs induce phosphorylation-dependent degradation of IκB, a cytoplasmic inhibitor of NF-κB, by activating IκB kinase. The subsequent nuclear translocation of NF-κB transcriptionally activates genes involved in B cell proliferation, differentiation, and survival. Dysregulated CSR in B cells induces autoimmune disorders such as systemic lupus erythematosus (SLE), or atopic disorders, which can be triggered or exacerbated by viral and bacterial infections. Recently, He et al.36 showed that EBV induced CD40-independent CSR from the Cµ gene to multiple downstream Cγ, Cα, and Cε genes through latent membrane protein 1 (LMP-1), a CD40-like viral protein that signals in a ligand-independent fashion and LMP-1 induces B cells to express BAFF and APRIL. Katsenelson et al.37 revealed that Toll-like receptor agonists, unmethylated deoxycytidyldeoxyguanosine oligodeoxynucleotides (CpG ODN) and lipopolysaccharide (LPS), strongly up-regulated TACI expression and BAFF-R was only up-regulated by CpG ODN. CpG ODN pre-treatment enhanced TACI expression on follicular and marginal zone B cells and increased their responses to BAFF- and APRIL- mediated immunoglobulin secretion.37 Moreover, tonsillar mononuclear cells (TMC) from patients with IgA nephropathy showed significantly higher production of BAFF, interferon-γ (IFN-γ), and IgA than those from healthy controls after stimulation by CpG ODN.38 Thus, it is suggested that T cell-independent antigens are closely related to aberrant IgA production in patients with IgA nephropathy.

O-Glycosylation of Serum IgA1 Antibody Against Antigen It is generally considered that circulating and mesangial IgA1 has abnormal O-linked hinge-region sugars with reduced galactosylation and sialylation in patients with IgA nephropathy. Floege et al.39 indicated that dysregulated activity of C1GalT1 (core-β1,3-galactosyltransferase)

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in patients with IgA nephropathy results in pathogenic under-galactosylation of IgA. Thus, IgA nephropathy is characterized by under-galactosylated IgA1 deposition in glomeruli and increase of serum under-galactosylated IgA1.40–42 Although the underlying mechanism of this O-glycosylation abnormality is poorly understood, possibilities include (i) a genetic factor, (ii) various antigenic stimulations such as food, virus and bacteria, and (iii) others. Thus, it is necessary to determine the genetic factors and antigens that produce aberrant IgA1 in patients with IgA nephropathy. Li et al.43 suggested that polymorphisms of C1GALTT1 gene were associated with the genetic susceptibility to IgA nephropathy in Chinese populations. Gharavi et al.44 reported that aberrant IgA1 glycosylation is inherited in familial and sporadic IgA nephropathy. They concluded that abnormal IgA1 glycosylation clusters were observed in most but not all families of IgA nephropathy patients. Measurement of galactose-deficient IgA1 may help distinguish patients by pathogenic mechanism of IgA nephropathy.44 Recently, studies of the origin of such aberrant molecules, their glycosylation and mechanisms of biosynthesis have provided new insights into pathogenesis in patients with IgA nephropathy (refer to Chapter 12). In the absence of galactose, the terminal saccharide of O-linked chains in the hinge region of IgA1 is terminal or sialylated N-acetylgalactosamine. The University of Alabama group41,42 developed an ELISA method using a lectin from Helix aspersa recognizing N-acetylgalactosamine for measurement of galactose-deficient IgA1 in serum. The median serum lectin-binding IgA1 level in Caucasian adult patients with IgA nephropathy is significantly higher than that in healthy Caucasian adult controls.41 Smith et al.45 used a lectin-binding assay to measure the level of serum IgA1 antibodies against mucosal and systemic antigens in patients with IgA nephropathy. They reported that the “under-galactosylated” form of IgA1 is not restricted to IgA nephropathy but is also produced by control subjects under certain conditions.

Conclusion Whether or not antigen-antibody dependent immune complexes play an important role in the pathogenesis of IgA nephropathy remains controversial. Some investigations suggested that antigen-antibody dependent immune complexes might induce glomerular injuries in patients with

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IgA nephropathy. Others indicated that IgA nephropathy is characterized by deposition of under-galactosylated IgA1 in glomerular mesangial areas with or without antigens. Obayashi et al. found that liquid chromatography electron spray ionization mass spectrometry (LC-ESI MS) did not detect obvious exogenous antigens in IgA binding protein of IgA nephropathy patients (in preparation for submission). It seems reasonable to suppose that there are at least two subtypes of IgA nephropathy. One is the classical type that involves is glomerular injury caused by exogenous antigen-endogenous IgA immune complex. The other is an autoimmune type which is induced by aberrant (under-galactosylated) IgA derived from subpopulations of B and plasma cells. Little is known about the relationships between these subtypes. Hence, in future examinations, it is necessary not only to detect specific antigens in the glomeruli but also to elute these antigens by newly developed techniques. It is also important to determine whether the eluted antigens bind to glomeruli and stimulate mesangial cells in vitro or in vivo. On the other hand, a great deal of effort should be made simultaneously to study the production of aberrant (under-galactosylated) IgA1 in patients with IgA nephropathy. Recent knowledge about innate immune systems might be helpful.

References 1. Tomino Y, Nomoto Y, Endoh M, et al. (1981) Deposition of IgA-dominant immune-complexes in muscular vessels from patients with IgA nephropathy. Acta Pathol Jpn 31: 361–365. 2. Tomino Y, Nomoto Y, Endoh M, et al. (1980) Double immunofluorescence studies on IgA-associated immune-complexes in glomerular deposits in patients with IgA nephropathy. Tokai J Exp Clin Med 5: 147–149. 3. Tomino Y, Sakai H, Endoh M, et al. (1982) Detection of immune complexes in polymorphonuclear leukocytes by double immunofluorescence in patients with IgA nephropathy. Clin Immunol Immunopathol 24: 63–71. 4. Lowance DC, Mullins JD, McPhaul JJ Jr. (1973) Immunoglobulin A (IgA) associated glomerulonephritis. Kidney Int 3: 167–176. 5. Clarkson AR, Woodroffe AJ, Bannister KM, et al. (1984) The syndrome of IgA nephropathy. Clin Nephrol 21: 7–14. 6. Coppo R, Amore A, Roccatello D, et al. (1991) IgA antibodies to dietary antigens and lectin-binding IgA in sera from Italian, Australian, and Japanese IgA nephropathy patients. Am J Kidney Dis 17: 480–487.

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7. Coppo R, Amore A, Gianoglio B, et al. (1995) Macromolecular IgA and abnormal IgA reactivity in sera from children with IgA nephropathy. Italian Collaborative Paediatric IgA Nephropathy Study. Clin Nephrol 43: 1–13. 8. Russell MW, Mestecky J, Julian BA, et al. (1986) IgA-associated renal diseases: antibodies to environmental antigens in sera and deposition of immunoglobulins and antigens in glomeruli. J Clin Immunol 6: 74–86. 9. Murakami T, Kawakami H. (1993) Questionable role of soy protein in childhood IgA nephropathy. Nephron 64: 395–398. 10. Almroth G, Axelsson T, Müssener E, et al. (2006) Increased prevalence of anti-gliadin IgA-antibodies with aberrant duodenal histopathological findings in patients with IgA-nephropathy and related disorders. Ups J Med Sci 111: 339–352. 11. Takeuchi E, Doi T, Shimada T, et al. (1989) Retroviral gp70 antigen in spontaneous mesangial glomerulonephritis of ddY mice. Kidney Int 35: 638–646. 12. Tomino Y, Yagame M, Omata F, et al. (1987) A case of IgA nephropathy associated with adeno- and herpes simplex viruses. Nephron 47: 258–261. 13. Tomino Y, Sakai H, Miura M, et al. (1986) Cytopathic effects of antigens in patients with IgA nephropathy. Nephron 42: 161–166. 14. Tomino Y, Yagame M, Suga T, et al. (1989) Detection of viral antigens in patients with IgA nephropathy. Jpn J Med 28: 159–164. 15. Nagy J, Uj M, Szücs G, et al. (1984) Herpes virus antigens and antibodies in kidney biopsies and sera of IgA glomerulonephritic patients. Clin Nephrol 21: 259–262. 16. Nagy J, Haikin H, Sarov B, et al. (1984) Altered humoral immunity against cytomegalovirus and Epstein-Barr virus without detectable virus antigens and virus-DNA in the glomeruli of patients with IgA nephropathy in remission phase. Acta Microbiol Immunol Hung 42: 179–187. 17. Iwama H, Horikoshi S, Shirato I, et al. (1998) Epstein-Barr virus detection in kidney biopsy specimens correlates with glomerular mesangial injury. Am J Kidney Dis 32: 785–793. 18. Sinniah R, Khan TN, Dodd S. (1993) An in situ hybridization study of herpes simplex and Epstein Barr viruses in IgA nephropathy and nonimmune glomerulonephritis. Clin Nephrol 40: 137–111. 19. Park JS, Song JH, Yang WS, et al. (1994) Cytomegalovirus is not specifically associated with immunoglobulin A nephropathy. J Am Soc Nephrol 4: 1623–1626. 20. Lai KN, Ho RT, Tam JS, Lai FM. (1996) Detection of hepatitis B virus RNA and RNA in kidneys of HBV related glomerulonephritis. Kidney Int 50: 1965–1977.

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21. Wang NS, Wu ZL, Zhang YE, et al. (2003) Role of hepatitis B virus infection in pathogenesis of IgA nephropathy. World J Gastroenterol 9: 2004–2008. 22. Woodroffe AJ, Gormly AA, McKenzie PE, et al. (1980) Immunologic studies in IgA nephropathy. Kidney Int 18: 366–374. 23. Suzuki S, Nakatomi Y, Sato H, et al. (1994) Haemophilus parainfluenzae antigen and antibody in renal biopsy samples and serum of patients with IgA nephropathy. Lancet 343: 12–16. 24. Yamamoto C, Suzuki S, Kimura H, et al. (2002) Experimental nephropathy induced by Haemophilus parainfluenzae antigens. Nephron 90: 320–327. 25. Ogawa Y, Ishizu A, Ishikura H, et al. (2002/2003) Elution of IgA from kidney tissues exhibiting glomerular IgA deposition and analysis of antibody specificity. Pathobiology 70: 98–102. 26. Lamm ME, Emancipator SN, Robinson JK, et al. (2008) Microbial IgA protease removes IgA immune complexes from mouse glomeruli in vivo: potential therapy for IgA nephropathy. Am J Pathol 172: 31–36. 27. Koyama A, Sharmin S, Sakurai H, et al. (2004) Staphylococcus aureus cell envelope antigen is a new candidate for the induction of IgA nephropathy. Kidney Int 66: 121–132. 28. Sharmin S, Shimizu Y, Hagiwara M, et al. (2004) Staphylococcus aureus antigens induce IgA-type glomerulonephritis in BALB/c mice. J Nephrol 17: 504–511. 29. Shimizu Y, Seki M, Kaneko S, et al. (2007) Patients with IgA nephropathy respond strongly through production of IgA with low avidity against Staphylococcus aureus. Contrib Nephrol 157: 139–143. 30. MacLennan IC. (1994) Germinal centers. Annu Rev Immunol 12: 117–139. 31. Fagarasan S, Honjo T. (2000) T-Independent immune response: new aspects of cell biology. Science 290: 89–92. 32. MacLennan I, Vinuesa C. (2002) Dendritic cells, BAFF, and APRIL: innate players in adaptive antibody responses. Immunity 17: 235–238. 33. Thompson JS, Bixler SA, Qian F, et al. (2001) BAFF-R, a newly identified TNF receptor that specifically interacts with BAFF. Science 293: 2108–2111. 34. Gross JA, Johnston J, Mudri S, et al. (2000) TACI and BCMA are receptors for a TNF homologue implicated in B-cell autoimmune disease. Nature 404: 995–999. 35. Mackay F, Browning JL. (2002) BAFF: a fundamental survival factor for B cells. Nat Rev Immunol 2: 465–475. 36. He B, Raab-Traub N, Casali P, et al. (2003) EBV-encoded latent membrane protein 1 cooperates with BAFF/BLyS and APRIL to induce T cellindependent Ig heavy chain class switching. J Immunol 171: 5215–5224.

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37. Katsenelson N, Kanswal S, Puig M, et al. (2007) Synthetic CpG oligodeoxynucleotides augment BAFF- and APRIL-mediated immunoglobulin secretion. Eur J Immunol 37: 1785–1795. 38. Goto T, Bandoh N, Yoshizaki T, et al. (2008) Increase in B-cell-activation factor (BAFF) and IFN-gamma productions by tonsillar mononuclear cells stimulated with deoxycytidyl-deoxyguanosine oligodeoxynucleotides (CpGODN) in patients with IgA nephropathy. Clin Immunol 126: 260–269. 39. Floege J, Eitner F, Barratt J, et al. (2007) Mutant mice provide new insight into the role of (mis-)glycation in IgA nephropathy and other glomerular diseases. Nephrol Dial Transplant 22: 1518–1520. 40. Hiki Y, Odani H, Takahashi M, et al. (2001) Mass spectrometry proves under-glycosylation of glomerular IgA1 in IgA nephropathy. Kidney Int 59: 1077–1085. 41. Moldoveanu Z, Wyatt RJ, Lee JY, et al. (2007) Patients with IgA nephropathy have increased serum galactose-deficient IgA1 levels. Kidney Int 71: 1148–1154. 42. Novak J, Kulian BA, Tomana M, et al. (2008) IgA glycosylation and IgA immune complexes in the pathogenesis of IgA nephropathy. Semin Nephrol 28: 78–87. 43. Li G-S, Zhang H, Lv J-C, et al. (2007) Variants of C1GALT1 gene are associated with the enetic susceptibility to IgA nephropathy. Kidney Int 71: 448–453. 44. Gharavi AG, Moldoveanu Z, Wyatt RJ, et al. (2008) Aberrant IgA1 glycosylation is inherited in familial and sporadic IgA nephropathy. J Am Soc Nephrol 19: 1008–1014. 45. Smith AC, Molyneux K, Feehally J, et al. (2006) O-Glycosylation of serum IgA1 antibodies against mucosal and systemic antigens in IgA nephropathy. J Am Soc Nephrol 17: 3520–3528.

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Chapter 17

Complement Activation Sydney C. W. Tang and Kar Neng Lai

Scientific Basis for Complement Activation in IgAN In addition to mesangial IgA deposits, biopsies of IgAN are commonly associated with the deposition of complement components, most notably C3, the membrane attack complex (C5b-9), and properdin,1–3 suggesting the participation of complement activation in disease pathogenesis. Early reports demonstrated the expression of C3, C4 and factor B in proximal tubular epithelial cells, mesangial cells, glomerular epithelial cells, Bowman’s capsule, and infiltrating mononuclear cells in the interstitium in patients with IgAN.4,5 These data suggest that local complement production6,7 by various intrinsic renal cells and infiltrating cells may contribute to tissue injury in IgAN. In support of this notion, local C3 transcription and translation has been found to correlate with clinical and histologic markers of severity and poor outcome of IgAN.8 Moreover, proteinuria but not serum creatinine, at the time of renal biopsy correlated with C3 mRNA expression. This last phenomenon may be attributed to the finding that apical proteins stimulated basolateral C3 synthesis by cultured human proximal tubular epithelial cells,9 in which transferrin and apotransferrin stimulated C3 biosynthesis more intensely.10 Locally secreted C3 may further activate tubular cells via the C3a receptor11 to enhance renal injury. This is supported by the observation of increased levels of split products of activated C3 in the circulation of patients with IgAN that are associated with increased proteinuria and hematuria, highlighting the

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involvement of the alternative pathway in IgAN.12 Indeed, in vitro as well as in vivo studies have shown that pIgA can activate the alternative pathway of complement directly, whereas monomeric IgA is a poor activator of the complement system.13 The molecular basis for the difference between monomeric IgA and pIgA is not clear. More recently, two Japanese groups14,15 reported that the serum IgA/C3 ratio may reflect the histological severity of IgAN and could serve as a marker of the progression of IgAN, and may be useful for prediction of diagnosis of IgAN and distinguishing it from other renal diseases. Another German study16 indicated that only alternative pathway complement activation can be demonstrated in patients with IgAN and its activation was associated with more severe renal disease. The clinical significance of such correlation studies requires confirmation.

Potential Role of the Lectin Pathway The recently described lectin pathway of the complement system forms an integral component of innate immunity. The key molecule of this pathway, mannose-binding lectin (MBL), binds directly to a number of microorganisms via carbohydrates expressed on their surface17 to activate complement as a first line host defense mechanism against pathogens. It is therefore not surprising that MBL may interact with IgA, an important mediator of mucosal immunity, and assume a role in IgAN. Evidence is accumulating that complement activation via MBL and the lectin pathway is associated with disease progression in IgAN.18,19 It has been shown that MBL is able to bind pIgA, leading to activation of the lectin pathway in vitro.20 However, there is no difference in the binding of MBL to IgA from healthy subjects or patients with IgAN.21 The carbohydrate recognition domain of MBL is able to bind in a calcium-dependent manner to a number of saccharides, such as D-mannose, L-fucose, and N-acetylglucosamine, whereas the binding of MBL to IgA has been proposed to be mediated through the oligomannose structures present in the N-linked sugars of the heavy chains of pIgA.21 Deposition of MBL in association with IgA as a marker for lectin pathway activation has been reported,18,19,22 but these findings were not consistently reproduced.23 Furthermore, the relationship of glomerular MBL deposition with parameters of renal damage and complement

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activation via the lectin pathway is inconsistent among different studies. More recent data suggest that IgA was co-deposited with MBL in about 25% of patients and that MBL deposition showed more severe renal disease as compared with MBL-negative cases, suggesting an important role for MBL in disease progression.24 These results rekindled the notion that activation of the lectin pathway occurs in a subpopulation of patients, and that MBL deposition may serve as a biomarker for disease progression in IgAN.

Conclusion There is evidence to suggest that activation of the alternative and lectin pathways of the complement cascade occurs in IgAN, and that such activation may provide prognostic value. For both pathways, pIgA is a more potent activator than monomeric IgA. Research interest in this area has been most intense in the last two decades, but appears to have dampened in recent years. The putative pathogenetic role of complement activation and its predictive and prognostic values remain to be elucidated more carefully. Findings at the biopsy level emphasize the importance of further delineating the precise composition of IgA in mesangial deposits because ultimately these data may unravel the mechanisms involved in IgA deposition and complement activation in IgAN.

References 1. Schena FP. (1992) IgA nephropathies. In: Oxford’s Textbook of Clinical Nephrology (eds.) Cameron S, Davison AM, Grunfield JP, Kerr D, Ritz E. Oxford University Press, Oxford, pp. 339–369. 2. Rauterberg EW, Lieberknecht HM, Wingen AM, et al. (1987) Complement membrane attack (MAC) in idiopathic IgA-glomerulonephritis. Kidney Int 31: 820–829. 3. Couser WG, Baker PJ, Adler S. (1985) Complement and the direct mediation of immune glomerular injury: a new perspective. Kidney Int 28: 879–890. 4. Oren R, Laufer J, Goldberg I, et al. (1995) C3, C4, factor B and HLA-DR alpha mRNA expression in renal biopsy specimens from patients with IgA nephropathy. Immunology 86: 575–583. 5. Miyazaki M, Abe K, Koji T, et al. (1996) Intraglomerular C3 synthesis in human kidney detected by in situ hybridization. J Am Soc Nephrol 7: 2428–2433.

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6. Zhou W, Marsh JE, Sacks SH. (2001) Intrarenal synthesis of complement. Kidney Int 59: 1227–1235. 7. Tang S, Zhou W, Sheerin NS, et al. (1999) Contribution of renal secreted complement C3 to the circulating pool in humans. J Immunol 162: 4336–4341. 8. Montinaro V, Gesualdo L, Ranieri E, et al. (1997) Renal cortical complement C3 gene expression in IgA nephropathy. J Am Soc Nephrol 8: 415–425. 9. Tang S, Sheerin NS, Zhou W, et al. (1999) Apical proteins stimulate complement synthesis by cultured human proximal tubular epithelial cells. J Am Soc Nephrol 10: 69–76. 10. Tang S, Lai KN, Chan TM, et al. (2001) Transferrin but not albumin mediates stimulation of complement C3 biosynthesis in human proximal tubular epithelial cells. Am J Kidney Dis 37: 94–103. 11. Peake PW, O’Grady S, Pussell BA, et al. (1999) C3a is made by proximal tubular HK-2 cells and activates them via the C3a receptor. Kidney Int 56: 1729–1736. 12. Zwirner J, Burg M, Schulze M, et al. (1997) Activated complement C3: a potentially novel predictor of progressive IgA nephropathy. Kidney Int 51: 1257–1264. 13. Hiemstra PS, Gorter A, Stuurman ME, et al. (1987) Activation of the alternative pathway of complement by human serum IgA. Adv Exp Med Biol 216B: 1297–1302. 14. Komatsu H, Fujimoto S, Hara S, et al. (2004) Relationship between serum IgA/C3 ratio and progression of IgA nephropathy. Intern Med 43: 1023–1028. 15. Nakayama K, Ohsawa I, Maeda-Ohtani A, et al. (2008) Prediction of diagnosis of immunoglobulin A nephropathy prior to renal biopsy and correlation with urinary sediment findings and prognostic grading. J Clin Lab Anal 22: 114–118. 16. Zwirner J, Burg M, Schulze M, et al. (1997) Activated complement C3: a potentially novel predictor of progressive IgA nephropathy. Kidney Int 51: 1257–1264. 17. Neth O, Jack DL, Dodds AW, et al. (2000) Mannose-binding lectin binds to a range of clinically relevant microorganisms and promotes complement deposition. Infect Immun 68: 688–693. 18. Endo M, Ohi H, Ohsawa I, et al. (1998) Glomerular deposition of mannosebinding lectin (MBL) indicates a novel mechanism of complement activation in IgA nephropathy. Nephrol Dial Transplant 13: 1984–1990. 19. Matsuda M, Shikata K, Wada J, et al. (1998) Deposition of mannan binding protein and mannan binding protein-mediated complement activation in the glomeruli of patients with IgA nephropathy. Nephron 80: 408–413. 20. Roos A, Bouwman LH, van Gijlswijk-Janssen DJ, et al. (2001) Human IgA activates the complement system via the mannan-binding lectin pathway. J Immunol 167: 2861–2868.

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21. Oortwijn BD, Roos A, Royle L, et al. (2006) Differential glycosylation of polymeric and monomeric IgA: a possible role in glomerular inflammation in IgA nephropathy. J Am Soc Nephrol 17: 3529–3539. 22. Hisano S, Matsushita M, Fujita T, et al. (2001) Mesangial IgA2 deposits and lectin pathway-mediated complement activation in IgA glomerulonephritis. Am J Kidney Dis 38: 1082–1088. 23. Lhotta K, Wurzner R, Konig P. (1999) Glomerular deposition of mannosebinding lectin in human glomerulonephritis. Nephrol Dial Transplant 14: 881–886. 24. Roos A, Rastaldi MP, Calvaresi N, et al. (2006) Glomerular activation of the lectin pathway of complement in IgA nephropathy is associated with more severe renal disease. J Am Soc Nephrol 17: 1724–1734.

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Chapter 18

Cytokines and Growth Factors Jürgen Floege and Tammo Ostendorf

Introduction IgA-nephropathy (IgAN) is a leading cause of renal failure worldwide and new treatment approaches are urgently needed. Curative therapies do not exist at present and treatment is usually targeted at delaying or even reversing renal damage. Over the last few years, the evidence base supporting therapeutic approaches, mostly by using high-dose ACE-inhibitors and/or angiotensin-II receptor blockers with or without immunosuppression, in patients at risk for progressive IgAN has markedly improved. Based on new insights into the pathogenesis of IgAN a considerable number of potential approaches might be envisioned and have recently been reviewed.1–5 These include decreasing the synthesis of IgA-containing immune complexes, limiting their mesangial uptake, antagonizing the effects of growth factors and cytokines as well as reducing glomerular neutrophil-mediated injury. Numerous cytokines and growth factors, such as for example, interleukin (IL)-5, -6, -8, monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-α (TNF-α), macrophage migration inhibitory factor (MIF), transforming growth factor (TGF)-β and platelet-derived growth factor (PDGF), have been identified to play important roles in the pathogenesis of IgAN and may emerge as attractive clinical targets in the future.6–13 Indications for an important role of other cytokines in the pathogenesis of IgAN are rather weak (e.g. for IL-46) or absent (e.g. for interferon-α14).

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Key Cytokines Involved in the Pathogenesis of IgAN Serum IgA is elevated in IgAN patients and predominantly consists of the IgA1 type with λ-light chains. IL-5 and TGF-β have been shown to promote the maturation of IgA secreting B cells and the expression of both factors is enhanced in CD4-positive cells from IgAN patients, correlating with the pathological severity.6 In addition, a recent allelic association study by Liu et al.15 suggests that variants of the gene for IL-5 alpha receptor may predispose to sporadic IgAN. A hallmark of IgAN is mesangial deposition of mostly polymeric IgA1. As a response, mesangial cells (MC) release cytokines and growth factors, which generally lead to a common pathway of increased extracellular matrix formation, glomerular and tubular inflammation, and finally, renal fibrosis. In vitro studies showed that binding of IgA to MC causes increased expression of IL-6, IL-8, MCP-1, MIF and TNFα.7–9,16,17 A potential pathogenetic role of IL-6 in mesangioproliferative glomerulonephritis is still controversial. Whereas urinary IL-6 is increased and may serve as a predictor of long-term renal outcome in patients with IgAN,18,19 an active pathogenetic role of IL-6 has never been shown. Certainly, IL-6 is not essential for the normal development of the mesangium, because the kidneys of IL-6 knockout mice are normal.20 In several experimental in vivo approaches, we demonstrated that IL-6 is not an important mediator of MC proliferation or matrix overproduction.20 Chemoattractant IL-8 and MCP-1-mediated renal infiltration and the accumulation of leukocytes have also been shown to be involved in the pathogenesis of IgAN. It was demonstrated that urinary MCP-1 levels and renal MCP-1 expression were significantly higher in patients with IgAN, which correlated with the interstitial infiltration of macrophages and tubulointerstitial damage.21,22 IL-8-expressing infiltrating mononuclear cells were detected in renal IgAN tissues, mostly monocytes/macrophages, and IL-8 serum levels have been shown to be increased in IgAN patients.23,24 Urinary levels of IL-8 were higher in patients with glomerular leukocyte infiltration, numbers of glomerular neutrophils correlated positively and significantly with the renal IL-8 expression and IL-8 has been demonstrated to be a key chemoattractant responsible for neutrophil infiltration and activation.25–27 Most likely, in IgAN this cytokine therefore causes migration of neutrophils into the

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glomeruli, further augmenting glomerular damage by the neutrophilic release of superoxide and lysosomal proteolytic enzymes. MIF regulates NFκB and therefore has considerable influence on the inflammatory response. It plays a key role in upstream events of inflammatory responses and is the only cytokine known to override the antiinflammatory action of glucocorticoids.28 Elevated MIF serum levels and glomerular expression have been shown in patients with different types of glomerulonephritis, including IgAN, and most importantly, antagonism of MIF in a murine model of IgAN reduced glomerular TFG-β expression and ameliorated kidney injury.29,30 Finally, glomerulo-tubular cross-talk and a mesangial-podocytic crosstalk could be identified, involving TNF-α as a central mediator.10,31 Produced upon activation of MC by polymeric IgA from patients with IgAN, TNF-α is able to stimulate proximal tubular epithelial cells to express inflammatory mediators like MIF or TNF-α and podocytes to upregulate TNF-α and its receptors in an autocrine fashion, thereby continuing the inflammatory response. In many of the above cases, however, the evidence invoking the cytokine or growth factor specifically in the pathogenesis of IgAN is limited or even inconsistent. Also, most of these factors, albeit very interesting and worth pursuing, are still far from entering diagnostic or therapeutic studies in patients. Since the hallmark of IgAN are mesangioproliferative changes,2 this chapter will focus on key growth factors (PDGF and TGF-β), that mediate such changes and whose targeting in renal disease is close to clinical trials.

PDGF PDGF, a pleiotropic cytokine, and in particular the PDGF-B and -D chains, appear to play a central role in mediating MC proliferation and stimulating matrix synthesis.13 PDGF-A and -B are secreted as homoor heterodimers and bind to dimeric PDGF receptors composed of αand/or β chains. Whereas PDGF-A binds to the α chain only, PDGF-B is a ligand for all receptor types (Figure 18.1). PDGF-C and -D are released as homodimers, PDGF-CC and -DD.32–35 These two new isoforms are produced as latent factors. Proteolytic cleavage of a CUB domain from each chain is then required for activation.36 Tissue plasminogen activator is one identified specific PDGF-CC-activating protease, whereas PDGF-DD is activated by urokinase-type plasminogen activator. Following

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Figure 18.1 Schematic outline of the PDGF and PDGF receptor system showing the differential binding of the various PDGF isoform combinations to the PDGF α- and β-receptor chains. tPA: tissue plasminogen activator; uPA: urokinase-type plasminogen activator; CUB: complement subcomponent C1r/C1s, Uegf, and Bmp1 domain; normal lines: high affinity binding; dotted lines: weak binding.

this proteolytic processing, the core domain of PDGF-CC appears to be largely a ligand for the PDGF-αα receptor, while PDGF-DD binds predominantly to the PDGF-ββ receptor (Figure 18.1).13 The PDGF receptor possesses tyrosine kinase activity and is autophosphorylated upon ligand binding.37 The receptor then interacts with several other cytoplasmic proteins containing SH2 domains, including phospholipase C (PLC-γ), ras GTPase activating protein, phosphatidylinositol 3-kinase (PI3kinase), members of the pp60src family of protein tyrosine kinase, tyrosine phosphatase SHP-2 and the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) pathway.13,37 Second messengers include inositol-(1,4,5)-triphosphate and diacylglycerol, intracellular calcium release, protein kinase C (PKC)-α, β, ε, and ζ, and prenylated, low molecular weight G proteins.13

In Vitro Studies PDGF synthesis is induced in cultured MC by various mediators, including PDGF itself, epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), TNF-α, TGF-β, angiotensin-II, endothelin,

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thrombin, lipoproteins, lysophosphatidylcholine, phospholipids and CpG nucleotides.13,38 Negative regulators of PDGF synthesis are platelet factor-4 and NOV/CCN3.39,40 In glomerular endothelial cells, PDGF-B is induced upon hypoxia and reduced by shear stress. In proximal tubular cells, glomerular ultrafiltered hepatocyte growth factor (HGF) and TGF-β may act as PDGF inducers.13 Stimulation of MC with different PDGF-ligands results in cellular proliferation and migration. PDGF-AA exerts only weak effects whereas DGF-BB induces a rapid mobilization of intracellular calcium, decreases p27 and increases cyclin A and CDK2, resulting in pronounced cell proliferation.13,41,42 PDGF-CC and -DD are also potent inducers of MC proliferation.43,44 Mitogenic PDGF effects on other renal cell types are less consistent. PDGFs also induce extracellular matrix synthesis in MC, parietal epithelial cells and, to a lesser degree, in tubular epithelial cells.45–48 They may have this effect by acting upstream of and/or in concert with other cytokines such as TGF-β. PDGF-BB stimulates the increased expression of numerous mediators of disease and inflammation in MC, including TGF-β1, CCL-2, CXC3CL1, PAI-1, IL-6, endothelin-1, iNOS, and YB-1. Through effects on MC contraction and prostanoid production, PDGF also contributes to the regulation of glomerular hemodynamics. Infusion of PDGF into isolated micro-perfused glomeruli increases intraglomerular pressure, vascular resistance and decreases flow rate.13

Constitutive Expression of PDGF and PDGFR in Adult Rodent and Human Kidneys PDGFR-α is widely expressed by renal interstitial cells, and to some degree by mesangial cells.49 The constitutive PDGFR-α expression by smooth muscle cells of the renal arterial vasculature has been identified, but is not uniform among these cells. PDGFR-β is expressed postnatally by mesangial cells, glomerular parietal epithelial cells and interstitial cells.50 The PDGF-A chain is normally expressed by mature podocytes, and epithelial cells of the distal nephron including collecting ductal cells and urothelium.51 In the mouse, the PDGF-A chain also appears to be expressed by cells of the loop of Henle.52 Though low levels of PDGF-B chain expression by mesangial cells in normal mature glomeruli may be present, it has been difficult to detect constitutive expression by these cells using immunohistochemistry. Localization of the more newly

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recognized PDGF isoforms has been hampered by the limited availability of reliable reagents. Important differences in patterns of expression in mouse, rodent, and human kidneys have been revealed. PDGF-C has been localized to arterial smooth muscle cells and collecting duct epithelial cells in the rat. In humans, PDGF-C has been localized to parietal epithelial cells in the glomerulus, tubular cells from all parts of the nephron distal to the proximal tubules, and arterial endothelial cells.43,53 In normal human adult kidneys, PDGF-D expression persists in podocytes and is constitutively expressed by vascular smooth muscle cells.54 Constitutive expression of PDGF-D in the rat is limited to vascular smooth muscle cells only.55 In the mouse, PDGF-D is constitutively expressed in glomeruli, but by mesangial cells and not by podocytes, in contrast to humans.56

Expression of PDGFs and PDGFR in Genetically Modified Mice and in Renal Disease Mice with combined homozygous deficiency for PDGF-A and -C, amongst other defects, lack elements of the renal cortical interstitium and largely appear to mirror the phenotype of mice deficient for PDGFR-α.57 These observations point to potential roles of PDGF-A, -C and/or PDGFRαα in mediating renal interstitial disease. Mice deficient for PDGF-B or PDGF-Rβ exhibit a complete lack of mesangial cell migration into the glomerular stalk.58–61 With respect to therapeutic interventions, it is important to note that the transgenic high-level overexpression of a soluble PDGF-B and -D antagonist (soluble PDGFR-β) in the liver during late embryogenesis and throughout postnatal life in mice was not associated with any phenotype.62 This suggests that, in contrast to embryogenesis, PDGF-B and -D are not required during normal adult life. Upregulated PDGF-A, -B, -C, and -D expression has been observed in a large number of rodent injury models including mesangioproliferative anti-Thy 1.1 glomerulonephritis and angiotensin II-induced renal damage as well as in human IgA nephropathy, in the case of PDGF-A and -B.13 An upregulation of PDGFR-α has been shown in vascular smooth muscle cells and in tubulointerstitial cells in the course of different renal diseases.56,63 Renal PDGFR-β overexpression has been detected in mesangial cells, but also in parietal epithelial cells, endothelial cells, tubular epithelial cells and interstitial cells in a large variety of renal diseases.12,50,64–67

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PDGF Overexpression or Pharmocologic Administration or Inhibition Infusion of recombinant PDGF-BB or its hepatic adenoviral overexpression into healthy rats led to a selective increase of glomerular mesangial cell proliferation.68,69 Mice with high circulating levels of PDGF-D following adenoviral transfection of the liver also developed a severe mesangial proliferative glomerulopathy.69 These data demonstrate potent roles of PDGF-B and -D in inducing mesangioproliferative changes as well as tubulointerstitial fibrosis in the case of PDGF-B. A number of specific interventions aimed at neutralizing PDGF-B or -D or blocking the PDGF β-receptor in a rat mesangioproliferative glomerulonephritis model have been shown to reduce mesangial cell proliferation and matrix accumulation as well as secondary tubulointerstitial fibrosis and renal failure (Table 18.1).13,55,70–74 PDGF-B antagonism did not affect the TGF-β system, suggesting that PDGF-B acts downstream or independently of TGF-β and may thus be a specific target to ameliorate both increased cellularity and matrix production.75 Low-molecular weight PDGF receptor tyrosine kinase blockers such as Imatinib also reduced mesangioproliferative changes in experimental glomerulonephritis76,77 but interpretation of these studies is difficult, since many of the kinase blockers only exhibit relative specificity for the PDGF receptor. Taken together, these data provide strong evidence that inhibition of PDGF-B and -D can be an effective approach to proliferative glomerulonephritis and that both can also directly or indirectly affect the progression of renal tubulointerstitial damage. While the potential benefits of PDGF blockade in human renal disease are not yet known, it is noteworthy that specific inhibition of PDGFR-beta in normal volunteers so far has shown a good safety profile, whereas in some tumor patients fluid retention and ascites have been noted.78

β TGF-β TGF-β is a key mediator in the development of renal fibrosis. It is a highly pleiotropic growth factor, that, in mammals, exists in three isoforms, TGFβ1, TGF-β2 and TGF-β3. The TGF-βs are part of a large superfamily of proteins, including TGF-βs, activins, inhibins, myostatin, bone morphogenetic proteins, anti-Müllerian hormones, and others.79–82 TGF-β is

Effects

Spontaneously hypertensive rats Murine unilateral ureteral obstruction Rat acute anti-thymocyte serum GN Rat acute anti-Thy 1.1 GN

PDGF-A antisense oligonucleotides Neutralizing anti-PDGFC antiserum Neutralizing anti-PDGF-AB IgG

Renal damage Tubulointerstitial fibrosis and leukocyte influx Mesangial cell proliferation and matrix accumulation Mesangial cell proliferation and matrix accumulation

Rat acute anti-Thy 1.1 GN

B-specific oligonucleotide aptamer

Rat chronic anti-Thy 1.1 GN

B-specific oligonucleotide aptamer


Neutralizing anti-PDGF-D IgG

Mesangial cell proliferation and matrix accumulation Mesangial cell proliferation and matrix accumulation Proteinuria, renal function, glomerulosclerosis and tubulointerstitial fibrosis Mesangial cell proliferation and matrix accumulation

(Continued )

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Table 18.1

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Neutralizing anti-PDGF-D IgG


Trapidil


Imatinib

Rabbit nephrotoxic nephritis

Trapidil

Murine streptozotocin diabetes

Imatinib

Murine lupus

Imatinib

Rat unilateral ureter obstruction Rat ischemia / reperfusion injury

AG 1295 Trapidil, Ki6896

± Proteinuria, renal function, glomerulosclerosis and tubulointerstitial fibrosis, EMT Mesangial cell proliferation and matrix accumulation Mesangial cell proliferation and matrix accumulation Trend towards worse clinical data and renal histology Albuminuria, glomerular and tubulointerstitial damage Survival, proteinuria, glomerular and tubulointerstitial damage Tubulointerstitial fibrosis Serum creatinine, mortality rate, proliferation of tubular epithelial cells

GN: Glomerulonephritis; EMT: epithelial-to-mesenchymal transition. For single references, see Ref. 13.

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important in many processes, including apoptosis control, angiogenesis, wound healing, inflammation, atherosclerosis, organ fibrosis, and malignancy.82 TGF-β1 to -β3 share 70% to 80% amino acid sequence identity, bind to the same receptors, induce similar responses, and for the most part are interchangeable.79,83 Nevertheless, the three isoforms are encoded by different genes and the individual promoters contain distinct elements, which may confer tissue-specific expression. Active, mature TGF-β is a 25-kDa homodimer. It is initially synthesized as a precursor protein which is proteolytically processed into an inactive, latent form composed of mature TGF-β non-covalently bound to the amino-terminal precursor remnant termed latency-associated protein (LAP). After being secreted by the cell, latent TGF-β can be activated via a variety of mechanisms.84 TGF-β superfamily members signal through binding to type I and type II serine/threonine kinase receptors which are almost universally expressed. The membrane-bound proteoglycan, betaglycan (also known as type III receptor), binds TGF-β and increases its affinity for the signaling receptors. Upon ligand binding and receptor complex activation, receptor-regulated (R)-Smads are phosphorylated (Figure 18.2). Phosphorylated R-Smads bind to their common partner Smad4, and subsequently translocate into the nucleus where they act as transcription factors. The type I receptor, also known as activin receptor-like kinase (ALK), and the R-Smads thereby determine specificity. TGF-βs bind ALK5 and activate Smad2 and -3.85 Differences in TGF-β signaling in various cells have been attributed to differential kinetics in biosynthesis, ligand-induced internalization, and downregulation of receptors.79

Modulation of Inflammation The immune modulatory actions of TGF-β are, at first glance, confusing in that TGF-β can exert potent proinflammatory actions but can also act as a potent immunosuppressive agent.86 This apparent contradictory influence of TGF-β is accounted for in part by the differential effects of TGF-β on resting and activated cells. As a general, but by no means exclusive, rule, resting, immature cells are stimulated by TGF-β, whereas the same cells, once activated, may be inhibited by TGF-β. Early proinflammatory effects of TGF-β, as long as its production remains locally confined, include leukocyte chemotaxis, increased expression of

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Figure 18.2 TGF-β signaling. The simplified scheme shows Smad signaling of TGF-β. Different molecules modify extracellularly the activity of TGF-β. Binding of TGF-β to its receptors induces heteromeric receptor complexes with kinase activation (Alk5) that leads to recruitment and phosphorylation of the receptor Smads (R-Smads), Smad2 and Smad3. These phospho-Smads form heteromers with Smad4 (Co-Smad) and are transported to the nucleus where they regulate gene expression, e.g. the upregulation of collagen I gene expression. Non-Smad TGF-β signaling, shown in the right side of the picture, can involve activation of p38 MAPK, JNK and Rho. The modulation of TGF-β-induced gene transcription by Smad co-repressors Ski and SnoN in the nucleus is also shown. Arrows indicate stimulatory effects and blunted lines inhibitory effects. “P” stands for phosphorylation. ALK5: TGF-β1 receptor I kinase; JNK: c-Jun amino-terminal kinase; p38 MAPK: p38 mitogen-activated protein kinase; TβR: TGF-β receptor.

adhesion molecules, and autoinduction of TGF-β, as well as induction of other cytokines in leukocytes and weak effects on angiogenesis.79 TGF-β has been shown to induce IgA isotype switch at the clonal level from a µ to an α chain in IgA secreting B cells and TGF-β expression is enhanced in CD4-positive cells from IgAN patients, correlating with the pathological severity.6,87 Interestingly, TGF-β-mediated signal transduction is suppressed by proinflammatory cytokines such as TNF-α and IL1β through NF-κB-dependent Smad7 synthesis indicating a diminished

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TGF-β effect during acute inflammation.88 Systemic administration or overproduction of TGF-β with increased serum levels mainly results in immunosuppression, which may relate to multiple anti-inflammatory actions.89 In vivo evidence for an immunosuppressive role of TGF-β, among other findings, is supported by the observation that genetically TGF-β1-deficient mice die of a multifocal, inflammatory wasting syndrome.90

In Vitro Studies with Renal Cells and Growth Regulation In cultured renal cells, TGF-β production as well as autoinduction of TGF-β has been described in mesangial cells and proximal tubular cells. Of potential relevance for the kidney, TGF-β can also be detected in cultured vascular smooth muscle cells, endothelial cells, monocytes, macrophages, neutrophils, T- and B-lymphocytes, and platelets. Numerous cytokines, growth factors and hormones can upregulate TGF-β in renal cells.89 TGF-β1 promotes differentiation of podocytes and can induce apoptosis in these cells.91,92 Upon stimulation with angiotensin II podocytes show increased expression of TGF-β type II receptor but no upregulation of TGF-β.93 Albumin-induced upregulation of TGF-β1 mRNA in cultured podocytes is associated with the increase of TGF-β1 protein release into the cell supernatant. Such conditioned supernatants are able to induce a sclerosing mesangial phenotype.94 Albumin challenge of cultured proximal tubular cells also results in increased TGF-β1 production and upregulates TGF-β type II receptor expression in these cells.95,96 Vascular endothelial growth factor (VEGF), important for glomerular capillary repair in the early phase of experimental mesangioproliferative glomerulonephritis in rats,97 upregulates TGF-β1 production and secretion by glomerular endothelial cells.98 TGF-β is an important regulator of renal cell growth. The effects on the growth of mesangial cells or renal interstitial fibroblasts can be either stimulatory or inhibitory, depending on cell density, the concentration of TGF-β, costimulatory signals, and length of cytokine exposure.89 Although TGF-β stimulates proliferation of certain renal cells such as fibroblasts,79 it exerts an antiproliferative effect on the majority of renal parenchymal cells.99,100 These cells are arrested in the G1-phase of the cell cycle after exposure to TGF-β and may undergo hypertrophy.99

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TGF-β transfection of normal rat glomeruli in vivo resulted in mild, presumably mesangial, cell proliferation.101

Expression of TGF-β in Normal and Diseased Kidneys In normal glomeruli, absent up to abundant amounts of TGF-β1 have been described. In the rat, TGF-β1 mRNA is found in all nephron segments. At least in the murine kidney, TGF-β3 follows a similar pattern of expression. TGF-β2 has been detected in glomeruli, mainly in the juxtaglomerular apparatus.89 Renal overexpression of TGF-β occurs in nearly all experimental diseases as well as in human pathology, e.g. in human IgAN.102,103 Polymeric IgA1 from patients with IgAN upregulates TGF-β in human mesangial cells.104 Also, increased renal TGF-β bioactivity and increased urinary excretion of TGF-β are often found in experimental or human renal scarring.89 However, given the complexity of TGF-β activation and regulation, caution is necessary when interpreting data on the renal overexpression of TGF-β. Indeed, one study on human renal biopsies from IgAN patients has shown widespread expression of TGF-β1 LAP, which markedly exceeded that of TGF-β1.12

TGF-β in Renal Fibrosis TGF-β is an important regulator involved in tissue repair and/or scar formation. With respect to matrix synthesis, TGF-β regulates the production of small proteoglycans, namely decorin and biglycan, fibronectin and collagens in cultured glomerular mesangial, epithelial, and endothelial cells as well as tubular cells.89 TGF-β can also contribute to matrix accumulation by inhibiting matrix-degrading enzymes such as plasmin. In fact, incubation of glomeruli or glomerular cells with TGF-β led to reduced plasmin activity via downregulation of the plasminogen activator and upregulation of plasminogen activator inhibitor synthesis.105 It has been demonstrated that angiotensin II stimulates extracellular matrix production through induction of TGFβ,106 and patients with IgAN treated with angiotensin-converting enzyme inhibitors (ACEi) showed a reduced renal TGF-β expression.107 Furthermore, TGF-β triggers the transdifferentiation of tubular epithelial cells to profibrotic myofibroblasts in a process called epithelial-tomesenchymal transition (EMT).108

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The best evidence for a profibrotic role of TGF-β derives from in vivo data, showing that transfection of normal rat glomeruli in vivo with TGF-β cDNA resulted in marked expansion of the extracellular matrix.101 TGF-β1 transgenic mice were characterized by accumulation of glomerular extracellular matrix, thickening of the glomerular basement membrane, crescent formation, and inflammatory arteritis.109

Intervention Studies Taking into account the pivotal role of TGF-β in renal fibrogenesis, multiple experimental studies have been performed to interfere with the TGF-β system. Therapies with anti-TGF-β antibodies, decorin, decorin gene transfer, transfected TGF-β antisense oligodeoxynucleotides, recombinant LAP and gene transfer with the extracellular domain of TGF-β type II receptor resulted in significant reductions of renal matrix protein accumulation in the anti-Thy 1.1 model of mesangioproliferative glomerulonephritis.89 Anti-TGF-β antibody treatment in the db/db mouse model of type 2 diabetes prevented glomerulosclerosis and partially reversed already established glomerular damage.110,111 Mice treated with a pan-specific TGF-β-neutralizing antibody showed reduced tubulointerstitial fibrosis in a murine model of cyclosporin A-induced nephropathy.112 In recent studies in experimental mesangioproliferative glomerulonephritis in rats113 and experimental diabetic nephropathy,114,115 it was demonstrated that a combination therapy with anti-TGF-β antibody and an ACEi was more effective than the anti-fibrotic effect of anti-TGF-β- or ACEi treatment alone. Such a combination effect was not seen in the unilateral ureteral obstruction model of renal fibrosis.116 Of clinical relevance were studies showing an anti-fibrotic effect of orally available TGF-β antagonists in experimental mesangioproliferative glomerulonephritis and in murine diabetic nephropathy.117,118 In conclusion, although many therapeutic approaches have been explored to antagonize TGF-β effects in experimental disease, especially in experimental mesangioproliferative glomerulonephritis, thus far no antiTGF-β therapy has been applied in a clinical setting, obviously because of its pleiotropic effects, e.g. on immune suppression. Identification of factors downstream of TGF-β that are directly involved in the accumulation of matrix perhaps might provide better targets for intervention. One potential candidate is connective tissue growth factor (CTGF, CCN2), a

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member of the CCN (CTGF, Cyr61, Nov) family of early response genes, since some of the profibrotic effects of TGF-β are actually mediated by this factor.119 CTGF is upregulated in the kidney of patients with IgAN120,121 and expression of CTGF mRNA in tubular epithelial cells correlates with the degree of tubulointerstitial damage.122

References 1. Floege J, Mertens P. (2000) Therapy of patients with IgA-nephropathy: a critical appraisal. Kidney Blood Press Res 23: 207–209. 2. Floege J, Feehally J. (2000) IgA nephropathy: recent developments. J Am Soc Nephrol 11: 2395–2403. 3. Floege J, Eitner F. (2005) Present and future therapy options in IgAnephropathy. J Nephrol 18: 354–361. 4. Lai KN. (2002) Future directions in the treatment of IgA nephropathy. Nephron 92: 263–270. 5. Lai AS, Lai KN. (2005) Molecular basis of IgA nephropathy. Curr Mol Med 5: 475–487. 6. Lai KN, Ho RT, Leung JC, et al. (1994) CD4-positive cells from patients with IgA nephropathy demonstrate increased mRNA of cytokines that induce the IgA switch and differentiation. J Pathol 174: 13–22. 7. van den Dobbelsteen ME, van der Woude FJ, Schroeijers WE, et al. (1994) Binding of dimeric and polymeric IgA to rat renal mesangial cells enhances the release of interleukin 6. Kidney Int 46: 512–519. 8. Duque N, Gomez-Guerrero C, Egido J. (1997) Interaction of IgA with Fc alpha receptors of human mesangial cells activates transcription factor nuclear factor-kappa B and induces expression and synthesis of monocyte chemoattractant protein-1, IL-8, and IFN-inducible protein 10. J Immunol 159: 3474–3482. 9. Leung JC, Tang SC, Chan LY, et al. (2003) Polymeric IgA increases the synthesis of macrophage migration inhibitory factor by human mesangial cells in IgA nephropathy. Nephrol Dial Transplant 18: 36–45. 10. Chan LY, Leung JC, Tsang AW, et al. (2005) Activation of tubular epithelial cells by mesangial-derived TNF-alpha: glomerulotubular communication in IgA nephropathy. Kidney Int 67: 602–612. 11. Gesualdo L, Pinzani M, Floriano JJ, et al. (1991) Platelet-derived growth factor expression in mesangial proliferative glomerulonephritis. Lab Invest 65: 160–167. 12. Niemir ZI, Stein H, Noronha IL, et al. (1995) PDGF and TGF-beta contribute to the natural course of human IgA glomerulonephritis. Kidney Int 48: 1530–1541.

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13. Floege J, Eitner F, Alpers CE. (2008) A new look at platelet-derived growth factor in renal disease. J Am Soc Nephrol 19: 12–23. 14. Floege J, Burg M, Al Masri AN, et al. (1999) Expression of interferoninducible Mx-proteins in patients with IgA nephropathy or HenochSchönlein purpura. Am J Kidney Dis 33: 434–440. 15. Liu XQ, Paterson AD, He N, et al. (2008) IL5RA and TNFRSF6B gene variants are associated with sporadic IgA nephropathy. J Am Soc Nephrol 19: 1025–1033. 16. Oortwijn BD, Roos A, Royle L, et al. (2006) Differential glycosylation of polymeric and monomeric IgA: a possible role in glomerular inflammation in IgA nephropathy. J Am Soc Nephrol 17: 3529–3539. 17. Leung JC, Tang SC, Chan LY, et al. (2008) Synthesis of TNF-alpha by mesangial cells cultured with polymeric anionic IgA — role of MAPK and NF-kappaB. Nephrol Dial Transplant 23: 72–81. 18. Harada K, Akai Y, Kurumatani N, et al. (2002) Prognostic value of urinary interleukin 6 in patients with IgA nephropathy: an 8-year follow-up study. Nephron 92: 824–826. 19. Ranieri E, Gesualdo L, Petrarulo F, et al. (1996) Urinary IL-6/EGF ratio: a useful prognostic marker for the progression of renal damage in IgA nephropathy. Kidney Int 50: 1990–2001. 20. Eitner F, Westerhuis R, Burg M, et al. (1997) Role of interleukin-6 in mediating mesangial cell proliferation and matrix production in vivo. Kidney Int 51: 69–78. 21. Grandaliano G, Gesualdo L, Ranieri E, et al. (1996) Monocyte chemotactic peptide-1 expression in acute and chronic human nephritides: a pathogenetic role in interstitial monocytes recruitment. J Am Soc Nephrol 7: 906–913. 22. Yokoyama H, Wada T, Furuichi K, et al. (1998) Urinary levels of chemokines (MCAF/MCP-1, IL-8) reflect distinct disease activities and phases of human IgA nephropathy. J Leukoc Biol 63: 493–499. 23. Yoshioka K, Takemura T, Murakami K, et al. (1993) In situ expression of cytokines in IgA nephritis. Kidney Int 44: 825–833. 24. Chen HC, Tomino Y, Yaguchi Y, et al. (1992) Oxidative metabolism of polymorphonuclear leukocytes (PMN) in patients with IgA nephropathy. J Clin Lab Anal 6: 35–39. 25. Wada T, Yokoyama H, Tomosugi N, et al. (1994) Detection of urinary interleukin-8 in glomerular diseases. Kidney Int 46: 455–460. 26. Sekikawa T, Kashihara N, Maruyama K, et al. (1998) Expression of interleukin-8 in human glomerulonephritis. Res Commun Mol Pathol Pharmacol 99: 217–224. 27. Peichl P, Ceska M, Broell H, et al. (1992) Human neutrophil activating peptide/interleukin 8 acts as an autoantigen in rheumatoid arthritis. Ann Rheum Dis 51: 19–22.

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58. Leveen P, Pekny M, Gebre-Medhin S, et al. (1994) Mice deficient for PDGF B show renal, cardiovascular, and hematological abnormalities. Genes Dev 8: 1875–1887. 59. Hellstrom M, Kal n M, Lindahl P, et al. (1999) Role of PDGF-B and PDGFR-beta in recruitment of vascular smooth muscle cells and pericytes during embryonic blood vessel formation in the mouse. Development 126: 3047–3055. 60. Lindahl P, Hellstrom M, Kalen M, et al. (1998) Paracrine PDGF-B/PDGFRbeta signaling controls mesangial cell development in kidney glomeruli. Development 125: 3313–3322. 61. Soriano P. (1994) Abnormal kidney development and hematological disorders in PDGF beta-receptor mutant mice. Genes Dev 8: 1888–1896. 62. Liao X, Escobedo JA, Williams LT. (1996) Viability of transgenic mice expressing a platelet derived growth factor (PDGF) antagonist in plasma. J Investig Med 44: 139–143. 63. Floege J, Hudkins KL, Davis CL, et al. (1998) Expression of PDGF alphareceptor in renal arteriosclerosis and rejecting renal transplants. J Am Soc Nephrol 9: 211–223. 64. Floege J, Burns MW, Alpers CE, et al. (1992) Glomerular cell proliferation and PDGF expression precede glomerulosclerosis in the remnant kidney model. Kidney Int 41: 297–309. 65. Kliem V, Johnson RJ, Alpers CE, et al. (1996) Mechanisms involved in the pathogenesis of tubulointerstitial fibrosis in 5/6-nephrectomized rats. Kidney Int 49: 666–678. 66. Ranieri E, Gesualdo L, Grandaliano G, et al. (2001) The role of alphasmooth muscle actin and platelet-derived growth factor-beta receptor in the progression of renal damage in human IgA nephropathy. J Nephrol 14: 253–262. 67. Waldherr R, Noronha IL, Niemir Z, et al. (1993) Expression of cytokines and growth factors in human glomerulonephritides. Pediatr Nephrol 7: 471–478. 68. Floege J, Eng E, Young BA, et al. (1993) Infusion of platelet-derived growth factor or basic fibroblast growth factor induces selective glomerular mesangial cell proliferation and matrix accumulation in rats. J Clin Invest 92: 2952–2962. 69. Hudkins KL, Gilbertson DG, Carling M, et al. (2004) Exogenous PDGF-D is a potent mesangial cell mitogen and causes a severe mesangial proliferative glomerulopathy. J Am Soc Nephrol 15: 286–298. 70. Johnson RJ, Raines EW, Floege J, et al. (1992) Inhibition of mesangial cell proliferation and matrix expansion in glomerulonephritis in the rat by antibody to platelet-derived growth factor. J Exp Med 175: 1413–1416.

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71. Floege J, Ostendorf T, Janssen U, et al. (1999) Novel approach to specific growth factor inhibition in vivo: antagonism of platelet-derived growth factor in glomerulonephritis by aptamers. Am J Pathol 154: 169–179. 72. Nakamura H, Isaka Y, Tsujie M, et al. (2001) Electroporation-mediated PDGF receptor-IgG chimera gene transfer ameliorates experimental glomerulonephritis. Kidney Int 59: 2134–2145. 73. Takahashi T, Abe H, Arai H, et al. (2005) Activation of STAT3/Smad1 is a key signaling pathway for progression to glomerulosclerosis in experimental glomerulonephritis. J Biol Chem 280: 7100–7106. 74. Iruela-Arispe L, Gordon K, Hugo C, et al. (1995) Participation of glomerular endothelial cells in the capillary repair of glomerulonephritis. Am J Pathol 147: 1715–1727. 75. Ostendorf T, Kunter U, van Roeyen C, et al. (2002) The effects of plateletderived growth factor antagonism in experimental glomerulonephritis are independent of the transforming growth factor-beta system. J Am Soc Nephrol 13: 658–667. 76. Gilbert RE, Kelly DJ, McKay T, et al. (2001) PDGF signal transduction inhibition ameliorates experimental mesangial proliferative glomerulonephritis. Kidney Int 59: 1324–1332. 77. Hirai T, Masaki T, Kuratsune M, et al. (2006) PDGF receptor tyrosine kinase inhibitor suppresses mesangial cell proliferation involving STAT3 activation. Clin Exp Immunol 144: 353–361. 78. Jayson GC, Parker GJ, Mullamitha S, et al. (2005) Blockade of plateletderived growth factor receptor-beta by CDP860, a humanized, PEGylated di-Fab’, leads to fluid accumulation and is associated with increased tumor vascularized volume. J Clin Oncol 23: 973–981. 79. Piek E, Heldin CH, Ten Dijke P. (1999) Specificity, diversity, and regulation in TGF-beta superfamily signaling. FASEB J 13: 2105–2124. 80. Blobe GC, Schiemann WP, Lodish HF. (2000) Role of transforming growth factor beta in human disease. N Engl J Med 342: 1350–1358. 81. Li MO, Wan YY, Sanjabi S, et al. (2006) Transforming growth factor-beta regulation of immune responses. Annu Rev Immunol 24: 99–146. 82. Prud’homme GJ. (2007) Pathobiology of transforming growth factor beta in cancer, fibrosis and immunologic disease, and therapeutic considerations. Lab Invest 87: 1077–1091. 83. Sharma K, Ziyadeh FN. (1994) The emerging role of transforming growth factor-beta in kidney diseases. Am J Physiol 266: F829–F842. 84. Yang Z, Mu Z, Dabovic B, et al. (2007) Absence of integrin-mediated TGFbeta1 activation in vivo recapitulates the phenotype of TGFbeta1-null mice. J Cell Biol 176: 787–793. 85. Bottinger EP, Bitzer M. (2002) TGF-beta signaling in renal disease. J Am Soc Nephrol 13: 2600–2610.

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86. Kitamura M, Suto TS. (1997) TGF-beta and glomerulonephritis: antiinflammatory versus prosclerotic actions. Nephrol Dial Transplant 12: 669–679. 87. van Vlasselaer P, Punnonen J, de Vries JE. (1992) Transforming growth factor-beta directs IgA switching in human B cells. J Immunol 148: 2062–2067. 88. Bitzer M, von Gersdorff G, Liang D, et al. (2000) A mechanism of suppression of TGF-beta/SMAD signaling by NF-kappa B/RelA. Genes Dev 14: 187–197. 89. Floege J, Ostendorf T, Wolf G. (2001) Growth factors and cytokines. In: Immunologic Renal Diseases (eds.) Couser WG, Neilson EG. LippincottRaven, Philadelphia, pp. 415–463. 90. Shull MM, Ormsby I, Kier AB, et al. (1992) Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease. Nature 359: 693–699. 91. Chen CA, Hwang JC, Guh JY, et al. (2006) TGF-beta1 and integrin synergistically facilitate the differentiation of rat podocytes by increasing alphasmooth muscle actin expression. Transl Res 148: 134–141. 92. Schiffer M, Bitzer M, Roberts IS, et al. (2001) Apoptosis in podocytes induced by TGF-beta and Smad7. J Clin Invest 108: 807–816. 93. Chen S, Lee JS, Iglesias-de la Cruz MC, et al. (2005) Angiotensin II stimulates alpha3(IV) collagen production in mouse podocytes via TGF-beta and VEGF signalling: implications for diabetic glomerulopathy. Nephrol Dial Transplant 20: 1320–1328. 94. Abbate M, Zoja C, Morigi M, et al. (2002) Transforming growth factorbeta1 is up-regulated by podocytes in response to excess intraglomerular passage of proteins: a central pathway in progressive glomerulosclerosis. Am J Pathol 161: 2179–2193. 95. Yard BA, Chorianopoulos E, Herr D, et al. (2001) Regulation of endothelin1 and transforming growth factor-beta1 production in cultured proximal tubular cells by albumin and heparan sulphate glycosaminoglycans. Nephrol Dial Transplant 16: 1769–1775. 96. Wolf G, Schroeder R, Ziyadeh FN, et al. (2004) Albumin up-regulates the type II transforming growth factor-beta receptor in cultured proximal tubular cells. Kidney Int 66: 1849–1858. 97. Ostendorf T, Kunter U, Eitner F, et al. (1999) VEGF(165) mediates glomerular endothelial repair. J Clin Invest 104: 913–923. 98. Li ZD, Bork JP, Krueger B, et al. (2005) VEGF induces proliferation, migration, and TGF-beta1 expression in mouse glomerular endothelial cells via mitogen-activated protein kinase and phosphatidylinositol 3kinase. Biochem Biophys Res Commun 334: 1049–1060.

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99. Wolf G, Schroeder R, Ziyadeh FN, et al. (1997) High glucose stimulates expression of p27Kip1 in cultured mouse mesangial cells: relationship to hypertrophy. Am J Physiol 273: F348–F356. 100. Li JM, Nichols MA, Chandrasekharan S, et al. (1995) Transforming growth factor beta activates the promoter of cyclin-dependent kinase inhibitor p15INK4B through an Sp1 consensus site. J Biol Chem 270: 26750–26753. 101. Isaka Y, Fujiwara Y, Ueda N, et al. (1993) Glomerulosclerosis induced by in vivo transfection of transforming growth factor-beta or platelet-derived growth factor gene into the rat kidney. J Clin Invest 92: 2597–2601. 102. Iwano M, Akai Y, Fujii Y, et al. (1994) Intraglomerular expression of transforming growth factor-beta 1 (TGF-beta 1) mRNA in patients with glomerulonephritis: quantitative analysis by competitive polymerase chain reaction. Clin Exp Immunol 97: 309–314. 103. Yoshioka K, Takemura T, Murakami K, et al. (1993) Transforming growth factor-beta protein and mRNA in glomeruli in normal and diseased human kidneys. Lab Invest 68: 154–163. 104. Lai KN, Tang SC, Guh JY, et al. (2003) Polymeric IgA1 from patients with IgA nephropathy upregulates transforming growth factor-beta synthesis and signal transduction in human mesangial cells via the reninangiotensin system. J Am Soc Nephrol 14: 3127–3137. 105. Tomooka S, Border WA, Marshall BC, et al. (1992) Glomerular matrix accumulation is linked to inhibition of the plasmin protease system. Kidney Int 42: 1462–1469. 106. Kagami S, Border WA, Miller DE, et al. (1994) Angiotensin II stimulates extracellular matrix protein synthesis through induction of transforming growth factor-beta expression in rat glomerular mesangial cells. J Clin Invest 93: 2431–2437. 107. Shin GT, Kim SJ, Ma KA, et al. (2000) ACE inhibitors attenuate expression of renal transforming growth factor-beta1 in humans. Am J Kidney Dis 36: 894–902. 108. Zeisberg M, Hanai J, Sugimoto H, et al. (2003) BMP-7 counteracts TGFbeta1-induced epithelial-to-mesenchymal transition and reverses chronic renal injury. Nat Med 9: 964–968. 109. Sanderson N, Factor V, Nagy P, et al. (1995) Hepatic expression of mature transforming growth factor beta 1 in transgenic mice results in multiple tissue lesions. Proc Natl Acad Sci USA 92: 2572–2576. 110. Ziyadeh FN, Hoffman BB, Han DC, et al. (2000) Long-term prevention of renal insufficiency, excess matrix gene expression, and glomerular mesangial matrix expansion by treatment with monoclonal antitransforming growth factor-beta antibody in db/db diabetic mice. Proc Natl Acad Sci USA 97: 8015–8020.

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111. Chen S, Iglesias-de la Cruz MC, Jim B, et al. (2003) Reversibility of established diabetic glomerulopathy by anti-TGF-beta antibodies in db/db mice. Biochem Biophys Res Commun 300: 16–22. 112. Ling H, Li X, Jha S, et al. (2003) Therapeutic role of TGF-beta-neutralizing antibody in mouse cyclosporin A nephropathy: morphologic improvement associated with functional preservation. J Am Soc Nephrol 14: 377–388. 113. Yu L, Border WA, Anderson I, et al. (2004) Combining TGF-beta inhibition and angiotensin II blockade results in enhanced antifibrotic effect. Kidney Int 66: 1774–1784. 114. Benigni A, Zoja C, Corna D, et al. (2003) Add-on anti-TGF-beta antibody to ACE inhibitor arrests progressive diabetic nephropathy in the rat. J Am Soc Nephrol 14: 1816–1824. 115. Benigni A, Zoja C, Campana M, et al. (2006) Beneficial effect of TGFbeta antagonism in treating diabetic nephropathy depends on when treatment is started. Nephron Exp Nephrol 104: e158–e168. 116. El Chaar M, Chen J, Seshan SV, et al. (2007) Effect of combination therapy with enalapril and the TGF-beta antagonist 1D11 in unilateral ureteral obstruction. Am J Physiol Renal Physiol 292: F1291–F1301. 117. Sugaru E, Sakai M, Horigome K, et al. (2005) SMP-534 inhibits TGF-betainduced ECM production in fibroblast cells and reduces mesangial matrix accumulation in experimental glomerulonephritis. Am J Physiol Renal Physiol 289: F998–F1004. 118. Petersen M, Thorikay M, Deckers M, et al. (2008) Oral administration of GW788388, an inhibitor of TGF-beta type I and II receptor kinases, decreases renal fibrosis. Kidney Int 73: 705–715. 119. Nguyen TQ, Goldschmeding R. (2008) Bone morphogenetic protein-7 and connective tissue growth factor: novel targets for treatment of renal fibrosis? Pharm Res, Feb 12 [Epub ahead of print] PMID: 18266088. 120. Ito Y, Aten J, Bende RJ, et al. (1998) Expression of connective tissue growth factor in human renal fibrosis. Kidney Int 53: 853–861. 121. Suzuki D, Toyoda M, Umezono T, et al. (2003) Glomerular expression of connective tissue growth factor mRNA in various renal diseases. Nephrology (Carlton) 8: 92–97. 122. Nonaka Takahashi S, Fujita T, Takahashi T, et al. (2008) TGF-beta1 and CTGF mRNAs are correlated with urinary protein level in IgA nephropathy. J Nephrol 21: 53–63. 123. Boor P, Sebekova K, Ostendorf T, et al. (2007) Treatment targets in renal fibrosis. Nephrol Dial Transplant 22: 3391–3407.

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Chapter 19

Monocytes and Macrophages Yohei Ikezumi and David J. Nikolic-Paterson

Introduction A major difficulty in how to treat IgA nephropathy (IgAN) lies in the fact that only 15%–40% of patients will progress to end-stage renal failure. Whether this represents the heterogeneous nature of this disease, perhaps decided by various genetic susceptibilities, or whether IgAN is not a single disease entity, has yet to be resolved. Clearly, it is undesirable to give individuals immunosuppressive therapy which is not required. Equally, it is desirable to identify those individuals who would benefit from some form of immunosuppressive therapy. Therefore, it is important to understand the underlying disease pathogenesis in order to distinguish between the “progressors” and “non-progressors.” This chapter describes the role of the monocyte/macrophage in the induction and progression of IgAN.

Monocyte/Macrophages — A Heterogeneous Cell Type Macrophages are highly pleomorphic cells which have many functions in tissue homeostasis, host defense, tissue remodeling and repair.1 Macrophages respond to infection through direct pathogen recognition in the innate immune response, interaction with antibody and complement, and activation of the adaptive immune response through antigen presentation. Upon entering a tissue, blood monocytes respond to signals within the local microenvironment and undergo differentiation to

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become resident tissue macrophages. Even greater heterogeneity in macrophage function ensues when blood monocytes enter tissues undergoing acute or chronic inflammation, coagulation, hypoxia, or repair. Thus, it can be difficult to classify macrophage function in any given pathologic situation. Various strategies have been used to characterize the different states of macrophage activation. Macrophages make a pro-inflammatory response to direct recognition of microbial pathogens (innate activation), binding of antibody or complement components (humoral activation), and to cytokines such as interferon-γ (classical activation) with production of high levels of reactive nitrogen and oxygen radicals and secretion of pro-inflammatory cytokines. This contrasts to the “alternative” response in which macrophages produce anti-inflammatory cytokines and prostaglandins when stimulated by interleukin-4 (IL-4), IL-10, IL-13, transforming growth factor-β1 (TGF-β1), glucocorticoids or by phagocytosis of apoptotic cells.2 Macrophage activation has also been described in terms of the M1/M2 phenotype which relates macrophage function to the Th1/Th2 response.3 Thus, simply identifying the presence of macrophages within a site of tissue damage does not necessarily indicate whether these cells are promoting inflammation and tissue damage, or if they are involved in tissue remodeling and repair — or both.

Macrophages in IgA Nephropathy Macrophage infiltration in the glomerulus and/or interstitium is a common feature in most types of glomerulonephritis.4 Analysis of renal biopsies using immunohistochemistry techniques has provided information on the localization and number of macrophages within the kidney in IgAN.5–9 The degree of glomerular macrophage accumulation varies considerably between different studies of IgAN, which probably reflects the variation in disease severity and the presence of active versus chronic lesions in the different patient cohorts examined (see Figure 19.1). Thus, some studies found no significant glomerular macrophage infiltrate in IgAN, while other studies found a significant glomerular infiltrate that correlated with the degree of proteinuria.6–8 In contrast, significant interstitial macrophage infiltration is a common

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Figure 19.1 Immunohistochemistry staining of CD68+ macrophages (brown). (a) An early proliferative lesion with many infiltrating glomerular CD68+ macrophages. (b) A chronic lesion in which the sclerotic glomerulus has few CD68+ macrophages, while the damaged tubulointerstitium exhibits a prominent CD68+ macrophage infiltrate. Original magnification, ×400.

feature in virtually all studies of IgAN and this correlates with renal dysfunction and histologic damage.5–10 Furthermore, the presence of macrophages in urine has been identified in patients with IgAN and this has been proposed as a tool for monitoring disease activity.11 Of note, a recent study identified a significant glomerular and interstitial macrophage infiltrate in new onset IgAN in both adults and children which correlated with proteinuria and histologic damage, suggesting a role for macrophages in early lesion development.12 Furthermore, longitudinal studies have found that the degree of interstitial macrophage accumulation is predictive of disease progression.8,13,14 Macrophage infiltration in IgAN is invariably accompanied by infiltration of T cells,5,6 which is illustrated in Figure 19.2. This T cell infiltrate also correlates with proteinuria and histologic damage.5–8,12,14 Interstitial filtration of B cells has also been described in IgAN.5,15 In addition, one study has reported increased numbers of interstitial mast cells in IgAN which is associated with a poor outcome.16 The role of T and B cells in IgAN is discussed in Chapter 14 and will not be considered here in detail, although clearly T cells play an important role in activating and orchestrating macrophage effector functions in the adaptive immune response.

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Figure 19.2 Co-localization of macrophages and T cells in IgAN. Immunofluorescence staining showing infiltration of CD68+ macrophages (green) in a predominant periglomerular localization. CD3+ T cells (red) co-localize with CD68+ macrophages, which is readily apparent in the merged field. Original magnification, ×400.

Mechanisms of Monocyte Recruitment in IgA Nephropathy Several mechanisms have been implicated in the recruitment of blood monocytes in IgAN, some of which may also contribute to monocyte/ macrophage activation. Monocyte recruitment into glomeruli and the interstitium requires a series of coordinated interactions between monocytes and the endothelium involving chemoattractants, leukocyte adhesion molecules and their respective ligands. Deposition of IgA, which is commonly accompanied by deposition of IgG and C3, may also contribute to monocyte recruitment and activation in the glomerulus. The up-regulation of P-selectin and E-selectin, and the up-regulation of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) are common finding in human and experimental glomerulonephritis.17 Studies in IgAN have identified up-regulation of E-selectin, ICAM-1 and VCAM-1 in cases with significant lesions and exhibiting macrophage and T cell infiltration.18–21 Of note in IgAN, there is mesangial expression of ICAM-1 and VCAM-1.19,21,22 The up-regulation of ICAM-1 and VCAM-1 correlates with interstitial macrophage and T cell infiltration and is associated with progressive histologic damage in longitudinal studies.21,22 Macrophage migration inhibitory factor (MIF) is a pro-inflammatory and chemotactic cytokine that has been shown to play a pathological role in macrophage accumulation and activation in experimental

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crescentic glomerulonephritis.23 A significant increase in renal MIF mRNA and protein expression is evident in most forms of glomerulonephritis, including IgAN.24 Urinary excretion of MIF is increased in IgAN and correlates with renal macrophage accumulation.25 Linking MIF to IgAN is the finding that both polymeric IgA and IgA-containing immune complexes can induce MIF production by human mesangial cells.26 A number of chemokines, most particularly monocyte chemoattractant protein-1 (MCP-1, also known as CCL2), have been shown to promote monocyte recruitment in human and experimental glomerulonephritis.27 Several studies have identified renal MCP-1 production and urinary MCP-1 excretion in IgAN which correlates with macrophage accumulation.28–30 Tubular epithelial cells are the main site of MCP-1 production in IgAN, which correlates with macrophage accumulation and tubulointerstitial damage. Furthermore, a recent study identified the urinary epidermal growth factor/MCP-1 ratio as a prognostic marker in the progression of IgAN to end-stage kidney disease,31 a result which implicates macrophages in disease progression. A mechanistic link between IgA deposition, MCP-1 production and monocyte recruitment is suggested by a study in which the addition of soluble IgA aggregates to human mesangial cells induced production of the chemokines MCP-1, IL-8, and IFN-inducible protein-10 via the Fc receptor for IgA (FcαRI, also known as CD89).32 In a similar fashion, transfection of mouse mesangial cells with the FcαRI enabled heat aggregated IgA to induce MCP-1 production.33 Furthermore, a number of pro-inflammatory factors up-regulated in IgAN, such as IL-1 and TNF-α, as well as aggregated IgG, have been shown to induce MCP-1 production by mesangial cells and tubular epithelial cells.34–36 Chemokine and chemokine receptors (IL-8, CCR1, CCR2, CCR5, and CXCR3) which promote the recruitment of monocytes, neutrophils and T cells have been shown to be up-regulated in IgAN.30,37–39 Osteopontin (OPN) is a secreted multifunctional protein that is highly acidic and contains an adhesive Arg-Gly-Asp sequence that binds to various integrins, CD44, fibronectin, and type I collagen.40,41 OPN is a potent chemoattractant for macrophages.42 Studies in experimental kidney disease have shown co-localization of tubular OPN expression with peri-tubular accumulation of CD44+ macrophages and T cells,43 while blockade of OPN function suppressed macrophage accumulation and renal injury in this disease model.44 Examination of IgAN also

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found de novo OPN expression in tubules with co-localization of peritubular CD44+ macrophages, and an excellent overall correlation between tubular OPN expression and interstitial macrophage accumulation.45,46 A significant correlation between renal OPN expression and serum creatinine, proteinuria and histologic damage was reported in one of these studies.45 It is known that pro-inflammatory cytokines, such as IL-1, can up-regulate tubular OPN expression in vitro and in vivo,47 providing a possible mechanism by which IgA-induced mesangial IL-1 or TNF-α secretion could act downstream on tubular epithelial cells to induce OPN expression (and MCP-1 production) thus promoting interstitial macrophage accumulation. The role of IgG and complement in glomerular recruitment of blood monocytes is well established in experimental models of antibodydependent glomerulonephritis, but evidence of a similar functional role in human kidney disease is more difficult to prove and rests mainly upon disease modifying mutations.48,49 A difficulty is that individual glomeruli may be affected at different times and monocyte/macrophage accumulation is a dynamic and reversible process so that a single “snap-shot” as presented by the biopsy may not reveal a role for IgG or complement in glomerular monocyte recruitment. Less still is known whether direct recognition of deposited IgA or IgA-containing immune complexes promote glomerular monocyte recruitment. However, this question has been addressed using an experimental model in which macrophages in mice are genetically modified to over-express FcαRI. Such mice develop marked mesangial IgA deposition, glomerular and periglomerular macrophage accumulation, histologic damage and mild albuminuria — although these mice do not develop progressive kidney disease.50 However, it needs to be appreciated that mouse models of “experimental IgAN” have significant limitations given the substantial differences in the IgA system between humans and rodents. Thus, both FcαRI and other potential mechanisms of blood monocyte recruitment in human IgAN may not be faithfully represented in animal models (also refer to Chapter 26).

Macrophage Activation in IgA Nephropathy Macrophages have the potential to cause renal injury through the production of a wide range of mediators, including reactive oxygen species,

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nitric oxide, pro-inflammatory cytokines, pro-fibrotic and pro-proliferative growth factors, matrix metalloproteinases and vasoactive molecules. Indirect evidence that macrophages mediate renal injury has come from experimental studies in which various strategies to inhibit renal macrophage accumulation have been shown to reduce renal injury.4 Direct evidence for an injurious role of macrophages has come from studies of antibody-induced glomerular injury in which proteinuria and mesangial cell proliferation are dependent upon adoptive transfer of macrophages.51 Classical activation of macrophages by interferon-γ augmented macrophage-dependent proteinuria and mesangial cell proliferation in this model, while inhibition of the c-Jun amino terminal kinase (JNK) signaling pathway or steroid treatment of macrophages was shown to suppress injury.52,53 There is ample evidence to indicate a macrophage pro-inflammatory response in IgAN. Examination of biopsies from a cohort of 40 cases of IgAN using immunohistochemistry and in situ hybridization identified macrophages as the main cell type producing a range of pro-inflammatory cytokines, including IL-1α, IL-1β, IL-6, IL-8 and TNF-α. Glomerular IL-1α, IL-6 and TNF-α expression correlated with mesangial hypercellularity, while interstitial IL-1α, IL-6, IL-8 and TNF-α expression correlated with tubulointerstitial damage and proteinuria.54 Similarly, interstitial IL-1β expression in IgAN has been shown to correlate with macrophage accumulation and progression to end-stage renal failure.14 Macrophage production of nitric oxide is considered a hallmark of the pro-inflammatory response in innate and classical macrophage activation.2 iNOS expression by interstitial macrophages has been detected in biopsies of IgAN, with the number of iNOS+ cells correlating with tubulointerstitial damage and loss of renal function.55 Macrophage production of various pro-inflammatory mediators including iNOS, IL-1 and TNF-α operates, in part, via the p38 mitogen-activated protein kinase (MAPK) signaling pathway. A recent study identified p38 MAPK signaling in macrophages, as well as many other cell types, in biopsies of IgAN providing another example of the macrophage pro-inflammatory response in this disease.56 Macrophages are also an important, but not unique, source of proliferative and pro-fibrotic growth factors that have been implicated in promoting mesangial proliferation and fibrosis in IgAN (see Chapter 18).

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Markers of Macrophage Activation Rather than measuring production of individual mediators, one can look for markers to define the macrophage activation status. One marker that has been widely used to identify activated, pro-inflammatory macrophages is expression of myeloid-related protein 8 (MRP8) and MRP14, members of the S100 family.57 MRP8 and MRP14 represent the predominant calcium-binding capacity of monocytes and neutrophils during their early stage of differentiation, but neither protein is detected on resting tissue macrophages or lymphocytes. The 27E10 antibody recognises an epitope of the MRP8/14 dimer that is expressed upon activated macrophages (and some neutrophils). Such 27E10+ macrophages can be found within sites of acute inflammation, but are mainly absent in sites of chronic inflammation.58,59 The presence of 27E10+ macrophages in glomeruli and the interstitium has been described in IgAN.60,61 Furthermore, a recent study found shown that the number of glomerular and interstitial 27E10+ cells correlated with the loss of renal function over a two-year period in a cohort of 32 IgAN patients,13 implicating pro-inflammatory macrophages in the progression of IgAN. CD86 is a T-cell co-stimulatory molecule implicated in promoting cellular immunity.62 In a study of IgAN, a significant infiltrate of glomerular and interstitial CD86+ cells was identified and these cells were found to be predominantly macrophages. Total glomerular macrophages and glomerular CD86+ cells correlated with the severity of histologic damage, but not with renal function. However, interstitial macrophages and CD86+ cells correlated with both histologic damage and renal function.63 The expression of CD169 (sialoadhesin) as a marker of macrophage activation has been examined in various glomerulonephridities.64 Sialoadhesin was originally identified as an erythrocyte receptor expressed by subsets of “activated’’ macrophages, and characterized as a member of the immunoglobulin superfamily uniquely expressed by macrophages and is a prototypical member of the family of sialic acid binding proteins.65 Sialoadhesin expression is normally restricted to a subset of tissue macrophages in lymphoid tissues, and is largely absent in non-lymphoid tissues such as the kidney.65 Sialoadhesin is thought to contribute to macrophage cell–cell and cell–matrix interactions during inflammatory reactions,66 including antigen presentation to T cells,67

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Figure 19.3 Immunofluorescence staining of macrophage activation in IgAN. An early proliferative lesion (top panel) shows the presence of glomerular and periglomerular CD68+ macrophages (red). Many of these macrophages express the activation marker, sialoadhesin (CD169, green), which is evident in the merged field. In a chronic lesion (bottom panel), many CD68+ macrophages are present around glomeruli and throughout the interstitium. A very similar distribution is seen for CD169+ macrophages (green), which is emphasized in the merged image. Original magnification, ×400.

although the function of this subset is not clearly understood. The presence of significant numbers of CD169+ macrophages was identified in both glomeruli and the interstitium in a cohort of adults and children with new onset IgAN.12 The co-expression of CD68 and CD169 by glomerular and interstitial macrophages in acute and chronic lesions is shown in Figure 19.3. Glomerular and interstitial CD169+ macrophages correlated with the degree of proteinuria and histologic damage.12 In addition, glucocorticoid-based therapy of patients was effective in reducing proteinuria and glomerular lesions, and this response correlated with a reduction in the number of glomerular and interstitial CD169+ macrophages. However, the number of CD169+ macrophages is undiminished in steroid-resistant IgAN, but this situation is responsive to mizoribine treatment.68 While this beneficial effect may relate to modification of the T cell response, mizoribine has been shown to

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exert direct effects upon macrophage functions.69 These data suggest that the CD169+ macrophage subset may play a role in mediating renal injury in IgAN.

Mechanisms of Macrophage Activation There are three main mechanisms by which macrophages are activated to make a pro-inflammatory response; activation by humoral reactants, activation by T cells, and activation of the innate immune response. These are considered below.

Macrophage Activation via the Humoral Immune Response Given that IgG deposition and complement activation are common findings in IgAN, these mechanisms could play an important role in macrophage activation as is seen in other antibody-dependent diseases, such as lupus nephritis.48,49 Indeed, polymorphisms of the FcgRIIa and FcgRIIIa have been shown to affect the severity of IgAN in Japanese patients, but not disease incidence, suggesting that IgG-containing immune complexes may promote the progression of IgAN.70 However, glomerular IgA deposition may play a specific role in macrophage activation. For example, IgA has been shown to induce the alternative pathway of complement activation via the mannan-binding lectin, and this is associated with more severe disease.71,72 Furthermore, a series of elegant animal studies by Monteiro and colleagues50,73,74 have provided strong evidence to support the postulate that FcαRI signaling promotes macrophage recruitment and activation in the development of renal injury in IgAN. Ligation of the FcαRI can transmit either a positive or negative regulatory signal to the macrophage through its interaction with the ITAM-bearing Fc receptor γ (FcRγ).74 Mice with transgenic expression of FcαRI in macrophages develop mesangial IgA deposition with macrophage infiltration, renal injury and albuminuria. In contrast, mice transgenic for a mutated form of FcαRI (FcαRIR209L that cannot associate with the FcRγ chain) show reduced macrophage infiltration, milder lesions and no albuminuria despite equivalent mesangial IgA deposition.73 Cross-linking the FcαRI provides a positive signal promoting a pro-inflammatory macrophage response. Inducing FcαRI cross-linking

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in vivo increased glomerular macrophage accumulation and caused more severe proteinuria in FcαRI transgenic mice without affecting IgA deposition, but no effect of the cross-linking strategy was seen in FcαRIR209L transgenic mice indicating a requirement for FcRγ signaling in this response.73 Furthermore, it is possible to induce a negative regulatory signal using a Fab fragment of a particular anti-FcαRI antibody. Administration of this Fab fragment suppressed macrophage accumulation, histologic damage and albuminuria in FcαRI transgenic mice despite unaltered mesangial IgA deposition.74

Macrophage Activation via the T Cell Response The best known example of T cells directing a macrophage proinflammatory response is the delayed-type hypersensitivity (DTH) reaction. In this response, memory T cells encountering antigen in the periphery induce the recruitment and subsequent activation of blood monocytes through the production of Th1 cytokines such as MIF, interferon-γ (IFN-γ) and IL-12. Active crescents are seen in a small subset of patients with IgAN and this is a poor prognostic indicator. These active crescents display the classic features of the DTH reaction with accumulation of activated T cells and macrophages,75 providing a strong argument for T cell-directed macrophage-mediated renal injury in this subset of IgAN. Most cases of IgAN do not exhibit crescent formation. However, many biopsies exhibit features of T cell-directed macrophage activation. There is a highly significant correlation between T cell and macrophage accumulation.8,12 T cell infiltration, particularly in the interstitium, correlates with histologic damage, proteinuria and disease progression,5–8,12,14 and renal expression of DTH cytokines is also apparent. Up-regulation of MIF expression has been described in IgAN,24 while the de novo expression of IL-12 in glomeruli correlates with both the grade of histologic damage and the degree of proteinuria (macrophages and T cells were not examined).76 In addition, spleen cells were shown to produce high levels of IL-12 in a model of spontaneous high IgA production in ddY mice. Furthermore, administration of IL-12 promoted glomerular accumulation of CD4+ T cells and macrophages with resultant crescent formation.77 Finally, mesangial IFN-γ production has been described,78 while serum IFN-γ levels correlate with glomerular HLA-DQ expression and acute exacerbation in patients with IgA nephropathy.79 However, it

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should be noted that a number of studies have failed to detect IFN-γ expression in IgAN.80

Macrophage Activation by the Innate Immune Response Macrophages express a wide range of receptors, known as the Toll-like receptors (TLR), which recognize pathogen-associated molecular patterns.81 Activation of these pattern recognition receptors leads to an innate immune response involving production of nitrogen and oxygen radicals and pro-inflammatory cytokines, and the initiation of an adaptive immune response. As yet, little is known of the innate immune response in IgAN, but this may be a fruitful area for future research based upon the association between flares of IgAN and infection.82 It may be the case that inappropriate activation of the innate immune response in gut macrophages promotes B cell production and maturation resulting in elevated IgA production. A second possibility is that infection in the upper respiratory tract or tonsils can drive IgA production via the innate immune response. A third possibility is that trace amounts of microbial agents present during acute infection can directly activate macrophages within the kidney, thereby exacerbating an existing disease process. This last possibility is supported by studies in which administration of various TLR ligands has been shown to exacerbate experimental models of immune complex disease.83

Targeting Macrophage-Mediated Renal Injury in IgA Nephropathy The macrophage pro-inflammatory response plays a central role in the glomerular and tubulointerstitial damage underlying the progression of IgAN. The two main avenues to target macrophage-mediated renal injury are the blockade of blood monocyte recruitment and/or preventing activation of the macrophage pro-inflammatory response. Chemokine antagonists are a promising strategy for the blockade of monocyte recruitment into the kidney. Administration of antagonists targeting the MCP-1 receptor (CCR2), CCR1 or CCR5 are highly effective in preventing macrophage accumulation and tissue injury in models of renal inflammation.84–86 Another strategy to inhibit macrophage accumulation and activation is blockade of MIF. The use of MIF inhibitors

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has demonstrated a pathogenic role for this cytokine in a wide range of diseases, including crescentic glomerulonephritis 23,87–89 The potential to induce a negative regulatory signal via the FcαRI is a very attractive therapeutic strategy for progressive IgAN. However, the potential consequences of such an approach on gut immunity and control of infectious microorganisms will need to be addressed before this approach could be considered for patients. Given the major importance of tubulointerstitial damage in the progression of IgAN, targeting tubular activation and interstitial inflammation is an appealing therapeutic strategy. One possibility is to block the JNK signaling pathway. A recent study identified marked JNK signaling in tubular cells in a variety of glomerulonephridities, including IgAN, which correlated with tubulointerstitial damage and declining renal function.90 Not only is JNK signaling involved in the macrophage pro-inflammatory response,53 but JNK signaling is involved in mesangial and tubular cell production of MCP-1 and TGF-β1,90–92 suggesting a cycle of JNK-dependent tubulointerstitial inflammation. Furthermore, a recent study has shown that systemic administration of a small molecule JNK inhibitor is highly effective in suppressing glomerular and tubulointerstitial damage in an experimental model of macrophagedependent glomerulonephritis.93 There has also been considerable interest in targeting T cells in IgAN which would also be expected to suppress macrophage-mediated renal injury. As yet, clinical trials using drugs such as mycophenolate mofetil have yet to establish the efficacy of such an approach in IgAN.94 An alternative approach is the use of glucocorticoids in IgAN. This has been effective in some, but not all studies, and the issues of patient selection and dosing regimen are still a matter of debate (see Chapter 21). A small number of repeat biopsy studies have shown that a positive response to glucocorticoid treatment is associated with a reduction in glomerular and/or interstitial macrophage accumulation,8,95 including a reduction in CD169+ activated macrophages.64 This is likely to involve inhibition of monocyte recruitment since glucocorticoids have been shown to suppress the up-regulation of various leukocyte adhesion molecules,96 and glucocorticoid treatment of macrophages can inhibit their ability to be recruited into the inflamed glomerulus.52 Glucocorticoids can also inhibit the Th1 response, which would be expected to be beneficial in IgAN; however, glucocorticoids can also augment the Th2 response,97 which could theoretically exacerbate IgA production and renal fibrosis

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through up-regulation of IL-4, IL-10 and IL-13. Currently, we have little information on the effect of glucocorticoid therapy on the state of macrophage activation in IgAN, and this may be a critical issue for the success or otherwise of this treatment.

Summary In recent years, we have made substantial progress in understanding the pathogenic mechanisms involved in the progression of IgAN. Identifying molecular targets to halt progressive tubulointerstitial damage in IgAN through inhibition of the macrophage pro-inflammatory response is becoming an achievable goal. Furthermore, the ability to monitor ongoing tubulointerstitial damage by non-invasive methods will assist in the selection of patients for immunosuppressive treatment and help in monitoring therapeutic efficacy.

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52. Ikezumi Y, Atkins RC, Nikolic-Paterson DJ. (2003) Interferon–gamma augments acute macrophage–mediated renal injury via a glucocorticoidsensitive mechanism. J Am Soc Nephrol 14: 888–898. 53. Ikezumi Y, Hurst L, Atkins RC, Nikolic-Paterson DJ. (2004) Macrophagemediated renal injury is dependent on signaling via the JNK pathway. J Am Soc Nephrol 15: 1775–1784. 54. Yoshioka K, Takemura T, Murakami K, et al. (1993) In situ expression of cytokines in IgA nephritis. Kidney Int 44: 825–833. 55. Kashem A, Endoh M, Yano N, et al. (1996) Expression of inducible-NOS in human glomerulonephritis: the possible source is infiltrating monocytes/ macrophages. Kidney Int 50: 392–399. 56. Stambe C, Nikolic-Paterson DJ, Hill PA, et al. (2004) p38 Mitogen-activated protein kinase activation and cell localization in human glomerulonephritis: correlation with renal injury. J Am Soc Nephrol 15: 326–336. 57. Odink K, Cerletti N, Bruggen J, et al. (1987) Two calcium-binding proteins in infiltrate macrophages of rheumatoid arthritis. Nature 330: 80–82. 58. Zwadlo G, Schlegel R, Sorg C. (1986) A monoclonal antibody to a subset of human monocytes found only in the peripheral blood and inflammatory tissues. J Immunol 137: 512–518. 59. Hessian PA, Fisher L. (2001) The heterodimeric complex of MRP-8 (S100A8) and MRP-14 (S100A9). Antibody recognition, epitope definition and the implications for structure. FEBS 268: 353–363. 60. Hisano S, Sasatomi Y, Kiyoshi Y, Takebayashi S. (2001) Macrophage subclasses and proliferation in childhood IgA glomerulonephritis. Am J Kidney Dis 37: 712–719. 61. Frosch M, Vogl T, Waldherr R, et al. (2004) Expression of MRP8 and MRP14 by macrophages is a marker for severe forms of glomerulonephritis. J Leuk Biol 75: 198–206. 62. Greenwald RJ, Freeman GJ, Sharpe AH. (2005) The B7 family revisited. Ann Rev Immunol 23: 515–548. 63. Wu Q, Jinde K, Endoh M, Sakai H. (2004) Clinical significance of costimulatory molecules CD80/CD86 expression in IgA nephropathy. Kidney Int 65: 888–896. 64. Ikezumi Y, Suzuki T, Hayafuji S, et al. (2005) The sialoadhesin (CD169) expressing a macrophage subset in human proliferative glomerulonephritis. Nephrol Dial Transplant 20: 2704–2713. 65. Munday J, Floyd H, Crocker PR. (1999) Sialic acid binding receptors (siglecs) expressed by macrophages. J Leuk Biol 66: 705–711. 66. Hartnell A, Steel J, Turley H, et al. (2001) Characterization of human sialoadhesin, a sialic acid binding receptor expressed by resident and inflammatory macrophage populations. Blood 97: 288–296.

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67. Muerkoster S, Rocha M, Crocker PR, et al. (1999) Sialoadhesin-positive host macrophages play an essential role in graft-versus-leukemia reactivity in mice. Blood 93: 4375–4386. 68. Ikezumi Y, Suzuki T, Karasawa T, et al. (2008) Use of mizoribine as a rescue drug for steroid-resistant pediatric IgA nephropathy. Pediatr Nephrol 23: 645–650. 69. Zhong B, Tajima M, Takahara H, et al. (2005) Inhibitory effect of mizoribine on matrix metalloproteinase-1 production in synovial fibroblasts and THP-1 macrophages. Mod Rheumatol 15: 264–268. 70. Tanaka Y, Suzuki Y, Tsuge T, et al. (2005) FcgammaRIIa-131R allele and FcgammaRIIIa-176V/V genotype are risk factors for progression of IgA nephropathy. Nephrol Dial Transplant 20: 2439–2445. 71. Roos A, Bouwman LH, van Gijlswijk-Janssen DJ, et al. (2001) Human IgA activates the complement system via the mannan-binding lectin pathway. J Immunol 167: 2861–2868. 72. Roos A, Rastaldi MP, Calvaresi N, et al. (2006) Glomerular activation of the lectin pathway of complement in IgA nephropathy is associated with more severe renal disease. J Am Soc Nephrol 17: 1724–1734. 73. Kanamaru Y, Arcos-Fajardo M, Moura IC, et al. (2007) Fc alpha receptor I activation induces leukocyte recruitment and promotes aggravation of glomerulonephritis through the FcR gamma adaptor. Eur J Immunol 37: 1116–1128. 74. Kanamaru Y, Pfirsch S, Aloulou M, et al. (2008) Inhibitory ITAM signaling by Fc alpha RI-FcR gamma chain controls multiple activating responses and prevents renal inflammation. J Immunol 180: 2669–2678. 75. Li HL, Hancock WW, Hooke DH, et al. (1990) Mononuclear cell activation and decreased renal function in IgA nephropathy with crescents. Kidney Int 37: 1552–1556. 76. Taniguchi Y, Yorioka N, Tanji C, et al. (2000) Immunohistochemical study of interleukin 12 in patients with IgA nephropathy. Nephron 86: 370–371. 77. Nogaki F, Muso E, Kobayashi I, et al. (2000) Interleukin 12 induces crescentic glomerular lesions in a high IgA strain of ddY mice, independently of changes in IgA deposition. Nephrol Dial Transplant 15: 1146–1154. 78. Lim CS, Yoon HJ, Kim YS, et al. (2003) Clinicopathological correlation of intrarenal cytokines and chemokines in IgA nephropathy. Nephrology 8: 21–27. 79. Yokoyama H, Takaeda M, Wada T, et al. (1992) Intraglomerular expression of MHC class II and Ki-67 antigens and serum gamma-interferon levels in IgA nephropathy. Nephron 62: 169–175. 80. Waldherr R, Noronha IL, Niemir Z, et al. (1993) Expression of cytokines and growth factors in human glomerulonephritides. Pediatr Nephrol 7: 471–478.

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81. Banerjee A, Gerondakis S. (2007) Coordinating TLR-activated signaling pathways in cells of the immune system. Immunol Cell Biol 85: 420–424. 82. Xie Y, Chen X, Nishi S, et al. (2004) Relationship between tonsils and IgA nephropathy as well as indications of tonsillectomy. Kidney Int 65: 1135–1144. 83. Anders HJ, Banas B, Schlondorff D. (2004) Signaling danger: toll-like receptors and their potential roles in kidney disease. J Am Soc Nephrol 15: 854–867. 84. Hasegawa H, Kohno M, Sasaki M, et al. (2003) Antagonist of monocyte chemoattractant protein 1 ameliorates the initiation and progression of lupus nephritis and renal vasculitis in MRL/lpr mice. Arthritis Rheum 48: 2555–2566. 85. Anders HJ, Belemezova E, Eis V, et al. (2004) Late onset of treatment with a chemokine receptor CCR1 antagonist prevents progression of lupus nephritis in MRL-Fas(lpr) mice. J Am Soc Nephrol 15: 1504–1513. 86. Panzer U, Schneider A, Wilken J, et al. (1999) The chemokine receptor antagonist AOP-RANTES reduces monocyte infiltration in experimental glomerulonephritis. Kidney Int 56: 2107–2115. 87. Mikulowska A, Metz CN, Bucala R, Holmdahl R. (1997) Macrophage migration inhibitory factor is involved in the pathogenesis of collagen type II-induced arthritis in mice. J Immunol 158: 5514–5517. 88. Chen Z, Sakuma M, Zago AC, et al. (2004) Evidence for a role of macrophage migration inhibitory factor in vascular disease. Arterioscler, Thromb Vasc Biol 24: 709–714. 89. Denkinger CM, Denkinger M, Kort JJ, et al. (2003) In vivo blockade of macrophage migration inhibitory factor ameliorates acute experimental autoimmune encephalomyelitis by impairing the homing of encephalitogenic T cells to the central nervous system. J Immunol 170: 1274–1282. 90. De Borst MH, Prakash J, Melenhorst WB, et al. (2007) Glomerular and tubular induction of the transcription factor c-Jun in human renal disease. J Pathol 213: 219–228. 91. Naito T, Masaki T, Nikolic-Paterson DJ, et al. (2004) Angiotensin II induces thrombospondin-1 production in human mesangial cells via p38 MAPK and JNK: a mechanism for activation of latent TGF-beta1. Am J Physiol 286: F278–F287. 92. Ma FY, Flanc RS, Tesch GH, et al. (2007) A pathogenic role for c-Jun amino-terminal kinase signaling in renal fibrosis and tubular cell apoptosis. J Am Soc Nephrol 18: 472–484. 93. Flanc RS, Ma FY, Tesch GH, et al. (2007) A pathogenic role for JNK signaling in experimental anti-GBM glomerulonephritis. Kidney Int 72: 698–708. 94. Navaneethan SD, Viswanathan G, Strippoli GF. (2008) Meta-analysis of mycophenolate mofetil in IgA nephropathy. Nephrology 13: 90.

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95. Hotta O, Furuta T, Chiba S, Tomioka S, Taguma Y. (2002) Regression of IgA nephropathy: a repeat biopsy study. Am J Kidney Dis 39: 493–502. 96. Pitzalis C, Pipitone N, Perretti M. (2002) Regulation of leukocyte-endothelial interactions by glucocorticoids. Ann N Y Acad Sci 966: 108–118. 97. Elenkov IJ. (2004) Glucocorticoids and the Th1/Th2 balance. Ann NY Acad Sci 1024: 138–146.

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Chapter 20

Renin-Angiotensin System Kar Neng Lai and Joseph C. K. Leung

Introduction The renin-angiotensin system (RAS) has been implicated in the development of progressive glomerulosclerosis in diabetic and non-diabetic nephropathy.1,2 Traditionally, angiotensin II (Ang II) plays a central role as a mediator of glomerular hemodynamic adaptation and injury. It has been suggested that ANG II-induced mesangial cell contraction with efferent arteriolar vasoconstriction initiates intraglomerular hypertension.3 Angiotensin II also play a pivotal role in the glomerulosclerosis through induction of transforming growth factor-β (TGF-β) expression in mesangial cells.4 Transforming growth factor-β stimulates extracellular matrix protein synthesis, increases matrix protein receptors, and alters protease/protease-inhibitor balances, thereby inhibiting matrix degradation. In vitro studies show TGF-β induces tubular epithelial-myofibroblast transdifferentiation supporting its involvement in the formation and evolution of glomerular and tubular fibrosis.5,6 The beneficial effect of either angiotensin converting enzyme inhibitor (ACEI) or angiotensin II subtype-1 receptor (ATR1) antagonist on proteinuria and creatinine clearance (independent of blood pressure reduction) further raise the importance of this system in IgA nephropathy (IgAN).7,8 In the present chapter, we review the RAS in IgAN and summarize the evidence that polymeric IgA (pIgA) isolated from patients with IgAN exerts pathophysiological effect on the intrarenal RAS of mesangial cells resulting tubulointerstitial damage. The data of RAS blockade in the treatment of IgAN is separately discussed in Chapter 22. 289

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Renin-Angiotensin System in the Kidney Systemic RAS has long been shown to be related to hypertension and cardiovascular risk.9 The classical view of the RAS as a circulating endocrine system has recently evolved to organ- and tissue-based systems that perform paracrine/autocrine functions. Local RAS exists in different organs including kidney, heart, pancreas and bone marrow. In the kidney, all of the RAS components are present in resident kidney cells.10 Intrarenal Ang II is formed by independent multiple mechanisms. In situ hybridization studies have demonstrated that the angiotensinogen gene is specifically present in the proximal tubules of the kidneys.11 Angiotensinogen mRNA is expressed largely in proximal convoluted tubules and proximal straight tubules, and only small amounts are present in glomeruli and vasa recta.12 In the kidney, angiotensinogen protein is specifically located in the proximal convoluted tubules by immunohistochemistry.13–15 A strong positive immunostaining for angiotensinogen protein is present in proximal convoluted tubules and proximal straight tubules, and there is weak positive staining in glomeruli and vasa recta; however there is no staining in distal tubules or collecting ducts.16 The synthesized angiotensinogen in the kidney is secreted into the lumen, leading to angiotensin I generation and subsequent formation of Ang II. Renin mRNA and renin-like activity are also present in cultured proximal tubular cells.17–19 In addition, low but measurable renin concentrations in proximal tubule fluid have been reported in rats.20 Abundant expression of angiotensin converting enzyme (ACE) mRNA and protein have also been shown to be present in brush borders of proximal tubules of human kidneys.21,22 Angiotensin converting enzyme has also been measured in proximal and distal tubular fluid but is more abundant in proximal tubule fluid.23 Thus conditions are present in proximal tubules for Ang II generation. In addition to the classic RAS pathways, prorenin receptors and chymase are also involved in local Ang II formation in the kidney. Moreover, circulating Ang II is actively internalized into proximal tubular cells by ATR1dependent mechanisms. Consequently, Ang II is compartmentalized in the renal interstitial fluid and the proximal tubular compartments with much higher concentrations than those existing in the circulation. Recent evidence has also revealed that inappropriate activation of the intrarenal RAS is an important contributor to the pathogenesis of

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hypertension and renal injury. Details of the intrarenal RAS and the differential regulation of Ang II are well summarized in a review by Kobori et al.24 Angiotensin II also stimulates the production of aldosterone. The role of aldosterone appears to be less important than Ang II in IgAN as the additive antiproteinuric effect of ACEI and ATR1 antagonist is not dependent on aldosterone breakthrough.25 Finally, the recently cloned prorenin receptor is an exciting new addition to the RAS.26 Prorenin binding to the (pro)renin receptor not only causes a nonproteolytic activation of prorenin leading to the activation of the RAS, but also stimulates the receptor’s own intracellular signaling pathways independent of the RAS. Within the kidneys, the (pro)renin receptor is present in the glomerular mesangium and podocytes, which play an important role in the maintenance of the glomerular filtration barrier. Therefore, prorenin-receptor blockers, which competitively bind to the receptor as a decoy peptide, have superior benefits with regard to proteinuria and glomerulosclerosis in experimental animal models with elevated plasma prorenin levels such as diabetes and hypertension compared with conventional RAS inhibitors, possibly by inhibiting both the nonproteolytic activation of prorenin and RAS-independent intracellular signals.

Angiotensin II Receptors in the Kidney There are two major types of Ang II receptor: type 1 receptor (ATR1) and type 2 receptor (ATR2). However, there is much less ATR2 expression in adult kidneys.27,28 It has been reported that ATR1 mRNA has been localized to proximal convoluted and straight tubules, thick ascending limbs of the loop of Henle, cortical and medullary collecting duct cells, glomeruli, arterial vasculature, vasa recta, and juxtaglomerular cells.29 Studies using polyclonal and monoclonal antibodies to the ATR1 demonstrated that ATR1 protein is on vascular smooth muscle cells throughout the vasculature, including the afferent and efferent arterioles and mesangial cells.30 In addition, ATR1 is present on proximal tubule brush border and basolateral membranes, thick ascending limb epithelia, distal tubules, collecting ducts, glomerular podocytes, and macula densa cells.27,28,30 These findings suggest that the intrarenal RAS works independently of the systemic RAS.

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ATR1 ATR2

93.5%

Human mesangial cells (HMC) Bmax (fmol/mg protein) 541.7 Kd (nM) 1.84

HMC

75%

Bmax (fmol/mg protein) Kd (nM)

Podocytes 52.0 3.3

Podocyte

54%

Proximal tubular epithelial cells (PTEC) Bmax (fmol/mg protein) 452.2 Kd (nM) 2.63

PTEC Figure 20.1 Percentage of Angiotensin II subtype receptor 1 (ATR1) and Angiotensin II subtype 2 (ATR2) in and saturation analysis of specific binding of Ang II to different renal cells. [Data adopted from Wang et al.,32 Chan et al.,33 and unpublished data from Lai.]

Saturation analysis of specific binding of Ang II to different renal cells revealed unique percentage of ATR1 and ATR2 in mesangial cells, podocytes and proximal tubular epithelial cells (Figure 20.1).31–33 The predominance of ATR1 over ATR2 in mesangial cells and podocytes explains the previous observation that there is much less ATR2 expression in adult kidneys.27,28 With functional difference between these receptors, their differential distribution has important bearing in the pathophysiology and treatment by RAS blockade in various kidney disorders.

RAS Data from Murine Animals Murine model has provided enormous data in the understanding of the importance of RAS in the development of salt-sensitive and genetic hypertension, and other renal diseases (summarized in a review by Kobori et al.24). However, murine data may not always be extrapolated to human being due to species difference.

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In rodents, two subtypes of ATR1 mRNA (AT1a receptor and AT1b receptor) have been demonstrated in the vasculature and glomerulus and in all nephron segments.28 The AT1a receptor mRNA is the predominant subtype in nephron segments, whereas the AT1b receptor is more abundant than AT1a receptor in the glomerulus.34 Luminal AT1a receptor mediates a biphasic regulation of bicarbonate absorption in proximal tubules by luminal Ang II in rodent, while no evidence is obtained for a role of ATR2.35 In contrast, Ang II induces apoptosis in proximal tubules (human and rodent) via ATR2 but not via ATR1.36,37 The human mast cell-specific protease “chymase” efficiently converts angiotensin I (Ang I) to Ang II independent of ACE, whereas rat chymase and some mouse mast cell protease degrades Ang I to inactive fragments instead of Ang II.38,39 Exogenous administration of Ang II elicits dose-dependent decreases in renal blood flow and glomerular filtration rate.40,41 Although there is an agreement that Ang II exerts substantial direct effects on the renal microvasculature and glomerular mesangium, there remains controversy regarding the intensity of actions at various sites and the relative contribution of systemically and intrarenally formed Ang II to the overall regulation of renal hemodynamics. The observation that Ang II increases the filtration fraction has frequently been used to support the notion that Ang II predominantly constricts the postglomerular arterioles. The plasma concentration of Ang II in rats receiving continuous administration of Ang II is hundred-fold higher than that in anesthetized rats with values between 50–100 pmol/L (10−10 M). Such concentration of Ang II is able to induce apoptosis in renal tubular epithelial cells.42 Hence, the pathophysiological findings in rats receiving super-pharmacological dosage of Ang II must be interpreted cautiously.

Intrarenal Expression of RAS in IgAN Miyake-Ogawa et al.43 identified mRNAs of the RAS components in renal biopsy from patients with IgAN including ACE and chymase in mesangial cells, glomerular epithelial cells, cells of Bowman’s capsule, tubular epithelial cells, vascular endothelial and smooth muscle cells and infiltrating cells. They observed that the levels of expression of RAS mRNAs varied with the progression of renal tissue injury. Messenger RNAs for these RAS components were increased in the glomeruli and

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that the levels of glomerular RAS correlated with the degree of mesangial hypercellularity in IgAN. These RAS components were expressed in tubular and interstitial areas and such expression also correlated with the degree of tubulointerstitial injury. Increased production of Ang II by the renal RAS was speculated in the tubulointerstitium of IgAN. Kobori et al.44 studied intrarenal activation of the RAS in renal specimens from 39 patients with IgAN. Angiotensinogen was localized predominantly in proximal tubular cells, and the immunoreactivity of intrarenal angiotensinogen in IgAN was significantly increased compared with that in normal kidney. Sakamoto-Ihara et al.45 found Ang II-expressing cells in both tubular cells and infiltrating lymphocytes in patients with IgAN. Chymase was detected in or around mast cells and these chymasepositive mast cells were not observed in the conglomerate of Ang II-positive cells but in the area surrounding it, suggesting chymase-dependent local Ang II synthesis may occur after the degranulation of mast cells releases chymase.

Intraglomerular Expression of Ang II Receptors in IgAN The intraglomerular findings of Ang II receptors in IgAN are more intriguing. While Miyake-Ogawa et al.43 identified ATR1 and ATR2 mRNA in mesangial cells and glomerular epithelial cells, others observed a down-regulation of ATR1 in the glomerular mesangium. Using a 125 I-labeled Ang II autoradiographic technique, Hale et al.46 first suggested a local down-regulation of Ang II receptors despite proliferation of glomerular mesangium in IgAN. Wagner et al.47 found a reduced gene expression of the ATR1 in isolated glomeruli from 14 patients with IgAN. Although not significantly, an interesting trend toward higher ATR1 mRNA levels was observed in patients on ACEI in that study. Del Prete et al.48 reported an over-expression of RAS genes (renin, angiotensinogen, and ACE) in kidney biopsy of IgAN. In isolated glomeruli, an inverse relationship between these RAS genes and mRNA encoding for ATR1 or ATR2 was observed. However, a paradoxical finding of lower glomerular Ang II receptor mRNA levels in controls than IgAN was observed since normal control subjects had lower intrarenal RAS activities. Recently, Lai et al.31 detected immunoreactive ATR1 or ATR2 protein in glomerular mesangial cells from normal or IgAN kidney. These receptors were also detected in tubular epithelium and arteriolar

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endothelium. Semiquantitative analysis showed a reduction of ATR1 protein in glomerular mesangial cells from IgAN, but not for the ATR2 protein. The finding is compatible with those of Hale et al.46 and Wagner et al.,47 supporting a local down-regulation of ATR1 in IgAN resulting from the negative feedback due to enhanced intraglomerular RAS, and hence, Ang II activity.49,50 These histological findings were supported by in vitro experiments examining the regulatory effect of IgA on the expression of these receptors in cultured human mesangial cells (HMC).31 In resting HMC, incubation with either an ACEI (captopril) or an ATR1 antagonist (losartan) resulted in increased expression of ATR1 in a dose-dependent manner. With decreased binding of Ang II to its receptor on HMC following blockade of the RAS, the increased expression of ATR1 is likely to mediate via the negative feedback loop. Interestingly, pIgA from patients with IgAN (at a concentration comparable to the serum concentration of pIgA concentration) significantly down-regulated the gene and protein expression of ATR1 in a dose-dependent manner, reaching a 17% protein reduction at a concentration of 0.5 mg/mL. The ATR1 expression was restored to that of resting cells when HMC preincubated with pIgA from patients with IgAN were treated with either captopril or losartan. ATR2 expression was not affected by incubation with pIgA at these concentrations. The supernatant concentration of Ang II (10−11 M) in HMC released by incubating with pIgA was too low to induce apoptosis via the binding to ATR2.37 The suppressive effect of pIgA from patients with IgAN on the RAS in mesangial cells was confirmed in patients with various histological grading. Polymeric IgA from IgAN patients down-regulated the ATR1 expression in HMC when compared with cells incubated with pIgA from healthy or glomerulopathic control subjects. The most interesting issue is the pathophysiologic significance of the down-regulation of mesangial ATR1 in IgAN. Regulation of Ang II receptors in renal tissues is complex. In general, ATR1 stimulates cell proliferation while ATR2 regulates cell growth inhibition and apoptosis.51,52 Previous studies showed a down-regulation of glomerular ATR1 mRNA in chronic renal failure, including diabetic nephropathy and IgAN.47,53 Ang II infusion studies in animal showed a reduction of ATR1 mRNA level in mesangial cells following exposure to Ang II.49,50 The downregulation is presumed to mediate through a negative feedback due to enhanced intraglomerular Ang II activity. This hypothesis is supported

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by the dose-response findings between RAS blockade and the expression of ATR1, and the negative correlation between supernatant Ang II levels and ATR1 expression in HMC incubated with pIgA in in vitro experiments conducted by Lai et al.31 It has been speculated that a decrease in ATR1 mRNA levels mirrors an adaptive response to high intrarenal Ang II levels in human glomerulonephritis and diabetes mellitus.47 The obvious question is why such adaptive mechanism operates in glomerulonephritides such as IgAN. In IgAN, Lai et al.31 hypothesized that this could arise from the differential expression of Ang II receptors in mesangial cells following the release of Ang II by pIgA. In renal proximal tubular cells exposed to Ang II, the growth-stimulatory effects through ATR1 may be counter-balanced by ATR2-mediated apoptosis and growth inhibition.36,54 Despite the fact that pIgA from patients with IgAN induces Ang II release from HMC, recent findings suggest that the Ang II level (10−11 M) is unlikely to be sufficient to stimulate the apoptotic (or even the antiproliferative) effect via enhanced expression of ATR2. Lai et al.31 demonstrated the Ang II concentration required to induce apoptosis in HMC (> 10−7 M) is 100-fold higher than that of human renal proximal tubules (10−9 M).37 Unbalanced Ang II receptor expression with excessive ATR1 has shown to contribute to hypertension and related renal injury in different experimental models.55 Hence, it has been postulated that the defective counterbalance of ATR1 by ATR2 in HMC exposed to pIgA from IgAN patients leads to an adaptive down-regulation of the ATR1.31 An immediate down-regulation of mesangial ATR1 expression will ameliorate the proliferative and inflammatory changes induced by Ang II released by pIgA. However, it is envisaged that this adaptive mechanism in HMC may gradually be altered with chronic exposure to Ang II released by pIgA in IgAN. Failure to suppress the ATR1 expression continuously in the presence of defective ATR2 activation is likely to permit the development of proliferative and inflammatory processes in the glomerulus that may finally lead to progressive renal deterioration in IgAN. This hypothesis has lent support from study by Lai et al.31 of HMC following prolonged exposure to pIgA from IgAN. The adaptive down-regulation of ATR1 gradually disappeared despite the maintenance of significant Ang II concentration in the supernatant. Furthermore, there was progressive increase in cell proliferation following prolonged culture of HMC with exposure to pIgA, but not with plain culture medium or IgG from the same disease subject.

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Tubular Expression of Ang II Receptors in IgAN The severity of tubulointerstitial damage in IgAN correlates closely with the declining renal function and the long-term clinical outcome. It is now clearly demonstrated that there is no binding of IgA to and absence of IgA receptors in renal tubular epithelial cells.56 Other than the tubulo-toxic effect of proteinuria, the tubulointerstitial damage in IgAN is an indirect sequel due to a novel glomerulo–tubular cross-talk mediated through soluble factors, mainly tumor necrosis factor-α (TNF-α) released by HMC following IgA deposition.56 ATR1 and ATR2 are constitutively present in tubular epithelial cells (TEC).33 The tubular expression of both receptors are up-regulated in IgAN.33,43 In vitro studies showed no change in Ang II receptors expression when TEC were cultured with IgA yet these receptors were up-regulated following incubation supernatant from HMC cultured with pIgA (IgA-HMC conditioned medium) from the same IgAN patient.33 These findings further support the notion that disturbance of tubular RAS in IgAN is an indirect event through signals released by HMC following mesangial IgA deposition. Dissociation in tubular expression of Ang II receptors is evident by the time course of in vitro experiments of TEC cultured with IgA-HMC conditioned medium. ATR1 expression was up-regulated in the first two days and decreased gradually to the basal level towards day 6. In contrast, significant increase in the ATR2 expression was detected only after day 2 and thereafter. Results from the [3H]-Ang II binding assay demonstrated that IgA-HMC conditioned medium increased the Ang II receptor density without affecting the affinity or the relative proportion of ATR1 and ATR2 on cultured TEC. Simultaneously, there was also increased production of interleukin 6 (IL-6) as early as 12 hours after culturing. The Ang II release and the expression of an apoptotic marker were increased from day 2 associated with increased ATR2 expression induced by IgA-HMC conditioned medium. These data suggest that although the initial Ang II level in TEC after culturing with IgA-HMC conditioned medium was not high enough to up-regulate Ang II receptors expression immediately, the concentration of TNF-α in the IgAHMC conditioned medium could induce a rapid and early increase of IL-6 level that in turn up-regulates ATR1 and ATR2 expression in “primed TEC.” Increased Ang II production through increased Ang II and its receptor binding could further up-regulate the production of

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AngII. The apoptosis of TEC is amplified by ATR1 antagonist but abolished by ATR2 antagonist. Normally, apoptosis mediated by ATR2 counter-balances growth-stimulatory effects of Ang II through ATR1 in renal proximal tubular cells.36,54 The role of ATR2 in inducing apoptosis in TEC is supported by the observation that expression of an apoptotic marker following incubation with IgA-HMC conditioned medium was increased or blocked by an ATR2 agonist and an ATR2 antagonist respectively. Angiotensin II stimulates both mitogen-associated protein kinase (MAPK) and protein kinase C (PKC) pathways.57 Chan et al.33 showed that IgA-MHC conditioned medium from IgAN patients or exogenous AngII alone activated p42/p44 MAPK and PKC pathways in TEC. Their in vitro experiments revealed ATR2 only counteracted the ATR1-mediated signal transduction pathway of MAPK but not PKC.

Pathophysiological Effects of pIgA on RAS in IgAN Few studies have addressed the pathophysiological effect of IgA from patients with IgAN on target cells such as the mesangial or tubular epithelial cells. Gomez-Guerrero et al.58 demonstrated that mesangial cells incubated with aggregated IgA elicited a dose-dependent increase in calcium flux. Other in vitro studies revealed binding of IgA to mesangial cells led to increased expression of the NFκB,58 c-jun,59 IL-6,60 interleukin-8,59 monocyte chemoattractant-protein 1,59 and TNF-α.60 The enhanced production of interleukin-8 may lead to the renal accumulation of neutrophils in patients with IgAN.61 Peruzzi et al.62 demonstrated that cultured mesangial cells conditioned with pIgA or aggregated IgA expressed more αv receptor per cell than those incubated with unconditioned medium suggesting pIgA may play a role in modulating the cellmatrix interaction in IgAN. Lai et al.63 showed pIgA isolated from patients with IgAN induced gene expression of renin in HMC in a dose-dependent manner. Similar findings were observed with the gene and protein expression of TGF-β and Ang II. When similar experiments were conducted with addition of either an ACEI or an ATR1 antagonist, there was a significant increase in the gene expression of renin by HMC yet the synthesis of TGF-β was markedly reduced. The up-regulation of TGF-β by pIgA was via the

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receptor-regulated Smad proteins (Smads 2 and 3) and common-partner Smad protein (Smad 4).

Gene Polymorphism of RAS in IgAN The angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D), the angiotensinogen (AGT) gene, M235T, and the ATR1 gene, A1166C, polymorphisms have been studied for association with the disease susceptibility of IgAN and its progression. Several studies on Caucasians and Asian patients have reported contradictory results.

Figure 20.2 Regulation of the expression of ATR1 (AT1) and ATR2 (AT2) in mesangial cells and proximal tubular epithelial cells (PTEC) following mesangial IgA deposition in IgAN. Mesangial cells exhibit adaptive changes with reduced ATR1 expression upon acute exposure to IgA. With prolonged and chronic exposure to IgA, such adaptive changes are lost with gradual increased ATR1 expression leading to proliferative and inflammatory changes. There is no change in ATR2 expression as the Ang II concentration is too low to stimulate ATR2 expression. Tubular cells might be stimulated by the spillover of mediators from injured glomeruli resulting in activation of both ATR1 and ATR2. On the other hand, Ang II increases cell proliferation and synthesis of extracellular matrix proteins in renal interstitial fibroblasts following enhanced ATR1 expression. These events lead to secondary expression of ATR2 in fibroblasts. [Adopted from author’s data in Chan et al.68]

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Hunley et al.64 examined the ACE genotype of 64 Caucasoid patients with IgAN who were followed up for an average of seven years. They found that the ACE D/D polymorphism was associated with progressive deterioration in renal function. On the contrary, Woo et al.65 reported the ACE DD genotype may predispose the individual to IgAN in a Chinese population. In two extensive reviews,66,67 convincing evidence indicating that ACE gene polymorphism related to the onset of IgAN still remains lacking. On the other hand, deletion polymorphism in the ACE gene, particularly in DD homozygotes, predicts the therapeutic efficacy of ACEI on proteinuria and preserving renal function that warrants further investigation.67

Mechanisms of Renal Injury Involving the RAS in IgAN Mesangial deposition of pIgA activates the mesangial cells to release Ang II.63 The initial down-regulation of ATR1 expression mirrors an adaptive response to high intrarenal Ang II level. An immediate downregulation of mesangial ATR1 expression will ameliorate the proliferative glomerulo-tubular cross-talk via TNF-α , IL-6 and angiotensin II

humoral factors (TNF- α)

Bcl-2 Bax

ATR1

x

Y Y

Y

HMC

ATR2

ATR1

x

Y

Y

Podocyte

tubulo-glomerular cross-talk favoring glomerulosclerosis

TEC

sclerosis

proteinuria IgA

Y no IgA binding

x

Y

tubular atrophy

Figure 20.3 Schematic model of the variable mechanisms operating between the glomerular mesangial cells (HMC), podocytes, and tubular epithelial cells (TEC) following mesangial IgA deposition in the development of tubulointerstitial injury in progressive IgAN. [Adopted from author’s data in Lai et al.42]

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and inflammatory changes. However, such adaptive changes might gradually be lost with prolonged exposure of mesangial cells to pIgA in IgAN. The supernatant concentration of Ang II (∼10−10 M) in HMC released by incubating with pIgA was far too low to induce apoptosis via activation of the ATR2 in mesangial cells. In contrast, similar concentration of Ang II was able to stimulate ATR1 expression and maintain proliferative activity. Hence, the failure to suppress the ATR1 expression continuously in the presence of defective ATR2 activation is likely to permit the development of proliferative and inflammatory processes

Figure 20.4 Hypothetical model of tubular regulation of Ang II receptors in IgAN. @ represents adaptive down-regulation of ATR1 that gradually disappears after chronic exposure to pathogenic IgA. The interaction of Ang II and early expressed ATR1 will activate the PKC and MAPK pathways, leading to inflammatory responses. The early phase of ATR1-dependent inflammation is followed by subsequent up-regulation of ATR2 expression with continued release of Ang II. The interaction between AngII and ATR2 leads to apoptosis through down-regulation of the MAPK pathway, and this will counterbalance the ATR1-induced MAPK activation (double arrow denotes interaction). [Adopted from author’s data in Chan et al.33]

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in the glomerular mesangium (Figure 20.2). This may perpetuate a glomerulo-tubular cross-talk involving TNF-α, IL-6 and Ang II that finally leads to progression of renal deterioration in IgAN (Figure 20.3).54 More interestingly, Ang II at a concentration of 10−10 M is able to induce apoptosis in TEC.68 In the tubular lumen, TNF-α released by mesangial cells first increases IL-6 production. The IL-6 in turn increases the ATR1 expression and then gradually enhances Ang II production. The interaction of Ang II and early expressed ATR1 will activate the PKC and MAPK pathways, leading to inflammatory responses. The early phase of ATR1-dependent inflammation is followed by subsequent up-regulation of ATR2 expression with continued release of Ang II. The interaction between Ang II and ATR2 leads to apoptosis through down-regulation of the MAPK pathway, and this will counterbalance the ATR1-induced MAPK activation (Figure 20.4).

Concluding Remarks Recent experimental findings suggest a differential expression of ATR1 and ATR2 in glomerular mesangial and tubular epithelial cells in response to raised intrarenal Ang II concentration following exposure to pIgA that may play a significant role in the pathogenesis of IgAN.

Acknowledgments The study was supported by the Research Grant Committee (Hong Kong) [HKU 7661/06M].

References 1. GISEN Group (Gruppo Italiano di Studi Epidemiologici in Nefrologia). (1997) Randomised placebo-controlled trial of effect of ramipril on decline in glomerular filtration rate and risk of terminal renal failure in proteinuric, non-diabetic nephropathy. Lancet 349: 1857–863. 2 Leehey DJ, Singh AK, Alavi N, Singh R. (2000) Role of angiotensin II in diabetic nephropathy. Kidney Int 58(Suppl 77): S93–S98. 3. Ketteler M, Noble NA, Border WA. (1994) Increased expression of transforming growth factor-β in renal disease. Curr Opin Nephrol Hyperten 3: 446–452. 4. Kagami S, Border WA, Miller DE, Noble NA. (1994) Angiotensin II stimulates extracellular matrix protein synthesis through induction of transforming

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19. Henrich WL, McAllister EA, Eskue A, et al. (1996) Renin regulation in cultured proximal tubular cells. Hypertension 27: 1337–1340. 20. Leyssac PP. (1986) Changes in single nephron renin release are mediated by tubular fluid flow rate. Kidney Int 30: 332–339. 21. Sibony M, Gasc JM, Soubrier F, et al. (1993) Gene expression and tissue localization of the two isoforms of angiotensin I converting enzyme. Hypertension 21: 827–835. 22. Schulz WW, Hagler HK, Buja LM, et al. (1988) Ultrastructural localization of angiotensin I-converting enzyme (EC 3.4.15.1) and neutral metalloendopeptidase (EC 3.4.24.11) in the proximal tubule of the human kidney. Lab Invest 59: 789–797. 23. Casarini DE, Boim MA, Stella RC, et al. (1997) Angiotensin I-converting enzyme activity in tubular fluid along the rat nephron. Am J Physio 272: F405–F409. 24. Kobori H, Nangaku M, Navar LG, Nishiyama A. (2007) The intrarenal renin-angiotensin system: from physiology to pathobiology of hypertension and kidney disease. Pharmcol Rev 59: 251–287. 25. Horita Y, Taura K, Taguchi T, et al. (2006) Aldosterone breakthrough during therapy with angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers in proteinuric patients with IgA nephropathy. Nephrology 11: 462–466. 26. Ischihara A, Kaneshiro Y, Takemitsu T, et al. (2007) The (pro)renin receptor and the kidney. Semin Nephrol 27: 524–528. 27. Wang ZQ, Millatt LJ, Heiderstadt NT, et al. (1999) Differential regulation of renal angiotensin subtype AT1a and AT2 receptor protein in rats with angiotensin-dependent hypertension. Hypertension 33: 96–101. 28. Miyata N, Park F, Li XF, Cowley AW Jr. (1999) Distribution of angiotensin AT1 and AT2 receptor subtypes in the rat kidney. Am J Physio 277: F437–F446. 29. Terada Y, Tomita K, Nonoguchi H, Marumo F. (1993) PCR localization of angiotensin II receptor and angiotensinogen mRNAs in rat kidney. Kidney Int 43: 1251–1259. 30. Harrison-Bernard LM, Navar LG, Ho MM, et al. (1997) Immunohistochemical localization of ANG II AT1 receptor in adult rat kidney using a monoclonal antibody. Am J Physiol 273: F170–F177. 31. Lai KN, Chan LY, Tang SC, et al. (2004) Mesangial expression of angiotensin II receptor in IgA nephropathy and its regulation by polymeric IgA1. Kidney Int 66: 1403–1416. 32. Wang L, Flannery PJ, Spurney RF. (2003) Characterization of angiotensin II-receptor subtypes in podocytes. J Lab Clin Med 142: 313–321. 33. Chan LY, Leung JC, Tang SC, et al. (2005) Tubular expression of angiotensin II receptors and their regulation in IgA nephropathy. J Am Soc Nephrol 16: 2306–2317.

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34. Bouby N, Hus-Citharel A, Marchetti J, et al. (1997) Expression of type 1 angiotensin II receptor subtypes and angiotensin II-induced calcium mobilization along the rat nephron. J Am Soc Nephrol 8: 1658–1667. 35. Zheng Y, Horita S, Hara C, et al. (2003) Biphasic regulation of renal proximal bicarbonate absorption by luminal AT(1A) receptor. J Am Soc Nephrol 14: 1116–1122. 36. Bhaskaran M, Reddy K, Radhakrishanan N, et al. (2003) Angiotensin II induces apoptosis in renal proximal tubular cells. Am J Physiol Renal Physiol 284: F955–F965. 37. Weikekamm C, Hauser P, Hansmann C, et al. (2002) Effect of AT1 and AT2 receptor blockade on angiotensin II induced apoptosis of human renal proximal tubular epithelial cells. Wien Klin Wochenschr 114: 725–729. 38. Caughey GH, Raymond WW, Wolters PJ. (2000) Angiotensin II generation by mast cell alpha- and beta-chymases. Biochim Biophys Acta 1480: 245–257. 39. Okunishi H, Oka Y, Shiota N, et al. (1993) Marked species-difference in the vascular angiotensin II-forming pathways: humans versus rodents. Jpn J Pharmacol 62: 207–210. 40. Yamamoto T, Hayashi K, Matsuda H, et al. (2001) In vivo visualization of angiotensin II and tubuloglomerular feedback-mediated renal vasoconstriction. Kidney Int 60: 364–369. 41. Paul M, Mehr AP, Kreutz R. (2006) Physiology of local renin-angiotensin systems. Physiol Rev 86: 747–803. 42. Lai KN, Chan LY, Leung JC. (2005) Mechanism of tubulointerstitial injury in IgA nephropathy. Kidney Int 94: S110–S115. 43. Miyake-Ogawa C, Miyazaki M, Abe K, et al. (2005) Tissue-specific expression of renin-angiotensin system components in IgA nephropathy. Am J Nephrol 25: 1–12. 44. Kobori H, Katsurada A, Ozawa Y, et al. (2007) Enhanced intrarenal oxidative stress and angiotensinogen in IgA nephropathy patients. Biochem Biophys Res Commun 358: 156–163. 45. Sakamoto-Ihara T, Suzuki Y, Kurusu A, et al. (2007) Possible involvement of mast cells in renal fibrosis in patients with IgA nephropathy. Inflamm Res 56: 421–427. 46. Hale GM, Howarth GS, Aarons I, et al. (1989) Quantitation of glomerular angiotensin II receptors in IgA nephropathy. Clin Nephrol 32: 5–9. 47. Wagner J, Gehlen F, Ciechanowicz A, Ritz E. (1999) Angiotensin II receptor type 1 gene expression in human glomerulonephritis and diabetes mellitus. J Am Soc Nephrol 10: 545–551. 48. Del Prete D, Gambaro G, Lupo A, et al. (2003) Precocious activation of genes of the renin-angiotensin system and the fibrogenic cascade in IgA glomerulonephritis. Kidney Int 64: 149–159.

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49. Makita N, Iwai N, Inagami T, Badr K. (1992) Two distinct pathways in the down-regulation of type-1 angiotensin II receptor gene in rat glomerular mesangial cells. Biochem Biophys Res Commun 185: 142–146. 50. Chansel D, Bizet T, Vandermeersch, et al. (1994) Differential regulation of angiotensin II and losartan binding sites in glomeruli and mesangial cells. Am J Physiol 266: F384–F393. 51. Matsubara H. (1998) Pathophysiological role of angiotensin II type 2 receptor in cardiovascular and renal diseases. Circ Res 83: 1182–1191. 52. Franco M, Paniagua R, Herrera-Acosta J. (1998) Renal effects of reninangiotensin system blockade. Curr Opin Nephrol Hypertens 7: 153–158. 53. Cao Z, Bonnet F, Candido R, et al. (2002) Angiotensin type 2 receptor antagonism confers renal protection in a rat model of progressive renal injury. J Am Soc Nephrol 13: 1773–1787. 54. Wolf G. (2002) Angiotensin II and tubular development. Nephrol Dial Transplant 17(Suppl 9): 48–51. 55. Sahajpal V, Ashton N. (2003) Renal function and angiotensin AT1 receptor expression in young rats following intrauterine exposure to a maternal low-protein diet. Clin Sci 106: 607–614. 56. Chan LY, Leung JC, Tsang AW, et al. (2005) Activation of tubular epithelial cells by mesangial-derived TNF-α: glomerulo-tubular communication in IgA nephropathy. Kidney Int 67: 602–612. 57. Berk BC, Corson MA. (1997) Angiotensin II signal transduction in vascular smooth muscle: role of tyrosine kinases. Circ Res 80: 607–616. 58. Gomez-Guerrero C, Duque N, Egido J. (1996) Stimulation of Fc(α) receptors induces tyrosine phosphorylation of phospholipase C-γ, phosphatidylinositol phosphate hydrolysis, and calcium mobilization in rat and human mesangial cells. J Immunol 156: 4369–4376. 59. Duque N, Gomez-Guerrero C, Egido J. (1997) Interaction of IgA with Fcα receptors of human mesangial cells activates transcription factor nuclear factor-kappa B and induces expression and synthesis, of MCP-1, IL-8, and IFN-inducible protein 10. J Immunol 159: 3474–3482. 60. Diven SC, Caflisch CR, Hammond DK, et al. (1998) IgA induced activation of human mesangial cells: independent of Fc alphaR1 (CD89). Kidney Int 54: 837–847. 61. van den Dobbelsteen ME, van der Woude FJ, Schroeijers WE, et al. (1994) Binding of dimeric and polymeric IgA to rat renal mesangial cells enhances the release of interleukin 6. Kidney Int 46: 512–519. 62. Gomez-Guerrero C, Lopez-Armada MJ, Gonzalez E, Egido J. (1994) Soluble IgA and IgG aggregates are catabolized by cultured rat mesangial cells and induce production of TNF-α and IL-6, and proliferation. J Immunol 153: 5247–5255.

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63. Lai KN, Tang SC, Guh JY, et al. (2003) Polymeric IgA1 from patients with IgA nephropathy upregulates transforming growth factor-beta synthesis and signal transduction in human mesangial cells via the renin-angiotensin system. J Am Soc Nephrol 14: 3127–3137. 64. Hunley TE, Julian BA, Phillips JA, et al. (1996) Angiotensin converting enzyme gene polymorphism: potential silencer motif and impact on progression in IgA nephropathy. Kidney Int. 49: 571–577. 65. Woo KT, Lau YK, Choong LH, et al. (2004) Polymorphism of reninangiotensin system genes in IgA nephropathy. Nephrology 9: 304–309. 66. Tang S, Lai KN. (2001) Gene polymorphism in IgA nephropathy. Nephrology 6: 63–70. 67. Dillon JJ. (2004) Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers for IgA nephropathy. Semin Nephrol 24: 218–224. 68. Chan LY, Leung JC, Lai KN. (2004) Novel mechanisms of tubulointerstitial injury in IgA nephropathy: a new therapeutic paradigm in the prevention of progressive renal failure. Clin Exp Nephrol 8: 297–303.

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Chapter 21

Corticosteroids Claudio Pozzi and Lucia Del Vecchio

Introduction For the past half a century, glucocorticoids (corticosteroids) have been among the most effective and widely used drugs for inflammatory diseases and transplantation. In the field of nephrology, they have been used in the treatment of glomerular diseases since the sixties and, given on a daily or alternate-day basis, have had variable success in patients with IgA nephropathy (IgAN). However, for decades these agents have been used with the concept of a non-specific but very potent antiinflammatory effect, without a clear understanding of the exact pathogenetic pathways they modify.

Mechanisms of Action of Steroids Recent research into the molecular mechanisms of action of these compounds have focused on the involvement of the glucocorticoid receptor (GR) in regulating the transcription of pro-inflammatory genes and sought to identify alternative pathways of glucocorticoid action either via the induction of anti-inflammatory mediators or through rapid nongenomic mechanisms.1 The latter may be of importance on the immunosuppression of T cells.2 In the “classic” model of GR activation, lipophilic glucocorticoids pass through the plasma membrane of cells and interact with cytoplasmic GRs. Subsequent release of chaperone molecules (such as hsp90) and phosphorylation events result in homo-dimerization of the receptor– ligand complex and transmigration to the cell nucleus. Here, the DNA 309

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310 ✦ C. Pozzi & L. Del Vecchio

binding domain directs dimerization on imperfect DNA palindromes known as simple glucocorticoid response elements (GREs) to transcriptionally activate (transactivate) a number of genes, such as tyrosine amino transferase (TAT) or tryptophan oxygenase.3 This mechanism has a key role in inducing metabolic side effects of glucocorticoids such as gluconeogenesis or amino acid catabolism. Transactivation is also partly involved in the mediation of other adverse reactions, such as osteoporosis, skin atrophy, growth retardation, and Cushingoid appearance. Conversely, beneficial effects of steroids lie in their ability to reduce inflammatory gene expression through transrepression at negative GREs. Such genes have binding sites for transcription factors including activator protein-1 (AP-1) and nuclear factor kappa-B (NF-κB) that are repressed by steroids. This research approach has opened the way to the possibility of a clearer split between molecular pathways involved in the beneficial effects of steroid and those causing side effects. Despite their large use for the treatment of glomerulonephritis, the specific mechanism of action of glucocorticoids in the kidney has not been investigated comparably. Glucocorticoids act as immunosuppressant agents, causing a selective suppression of the Th1-cellular immunity axis, and a shift toward Th2-mediated humoral immunity.4 This may turn down immunological pathogenetic factors causing and perpetuating glomerulonephritis. In addition, it is well known that both AP-1 and NF-κB regulate the expression of various genes implicated in the pathogenesis of glomerular injury, such as transforming growth factor-βl (TGF-β1), endothelin, interleukin 6, interleukin 1β, interleukin 8, and tumor necrosis factor-α (TNF-α).5 In vitro data showed that glucocorticoids suppress AP-1 and NF-κB activation.6,7 These findings were confirmed in vivo in several experimental models of glomerulonephritis.5,8–11 In turn, reduced NF-κB activation decreases cell proliferation and apoptosis induced by TNF-α in cultured mesangial cells.9,12 Another possible molecular mechanism is cell cycle arrest of mesangial cells by a functional link between the glucocorticoid receptor and the transcriptional control of p21(CIP1), a cyclin-dependent kinase (CDK) inhibitor which reduce cell proliferation.13 Glucocorticoids also inhibit the production of monocyte chemoattractant protein-1 (MCP-1) produced by glomerular epithelial cells, which may play a role in the recruitment of monocytes/ macrophages in glomerulonephritis.14 Finally, glucocorticoids exert antiapoptotic effect on podocytes.15 The interpretation of the conflicting

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finding that proteinuria is exacerbated by glucocorticoid in rats with mesangial glomerulonephritis remains unavailable.16

Results from Non-Randomized and Randomized Clinical Trials The first studies using glucocorticoids for the treatment of IgAN were performed in the eighties, but their findings are difficult to interpret since different doses and schemes of therapy were used and many of them relate to small, non-randomized controlled studies of patients differing in terms of age (adults and children), severity of IgAN and, more importantly, degree of proteinuria. A large contribution in this field has been given by Japanese researchers. In 1986 Kobayashi et al.17 firstly reported their experience coming from a prospective, non-randomized study of 14 IgAN patients with proteinuria between 1.0 and 2.0 g/day who received an initial dose of 40 mg/day of prednisolone, followed by gradual reduction of the dose over an average period of about 19 months. Compared to the 29 control subjects, patients treated with steroids had considerable reduction in proteinuria and better preserved renal function; those with creatinine clearance higher than 70 ml/min seemed to benefit more from therapy. Two years later they published a broaden series of 29 adult IgAN patients with proteinuria of more than 2 g/day who received prednisolone treatment for one to three years.18 After ten years from their first report, they published interesting retrospective data about the effects of steroids in the long term in the early stage of IgAN (defined as proteinuria between 1 and 2 g/day, creatinine clearance values of 70 ml/min or more, and a histological severity score of 7 or more). Among the 46 patients fulfilling these criteria, 20 were treated with steroids. During a ten-year follow-up, renal survival was significantly better in those receiving steroids (100% vs. 84% at five years and 80% vs. 34% ten years later). Of note is the fact that patients with mild histological changes or decreased renal function showed no significant differences in the final outcome. However, these subgroups were too small to gain reliable information. Encouraging results were also obtained in 13 children who were treated with alternate day prednisone 60 mg/m2 for three months, reduced to 30 mg/m2 by one year and 15 mg/m2 by two years.18 In comparison with a historical group, Waldo et al.19 showed a significant

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improvement in urine analysis (both proteinuria and hematuria) and a preserved normal GFR. Follow-up biopsy after two years of treatment revealed a significant fall in the activity score (from 5.2 to 4.3), without any significant increase in the chronicity score. There were no treatmentrelated complications. Conversely, first reports coming from small, randomized clinical trials were mostly negative. Lai et al.20 found no benefit of prednisone (1 mg/kg/day for two months and a tapered dosage for another two months) in a controlled trial involving 34 patients with nephrotic syndrome. However, the length of treatment (only four months) was perhaps not long enough to detect a significant effect in nephrotic patients. Negative findings were also obtained by Nicholls et al.,21 who failed to detect favorable effects on proteinuria and glomerular filtration rate (GFR) in 33 IgAN patients randomly allocated to receive either prednisolone (25 mg/day for one month, progressively tapered to 10 mg/day at six months), or symptomatic treatment. Welch et al.22 performed a double-blind, controlled trial of short-term therapy with prednisone (2 mg/kg/day for two weeks, then every other day for ten weeks) in 20 children with IgAN, and also found that the treatment did not seem to be effective. In addition to a too short schedule of treatment, the crossover design of the study may have affected the results because average proteinuria at baseline significantly differed between the placebo phase (16 mg/h) and the steroid phase (28 mg/h). Julian et al.23 made a multicenter prospective trial in IgAN patients with proteinuria greater than 2 g/day by comparing symptomatic therapy with alternate-day prednisone (60 mg/day tapered by 10 mg every three months to 10 mg/day over 24 months). However, they published only preliminary data of a small set of patients not supporting a favorable effect of steroids (only a modest reduction in proteinuria was observed). However, the lack of effectiveness on renal function may be due to a too short follow-up (nearly two years). Starting from encouraging findings obtained with a steroid schedule in membranous nephropathy and from accumulating evidence about the role of proteinuria as the main risk factor for the progression of IgAN,24 in 1987 our group started a large, multicenter, randomized, open-label, controlled trial in order to evaluate the effects of corticosteroids in 86 adult biopsy-proven IgAN patients with normal renal function (serum creatinine ≤ 1.5 mg/dl) and moderate proteinuria (1–3.5 g/day).25 The patients were randomly assigned to receive either supportive therapy or

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six-months’ steroid treatment (methylprednisolone 1 g intravenously for three consecutive days at the beginning of months 1, 3 and 5, plus oral prednisone 0.5 mg/kg every other day for six months). Baseline characteristics were comparable in the two groups. After five years’ follow-up, renal survival was significantly better in the steroid-treated patient group than in the control group for both the primary endpoints of 50% and 100% increase from baseline plasma creatinine levels (respectively of 17% and 21%; log-rank test p < 0.048 and p < 0.005). Three patients in the control group and none in the steroid group required dialysis. Evaluation of renal survival after ten years of followup confirmed that outcomes in the steroid-treated group were better than those in the control group (97% vs. 53%, p = 0.0003).26 Mean urinary protein excretion also significantly decreased in the steroid group (from 1.93 ± 0.45 g/day at baseline to 0.78 ± 0.41 g/day at one year), and this decrease persisted throughout the follow-up, whereas proteinuria remained unchanged in the control group. The positive effect of steroids was confirmed by analyzing proteinuria as a categorical variable. After 12 months, proteinuria in 31 steroid-treated patients (72%) had dropped below 1 g/day; only 13 members (30%) of the control group experienced a similar improvement of proteinuria.26 It is likely that treatment with ACE inhibitors or ARBs did not affect our findings, since a similar percentage of patients in both groups received these agents. Interestingly, glucocorticoids were effective in every histological class. This suggests that the main indication to steroid treatment in patients with IgAN should be proteinuria level and not indexes of activity and/or chronicity at renal biopsy examination. This is also sustained by the fact that at Cox multivariate regression analyses proteinuria behavior during follow-up (a reduction after six months or no increase) independently predicted a positive patient outcome, together with steroid use and a low baseline histological score. None of the patients in the steroid group experienced any major side effects.25,26 More recently, in an open-label study Katafuchi et al.27 randomized 90 IgAN patients with normal renal function to steroids (oral prednisolone 20 mg/day for one month followed by 15 mg/day for one month, 10 mg/day for one month, 7.5 mg/day for three months and 5 mg/day for 18 months) plus dipyridamole (150 or 300 mg/day) or dipyridamole alone at the same dose. Steroids significantly reduced proteinuria, but were ineffective on renal survival. However, the event rate was very low

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(only three patients in each group progressed to end-stage renal disease during follow-up) and the study was severely underpowdered to show any effect on end-stage renal disease. Moreover, treatment groups were not homogeneous for IgAN activity, since the patients in the steroid group had significantly higher proteinuria and proliferative indices at baseline. Finally, as acknowledged by the authors themselves, the dose of steroids used was perhaps too low to halt the progression of the nephropathy. The same authors also reported data from a randomized controlled trial studying 95 patients with IgAN showing segmental lesion such as tuft adhesion, crescent and segmental sclerosis in over 10% of glomeruli.28 These patients were divided in two groups according to urine protein-creatinine ratio (between 1 and 3.5 or lower than 1) and treated either with prednisolone 30 mg/day tapered gradually or dipyridamole. Unfortunately, the period of treatment and the overall follow-up period are not reported in their report. More intriguingly, this steroid protocol was found effective in reducing proteinuria only in the subgroup of patients with proteinuria levels below 1 g/24 h.

Intravenous versus Oral Corticosteroids The administration route of steroids may produce a different response. In 1999, Sato et al.29 published a retrospective, five-year study of 59 IgAN patients with serum creatinine higher than 1.5 mg/dl; 40 of them were administered intravenous pulses of steroids and 19 were administered oral steroids. The progression of renal damage in the following five years was observed in five out of 40 patients treated with pulse glucocorticoids (12.3%) and in eight out of 19 patients treated with oral steroids (42.1%) with a statistical difference ( p = 0.01). The favorable effect of pulse steroid was evident only in patients with serum creatinine less than 2 mg/dl. The findings of our trial, in which pulse glucocorticoids were given in addition to oral steroids, go in the same direction.25 At this point one may wonder why intravenous pulse glucocorticoid therapy is better than oral steroid therapy. As discussed in the previous section, the mechanisms of the beneficial effect of glucocorticoids in the kidney are not completely known. This is even more true for pulse glucocorticoids. In the past, decreased immune complex formation, decrease of vasoactive inflammatory products, alterations of glomerular basement membrane permeability, change of glomerular plasma flow rate, and vasodilatory effects have been proposed to explain

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the favorable effects of pulse glucocorticoids in immune-mediated renal diseases. More recently, in patients with IgAN pulse glucocorticoids but not oral corticosteroids was found to increase plasma levels of adiponectin, which possesses anti-inflammatory and antiatherogenic properties. Moreover, pulse glucocorticoids increase plasma levels of hepatocyte growth factor and asymmetric dimethylarginine (ADMA), and restore endothelial dysfunction.30 The impact of these biochemical changes on kidney function needs further investigations, but the experience of clinical practice, together with a review of the results of clinical trials seems to indicate that the therapeutic schedules including pulse glucocorticoid are more effective than steroids given only orally.25,31 However, no controlled, randomized studies have yet been conducted comparing intravenous pulse with oral steroid for IgAN.

Steroids and Histological Lesions In IgAN the progression of renal damage goes together with a worsening of histological lesions: active lesions observed at early stages turn into chronic lesions that are less sensitive to therapy. It is important to know if a specific treatment can ameliorate the morphological picture or arrest the progressive damage, because a positive effect on histological lesions could predict a better course of the glomerulonephritis. In the literature there are few studies evaluating the effect of glucocorticoids on histological lesions through renal biopsy performed before and after glucocorticoid therapy. Yoshikawa et al.32 studied 78 children with IgAN and normal renal function, 40 of whom received prednisolone, azathioprine, heparin/warfarin and dipyridamole for two years, and 38 heparin/warfarin and dipyridamole alone. Clinical and pathological data before treatment were similar in the two groups. In the second biopsy, performed after treatment, the mean percentage of glomeruli showing segmental or global sclerosis was unchanged in patients treated with glucocorticoid and azathioprine, but increased from 3.9% to 16.4% in patients who did not receive glucocorticoids; the variation of crescents and capsular adhesions was similar in the two groups of patients. Given these findings these authors concluded that immunosuppressive therapy may slow progression to chronic renal failure and prevent the worsening of glomerular sclerosis. However, side effects were frequent and important in children who received immunosuppressive

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drugs. Perhaps a less toxic therapy may have similar advantages on histological lesions. Shoji et al.33 conducted a study to determine whether early treatment with corticosteroids alone was effective in adults with diffuse proliferative IgAN (11 patients received corticosteroids and eight antiplatelet drugs). Mesangial cell proliferation, mesangial matrix accumulation and cellular crescents decreased in steroid-treated and not in the antiplatelet-treated group; segmental sclerosis decreased also from 7.9% to 4.1% in the steroid-treated group but increased from 4.1% to 8.2% in the antiplatelet-treated group. This difference, although not statistically significant given the low number of patients, suggests a positive effect of glucocorticoids on chronic histological lesions. Consistently, proteinuria decreased only in patients receiving glucocorticoids. According to these studies, low dose of glucocorticoids ameliorate histological lesions as high dose of corticosteroids associated to azathioprine but with lesser side effects (Figure 21.1). In our opinion glucocorticoids may be the best choice to obtain an improvement of renal lesions with the minimum burden of side effects, at least in the early phase of the disease.

Steroids in Patients with Chronic Renal Failure There are few clinical studies testing steroid therapy in IgAN patients with advanced disease. Tamura et al.34 studied retrospectively 60 IgAN patients with creatinine clearance below 70 ml/min at the time of renal biopsy (on average

Yoshikawa

Shoji

%

%

18 16 14

18 16 14 12 10 8 6 4 2 0

12 10 8 6 4 2 0 St+Aza

Antiplatelets

Steroids

Antiplatelets

Figure 21.1 Percentage of glomeruli with sclerotic lesions pre-(black) and post(white) therapy.

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58 ml/min), 20 of whom received steroids. The mean follow-up period was about 4.5 years. After one year, proteinuria decreased in the steroid group (from 2.33 to 1.02 g/day), but remained unchanged in the non-steroid group (from 1.39 to 1.28 g/day). Interpretation of results is slightly biased by the fact that before treatment proteinuria was higher in patients receiving steroids (2.33 vs. 1.39 g/day in the control group). Even if serum creatinine was unchanged after one year in the two groups, at the final observation patients not treated with steroids had higher creatinine values compared to those receiving steroids (2.51 vs. 1.79 mg/dl, respectively). Among the steroid group, five patients had worsening renal function; baseline serum creatinine and proteinuria values of these patients were significantly higher than those of stable patients. These authors raised a testing hypothesis that steroid therapy can reduce the amount of proteinuria and prevent deterioration of renal function in IgAN patients with renal impairment if renal histology shows active lesions as most of the patients treated with steroids had cellular crescents and mesangial cell proliferation at first renal biopsy. In 2007 we presented preliminary results of a multicenter, randomized, controlled trial comparing a six-month steroid course with steroid plus azathioprine in 253 patients with IgAN and proteinuria higher than 0.95 g/day.35 Patients were divided in three groups according to baseline renal function and the timing of renal biopsy; group 1: plasma creatinine less than 2.1 mg/dl and renal biopsy performed in the previous year; group 2: plasma creatinine less than 2.1 mg/dl and renal biopsy made more than one year before enrolment; group 3: plasma creatinine more than 2.1 mg/dl and renal biopsy with no time limit. After five years, the renal survival, evaluated as a lack of a 50% increase of plasma creatinine from baseline, was similar in the first two groups. Among the 46 patients with chronic renal insufficiency (CRI) at baseline (group 3), 26 received steroids alone and 20 steroids and azathioprine. After five years the renal survival was 58%. This was better than renal survival observed in other series of untreated IgAN patients with CRI,24,36,37 but similar in the two groups of treatment ( p = 0.47). These data suggest that steroids are effective also in more advanced stages of the glomerulonephritis; azathioprine does not add any benefit, at least in the middle term.

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Conclusion There is evidence that corticosteroids can steadily reduce proteinuria and slow down the progression of IgAN towards end-stage renal disease. This applies at least to patients with normal or slightly reduced renal function. In patients with CRI steroids effectiveness is not yet clearly proven, even if there are some suggestions heading towards possible effectiveness.

References 1. Goulding NJ. (2004) The molecular complexity of glucocorticoid actions in inflammation — a four-ring circus. Curr Opin Pharmacol 4: 629–636. 2. Löwenberg M, Verhaar AP, van den Brink GR, Hommes DW. (2007) Glucocorticoid signaling: a nongenomic mechanism for T-cell immunosuppression. Trends Mol Med 13: 158–163. 3. Newton R, Holden NS. (2007) Separating transrepression and transactivation: a distressing divorce for the glucocorticoid receptor? Mol Pharmacol 72: 799–809. 4. Elenkov IJ. (2004) Glucocorticoids and the Th1/Th2 balance. Ann NY Acad Sci 1024: 138–146. 5. Seto M, Kim S, Yoshifusa H, et al. (1998) Effects of prednisolone on glomerular signal transduction cascades in experimental glomerulonephritis. J Am Soc Nephrol 9: 1367–1376. 6. Koning H, Ponta H, Rahmsdorf U, Herrlich H. (1992) Interference between pathway-specific transcription factors: glucocorticoids antagonize phorbol ester-induced AP-1 activity without altering AP-l site occupation in vivo. EMBO J 11: 2241–2246. 7. Scheinman RI, Cogswell PC, Lofquist AK, Baldwin A, Jr. (1995) Role of transcriptional activation of I kappa B alpha in mediation of immunosuppression by glucocorticoids. Science 270: 283–286. 8. Sakurai H, Shigemori N, Hisada Y, et al. (1997) Suppression of NF-kappa B and AP-1 activation by glucocorticoids in experimental glomerulonephritis in rats: molecular mechanisms of anti-nephritic action. Biochim Biophys Acta 1362: 252–262. 9. Maruyama K, Kashihara N, Yamasaki Y, et al. (2001) Methylprednisolone accelerates the resolution of glomerulonephritis by sensitizing mesangial cells to apoptosis. Exp Nephrol 9: 317–326. 10. Auwardt RB, Mudge SJ, Chen CG, Power DA. (1998) Regulation of nuclear factor kappaB by corticosteroids in rat mesangial cells. J Am Soc Nephrol 9: 1620–1628.

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11. Nakamura T, Ebihara I, Nagaoka I, et al. (1993) Effect of methylprednisolone on transforming growth factor-beta, insulin-like growth factor-I, and basic fibroblast growth factor gene expression in the kidneys of NZB/W F1 mice. Ren Physiol Biochem 16: 105–116. 12. Messmer UK, Winkel G, Briner VA, Pfeilschifter J. (2000) Suppression of apoptosis by glucocorticoids in glomerular endothelial cells: effects on proapoptotic pathways. Br J Pharmacol 129: 1673–1683. 13. Terada Y, Okado T, Inoshita S, et al. (2001) Glucocorticoids stimulate p21(CIP1) in mesangial cells and in anti-GBM glomerulonephritis. Kidney Int 59: 1706–1716. 14. Natori Y, Natori Y, Nishimura T, et al. (1997) Production of monocyte chemoattractant protein-1 by cultured glomerular epithelial cells: inhibition by dexamethasone. Exp Nephrol 5: 318–322. 15. Wada T, Pippin JW, Marshall CB, et al. (2005) Dexamethasone prevents podocyte apoptosis induced by puromycin aminonucleoside: role of p53 and Bcl-2-related family proteins. J Am Soc Nephrol 16: 2615–2625. 16. Ha IS, Um EY, Jung HR, et al. (2002) Glucocorticoid diminishes vascular endothelial growth factor and exacerbates proteinuria in rats with mesangial proliferative glomerulonephritis. Am J Kidney Dis 39: 1001–1010. 17. Kobayashi Y, Fujii K, Hiki Y, Tateno S. (1986) Steroid therapy in IgA nephropathy: a prospective pilot study in moderate proteinuric cases. Q J Med 61: 935–943. 18. Kobayashi Y, Fujii K, Hiki Y, et al. (1988) Steroid therapy in IgA nephropathy: a retrospective study in heavy proteinuric cases. Nephron 48: 12–17. 19. Waldo FB, Wyatt RJ, Kelly DR, et al. (1993) Treatment of IgA nephropathy in children: efficacy of alternate-day oral prednisone. Pediatr Nephrol 7: 529–532. 20. Lai KN, Lai FM, Chan KW, et al. (1986) Corticosteroid therapy in IgA nephropathy with nephrotic syndrome: a long-term controlled trial. Clin Nephrol 26: 174–180. 21. Nicholls K, Kincaid-Smith P, Becker G. (1994) Prednisolone decreases hematuria in IgA nephropathy. Kidney Int 46: 929 (Abstract). 22. Welch TR, Fryer C, Shely E, et al. (1992) Double-blind, controlled trial of short-term prednisone therapy in immunoglobulin A glomerulonephritis. J Pediatr 121: 474–477. 23. Julian B, Barker C. (1993) Alternate-day prednisone therapy in IgA nephropathy: preliminary analysis of a prospective randomized controlled trial. Contrib Nephrol 104: 198–206. 24. D’Amico G, Imbasciati E, Barbiano De Belgioioso G, et al. (1985) Idiopathic IgA mesangial nephropathy. Clinical and histological study of 374 patients. Medicine 64: 49–60.

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25. Pozzi C, Bolasco PG, Fogazzi GB, et al. (1999) Corticosteroids in IgA nephropathy: a randomised controlled trial. Lancet 353: 883–887. 26. Pozzi C, Andrulli S, Del Vecchio L, et al. (2004) Corticosteroid effectiveness in IgA nephropathy: long-term results of a randomized, controlled trial. J Am Soc Nephrol 15: 157–163. 27. Katafuchi R, Ikeda K, Mizumasa T, et al. (2003) Controlled, prospective trial of steroid treatment in IgA nephropathy: a limitation of low-dose prednisolone therapy. Am J Kidney Dis 41: 972–983. 28. Katafuchi R, Ikeda K, Kumagai H, Masutani K. (2004) A limitation and efficacy of low dose steroid therapy in IgA nephropathy: Prospective randomized control trial in the two study groups according to the amount of urinary protein excretion. Nephrology 9(Suppl 2): A58. 29. Sato M, Hotta O, Furuta T, et al. (1999) The limitation of steroid pulse therapy for advanced IgA nephropathy. J Am Soc Nephrol 10: AO448 (Abstract). 30. Uchida HA, Nakamura Y, Kaihara M, et al. (2006) Steroid pulse therapy impaired endothelial function while increasing plasma high molecule adiponectine concentration in patients with IgA nephropathy. Nephrol Dial Transplant 21: 3475–3480. 31. Hotta O, Miyazaki M, Furuta T, et al. (2001) Tonsillectomy and steroid pulse therapy significantly impact on clinical remission in patients with IgA nephropathy. Am J Kidney Dis 38: 736–743. 32. Yoshikawa N, for the Japanese Pediatric IgA Nephropathy Study Group. (1999) A controlled trial of combined therapy for newly diagnosed severe childhood IgA nephropathy. J Am Soc Nephrol 10: 101–109. 33. Shoji T, Nakanishi I, Suzuki A, et al. (2000) Early treatment with corticosteroids ameliorates proteinuria, proliferative lesions, and mesangial phenotypic modulation in adult diffuse proliferative IgA nephopathy. Am J Kidney Dis 2: 194–201. 34. Tamura S, Ueki K, Ideura H, et al. (2001) Corticosteroid therapy in patients with IgA nephropathy and impaired renal function. Clin Nephrol 55: 192–195. 35. Pozzi C, Del Vecchio L, Andrulli S, et al. (2007) Steroids and azathioprine vs. steroids alone in IgA nephropathy. Nephrol Dial Transplant 22(Suppl 6): vi10 (Abstract). 36. Scholl U, Wastl U, Risler T, et al. (1999) The “point of no return” and the rate of progression in the natural history of IgA nephritis. Clin Nephrol 52: 265–292. 37. Komatsu H, Fujimoto S, Sato Y, et al. (2005) “Point of no return (PNR)” in progressive IgA nephropathy: significance of blood pressure and proteinuria management up to PNR. J Nephrol 18: 690–695.

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Chapter 22

Treatment for IgA Nephropathy: Renin-Angiotensin Blockade Rosanna Coppo and Licia Peruzzi

Introduction Renin-angiotensin system (RAS) plays a pivotal role in chronic kidney disease progression, promoting both intra-glomerular and systemic hypertension, and triggering glomerular and interstitial fibrosis by interaction with mesangial and tubular cells. In IgA nephropathy (IgAN) the RAS has a unique role, since its effects are amplified by local hyperactivity and because of the amplification of the RAS transcriptional signaling in mesangial cells by IgA deposits. For these reasons, RAS blockade by angiotensin-converting enzyme inhibitors (ACEi) or angiotensin receptors blockers (ARB) has a theoretical disease-specific benefit for treating IgAN. In hypertensive cases of IgAN, RAS blockade was found to provide superior protection against renal function detriment in comparison to other drugs, and short-term antiproteinuric effects have been thoroughly demonstrated. These data induced several nephrologists to adopt RAS blockade also in normotensive proteinuric IgAN, without properly designed randomized controlled trials (RCT) and in spite of sub-analyses of IgAN patients enrolled in large studies on unselected nephropathies which failed to prove a significant benefit of ACEi against progression to renal failure. In recent years two prospective RCTs eventually proved, in proteinuric IgAN with rather good glomerular filtration rate, a significant effect of ACEi not only in reducing proteinuria but also in preserving renal function, and another RCT proved that ARB decreases proteinuria and slows renal deterioration 321

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322 ✦ R. Coppo & L. Peruzzi

after adjustment for blood pressure control. The additional benefit of a combination therapy has never been adequately addressed in IgAN by properly designed RCT, and only short-term studies or RCT subanalysis are available, which suggest a possible superior effect of the combination therapy in reducing proteinuria and possibly renal disease progression. In conclusion, ACEi and angiotensin receptors blockers (ARB) have a definite role in treating IgAN, particularly the hypertensive and proteinuric forms. These patients should be treated to target BP to < 130/70 mmHg and proteinuria to < 0.5 g/day.

Rationale for Using Renin-Angiotensin Blockade in IgAN Renin-angiotensin system plays a central role in chronic renal disease progression as mediator of renal hemodynamics and glomerular permselectivity and triggering glomerular and interstitial fibrosis by interaction with mesangial and tubular cells.1 In IgA nephropathy (IgAN) the RAS has a unique role, since its effects are amplified by local hyperreactivity2–5 and because of the amplification of the RAS transcriptional signaling in mesangial cells by IgA deposits.6–8 Moreover, a glomerulartubular cross talk triggered by deposited IgA activates an overexpression of angiotensin II receptors type 1 (ATR1) in tubular epithelial cells, possibly contributing to the tubulointerstitial damage.9 The most relevant risk factor for progression of IgAN is proteinuria.10,11 In the natural history of IgAN proteinuria develops after years of microscopic hematuria and in general it precedes the other clinical risk factors such as hypertension and reduced renal function, which tend to be more related to irreversible sclerotic changes. Nephrotic-range proteinuria detected in IgAN at renal biopsy has been found to be associated with very poor outcome,11 but also moderate proteinuria has been recognized as a risk factor for progression of IgAN.12 More than the absolute amount of proteinuria at renal biopsy, the persistence and the level of proteinuria over long-term follow-up (recently defined as timeaverage proteinuria)13 is the most relevant risk factor associated with the outcome. Proteinuria may activate tubular cells and trigger a local activation of the RAS leading to lymphomonocyte interstitial infiltration, and eventually renal fibrosis.1

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Renin-Angiotensin Blockade ✦ 323

Table 22.1

Rationale for using renin-angiotensin blockade in IgAN.

Effects

References

RAS effects in IgAN are amplified by local hyperreactivity IgA deposits amplify RAS transcriptional signaling in mesangial cells IgA deposits activate NFkB nuclear translocation Aberrantly glycosylated IgA trigger NFkB nuclear translocation in mesangial cells ACE-I and ARB blunt NFkB nuclear translocation Polymeric IgA induce TNFα and IL-6 via p42/p44 MAPK and NFkB Altered ATR1 expression on glomerular cells in IgAN IgA deposits activate overexpression of ATR1 in tubular cells Proteinuria is a risk factor for progression also in IgAN Time average proteinuria is negatively bound to outcome Proteinuria activates tubular cells and triggers local activation of RAS Hypertension is an additive risk factor for progression also in IgAN

1, 2, 3, 5, 7 3, 7 4 7 7 6 8 9 10–12 13 1 10, 11,14

Finally, hypertension is one of the major risk factors for progression of IgAN,10,11 as recognized by several investigators, who recently stressed that even border-line high values of BP may be harmful, particularly when proteinuria is associated.14 For these reasons, RAS blockade by ACEi or ARB has a theoretical disease-specific indication for treating IgAN, particularly the hypertensive and proteinuric forms (Table 22.1).

Effects of Angiotensin Blockade in Patients with IgAN Rationale of Choosing ACEi or ARB Inhibition of the RAS can be achieved by means of ACEi or ARB. Both drugs have positive effects and drawbacks.1–15 ACEi drugs depress aldosterone synthesis, which has independent deleterious effects, and limits

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the degradation of bradykinin, with some additional favorable effects on reduction of proteinuria and of glomerular hypertension. On the other hand, ACEi also reduce the effects related to ATR type 2 (ATR2) stimulation, which are thought to lead to vasodilation and inhibition of fibrosis. ARB have the advantage of being placebo-like without any relevant side effect, but their main supposed advantage, the lack of inhibition and even of stimulation of ATR2, seems indeed more harmful than benign, after the last reports indicating that ATR2 may trigger NF-κB.1 No reduction of aldosterone is induced by ARB, while angiotensin II and angiotensin IV are left active with consequent increase in plasminogen-activation inhibitor 1 (PAI-1) and proteolysis. The combination of these two drugs has the advantage of overcoming the limitations of either individual drug, and an effective blocking of TGF-β has been observed.

Treatment of IgAN with ACEi Most of the retrospective studies which investigated the effects of angiotensin II blockade in hypertensive IgAN reported superior results of ACE-I in comparison to other antihypertensive drugs as far as the protective effects in limiting the glomerular filtration rate (GFR) loss and the reduction of proteinuria were concerned16,17 (Table 22.2). The target blood pressure (BP) values in these cohorts retrospectively analyzed were those adopted when the patients were investigated, in general with the BP normal upper limit of 140/90 mmHg. A more recent prospective study pointed out a significant stabilization of GFR in IgAN only in the intensive treatment group, when BP was lowered to < 130/70 mmHg (often using multidrug combinations), while patients with BP > 135/75 mmHg failed to be protected against functional decline.18 The antiproteinuric effect of angiotensin blockade was reported in early short-term investigations;19,20 however the effect was not reproduced in each patient and did not lead to complete remission of proteinuria, as 40% only of the cases showed a reduction of urinary protein excretion of more than 50%. No significant indication of relevant benefits of ACEi in proteinuric IgAN resulted from a sub-analysis of patients with IgAN enrolled in the REIN randomized controlled trial (RCT) where unselected cohorts of proteinuric nephropathies were treated with ACEi.21 In a subgroup of 75 IgAN patients enrolled in the REIN with proteinuria higher than 1 g/day, ACEi saved a loss of 2.3 ml/min/year in

Author (year) characteristics

Proteinuria g/day

< 140/90

2g mean

Different BP targets

>1 g

MAP 92

Follow-up

Efficacy of treatment

3 years

Significant reduction of GFR loss Significant reduction of GFR loss and proteinuria Mild significant reduction in proteinuria

30 months

20 mg

12 months

Benazepril and amlodipine

2.5–10 mg 2.5–10 mg

3 years

Ramipril plus candesartan vs. ramipril plus placebo

5–7.5 mg 4–8 mg

33 weeks

Stabilization of GFR only in intensive treatment group (BP135/75 had GFR decline Significant mild reduction in proteinuria by combination therapy; no BP effect (Continued )

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< 140/90

Enalapril vs. β blockers ACEi vs. other treatments Fosinopril vs. placebo

Dose

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1–2.5 g

Regimen

Renin-Angiotensin Blockade ✦ 325

Song (2003) prospective cross-over study31

Target BP mmHg

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Angiotensin blockade in patient with IgA nephropathy.

< 140/90

Rekola (1991) retrospective16 Cattran (1994) retrospective17

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Table 22.2

Target BP mmHg 125/75

0.5–5 g

< 140/90

Li (2006) RCT multicentric placebo27

2.3 g mean

< 140/90

Follow-up

Efficacy of treatment

Losartan vs. amlodipine Enalapril titrated on BP

50 mg 5 mg 5–40 mg

12 weeks

Valsartan titrated on BP

80–160 mg

2 years

ARB reduced proteinuria ACEi significantly improved renal survival (end point 50% increase in serum creatinine) ARB significantly decreased proteinuria and slowed renal deterioration after adjustment for PB values

6 years

(Continued )

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2–2.3 g

Dose

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Park (2003) prospective26 Praga (2003) RCT monocentric no placebo23

Regimen

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Proteinuria g/day

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Author (year) characteristics

(Continued )


Table 22.2

Proteinuria g/day

Coppo (2007) RCT multicentric placebo24

1–3.5

50 ml/min/1.73 m2. Sixty-six patients, meanly 20 years old (range 9–35), were randomized to receive benazepril 0.2 mg/kg/day or placebo, and were followed for a median of 38 months. The end point of progression of IgAN was defined as >30% decrease of baseline creatinine clearance (CrCl) and also as a composite end point of >30% decrease of baseline CrCl and/or worsening of proteinuria until ≥ 3.5 g/day/1.73 m2 was considered. Secondary outcomes included proteinuria partial ( 1.5 g/day. Patients who received cyclosporin had significant reduction of proteinuria, serum IgA, and increase of plasma albumin concentration compared with placebo. However, there was transient deterioration of renal function during treatment, despite within-range trough drug levels. The authors discouraged indiscriminate use of cyclosporin in IgAN due to nephrotoxicity.

Azathioprine Few studies have examined the potential benefit of azathioprine in IgAN. Goumenos et al.11 performed a retrospective analysis of 74 IgAN patients followed for ten years, and found that long-term azathioprine combined with low-dose prednisone did not alter the clinical course compared to untreated controls. However, in a subgroup of patients with heavy proteinuria greater than 3 g/day and baseline serum creatinine between 1.4–2.5 mg/dl, this immunosuppressive regimen reduced the risk of doubling serum creatinine compared to controls (27% vs. 78%) and delayed progression to end-stage renal failure (17% vs. 55%). The Japanese Pediatric IgA Nephropathy Treatment Study Group12 randomized 78 children with newly diagnosed early IgAN to receive either prednisolone, azathioprine, heparin-warfarin, and dipyridamole or the combination of heparin-warfarin, and dipyridamole only. After two years, there was significant reduction of proteinuria and serum IgA levels in the prednisolone/azathioprine group, while there was no difference in renal function between the two groups. The study was flawed by a lack of data on baseline proteinuria and creatinine clearance as well as blood pressure control in both groups. Sequential therapy in which azathioprine replaces cyclophosphamide after six months in patients with advanced IgAN has been used by Ballardie et al.6 with success, as described above. A prospective randomized study is currently underway in Italy to provide a more definitive role of azathioprine added to steroids versus steroids alone in

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Other Immunomodulatory Agents ✦ 343

the treatment of IgAN patients with proteinuria > 1 g/24 hours and plasma creatinine < 2.0 mg/dl.13 Preliminary data suggest the addition of azathioprine was ineffective and may even be more toxic.

Mycophenolate Mofetil Mycophenolate mofetil (MMF) acts by releasing mycophenolic acid that selectively suppresses the proliferation of T and B lymphocytes, antibody formation, and the glycosylation of adhesion molecules through inhibition of de novo guanine nucleotide synthesis.14 The first clinical report of MMF in IgAN was in the prevention of progression to allograft failure in recurrent IgAN of the transplant kidney.15 To date, four randomized clinical trials have been published on the use of MMF in IgAN, which add more controversy than consensus. Although these trials have produced conflicting results, they differ significantly in patient selection and treatment duration and deserve attention. The first randomized study, published in 2002 in the Chinese literature,16 was conducted in Beijing in which 62 Chinese patients with severe IgAN with Lee’s grade IV and V renal histology and urinary protein > 2.0 g/d received MMF or oral prednisone for at least 12 months. After 18 months’ follow up, the MMF group showed significant improvement in proteinuria and serum lipids than the prednisone group. In 2004 Maes et al.17 described a prospective study in 34 Belgian patients with impaired renal function who were randomized to 2 g of MMF (n = 21) or placebo (n = 13) after instituting salt restriction and angiotensin-converting enzyme inhibitor therapy in all. They only included patients with histologic unfavorable criteria and arterial hypertension, and excluded those with mild histopathologic changes despite heavy proteinuria. After three years of follow-up evaluation, inulin clearances and proteinuria did not differ between the groups. Both groups continued clinical decline in terms of proteinuria and parenchymal thickness. In 2005 Tang et al.18 published a prospective study in 40 Chinese patients with IgAN and mild tubulointerstitial lesions who were randomized 1:1 to 1.5 (BW < 60 kg) or 2.0 g/day MMF for six months or continuation of contemporaneous medication only after blockade of the renin-angiotensin system failed to reduce proteinuria to < 1 g/d. Twelve months after stopping MMF, the overall remission rate (proteinuria < 0.3 g/d or 50% of baseline) was significantly higher in MMF-treated

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patients whose proteinuria dropped to 62% of baseline, whereas urine protein in control patients increased to 120% of baseline. Serum interleukin-6 levels and, more intriguingly, in vitro binding of IgA to mesangial cells were elevated at baseline in both groups compared with normal healthy subjects; however, after MMF treatment these parameters were comparable to those of the healthy subjects. Serum interleukin 6 concentration and mesangial binding of IgA in patients who did not receive MMF showed no change. Adverse events in the MMF group included anemia, urinary tract infections and cervical lymphadenitis. There were no adverse events in the control group. In late 2005, Frisch et al.19 published a randomized controlled trial in which 32 predominantly Caucasoid North American patients with advanced IgAN (mean serum creatinine, 2.5 mg/dl) were randomized to MMF or placebo. MMF was given for one year as a “salvage” therapy in 16 patients with advanced renal insufficiency. Notably, the presence of glomerulosclerosis or tubulointerstitial atrophy and fibrosis on renal biopsy was an inclusion criterion. The study was terminated prematurely after observing a trend towards worse outcome in the MMF group. Lately, Rasche et al.20 reported MMF preserved renal function and reduced proteinuria in 20 advanced IgAN subjects who continued to show a significant renal function decline after pulse cyclophosphamide or pulse steroid. However, this is a non-randomized report lacking a control group and the results require validation. Overall, MMF appears to be effective in reducing proteinuria in Chinese but not Caucasoid IgAN subjects. Therefore, ethnic differences may be one possible reason to account for the differences observed in these studies. Another possibility is the mild histologic grade in Tang’s study18 versus the moderate-to-severe grades in the studies by Maes17 and Frisch.19 Further observation and studies are needed to provide more definitive answers on the efficacy of MMF in IgAN. Randomized clinical trials in North America21 and Italy22 are currently underway.

Other Immunomodulatory Therapy Other immunomodulatory approaches have been assessed in recent studies. The study design, non-randomized nature, lack of controls, and/or small group sizes preclude any firm conclusions to be drawn from these trials, which are outlined here briefly.

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Lai et al.23 had performed plasma exchanges for two patients with crescentic IgA in whom corticosteroid and immunosuppressive therapy failed to control the progression of the disease. In both cases, the rapid progression of renal failure was apparently halted. Nevertheless, the long-term benefit of plasma exchange in crescentic IgA nephropathy was unsatisfactory as the renal function continued to deteriorate in the following 12 months despite an initial stabilization. Plasmapheresis appears to be more effective in children with aggressive forms of crescentic IgAN,24,25 but a randomized study is needed. Leflunomide is a novel immunosuppressive agent inhibiting T and B cell functions by an action on dihydroorotate dehydrogenase and several tyrosine kinase signaling molecules involved in immune function. Lou et al.26 showed in 60 patients randomized to leflunomide or fosinopril that leflunomide effectively suppressed proteinuria, however this effect was not superior to that achieved by fosinopril. Mizoribine is an imidazole nucleotide originally isolated in Japan that blocks the purine biosynthesis pathway and inhibits mitogenstimulated T and B cell proliferation. In a study that employed 41 historical pediatric controls who received prednisolone, warfarin, and dipyridamole therapy before 1989, the addition of mizoribine in 20 subjects after 1990 appeared to be more effective in ameliorating proteinuria and histological severity on repeat biopsy at two years.27 Intravenous immunoglobulins, given monthly at a dose of 2 g/kg body weight for six months to eight patients with progressive IgAN, showed some benefit in prolonging renal survival by 3.5 years compared with eight patients with IgAN and similar level of renal function without receiving immunoglobulins.28 Information of Rituximab (anti-CD20) for treatment of IgAN is lacking.

Choice of Immunomodulatory Therapy This remains a controversial area. We advocate the use of immunomodulatory agents (cyclophosphamide for Caucasians and MMF for Orientals for six months) as an adjunctive therapy in patients with proteinuria > 1 g/day despite achieving target blood pressure of 125/75 mm Hg with full renin–angiotensin blockade. More aggressive therapy should be reserved for patients with nephrotic-range proteinuria, crescentic lesions and/or rapidly progressive renal failure. On the other hand, patients with advanced renal failure (serum creatinine > 300 µmol/l)

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and considerable tubulointerstitial fibrosis in the kidney will unlikely benefit from immunomodulation.

References 1. Lai KN, To WY, Li PK, et al. (1996) Increased binding of polymeric lambdaIgA to cultured human mesangial cells in IgA nephropathy. Kidney Int 49: 839–845. 2. O’Donoghue DJ, Darvill A, Ballardie FW. (1991) Mesangial cell autoantigens in immunoglobulin A nephropathy and Henoch-Schönlein purpura. J Clin Invest 88: 1522–1530. 3. Rifai A. (2007) IgA nephropathy: immune mechanisms beyond IgA mesangial deposition. Kidney Int 72: 239–241. 4. Floege J, Eitner F. (2008) Immune modulating therapy for IgA nephropathy: rationale and evidence. Semin Nephrol 28: 38–47. 5. Samuels JA, Strippoli GF, Craig JC, et al. (2004) Immunosuppressive treatments for immunoglobulin A nephropathy: a meta-analysis of randomized controlled trials. Nephrology (Carlton) 9: 177–185. 6. Ballardie FW, Roberts IS. (2002) Controlled prospective trial of prednisolone and cytotoxics in progressive IgA nephropathy. J Am Soc Nephrol 13: 142–148. 7. Tumlin JA, Lohavichan V, Hennigar R. (2003) Crescentic, proliferative IgA nephropathy: clinical and histological response to methylprednisolone and intravenous cyclophosphamide. Nephrol Dial Transplant 18: 1321–1329. 8. Rasche FM, Klotz CH, Czock D, et al. (2003) Cyclophosphamide pulse therapy in advanced progressive IgA nephropathy. Nephron Clin Pract 93: C131–C136. 9. Mitsuiki K, Harada A, Okura T, et al. (2007) Histologically advanced IgA nephropathy treated successfully with prednisolone and cyclophosphamide. Clin Exp Nephrol 11: 297–303. 10. Lai KN, Lai FM, Li PK, et al. (1987) Cyclosporin treatment of IgA nephropathy: a short term controlled trial. Br Med J (Clin Res Ed) 295: 1165–1168. 11. Goumenos DS, Davlouros P, El Nahas AM, et al. (2003) Prednisolone and azathioprine in IgA nephropathy — a ten-year follow-up study. Nephron Clin Pract 93: C58–C68. 12. Yoshikawa N, Ito H. (1999) Combined therapy with prednisolone, azathioprine, heparin-warfarin, and dipyridamole for paediatric patients with severe IgA nephropathy — is it relevant for adult patients? Nephrol Dial Transplant 14: 1097–1099.

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13. Locatelli F, Pozzi C, Del VL, et al. (1999) Combined treatment with steroids and azathioprine in IgA nephropathy: design of a prospective randomised multicentre trial. J Nephrol 12: 308–311. 14. Allison AC, Eugui EM. (1996) Purine metabolism and immunosuppressive effects of mycophenolate mofetil (MMF). Clin Transplant 10: 77–84. 15. Nowack R, Birck R, van der Woude FJ. (1997) Mycophenolate mofetil for systemic vasculitis and IgA nephropathy. Lancet 349: 774. 16. Chen X, Chen P, Cai G, et al. (2002) A randomized control trial of mycophenolate mofeil treatment in severe IgA nephropathy. Zhonghua Yi Xue Za Zhi 82: 796–801. 17. Maes BD, Oyen R, Claes K, et al. (2004) Mycophenolate mofetil in IgA nephropathy: results of a 3-year prospective placebo-controlled randomized study. Kidney Int 65: 1842–1849. 18. Tang S, Leung JC, Chan LY, et al. (2005) Mycophenolate mofetil alleviates persistent proteinuria in IgA nephropathy. Kidney Int 68: 802–812. 19. Frisch G, Lin J, Rosenstock J, et al. (2005) Mycophenolate mofetil (MMF) vs. placebo in patients with moderately advanced IgA nephropathy: a double-blind randomized controlled trial. Nephrol Dial Transplant 20: 2139–2145. 20. Rasche FM, Keller F, von ML, et al. (2007) Sequential immunosuppressive therapy in progressive IgA nephropathy. Contrib Nephrol 157: 109–113. 21. Hogg RJ, Wyatt RJ. (2004) A randomized controlled trial of mycophenolate mofetil in patients with IgA nephropathy [ISRCTN6257616]. BMC Nephrol 5: 3. 22. Dal CA, Amore A, Barbano G, et al. (2005) One-year angiotensin-converting enzyme inhibition plus mycophenolate mofetil immunosuppression in the course of early IgA nephropathy: a multicenter, randomised, controlled study. J Nephrol 18: 136–140. 23. Lai KN, Lai FM, Leung AC, et al. (1987) Plasma exchange in patients with rapidly progressive idiopathic IgA nephropathy: a report of two cases and review of literature. Am J Kidney Dis 10: 66–70. 24. Fujinaga S, Ohtomo Y, Umino D, et al. (2007) Plasma exchange combined with immunosuppressive treatment in a child with rapidly progressive IgA nephropathy. Pediatr Nephrol 22: 899–902. 25. Shenoy M, Ognjanovic MV, Coulthard MG. (2007) Treating severe HenochSchonlein and IgA nephritis with plasmapheresis alone. Pediatr Nephrol 22: 1167–1171. 26. Lou T, Wang C, Chen Z, et al. (2006) Randomised controlled trial of leflunomide in the treatment of immunoglobulin A nephropathy. Nephrology (Carlton) 11: 113–116.

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27. Kawasaki Y, Hosoya M, Suzuki J, et al. (2004) Efficacy of multidrug therapy combined with mizoribine in children with diffuse IgA nephropathy in comparison with multidrug therapy without mizoribine and with methylprednisolone pulse therapy. Am J Nephrol 24: 576–581. 28. Rasche FM, Keller F, Lepper PM, et al. (2006) High-dose intravenous immunoglobulin pulse therapy in patients with progressive immunoglobulin A nephropathy: a long-term follow-up. Clin Exp Immunol 146: 47–53.

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Chapter 24

Other Non-Immunomodulatory Agents Jonathan Barratt and John Feehally

Introduction A lack of high quality, appropriately designed randomized controlled trials (RCTs) has meant there is little convincing evidence for many of the treatments proposed to be beneficial in IgAN.1,2 This is even more so when we consider the evidence for the interventions discussed in this chapter. We have reviewed the literature published on the treatment of IgAN since 1976 and identified all studies where non-immunomodulatory agents were used. Despite the prevalence of IgAN, published RCTs were few in number, and even recent RCTs were not always sufficiently powered to provide definitive information on tested interventions. Most studies reviewed were small, single center, non-randomized, and commonly used historical control groups for comparison. In this chapter we review, in alphabetical order, those interventions where there is a sufficient body of evidence.

Antioxidants Rationale for Use Increased production of reactive oxygen species and reduced antioxidant defense mechanisms have been demonstrated in chronic kidney disease3,4 and there is evidence for an increase in oxygen-free radical release both in an animal model of IgAN5 and by peripheral polymorphonuclear leukocytes and monocytes isolated from patients with IgAN.6,7 349

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In addition, IgA-containing immune-complexes (IgA-IC) stimulate the production of oxygen-free radicals by mesangial cells in vitro8 and modest supplementation of the diet with vitamin E (100 IU α-tocopherol/ kg/day) has been shown to reduce proteinuria, ameliorate renal deterioration and prevent glomerular damage in an animal model of IgAN.5 Vitamin E has both antioxidant and anti-inflammatory properties: it preserves the integrity of biological membranes, prevents apoptosis due to oxidative stress, decreases superoxide production by activated phagocytes and inhibits neutrophil chemotaxis and platelet aggregation.9–11

Trial Evidence There has been a single pilot RCT of antioxidants in IgAN.12 The study was undertaken in children and young adults (age < 21 years) with mild disease (GFR 20%–100% of normal for age) and was a prospective, double blinded and placebo controlled RCT. Children less than 30 kg body weight received 400 IU vitamin E/day; children of 30 kg body weight and above received 800 IU/day and treatment duration was for two years. Twenty-eight children were randomized to receive placebo and 27 received vitamin E. The primary end points were changes in GFR and proteinuria, with prevalence of hematuria as a secondary end point. Vitamin E treatment was associated with significantly lower proteinuria, but no effect on hematuria. There was also a trend towards stabilization of GFR in the vitamin E-treated patients. By contrast, a smaller uncontrolled study of 28 adult patients with IgAN given 400 IU vitamin E/day for six months failed to show any improvement in proteinuria or preservation of GFR.13

Conclusion The benefits of vitamin E reported in early observational studies of chronic kidney disease and cardiovascular disease have not been confirmed in large-scale, placebo-controlled RCTs. Similarly, there is insufficient evidence at present to support the use of vitamin E in IgAN. We are not aware of any ongoing RCTs addressing the use of vitamin E in IgAN.

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Other Non-Immunomodulatory Agents ✦ 351

Antiplatelet Agents, Anticoagulants and Fibrinolytics Rationale for Use Antiplatelet agents interfere with a number of processes thought to be important in the pathogenesis of glomerular injury including the release of chemical mediators from platelets such as serotonin and platelet-derived growth factor14 and they inhibit mesangial cell proliferation.15 Intraglomerular coagulation either through local activation of blood coagulation or impaired removal by the fibrinolytic system, has been proposed as one of the factors causing glomerular injury in IgAN.16–18 Use of low dose warfarin and the fibrinolytic urokinase may ameliorate this injury.

Trial Evidence The main studies are summarized in Table 24.1 and as can be seen have generated conflicting results. A number of these studies used dipyridamole with low dose warfarin in combination with other treatments and it is therefore often impossible to determine the effect independent of concurrent immunosuppression. A study by the Japanese Pediatric IgAN Treatment Study Group failed to show any benefit (reduction in proteinuria, serum IgA concentration, mesangial IgA deposition, and risk of glomerulosclerosis) following two years of treatment with heparin-warfarin and dipyridamole.19 The use of antiplatelet agents alone (dipyridamole/aspirin) similarly failed to decrease the rate of progression of IgAN after three years of treatment.20 A reduction in proteinuria (but no effect on preservation of renal function) was seen in an Australian study following two years of dipyridamole and warfarin, however the patients had also received six months of cyclophosphamide.21 A similar study from Singapore (cyclophosphamide for six months combined with three years of dipyridamole and warfarin) demonstrated a reduction in proteinuria, preservation of renal function and less damage on repeat renal biopsy.22 A follow-up study five years later noted that those patients from the initial study that had continued with dipyridamole and warfarin (n = 13) were less likely to have developed end-stage renal disease (ESRD) than those who had stopped treatment (n = 14).23 In a separate study from the same group, dipyridamole

Treatment

Lee et al.24

RCT

20

Dipyridamole/warfarin

36

Chan et al.20 Walker et al.21

RCT RCT

38 52

33 24

Woo et al.23

RCT

48

Dipyridamole/aspirin Dipyridamole/warfarin (+ cyclophosphamide) Dipyridamole/warfarin (+ cyclophosphamide)

Yoshikawa et al.19

RCT

78

Chen et al.25

RCT

71

Dipyridamole/warfarin (+ azathioprine) (+ prednisolone) Urokinase (+ benazepril)

Follow-up (months)

60

24

12

Results ↓ proteinuria GFR maintained No benefit ↓ proteinuria GFR maintained ↓ proteinuria Glomerulosclerosis prevented No benefit

↓ proteinuria GFR maintained

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N

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Design

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Author

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Trials of antiplatelet, anticoagulant and fibrinolytic treatment in IgA nephropathy.


Table 24.1

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and low dose warfarin treatment for three years reduced the risk of ESRD but had no effect on proteinuria.24 There have been two small studies of urokinase in IgAN.25,26 The largest of these is a RCT in which 71 patients were allocated either benazepril or benazepril and urokinase 100,000 IU/day for 10 days/ month for 12 months. The addition of urokinase was associated with a greater reduction in proteinuria and preservation of GFR.

Conclusion A recent meta-analysis of antiplatelet treatments (dipyridamole, aspirin, trimetazidine and dilazep) in IgAN suggested some benefit in terms of reduction in proteinuria and preservation of renal function.27 However the authors noted that the quality of the published trials was not high, that most studies did not assess valid end points and that the study periods were not long enough to evaluate progression adequately. The authors also acknowledged that each of the studies included patients who were receiving concomitant drugs and so it was impossible to evaluate the effect of antiplatelet agents alone. Because of a lack of high-quality trials, further studies with an appropriate design are needed in order to reach a definitive conclusion regarding the role of antiplatelet agents and anticoagulants in the treatment of IgAN. Likewise, the lack of sufficient data makes it impossible to draw any firm conclusions on the utility of fibrinolytics IgAN.

Dietary Modification and Manipulation of Intestinal Permeability Rationale for Use Many studies have found elevated circulating IgA-IC containing food antigens in IgAN28–32 and a number of studies have reported changes in various clinical and laboratory parameters on exposure to specific foods.32,33 Circulating IgA antibodies to a variety of milk and egg proteins including casein and bovine serum albumin have been reported in IgAN33,34 and indirect immunofluorescence has identified mesangial IgA-IC deposits containing casein, soybean protein and rice protein.30,34 There is also the theoretical possibility that systemic absorption of food

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lectins with a propensity to bind aberrantly glycosylated IgA1 may promote the formation of IgA-IC in the circulation and therefore drive mesangial IgA deposition. At present little is known about the IgA1 binding properties of commonly encountered lectins including those found in commonly encountered pulses (e.g. beans, peas and lentils), vegetables and fruits. An increased mucosal permeability, allowing excessive antigen presentation to the mucosal immune system, has also been reported in IgAN.35 Clinical conditions that alter intestinal permeability such as ulcerative colitis and Crohn’s disease may be associated with the development of IgAN and improvement in urinary abnormalities can follow remission of the bowel disease.36 Disodium cromoglycate (SCG) and 5-aminosalicylic acid (5-ASA) have been shown to alter mucosal permeability and mucosal immune activation in animal models of IgAN and inflammatory bowel disease.36,37

Trial Evidence Two small studies have reported short term improvements in some parameters of renal injury in some patients with IgAN following manipulation of dietary antigen exposure. In the first uncontrolled study, 21 patients were given a low-antigen content diet for 14–24 weeks and clinical and serological parameters evaluated, 11 patients underwent repeat renal biopsy.38 The low-antigen diet was normocaloric with restriction of foods rich in putative macromolecular antigens, such as dairy products, eggs and meats. Introduction of a low antigen diet was associated with a reduction in proteinuria and the extent of IgA/ complement/fibrinogen mesangial deposits on re-biopsy. Unfortunately, the investigators did not return the subjects to a “normal” (non-oligo-antigenic) diet to see if proteinuria increased to pre-intervention levels. It is also unclear how long the effects were maintained for, or the long term palatability of such a diet in otherwise healthy subjects. The second uncontrolled study included 29 patients without coelic disease who were given a gluten-free diet for six months.33 Patients were followed up for between one to four years. As in the previous study dietary restriction led to a reduction in proteinuria and reduced levels of IgA-IC, dietary antigen-specific IgA, and microscopic hematuria. However, there was no effect on the rate of decline of GFR in the treated group.

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A further two small studies have evaluated the role of SCG and 5-ASA in IgAN. The first was an uncontrolled study in which nine patients received 5-ASA (2.4 g/day for six months) and nine patients received SCG (400 mg/day for six months).39 At 12 months there was no difference in the levels of serum IgA-IC, proteinuria or GFR when compared to pre-treatment levels. The second study looked at 30 patients with IgAN of which 15 were treated with SCG (1200 mg/day for 16 weeks) and 15 had standard medical care.40 At 16 weeks there was a significant reduction in proteinuria in the SCG group but there was no difference in GFR, serum IgA concentration or IgA-IC between the groups. It is not known whether this reduction in proteinuria was maintained following cessation of the SCG.

Conclusion What is clear from these, and other, studies is that no single environmental antigen is responsible for driving IgA immune activation and mesangial IgA deposition in IgAN. It seems that a wide range of environmental (and microbial) antigens drive the synthesis of IgA-IC and therefore it is unlikely that excluding a small percentage of the antigens, an individual encounters in their normal day will affect the clinical course of IgAN. From the data available there is insufficient evidence to recommend either dietary restriction or manipulation of mucosal permeability in IgAN.

Fish Oil Rationale for Use The rationale for using fish oil supplements in patients with IgAN is based on experimental data suggesting that omega-3 polyunsaturated fatty acids may limit the immunologic renal injury in IgAN. The two major omega-3 polyunsaturated fatty acids in fish oil are eicosapentanoic acid (EPA) and docosahexanoic acid (DHA). These omega-3 fatty acids compete with arachidonic acid to produce trienoic eicosanoids which, in turn, may slow renal disease progression by reducing glomerular and interstitial inflammation, mesangial cell contractility, platelet aggregation, and vasoconstriction in response to renal injury.41

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Trial Evidence There have been six RCTs of fish oil (EPA and DHA) in IgAN (Table 24.2). Two trials by the Mayo Nephrology Collaborative Group have demonstrated a renoprotective effect of fish oil in patients with persistent proteinuria.42–44 The first of these was an RCT of 106 patients with proteinuria > 1 g/24 hours and impaired renal function at enrolment (60% also hypertensive) which found that those treated with fish oil had a slower rate of decline in GFR (but no improvement in proteinuria) at both two and five years.42,43 A second RCT from the same center, included a further 73 patients with similar baseline characteristics, but used a historical control group (the authors argued it was inappropriate to include a control group in light of the benefits of fish oil in the initial study).44 Again, fish oil was associated with a slower rate of decline in GFR compared to the historical control group and this effect was independent of the dose of fish oil used. These results have not been replicated in three other RCTs studying similar patient cohorts45–47 and a meta-analysis (three trials, 175 patients25,27,42) failed to detect a benefit of fish oils on renal outcome in IgAN.48 One explanation proposed for the observed differences in clinical effectiveness of fish oil is that the effect is associated with a dosagedependent effect on plasma phospholipid EPA and DHA levels.49 A post-hoc analysis by the Mayo Nephrology Collaborative Group of one of their earlier trials44 however failed to confirm an association between body size, plasma omega-3 polyunsaturated fatty acid levels, and renal outcome.50 This lack of association is supported by a small RCT of fish oil in patients at high risk of progressive disease in which benefit (better preservation of renal function and lower urine protein) was reported despite the use of a low dose daily regimen of EPA 0.85 g and DHA 0.57 g.51

Conclusion The use of fish oil is rarely associated with significant side effects and does not have the drawbacks associated with immunosuppressive treatment. It is safe apart from a decrease in blood coagulability, which is not usually a practical problem, and an unpleasant taste with flatulence, which may make compliance difficult. At present the available evidence does not yet give unequivocal support for the use of fish oil and a further

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Author

Design

N

Pettersson et al.47

RCT

32

Donadio et al.42,43

RCT

106

Donadio et al.44

RCT

73

Alexopoulos et al.51

RCT

28

Hogg et al.46

RCT

96

EPA-DHA 1.8–1.2 g daily EPA-DHA 3.3–1.8 g daily EPA-DHA 1.8–1.2 g daily EPA-DHA 3.8–2.9 g daily vs. 1.9–1.5 g daily EPA-DHA 0.85–0.57 g daily EPA-DHA 1.88–1.48 g

EPA, eicosapentanoic acid; DHA, docosahexanoic acid; GFR, glomerular filtration rate.

Results

24

No effect on GFR decline

6

↓ GFR No effect on proteinuria Slower ↓ GFR

24 and 60 24

48 24

Slower ↓ GFR But no difference between high and low dose EPA-DHA Slower ↓ GFR No effect on GFR decline ↓ proteinuria

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37

Follow-up (months)

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RCT

Treatment


Bennett et al.45

Trials of fish oil in IgA nephropathy.

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Table 24.2

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confirmatory study of fish oil in IgAN would be of great value. In spite of this the use of fish oil is common in patients at risk of progressive renal impairment. Use of fish oil should not be used as an alternative to maximal inhibition of the renin angiotensin system with ACE inhibition and angiotensin receptor blockade, and achieving a blood pressure of 125/75 mmHg. There is no data in published clinical trials suggesting a synergistic or otherwise effect of co-administration of ACEI/ARB and fish oil.

3-Hydroxy-3-Methylglutaryl Coenzyme A (HMG-CoA) Reductase Inhibitors Rationale for Use HMG-CoA reductase is a major rate-limiting enzyme in cholesterol biosynthesis that converts HMG-CoA to mevalonate, an early precursor of cholesterol. HMG-CoA reductase inhibitors lower plasma total and low density lipoprotein cholesterol levels.52 Experimental data suggest that inhibitors of HMG-CoA reductase may also protect against glomerular and mesangial injury independent of a reduction in circulating lipids. In animal models of renal disease, administration of HMG-CoA reductase inhibitors reduces proteinuria and the degree of glomerulosclerosis.53,54 Small clinical trials, meta-analyses, observational studies and post-hoc analyses of cardiovascular intervention studies all support the concept that HMG-CoA reductase inhibitors can reduce kidney damage in humans.

Trial Evidence Two studies have evaluated the HMG-CoA reductase inhibitor fluvastatin in normotensive, normocholesterolemic IgAN. In the first study, 30 children with early IgAN were randomly assigned to receive both 20 mg of fluvastatin and 5 mg/kg of dipyridamole, or 5 mg/kg of dipyridamole only for one year.55 Treatment with fluvastatin resulted in a greater reduction in proteinuria, hematuria and improvement in GFR than in the control group and was associated with a fall in serum total cholesterol, triglyceride and LDL cholesterol levels. The second study involved randomized adult patients receiving either 40 mg of fluvastatin

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for six months (n = 8) or placebo (n = 13).56 All patients were moderately proteinuric (< 1 g/24 hours) with stable renal function (Cr < 160 µmol/l), and no indicators of poor long-term prognosis. As in the study in children there was a significant reduction in proteinuria with fluvastatin.

Conclusion It is unlikely that the anti-proteinuric effect of fluvastatin observed in these studies is specific to IgAN. As with all other treatments used in IgAN the putative renoprotective effect of HMG-CoA reductase inhibitors is likely to be common to all forms of proteinuric renal disease. Despite these encouraging early studies, it is appropriate to wait for the results of large RCTs such as the Study of Heart and Renal Protection (SHARP)57 before we can recommend the widespread use of HMG-CoA reductase inhibitors in normocholesterolaemic IgAN.

Phenytoin Sodium Rationale for Use Phenytoin sodium has been shown by a number of investigators to lower serum IgA concentrations, and in particular polymeric IgA levels.58,59 This effect is probably caused by reduced production of IgA rather than by a selective increase in systemic clearance as phenytoin sodium has been shown to suppress a number of parameters of both the cellular and humoral immune response.58,60 Phenytoin sodium does not however appear to affect levels of circulating IgA-IC in IgAN.61

Trial Evidence There have been two trials of phenytoin sodium in IgAN. The first was a RCT of 47 adults of which 23 received 5–6 mg phenytoin sodium/ kg/day (serum phenytoin level 10–20 µg/ml) for two years.62 While serum IgA concentrations fell significantly in the treated group, there were no clinical, biochemical, serological or pathological differences between the treatment and control groups. The second study was a non-randomized case-control trial of 73 patients (41 received phenytoin sodium) which again reported a reduction in serum IgA levels

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in the treated group but no improvement in either clinical parameters or pathological lesions with phenytoin sodium.63

Conclusion Despite reducing serum IgA levels there is no evidence that this translates into an improved clinical outcome in IgAN and therefore the use of phenytoin sodium is not recommended in IgAN.

Traditional Chinese Medicine Rationale for Use Traditional Chinese medicine (TCM) includes a range of traditional medical practices originating in China that has developed over several thousand years. TCM practices include theories, diagnosis and treatments such as herbal medicine, acupuncture, moxibustion and massage. TCM along with the other components of Chinese medicine, is based on the concepts of Yin and Yang. It aims to understand and treat the many ways in which the fundamental balance and harmony between the two may be undermined and the ways in which a person’s Qi or vitality may be depleted or blocked. Clinical strategies are based upon diagnosis of patterns of signs and symptoms that reflect an imbalance. There is data emerging from animal models and in vitro human studies to suggest some TCM can affect a number of pathways important in the pathogenesis of IgAN.64,65

Trial Evidence Over the past ten years there has been a steady flow of small clinical trials of TCM in the treatment of IgAN (Table 24.3). Most have attempted to compare TCM with an integrated TCM and Western medicine approach. One challenge when interpreting the findings of such trials is the choice of the primary and secondary end points which can be very different when assessed using TCM evaluation criteria compared to Western medicine parameters. In most instances the trials reported have been short term studies and therefore have only been able to report changes in surrogate markers of risk of progression in IgAN, principally proteinuria.

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Trials of traditional Chinese medicine for the treatment of IgA nephropathy.

Design

Follow-up (months)

Results

Shenle Capsule vs. Fosinopril Huobahuagen Tablets vs. Irbesartan Dan Shao Tang Shenning Mixture Sairei-to Hirudo

3

↓ proteinuria equivalent to that seen with fosinopril ↓ proteinuria but less than that seen with irbesartan

Chen et al.66

RCT

70

Guan et al.67

RCT

22

Wu et al.68 Bo et al.69 Yoshikawa et al.70 Dong et al.71

RCT RCT RCT non-RCT

90 34 101 31

3

6 6 24 1

↓ proteinuria ↓ proteinuria ↓ proteinuria ↓ proteinuria

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Treatment


N

9:53 AM

Author

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Table 24.3

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Conclusion At the present time there is insufficient evidence to recommend the use of TCM in IgAN. No doubt the quality and number of trials will increase and it will be interesting to see whether in the future trial data supports an integrated TCM and Western medicine approach to the management of patients with IgAN.

Future Prospects The lack of a basic understanding of the pathogenesis of IgAN has meant that there has been little progress in the development of specific treatments for this common glomerulonephritis. In line with other chapters dealing with the treatment of IgAN, the treatments we have reviewed here are likely to be equally as effective in other forms of proteinuric renal disease. Also, the lack of high quality, well designed and appropriately sized clinical trials means that very few firm recommendations can be made using currently available clinical trial data. If any progress is to be made in clarifying the optimum treatment for IgAN then there must be a concerted effort by clinicians to conduct high quality clinical trials, starting with those interventions most likely to afford some benefit over and above good blood pressure control (< 125/75 mmHg) and maximal inhibition of the renin angiotensin system.

References 1. Appel GB, Waldman M. (2006) The IgA nephropathy treatment dilemma. Kidney Int 69: 1939–1944. 2. Barratt J, Feehally J. (2006) Treatment of IgA nephropathy. Kidney Int 69: 1934–1938. 3. Boaz MS, Smetana T, Weinstein Z, et al. (2000) Secondary prevention with antioxidants of cardiovascular disease in endstage renal disease (SPACE): randomised placebo-controlled trial. Lancet 356: 1213–1218. 4. Kosieradzki MJ, Kuczynska J, Piwowarska I, et al. (2003) Prognostic significance of free radicals: mediated injury occurring in the kidney donor. Transplantation 75: 1221–1227. 5. Trachtman H, Chan JC, Chan W, et al. (1996) Vitamin E ameliorates renal injury in an experimental model of immunoglobulin A nephropathy. Pediatr Res 40: 620–626.

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6. Kashem A, Endoh M, Nomoto Y, et al. (1994) Fc alpha R expression on polymorphonuclear leukocyte and superoxide generation in IgA nephropathy. Kidney Int 45: 868–875. 7. Kashem A, Endoh M, Nomoto Y, et al. (1996) Monocyte superoxide generation and its IgA-receptor in IgA nephropathy. Clin Nephrol 45: 1–9. 8. Chen A, Chen WP, Sheu LF, Lin CY. (1994) Pathogenesis of IgA nephropathy: in vitro activation of human mesangial cells by IgA immune complex leads to cytokine secretion. J Pathol 173: 119–126. 9. Forrest VJ, Kang YH, McClain DE, et al. (1994) Oxidative stress-induced apoptosis prevented by Trolox. Free Radic Biol Med 16: 675–684. 10. Luostarinen R, Siegbahn A, Saldeen T. (1991) Effects of dietary supplementation with vitamin E on human neutrophil chemotaxis and generation of LTB4. Ups J Med Sci 96: 103–111. 11. Freedman JE, Farhat JH, Loscalzo J, Keaney Jr JF. (1996) Alpha-tocopherol inhibits aggregation of human platelets by a protein kinase C-dependent mechanism. Circulation 94: 2434–2440. 12. Chan JC, Mahan JD, Trachtman H, et al. (2003) Vitamin E therapy in IgA nephropathy: a double-blind, placebo-controlled study. Pediatr Nephrol 18: 1015–1019. 13. Ong-ajyooth L, Ong-ajyooth S, Parichatikanond P. (2006) The effect of alpha-tocopherol on the oxidative stress and antioxidants in idiopathic IgA nephropathy. J Med Assoc Thai 89(Suppl 5): S164–S170. 14. Takehara K, Igarashi A, Ishibashi Y. (1990) Dipyridamole specifically decreases platelet-derived growth factor release from platelets. Pharmacology 40: 150–156. 15. Gohda T, Makita Y, Shike T, et al. (2000) Effect of dilazep hydrochloride, an antiplatelet agent, on the proliferation of cultured mouse glomerular mesangial cells. Nephron 84: 90–91. 16. Yamabe H, Sugawara N, Ozawa K, et al. (1984) Glomerular deposition of Hageman factor in IgA nephropathy. Nephron 37: 62–63. 17. Tan C, Lee G, Lee EJ, Woo KT. (1996) Plasma activity of contact coagulation factors in patients with IgA nephritis. Ann Acad Med Singapore 25: 218–221. 18. Colucci M, Semeraro N, Montemurro P, et al. (1991) Urinary procoagulant and fibrinolytic activity in human glomerulonephritis. Relationship with renal function. Kidney Int 39: 1213–1217. 19. Yoshikawa N, Ito H, Sakai T, et al. (1999) A controlled trial of combined therapy for newly diagnosed severe childhood IgA nephropathy. The Japanese Pediatric IgA Nephropathy Treatment Study Group. J Am Soc Nephrol 10: 101–109. 20. Chan MK, Kwan SY, Chan KW, Yeung CK. (1987) Controlled trial of antiplatelet agents in mesangial IgA glomerulonephritis. Am J Kidney Dis 9: 417–421.

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21. Walker RG, Yu SH, Owen JE, Kincaid-Smith P. (1990) The treatment of mesangial IgA nephropathy with cyclophosphamide, dipyridamole and warfarin: a two-year prospective trial. Clin Nephrol 34: 103–107. 22. Woo KT, Chiang GS, Yap HK, Lim CH. (1988) Controlled therapeutic trial of IgA nephritis with follow-up renal biopsies. Ann Acad Med Singapore 17: 226–231. 23. Woo KT, Lee GS, Lau TYK, et al. (1991) Effects of triple therapy in IgA nephritis: a follow-up study 5 years later. Clin Nephrol 36: 60–64. 24. Lee GS, Choong HI, Chiang GS, Woo KT. (1997) Three-year randomized controlled trial of dipyridamole and low-dose warfarin in patients with IgA nephropathy and renal impairment. Nephrology 3: 117–121. 25. Chen X, Qiu Q, Tang L, et al. (2004) Effects of co-administration of urokinase and benazepril on severe IgA nephropathy. Nephrol Dial Transplant 19: 852–857. 26. Miura M, Endoh M, Nomoto Y, Sakai H. (1989) Long-term effect of urokinase therapy in IgA nephropathy. Clin Nephrol 32: 209–216. 27. Taji Y, Kuwahara T, Shikata S, Morimoto T. (2006) Meta-analysis of antiplatelet therapy for IgA nephropathy. Clin Exp Nephrol 10: 268–273. 28. Jackson S, Moldoveanu Z, Kirk KA, et al. (1992) IgA-containing immune complexes after challenge with food antigens in patients with IgA nephropathy. Clin Exp Immunol 89: 315–320. 29. Nagy J, Scott H, Brandtzaeg P. (1988) Antibodies to dietary antigens in IgA nephropathy. Clin Nephrol 29: 275–279. 30. Sato M, Kojima H, Takayama K, Koshikawa S. (1988) Glomerular deposition of food antigens in IgA nephropathy. Clin Exp Immunol 73: 295–299. 31. Russell MW, Mestecky J, Julian BA, Galla JH. (1986) IgA-associated renal diseases: antibodies to environmental antigens in sera and deposition of immunoglobulins and antigens in glomeruli. J Clin Immunol 6: 74–86. 32. Feehally J, Beattie TJ, Brenchley PE, et al. (1987) Response of circulating immune complexes to food challenge in relapsing IgA nephropathy. Pediatr Nephrol 1: 581–586. 33. Coppo R, Roccatello D, Amore A, et al. (1990) Effects of a gluten-free diet in primary IgA nephropathy. Clin Nephrol 33: 72–86. 34. Yap HK, Sakai RS, Woo KT, et al. (1987) Detection of bovine serum albumin in the circulating IgA immune complexes of patients with IgA nephropathy. Clin Immunol Immunopathol 43: 395–402. 35. Jenkins DA, Bell GM, Ferguson A, Lambie AT. (1988) Intestinal permeability in IgA nephropathy. Nephron 50: 390. 36. Hubert D, Beaufils M, Meyrier A. (1984) Immunoglobulin A glomerular nephropathy associated with inflammatory colitis. Apropos of 2 cases. Presse Med 13: 1083–1085.

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37. Sato M, Nakajima Y, Koshikawa S. (1987) Effect of sodium cromoglycate on an experimental model of IgA nephropathy. Clin Nephrol 27: 141–146. 38. Ferri C, Puccini R, Longombardo G, et al. (1993) Low-antigen-content diet in the treatment of patients with IgA nephropathy. Nephrol Dial Transplant 8: 1193–1198. 39. Bazzi C, Sinico RA, Petrini C, et al. (1992) Low doses of drugs able to alter intestinal mucosal permeability to food antigens (5-aminosalicylic acid and sodium cromoglycate) do not reduce proteinuria in patients with IgA nephropathy: a preliminary noncontrolled trial. Nephron 61: 192–195. 40. Sato M, Takayama K, Kojima H, Koshikawa S. (1990) Sodium cromoglycate therapy in IgA nephropathy: a preliminary short-term trial. Am J Kidney Dis 15: 141–146. 41. Grande JP, Donadio Jr JV. (1998) Dietary fish oil supplementation in IgA nephropathy: a therapy in search of a mechanism? Nutrition 14: 240–242. 42. Donadio Jr JV, Bergstralh EJ, Offord KP, et al. (1994) A controlled trial of fish oil in IgA nephropathy. Mayo Nephrology Collaborative Group. N Engl J Med 331: 1194–1199. 43. Donadio Jr JV, Grande JP, Bergstralh EJ, et al. (1999) The long-term outcome of patients with IgA nephropathy treated with fish oil in a controlled trial. Mayo Nephrology Collaborative Group. J Am Soc Nephrol 10: 1772–1777. 44. Donadio Jr JV, Larson TS, Bergstralh EJ, Grande JP. (2001) A randomized trial of high-dose compared with low-dose omega-3 fatty acids in severe IgA nephropathy. J Am Soc Nephrol 12: 791–799. 45. Bennett WM, Walker RG, Kincaid-Smith P. (1989) Treatment of IgA nephropathy with eicosapentanoic acid (EPA): a two-year prospective trial. Clin Nephrol 31: 128–131. 46. Hogg RJ, Lee J, Narelli N, et al. (2003) Multicenter placebo-controlled trial of alternate day prednisolone or daily omega-3 fatty acids in children and young adults with IgA nephropathy. Report from the Southwest Pediatric Nephrology Study Group. J Am Soc Nephrol 14: 751A. 47. Pettersson EE, Rekola S, Berglund L, et al. (1994) Treatment of IgA nephropathy with omega-3-polyunsaturated fatty acids: a prospective, double-blind, randomized study. Clin Nephrol 41: 183–190. 48. Strippoli GF, Manno C, Schena FP. (2003) An “evidence-based” survey of therapeutic options for IgA nephropathy: assessment and criticism. Am J Kidney Dis 41: 1129–1139. 49. Hogg RJ, Fitzgibbons L, Atkins C, et al. (2006) Efficacy of omega-3 fatty acids in children and adults with IgA nephropathy is dosage- and sizedependent. Clin J Am Soc Nephrol 1: 1167–1172. 50. Donadio Jr JV, Bergstralh EJ, Bibus DM, Grande JP. (2006) Is body size a biomarker for optimizing dosing of omega-3 polyunsaturated fatty acids in

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51.

52. 53.

54.

55.

56.

57. 58.

59.

60.

61.

62. 63. 64.

the treatment of patients with IgA nephropathy? Clin J Am Soc Nephrol 1: 933–939. Alexopoulos E, Stangou M, Pantzaki A, et al. (2004) Treatment of severe IgA nephropathy with omega-3 fatty acids: the effect of a “very low dose” regimen. Ren Fail 26: 453–459. Endo A. (1992) The discovery and development of HMG-CoA reductase inhibitors. J Lipid Res 33: 1569–1582. Harris KP, Purkerson ML, Yates J, Klahr S. (1990) Lovastatin ameliorates the development of glomerulosclerosis and uremia in experimental nephrotic syndrome. Am J Kidney Dis 15: 16–23. Kasiske BL, O’Donnell MP, Cleary MP, Keane WF. (1988) Treatment of hyperlipidemia reduces glomerular injury in obese Zucker rats. Kidney Int 33: 667–672. Kano K, Nishikura K, Yamada Y, Arisaka O. (2003) Effect of fluvastatin and dipyridamole on proteinuria and renal function in childhood IgA nephropathy with mild histological findings and moderate proteinuria. Clin Nephrol 60: 85–89. Buemi M, Allegra A, Corica F, et al. (2000) Effect of fluvastatin on proteinuria in patients with immunoglobulin A nephropathy. Clin Pharmacol Ther 67: 427–431. Baigent C, Landry M. (2003) Study of Heart and Renal Protection (SHARP). Kidney Int Suppl 84: S207–S210. Sorrell TC, Forbes IJ. (1975) Depression of immune competence by phenytoin and carbamazepine. Studies in vivo and in vitro. Clin Exp Immunol 20: 273–285. Trascasa ML, Egido J, Sancho J, Hernando L. (1979) Evidence of high polymeric IgA levels in serum of patients with Berger’s disease and its modification with phenytoin treatment. Proc Eur Dial Transplant Assoc 16: 513–519. MacKinney Jr AA, Vyas R. (1972) Diphenylhydantoin-induced inhibition of nucleic acid synthesis in cultured human lymphocytes. Proc Soc Exp Biol Med 141: 89–92. Coppo R, Basolo B, Bulzomi MR, Piccoli G. (1984) Ineffectiveness of phenytoin treatment on IgA-containing circulating immune complexes in IgA nephropathy. Nephron 36: 275–276. Clarkson, AR, Seymour AE, Woodroffe AJ, et al. (1980) Controlled trial of phenytoin therapy in IgA nephropathy. Clin Nephrol 13: 215–218. Egido J, Rivera F, Sancho J, et al. (1984) Phenytoin in IgA nephropathy: a long-term controlled trial. Nephron 38: 30–39. Yu DJ, Nie LF, Xu YG. (2006) Regulatory effects of yiqi zishen granule on helper T-lymphocyte subsets in IgA nephropathy patients. Zhongguo Zhong Xi Yi Jie He Za Zhi 26: 836–838.

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65. Zhong Q, Leung JC, Chan LY, et al. (2005) The study of Chinese medicinal herbal formula Shen San Fang in the treatment of experimental IgA nephropathy. Am J Chin Med 33: 613–626. 66. Chen XM, Chen YP, Zhou ZL. (2006) Prospective, multi-centered, randomized and controlled trial on effect of Shenle Capsule in treating patients with IgA nephropathy of Fei-Pi qi-deficiency syndrome. Zhongguo Zhong Xi Yi Jie He Za Zhi 26: 1061–1065. 67. Guan XD, Wu YF, Zhao W. (2005) Clinical observation on treatment of IgA nephropathy with Huobahuagen Tablets and irbesartan. Zhong Xi Yi Jie He Xue Bao 3: 366–369. 68. Wu X, Li J, Liu B. (2003) Clinical study on dan shao tang in treating IgA nephropathy of deficiency of yin with damp-heat symptom. Zhong Yao Cai 26: 844–846. 69. Bo S, Ju J, Chu D. (2000) Clinical study on Shenning Mixture in treating IgA nephropathy. Zhongguo Zhong Xi Yi Jie He Za Zhi 20: 729–730. 70. Yoshikawa N, Ito H, Sakai T, et al. (1997) A prospective controlled study of sairei-to in childhood IgA nephropathy with focal/minimal mesangial proliferation. Japanese Pediatric IgA Nephropathy Treatment Study Group. Nippon Jinzo Gakkai Shi 39: 503–506. 71. Dong K, Chen X, Tang L. (1995) The effect of hirudo on proteinuria, lipid metabolism and coagulation system in the patients with chronic glomerulonephritis. Zhonghua Nei Ke Za Zhi 34: 250–252.

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Chapter 25

Treatment of IgA Nephropathy: Tonsillectomy Osamu Hotta

Introduction The well-known “acute worsening of hematuria coinciding with pharyngitis” frequently observed in patients with IgA nephropathy (IgAN) strongly suggests the relationship between pharyngeal mucosal infection and IgAN. In addition, disappearance of IgA mesangial deposits from kidneys that are inadvertently transplanted into patients without IgAN has been reported.1,2 Conversely, IgAN frequently relapses after transplantation.3–5 These observations suggest that the mesangial IgA deposits in IgAN originate from an extrarenal source. Moreover, there are many experimental studies suggesting the involvement of a tonsillar autoimmune response in the pathogenesis of IgAN.6–10 On the basis of these findings, tonsillectomy has been employed for decades as a treatment strategy in patients with IgAN. Nonetheless, the efficacy of tonsillectomy for IgAN still remains controversial. In fact, tonsillectomy is commonly performed in Japan for IgAN, especially combined with steroid pulse therapy, whereas it is only rarely performed in European countries and the USA. The main reason for this deep controversy is the lack of evidence from randomized controlled trials (RCTs). Reviews from Europe and the USA insist that tonsillectomy cannot be recommended as a uniform treatment measure for patients with IgAN because of the lack of sufficient evidence, i.e. lack of RCTs.11–14 369

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On the other hand, in recent years, many clinicians have noticed that while evidence from RCTs is the most reliable, it is not necessarily useful in clinical practice, and there are indeed some treatments which cannot easily be subjected to the classical criterion of double-blind therapeutic evaluation. The purpose of this chapter is to focus on the current status of tonsillectomy, with or without steroid therapy, for IgAN and to discuss the future prospects of tonsillectomy in combination with steroid pulse therapy.

History of Tonsillectomy in Patients with IgA Nephropathy The theoretical background of tonsillectomy for IgAN dates back to the early 20th century when the “focal infection theory” was floated.15 This theory was widely offered to explain the etiology of various types of inflammatory disease during the first three decades of the 20th century.16 Focal infection was implicated in the development and maintenance of inflammatory diseases as diverse as chronic arthritis,17 myositis,18 iritis,19 thyroid disease,20 peptic ulcer,21 and nephritis.22 Billings22 described six cases of subacute and chronic parenchymatous nephritis in all of whom tonsillectomy was performed and amelioration of urinary abnormalities was obtained. Thus, there is no doubt that tonsillectomy had begun to be employed for patients with chronic glomerulonephritis long before IgA nephropathy was first reported by Berger and Hinglais.23 As antibiotics became widely available, the theory of focal infection was generally discarded. However, some physicians, especially in Japan, still believe that inflammatory diseases, e.g. some types of dermatitis24 and sternocostoclavicular hyperostosis,25 may be triggered by microorganisms in the palatine tonsils. In 1983, Japanese otolaryngolosists published the earliest case reports describing the beneficial effects of tonsillectomy in patients with IgAN.26,27 However, in Xie’s report28 of a retrospective cohort study performed in Niigata in 2003, 48 patients with IgAN underwent tonsillectomy between 1973 and 1980. Thus, it is obvious that tonsillectomy was sporadically performed as treatment for patients with IgAN as early as in the 1970s in Japan. Anecdotal reports suggesting the efficacy of tonsillectomy for IgAN accumulated in the 1990s. However, until

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Tonsillectomy ✦ 371

recent years, tonsillectomy had been regarded as a heretical treatment for IgAN. In addition to the clinical experiences, in 1994, Suzuki et al.29 reported the possible causative role of Haemophilus parainfluenzae in IgAN, hypothesizing that Haemophilus parainfluenzae in the tonsils and pharynx may play a pivotal role in the production of IgA in patients with IgAN. Similarly, in 2004, Koyama et al.30 demonstrated that the cell envelope antigen of Staphylococcus aureus may be a candidate for the induction of IgAN. Both Haemophilus parainfluenzae and Staphylococcus aureus are frequently isolated from the tonsils of patients with IgAN.31 More recently, a high prevalence of Helicobacter pylori was reported in the palatine tonsils of patients with IgAN. Kusano et al.32 demonstrated the presence of Helicobacter pylori in the palatine tonsils in all of 32 IgAN patients, whereas the bacterium could be isolated from the tonsils in only 94 (66.7%) of 141 patients with recurrent pharyngotonsillitis. On the basis of these findings, increasing attention has been drawn to the relationship between chronic tonsillar infection and IgAN, especially by Japanese nephrologists. In 1988, we began to perform tonsillectomy combined with high-dose methylprednisolone therapy (steroid pulse) on a trial basis for patients with IgAN. Based on the accumulated data over more than a decade since, we recently reported that tonsillectomy and steroid pulse therapy were independent factors predicting the disappearance of urinary abnormalities, i.e. “clinical remission,”33 and showed histological regression of IgAN following tonsillectomy plus steroid pulse therapy.34 Thereafter, many Japanese nephrologists have reconfirmed the efficacy of this treatment on the basis of experience but not of any RCTs — this is the reason for the controversy that exists about the efficacy of the treatment. In recent years, tonsillectomy combined with steroid pulse therapy, supported not only by physicians but also desired by patients with IgAN who wish to obtain clinical remission, is becoming a popular choice as the first-line treatment for IgAN patients in Japan. However, outside Japan, tonsillectomy is still considered as an exceptional treatment option.

Tonsils in IgAN Several lines of evidence have suggested some characteristic features of tonsillar inflammation shared by IgAN patients are different from those of recurrent tonsillitis in patients without nephropathy.

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372 ✦ O. Hotta

First, a poorly developed lymphoepithelial symbiosis is observed in the palatine tonsils of IgAN patients.35 As reticulization of the tonsillar crypt epithelium is important in tonsillar immunity, the low level of reticulization observed in IgAN patients may induce the unusual immunity underlying the pathogenesis of IgAN. Second, enlarged primary T nodules are observed in the tonsils of IgAN patients. Most T nodules, which are defined as the sum of the small areas of accumulated T lymphocytes, are enlarged and a few T nodules contain high endothelial venules and non-lymphoid cells. In contrast, the T nodules in cases of recurrent tonsillitis are not expanded, and non-lymphoid cells and high endothelial venules are distributed peripherally around the nodules.36 Interestingly, T lymphocytes in the T nodules expressed class II antigens, and the T nodules are particularly expanded in the tonsils of patients with early-phase IgAN.37 B cells in the germinal center leave the follicles, transform into immunoblasts under the influence of helper T cells, and finally mature into plasma cells. Thus, extrafollicular maturation of B lymphocytes, stimulated by activated T lymphocytes in the T nodules, into plasma cells is likely to occur more frequently in the tonsils of IgAN patients than in those of patients with habitual tonsillitis. Furthermore, tonsillar cells of IgAN patients express characteristic molecules. Increase in the numbers of J-chain mRNA-positive IgAbearing cells,9 IgA cell/IgG cell ratio,6 polymeric IgA cells,7 IgA1-positive follicular dendritic cells,8 and CD5-positive B cells10 have been reported. In addition, IgA1 molecules produced by tonsillar lymphocytes from patients with IgAN are underglycosylated in their O glycans, just like those in the serum or glomerular deposits of IgAN patients.38

Effect of Tonsillectomy on IgAN While the efficacy of tonsillectomy in IgAN remains controversial, the results from reports up to the 1990s yielded two seemingly conflicting conclusions: (i) tonsillectomy is effective for achieving clinical remission and (ii) tonsillectomy is ineffective for preventing the decline of renal function (Table 25.1). The reasons for these apparently conflicting conclusions may be the differences in the stage of nephropathy in the selected patient populations and the short durations of the observation period.

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Table 25.1

Effects of tonsillectomy on IgAN.

1988 1993 1993

Tamura et al.42 Bene et al.64 Kosaka43

1993 1993 1998

Hattori44

1998

Tonsillectomy Tonsillectomy Tonsillectomy Non-tonsillectomy Tonsillectomy Tonsillectomy Tonsillectomy Non-tonsillectomy Tonsillectomy

16 28 35 15 26 35 43 42 71

Rasche et al.46

1999

Xie et al.28

2003

Akagi et al.47

2003

Chen et al.45

2007

Tonsillectomy Non-tonsillectomy Tonsillectomy Non-tonsillectomy Tonsillectomy Non-tonsillectomy Tonsillectomy Non-tonsillectomy

16 39 48 73 41 30 54 58

Renal survival

36 61 36

56.3% 32.1% 25.8%

Not effective

24 48 105

7.6%

106

46.5% 11.9% 42% (stage 1) 25% (stage 2) 19% (stage 3) 0% (stage 4)

41

Not effective

193 159 151 130

Not effective Not effective

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Masuda et al.39 Sugiyama40 Iino41

Remission rate

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Treatment

Outcome

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Year

Observation period, months

Effective 24.4% 13.3% 46.3% 27.6%

Effective Not effective

Note: Refs. 43 and 47 represent the same group. The effect of tonsillectomy became statistically significant as the observation period extended.


Author

No. of Patients

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374 ✦ O. Hotta

Studies supporting the first concept were mostly from Japanese groups.39–45 Japan has a well-developed system of annual mass screening by urinalysis and there is a higher likelihood of IgAN being diagnosed at a relatively earlier stage. Indeed, the patient populations of those studies which showed positive effects of tonsillectomy on clinical remission include a large number of patients with early-stage IgAN.39,40,43–45 When the study population includes patients with earlystage IgAN, unfavorable results in terms of the renal function prognosis are unlikely to be obtained, especially when the duration of follow-up is short, that is, less than five to ten years. Rasche et al.46 demonstrated that tonsillectomy did not reduce the risk of progression to end-stage renal disease (ESRD). However, as many as five (31%) of 16 patients with tonsillectomy and nine (23%) of 39 patients without tonsillectomy in their study progressed to ESRD, even within a short follow-up period (3.4 ± 4 years). As the percentage of cases that showed progression to ESRD in their study was apparently higher than those generally expected in the entire IgAN population, it is assumed that a considerable proportion of the patients in their study had advanced-stage IgAN at the time of tonsillectomy. It is obvious that it is difficult to obtain remission of urinary abnormalities in patients with advanced IgAN. Since non-immunological mechanisms are considered to play a major role in the progression of renal disease in the advanced stage of IgAN, a negative result on renal function prognosis following tonsillectomy is quite conceivable. In this connection, two recent reports from Okayama and Niigata in Japan are illuminating. The Okayama group followed 85 IgAN patients, 43 of whom had undergone tonsillectomy. They originally reported unfavorable results on renal survival at five years after the tonsillectomy.43 However, they subsequently recognized the favorable effects of tonsillectomy on renal survival rates after an observation period of ten years.47 The renal survival rate at ten years was 95.1% in the tonsillectomy group and 73.3% in the non-tonsillectomy group. Similarly, the Niigata group followed 118 patients with IgAN in which 48 underwent tonsillectomy, for 192.9 ± 74.8 months, and reported a favorable renal survival rate, as assessed by Kaplan-Meier analysis, in the tonsillectomy group.28 The estimated renal survival rates were 89.9% and 63.7% at 240 months in the patients who had and had not undergone tonsillectomy, respectively. In their analysis, however, there was no significant difference in the renal survival rate between the two

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groups at the ten-year follow-up. Moreover, not surprisingly, the favorable results were obtained only in those patients who had had relatively early-stage IgAN at the time of the tonsillectomy, i.e. urinary protein excretion of less than 1.0 g/day and a global glomerular sclerosis rate of less than 25%. None of 26 such patients who had undergone tonsillectomy needed dialysis, whereas five (13.2%) of 38 patients who had not undergone tonsillectomy required dialysis. The percentage of patients with a daily urinary protein excretion level of > 1.0 g but global glomerular sclerosis rate of < 25% who needed to be initiated on dialysis was less than 50% in the tonsillectomy group as compared with that in the non-tonsillectomy group. On the other hand, the progression rate to renal failure among the patients with severe renal damage, that is with a daily urinary protein excretion level of > 1.0 g, global glomerular sclerosis rate of > 25% and/or crescent formation rate of > 25% was similar in the tonsillectomy and non-tonsillectomy group. The long-term renal survival rate in the non-tonsillectomy group of these two reports seems to be in accordance with the renal survival rate of the entire population of IgAN patients. Thus, it is assumed that not only clinical remission, but also amelioration of the rate of progression to renal failure can be expected following tonsillectomy in patients with early-stage IgAN.

Effect of Tonsillectomy plus Steroid Pulse Therapy (Table 25.2) Tonsillectomy and steroid pulse therapy have been demonstrated to be independent contributing factors for clinical remission.33,48 The likelihood of clinical remission (i.e. disappearance of both hematuria and proteinuria) with tonsillectomy per se is less than 50% even in patients with early-stage IgAN. On the other hand, a marked increase in the likelihood of clinical remission may be expected when tonsillectomy is combined with steroid pulse therapy in patients with earlystage IgAN,33,48–50 approximately 80% of patients with an early histological grade treated thus showed clinical remission. However, the rate of proteinuria disappearance decreased in tandem with an increasing histological score, while hematuria disappeared in more than 80% of the patients, regardless of the histological score (remission rate of proteinuria: index of glomerular lesion (IGL) ≤ 1.5: 86.3%, 1.5 < IGL ≤ 2.0: 66.7%, 2.0 < IGL ≤ 2.5: 47.6%, IGL > 2.5: 24.5%;

Treatment

Observation Outcome period (months) Remission Renal survival 82

Hotta et al.34 2002 Tonsillectomy + SP

35

77

Sato et al.52

30

70

2003 Tonsillectomy + SP Oral steroid Others

25 15

47.7%

Tonsillectomy and SP, but not oral steroid and ACEI, were independent contributory factors to clinical remission. A repeat biopsy study in IgAN patients treated with tonsillectomy + SP. Resolution of IgAN could be achieved if clinical remission was obtained and maintained for years. 82.8% 51.0% 40.6%

A retrospective cohort study of IgAN with Cr > 1.5 mg/dl. Renal protective effect of tonsillectomy + SP was observed in patients with Cr < 2.0 mg/dl. (Continued)

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329

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Hotta et al.33 2001 Tonsillectomy, SP, ACEI, others

Comments

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Year

No. of patients

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Author

Effects of tonsillectomy plus steroid pulse (SP) therapy on IgAN.

376 ✦ O. Hotta

Table 25.2

Komatsu et al.48

2005 Tonsillectomy + others Others

Suwabe et al.49

2006 Tonsillectomy + SP Cocktail therapy

2007 Tonsillectomy + SP

104

69

31.7%

87.8%

133

57

16.5%

64.2%

16

24

16

24

72

20

Proteinuria 97 → 8 mg/m2/h 93 → 10 mg/m2/h

Comments Tonsillectomy was a contributory factor to clinical remission. Acute worsening of urinary abnormalities was observed in six patients (38%) of the cocktail group, but not in the tonsillectomy + SP group ( p < 0.05).

(Continued)


Proteinuria 1.32 → 0.86 g/day ( p < 0.005) Hematuria (grade) 3.75 → 1.94 ( p < 0.001)

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Kawasaki et al.54

Treatment

Observation Outcome period (months) Remission Renal survival

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Year

(Continued)

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Author

No. of patients

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Table 25.2

Treatment

2007 Tonsillectomy + SP SP

75

60

18

43.8% (initial proteinuria > 1 g/day) 11.1%

Comments A multi-center prospective cohort study.

2007 Tonsillectomy + SP

380

> 60

87.1% (duration of urinary Values from annual urinary abnormalities < 3 years) screening were evaluated. 54.3% (duration of urinary abnormalities > 3 years)

Suzumoto et al.55


21

> 12

Relapse rate: 19.0%


35

Komatsu et al.56

11

20

54.5% 54

Proteinuria 76.5% 41.2%

Hematuria 79.4% 17.6%

Relapse rate after clinical remission achieved was compared. A prospective controlled study.

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Ieiri et al.

50

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Miyazaki et al.53

Observation Outcome period (months) Remission Renal survival

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Year

(Continued)

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Author

No. of patients

378 ✦ O. Hotta

Table 25.2

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remission rate of hematuria: IGL ≤ 1.5: 87.0%, 1.5 < IGL ≤ 2.0: 83.8%, 2.0 < IGL ≤ 2.5: 93.7%, IGL > 2.5: 85.7%).51 In cases in which clinical remission could be achieved and maintained thereafter, histological cure could be obtained.34 While clinical remission is highly unlikely, slowing of disease progression by tonsillectomy plus steroid pulse therapy may be expected even in patients with advanced IgAN, if the serum creatinine level is under 2.0 mg/dl.52 Unfortunately, there are no RCTs comparing steroid pulse therapy combined with tonsillectomy versus steroid pulse therapy alone. A multicenter prospective cohort study from Japan indicates a higher likelihood of clinical remission with steroid pulse therapy combined with tonsillectomy than with steroid pulse therapy alone, even in moderately advanced IgAN patients.53 Furthermore, an RCT conducted by Kawasaki et al.54 showed that acute exacerbation associated with pharyngitis was more often observed in IgAN children treated with multiple drugs (prednisolone, warfarin, dipyridamole and mizoribine, an immunosuppressive agent) than in those treated with steroid pulse therapy combined with tonsillectomy. Moreover, Suzumoto et al.55 reported that the recurrence rate of urinary abnormalities following initial clinical remission was higher in IgAN patients administered with steroid pulse therapy alone than in those treated with steroid pulse therapy plus tonsillectomy. More recently, Komatsu et al.56 conducted a prospective controlled study and showed a higher likelihood of clinical remission with steroid pulse therapy combined with tonsillectomy than with steroid pulse therapy alone.

Indications of Tonsillectomy in Patients with IgAN The indications for tonsillectomy in patients with IgAN remain controversial. Some nephrologists contend that tonsillectomy should be restricted to IgAN patients suffering from recurrent episodes of tonsillitis or showing macroscopic hematuria after an episode of pharyngitis. Matsutani et al.,57 however, demonstrated that the remission rates of both proteinuria and hematuria following tonsillectomy plus steroid pulse therapy were similar regardless of the history of recurrent tonsillitis, history of synpharyngitic gross hematuria, presence of pus plugs in the tonsillar lacunae, size of the tonsils, age or the results of the tonsillar provocation test. Similar results were also reported by Akagi et al.58

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treating IgAN patients by tonsillectomy alone, without steroids. On the other hand, there seems to be agreement on the suggestion that advancing histological score or clinical stage decreases the likelihood of clinical remission by tonsillectomy, regardless of whether or not it is combined with steroid therapy. Therefore, the indications for tonsillectomy should be tentatively determined based mainly on the clinical or histological stage, with less importance attached to other parameters such as episodes of synpharyngitic gross hematuria, gross appearance of the tonsils or results of the tonsillar provocation test. The principle for tonsillectomy in IgAN patients is “the earlier the better.”

Future Perspectives What Should be the Goal of Treatment for IgAN? The primary goal of treatment for IgAN is slowing of the disease progression, like for any other progressive chronic kidney disease (CKD), such as diabetic nephropathy or hypertensive nephrosclerosis. However, if remission or cure of the disease is possible to achieve, “remission or cure of the nephropathy” rather than “slowing of progression of the nephropathy” should be the goal of treatment. The major contributory factor for the progression of IgAN is glomerular capillaritis itself, which is usually smoldering. However, as chronic kidney injury progresses, various other factors, such as glomerular hypertension, protein-loading tubulointerstitial injuries and ischemic kidney injuries rather than glomerular capillaritis become major contributory factors for progressive nephron loss. Thus, tonsillectomy plus steroid pulse therapy may be expected to be effective only if it is undertaken at a relatively early stage, as the target of this combination therapy is the smoldering glomerular capillaritis. In the course of IgAN, there are two important concepts that must be borne in mind in relation to treatment, namely, the “point of no remission” and the “point of no slowing.” If tonsillectomy plus steroid pulse therapy is undertaken before the “point of no remission,” clinical remission is highly likely, whereas if initiated after this point, while slowing of disease progression may be achieved, clinical remission may no longer be expected. However, after the stage of the “point of no slowing,” no beneficial effect whatsoever may be expected and, on the

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Progressive factors

Point of no remission

100 (%)

Renal function

Glomerular hypertension Ischemic kidney injury Point of no slowing

Protein-loading tubulo-interstitial injury Smoldering glomerular capillaritis onset

Time

renal death

Figure 25.1 Time-course of changes in IgAN and factors contributing to progression of kidney injury.

contrary, treatment may even accelerate the progression (Figure 25.1). Thus, to obtain clinical remission, IgAN must be detected at an early stage (i.e. prior to the “point of no remission”). For this purpose, annual mass screening by urinalysis is very effective.50 Therefore, the goal of treatment of IgAN and the indications of tonsillectomy plus steroid pulse therapy are determined based on the stage of progression of renal function impairment. In CKD stage 1 (GFR ≥ 90 ml/min), the goal of treatment should be clinical remission. Tonsillectomy plus steroid pulse therapy may be expected to be effective to achieve that goal. Clinical remission may still be achieved in many cases of CKD stage 2 (60 ≤ GFR ≤ 89); however, a lower rate of remission of proteinuria than that of hematuria may be expected at this stage. In cases with CKD stage 3 (30 ≤ GFR ≤ 59), the treatment goal should shift from “clinical remission” to “slowing of disease progression.” In this stage although clinical remission is unlikely to be achieved, tonsillectomy plus steroid pulse therapy may still be effective for slowing the disease progression. In CKD stage 4 (15 ≤ GFR ≤ 29), tonsillectomy plus steroid pulse therapy may no longer be expected to halt the progression of IgAN, with the exception of those cases with a rapidly progressive course, in which severe glomerular capillaritis is the major contributory factor for progression, until the renal function is severely impaired.

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Requirement of Clinical Study Recent reviews of Japanese studies about the effects of tonsillectomy in IgAN insist that tonsillectomy cannot be recommended due to lack of sufficient evidence (i.e. lack of RCTs).11–14 This criticism, while correct, may not necessarily be realistic. Unfortunately, no RCTs of tonsillectomy in patients with IgAN have been conducted until today. In fact, RCTs of surgical operations on asymptomatic organs, such as tonsillectomy in cases of IgAN, are difficult to execute partly because of ethical reasons. In RCT of the efficacy of tonsillectomy in IgAN, those individuals who accept the potential effectiveness of tonsillectomy and wish to undergo tonsillectomy enter the trial, but those who do not desire tonsillectomy would never enter the trial. However, a certain proportion of patients may inevitably be categorized into the control group and followed without tonsillectomy even if they have hoped to receive that treatment. There have been only a few RCTs on tonsillectomy so far, and all have been conducted in patients with recurrent tonsillitis (i.e. patients with symptomatic tonsillar disease).59–61 Considering the clinical heterogeneity of IgAN, small RCTs may provide some insight. Moreover, retrospective studies on tonsillectomy indicate that RCTs with follow-up less than five to ten years are inadequate to draw a conclusion. Thus, a big budget is needed to conduct a reliable RCT of tonsillectomy on a large scale with long-term follow-up. However, RCTs of tonsillectomy are unlikely to be attractive to any pharmaceutical support. Therefore, it is practically impossible to perform a high-quality RCT of tonsillectomy. Observation studies have several advantages over RCTs, including lower cost, greater timeliness, and a broader range of patients.62 Moreover, it was shown that estimates of the effects of the treatment obtained by sophisticated observational studies were similar to those from RCTs in most areas.63 To clarify the efficacy of tonsillectomy plus steroid pulse therapy over that of steroid pulse therapy alone, adequate RCTs may be essential. However, to clarify the likelihood of clinical remission depending on the clinical stage of IgAN, and to elucidate the precise effects of tonsillectomy plus steroid pulse therapy, a large scale prospective cohort study may be the most realistic and reliable type of clinical study.

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References 1. Sanfilippo F, Croker BP, Bollinger RR. (1982) Fate of four cadaveric renal allografts with mesangial IgA deposits. Transplantation 33: 370–376. 2. Silva FG, Chander P, Pirani CL, et al. (1982) Disappearance of mesangial IgA deposits after allograft transplantation. Transplantation 33: 214–216. 3. Berger J, Yaneva H, Nabarra B, et al. (1975) Recurrence of mesangial IgA deposition of IgA after renal transplantation. Kidney Int 7: 232–241. 4. Odum J, Peh CA, Clarkson AR, et al. (1994) Recurrent mesangial IgA nephritis following renal transplantation. Nephrol Dial Transplant 9: 309–312. 5. Wang AYM, MacMoune Lai F, Yu A, et al. (2001) Recurrent IgA nephropathy in renal transplant allograft. Am J Kidney Dis 38: 588–596. 6. Bene MC, Hurault DLB, Kessler M, et al. (1991) Confirmation of tonsillar anomalies in IgA nephropathy: a multicenter study. Nephron 58: 425–428. 7. Egido J, Blasco R, Lozano L, et al. (1984) Immunological abnormalities in the tonsils of patients with IgA nephropathy: inversion in the ratio of IgA: IgG bearing lymphocytes and increased polymeric IgA synthesis. Clin Exp Immunol 57: 101–106. 8. Kusakari C, Nose M, Takasaka T, et al. (1994) Immunopathological features of palatine tonsil characteristic of IgA nephropathy: IgA1 localization in follicular dendritic cells. Clin Exp Immunol 95: 42–48. 9. Harper SJ, Allen AC, Bene MC, et al. (1995) Increased dimeric IgA-producing B cells in tonsils in IgA nephropathy determined by in situ hybridization for J chain mRNA. Clin Exp Immunol 101: 442–448. 10. Kodama S, Suzuki M, Arita M, et al. (2001) Increase in tonsillar germinal center B-1 cell numbers in IgA nephropathy (IgAN) patients and reduced susceptibility to Fas-mediated apoptosis. Clin Exp Immunol 123: 301–308. 11. Locatelli F, Vecchio LD, Pozzi C. (2006) IgA glomerulonephritis: beyond angiotensin-converting enzyme inhibitors. Nat Clin Pract Nephrol 2: 24–31. 12. Appel GB, Waldman M. (2006) The IgA nephropathy treatment dilemma. Kidney Int 69: 1939–1944. 13. Locatelli F, Pozzi C, Andrulli S. (2006) IgA nephritis: ACE inhibitors, steroids, both or neither? Nephrol Dial Transpant 21: 3357–3361. 14. Appel GB. (2006) To treat or not treat IgA nephropathy? That is the question! Clin J Am Soc Nephrol 1: 347–348. 15. Billings F. (1916) Focal Infection: The Lane Medical Lectures. Appleton and Company, New York. 16. Hughes RA. (1994) Focal infection revisited. Br J Rheumatol 33: 370–377. 17. Willcox WH. (1921) Infective arthritis and allied conditions: with special reference to etiology and treatment. Br Med J 1: 804–807.

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18. Resenow EC, Ashby W. (1921) Focal infection and elective localization in the etiology of myositis. Arch Int Med 28: 3–40. 19. Butler TH. (1911) The etiology of iritis. Br Med J 1: 804–806. 20. Hoxie GH. (1924) The differential diagnosis between beginning or lowgrade hypothyroidism and exhaustion of body to focal infections. Med Clin N Am 7: 1119–1126. 21. Rosenow EC. (1921) Focal infection and elective localization of bacteria in appendicitis, ulcer, of the stomach, cholecystitis and pancreatitis. Surg Gynecol Obstet 33: 19–26. 22. Billings F. (1912) Chronic focal infections and their etiological relations to arthritis and nephritis. Arch Int Med 8: 484–498. 23. Berger J, Hinglais N. (1968) Les depots intercapillaries d’IgA-IgG. J Urol Nephrol 74: 694–695. 24. Nakayama N, Shindo E, Kataura A. (1989) Tonsillectomy-induced changes in anti-keratin antibodies in patients with pustulosis palmaris et plantaris: a clinical correlation. Arch Otorhinolaryngol 246: 109–112. 25. Kataura A, Thubota H. (1996) Clinical analyses of focus tonsil and related diseases in Japan. Acta Otolaryngol 523(Suppl): 161–164. 26. Sugiyama N, Masuda Y. (1983) Effect of tonsillectomy in 8 cases with IgA nephropathy accompanied with chronic tonsillitis (in Japanese). Jpn J Tonsil 22: 132–137. 27. Sohma S, Sambe S, Himi T, et al. (1983) A case of IgA nephropathy improved by tonsillectomy. Jpn J Tonsil 22: 138–143 (in Japanese). 28. Xie Y, Nishi S, Ueno M, et al. (2003) The efficacy of tonsillectomy on longterm renal survival in patients with IgA nephropathy. Kidney Int 63: 1861–1867. 29. Suzuki S, Nakatomi Y, Sato H, et al. (1994) Haemophilus parainfluenzae antigen and antibody in renal biopsy samples and serum of patients with IgA nephropathy. Lancet 343: 12–15. 30. Koyama A, Sharmin S, Sakurai H, et al. (2004) Staphylococcus aureus cell envelope antigen is a new candidate for the induction of IgA nephropathy. Kidney Int 66: 121–132. 31. Matsutani S, Hotta O. (2003) Bacterial florae of palatine tonsils in patients with IgA nephropathy. Int Congr Ser 1257: 235–237. 32. Kusano K, Tokunaga O, Ando T, et al. (2007) Helicobacter pylori in the palatine tonsils of patients with IgA nephropathy compared with those of patients with recurrent pharyngotonsillitis. Human Pathol 38: 1788–1797. 33. Hotta O, Miyazaki M, Furuta T, et al. (2001) Tonsillectomy and steroid pulse therapy significantly impact in patients with IgA nephropathy. Am J Kidney Dis 38: 736–742. 34. Hotta O, Furuta T, Chiba S, et al. (2002) Regression of IgA nephropathy: a repeat biopsy study. Am J Kidney Dis 39: 493–502.

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35. Sato Y, Hotta O, Taguma Y, et al. (1996) IgA nephropathy with poorly developed lymphoepithelial symbiosis of the palatine tonsils. Nephron 74: 301–308. 36. Kawaguchi M, Sakai T, Sakamaki A, et al. (1993) Expanded primary T nodules in the palatine tonsils from patients with IgA nephropathy. Acta Otolaryngol 508(Suppl): 36–42. 37. Takechi H, Miyazaki M, Ieiri N, et al. (2006) Clinical and immunological study of the tonsils in IgA nephropathy: effects of tonsillectomy and steroid pulse therapy. J Am Soc Nephrol 17: 568A. 38. Horie A, Hiki Y, Odani H, et al. (2003) IgA1 molecules produced by tonsillar lymphocytes are under-O-glycosylated in IgA nephropathy. Am J Kidney Dis 42: 486–496. 39. Masuda Y, Terazawa K, Kawakami S, et al. (1988) Clinical and immunological study of IgA nephropathy before and after tonsillectomy. Acta Otolaryngol 454(Suppl): 248–255. 40. Sugiyama N. (1993) Clinicopathological study of the effectiveness of tonsillectomy in IgA nephropathy accompanied by chronic tonsillitis. Acta Otolaryngol 508(Suppl): 43–48. 41. Iino Y, Ambe K, Kato Y, et al. (1993) Chronic tonsillitis and IgA nephropathy. Acta Otolaryngol 508(Suppl): 29–35. 42. Tamura S, Masuda Y, Inokuchi I, et al. (1993) Effect and indication of for tonsillectomy in IgA nephropathy. Acta Otolaryngol 508: 23–28. 43. Kosaka M. (1998) Long-term prognosis of tonsillectomy patients with IgA nephropathy. J Otolaryngol Jpn 101: 916–923. 44. Hattori K. (1998) Therapeutic effects and prognostic factors of tonsillectomy for IgAN nephropathy in long-term follow-up. J Otolaryngol Jpn 101: 1412–1422. 45. Chen Y, Tang Z, Wang Q. (2007) Long-term efficacy of tonsillectomy in Chinese patients with IgA nephropathy. Am J Nephrol 27: 170–175. 46. Rasche FM, Schwarz A, Keller F. (1999) Tonsillectomy does not prevent a progressive course in IgA nephropathy. Clin Nephrol 51: 147–152. 47. Akagi H, Fukushima K, Kosaka M. (2003) A 10-year retrospective case-control study for IgA nephropathy after tonsillectomy. Int Congr Ser 1257: 147–150. 48. Komatsu H, Fujimoto S, Hara S, et al. (2005) Multivariate analysis of prognostic factors and effect of treatment in patients with IgA nephropathy. Ren Fail 27: 45–52. 49. Suwabe T, Ubara Y, Sogawa Y, et al. (2007) Tonsillectomy and corticosteroid therapy with concomitant methylprednisolone pulse therapy for IgA nephropathy. Contrib Nephrol 157: 99–103. 50. Ieiri N, Hotta O, Taguma Y. (2007) Impact of annual urine health check-up system to obtain clinical remission in patients with IgA nephropathy. Contrib Nephrol 157: 104–108.

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51. Hotta O. (2004) Use of corticosteroids, other immunosuppressive therapies, and tonsillectomy in the treatment of IgA nephropathy. Semin Nephrol 24: 244–255. 52. Sato M, Hotta O, Tomioka S, et al. (2003) Cohort study of advanced IgA nephropathy: efficacy and limitations of corticosteroids with tonsillectomy. Nephron 93: 137–145. 53. Miyazaki M, Hotta O, Komatsuda A, et al. (2007) A multicenter prospective cohort study of tonsillectomy and steroid therapy in Japanese patients with IgA nephropathy: a 5-year report. Contrib Nephrol 157: 94–98. 54. Kawasaki Y, Takano K, Suyama K, et al. (2006) Efficacy of tonsillectomy pulse therapy versus multiple-drug therapy for IgA nephropathy. Pediatr Nephrol 21: 1701–1706. 55. Suzmoto M, Yasutomi M, Fujiwara K, et al. (2007) Effect of tonsillectomy on relapse rates in patients with IgA nephropathy. Stomato-pharyngology 20: 67 (Abstract, in Japanese). 56. Komatsu H, Fujimoto S, Hara S, et al. (2008) Effect of tonsillectomy plus steroid pulse therapy on clinical remission of IgA nephropathy: a controlled study. Clin J Am Soc Nephrol 3: 1301–1307. 57. Matutani S, Honma R, Adachi M, et al. (2004) Clinical observation of palatine tonsils with IgA nephropathy. Acta Otolaryngol 555(Suppl): 58–61. 58. Akagi H, Kosaka M, Hattori K, et al. (2004) Long-term results of tonsillectomy as a treatment for IgA nephropathy. Acta Otolaryngol 555(Suppl): 38–42. 59. Paradise JL, Bluestone CD, Colborn DK, et al. (1999) Adenoidectomy and adenotonsillectomy for recurrent acute otitis media: parallel randomized clinical trials in children not previously treated with tympanostomy tubes. J Am Med Assoc 282: 945–953. 60. van Staaij BK, van den Akker EH, Rovers MM, et al. (2005) Effectiveness of adenotonsillectomy in children with mild symptoms of throat infections or adenotonsillar hypertrophy: open, randomised controlled trial. Clin Otolaryngol 30: 60–63. 61. Alho OP, Koivunen P, Penna T, et al. (2007) Tonsillectomy versus watchful waiting in recurrent streptococcal pharyngitis in adults: randomised controlled trial. Br Med J 334: 939. 62. Feinetein AR. (1989) Epidemiologic analyses of causation: the unlearned scientific lessons of randomized trials. J Clin Epidemiol 42: 481–489. 63. Benson K, Hartz AJ. (2000) A comparison of observational studies and randomized, controlled trial. N Engl J Med 342: 1878–1886. 64. Bene MC, Hurault de Ligny B, Kessler M, et al. (1993) Tonsils in IgA nephropathy. Contrib Nephrol 104: 153–161.

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Chapter 26

Experimental Model of IgA Nephropathy Yusuke Suzuki and Yasuhiko Tomino

Introduction IgA nephropathy (IgAN) is defined by deposition of IgA in the glomerular mesangium. Despite a single histopathological definition, patients with IgAN can have variable clinical and histopathological features. Since the first definition by Berger in 1968,1 this heterogeneity may be one of the major reasons why the pathogenesis of this disease remains unclear. Since accumulating evidence suggests that up to 30%–40% of cases progress to end-stage renal disease (ESRD) by 20 years,2–4 radical treatments are urgently required for this disease. There remains, however, no clear treatment strategy principally due to the lack of a comprehensive understanding of this multifactorial disease. In this chapter, we attempt to correlate the results of experimental IgAN (mainly murine) to the clinicopathological findings in humans. The animal experiments were undertaken to explain observations in human suffering from IgAN. Intrinsically, there are differences in the IgA system between man and mice, particularly since mice do not have the equivalent of an IgA1 system and IgA monomers.

Mucosa-Bone Marrow Axis in IgAN Recurrent IgA deposition in the allograft and recurrence of IgAN in recipients are seen after kidney transplantation in approximately 50% of recipients.5 On the other hand, one report demonstrated that accidental 387

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transplantation of a kidney of an IgAN patient into a recipient with primary renal disease other than IgAN, resulted in the disappearance of IgA.6,7 These clinical observations reinforce the importance of systemic abnormalities of the IgA immune system in IgAN, arguing convincingly against IgAN being a disease limited to intrinsic renal abnormalities. In fact, we know that many IgAN patients show episodic macrohematuria, which coincides with mucosal infection especially in the upper respiratory tract,8,9 suggesting pathological involvement of abnormal immune responses after encounters of exogenous antigens in mucosal sites. However, we also know that mild mesangial IgA deposition is not always accompanied by proteinuria and hematuria in apparently healthy individuals or secondary IgAN such as liver cirrhosis, emphasizing that a coupling of mesangial IgA deposition and initiation and/ or perpetuation of glomerular injury after encounters of exogenous antigens may require some additional factors. On the other hand, high levels of polymeric IgA (pIgA) are present in sera of patients with IgAN. In addition, it is generally accepted that mesangial IgA deposits consist primarily of under-glycosylated pIgA1.10 There is a general agreement that plasma IgA is produced mainly in the bone marrow (BM) while the mucosal contribution to circulating IgA levels is small. Previous clinical studies provided some clues. For example, systemic antigen challenge results in increased titers of circulating pIgA1 antibodies with normal levels in mucosal secretions.11,12 Large numbers of pIgA1-positive plasma cells are found in the BM of IgAN patients.13 Moreover, BM transplantation (BMT) in patients with leukemia and IgAN resulted in cure of not only leukemia but also IgAN.14 Accordingly, these findings suggest that overproduction of pIgA1 seems to be based in systemic immune sites, such as the BM. There is a growing body of evidence to suggest that mucosal type pIgA1 is produced in the BM of IgAN patients. Therefore, the cross talk between mucosa and BM should be carefully discussed. Almost 20 years ago now, Van Es and colleagues in a series of elegant studies identified impaired IgA immune responses in the mucosa-bone marrow axis in IgAN.12,13,15,16 In the last decade, clinical and experimental studies have revealed continued trafficking of antigen-specific lymphocytes and antigen presenting cells between the mucosa and BM in humans.17 The patterns of integrins and chemokine receptors in these lymphocytes including memory B cells and IgA plasma cells are slightly different and depend on the site of their induction. This migration is

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directed by the local synthesis of specific chemokines and appropriate adhesion/homing-receptor engagement. There is increasing recognition for the presence of a mucosa-bone marrow axis in humans, and abnormalities in this axis may play an important role in the development of IgAN.18 How then can we study the mucosa-bone marrow axis in IgAN and correlate any changes with the well documented clinical features of this disease? Undoubtedly there are a number of challenges to the study of this dynamic and complex immune axis in humans; a number of investigators have therefore used experimental animal models. Although there are inter-strain differences in murine IgA immune responses and the ability to induce glomerulonephritis, animal models still serve a useful purpose in investigating the pathogenesis of IgAN. In this chapter, we describe how experimental animal models have provided a better understanding of the mucosa-bone marrow axis and how this data may be applicable to human IgAN.

Characteristics of Nephritogenic IgA and IgA-IC Several clinical studies have identified the importance of IgA or IgA immune complex (IgA-IC) deposition as a fundamental causative factor in IgAN. The observed clinicopathological heterogeneity may, at least in part, be dependent on the characteristics of the deposited IgAIC itself or changes in the IgA immune system.10 We believe that understanding the mechanisms involved in the generation of nephritogenic IgA, formation of IgA-IC and their deposition will help us explain the clinicopathological heterogeneity characteristic of IgAN.18,19 Rifai et al.20 described the first animal (mouse) model of IgAN in 1979. Using murine anti-dinitrophenole (DNP) and DNP-conjugated bovine serum albumin (DNP-BSA), they generated circulating IgA-IC and demonstrated that these complexes were prone to mesangial deposition. They found that for mesangial deposition to occur IgA-IC needed to be either administered repeatedly or to be present persistently in the circulation.20 These investigators also demonstrated the importance of IgA-IC size in mesangial deposition by studying different pIgA-antigen complexes.21,22 In the early 1980s, Isaacs et al.23,24 confirmed the importance of circulating IgA-IC in mesangial IgA deposition and initiation of glomerular injury. In these studies, mice were immunized with a bacterialderived polysaccharide or chemically-modified dextran. These studies

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emphasized both the importance of continual IgA-IC formation as a driver for mesangial IgA deposition and progression of IgAN, and the critical role played by pIgA in the formation of circulating nephritogenic IgA-IC. It remains unclear whether these nephritogenic circulating and mesangial IgA-IC contain exogenous antigens. Evidence from several experimental studies suggests a potential pathological role of pIgA complexed with endogenous protein in the induction of IgAN. It is widely accepted that mesangial IgA is predominantly IgA1 and displays abnormal O-glycosylation.25,26 Suzuki et al.27 recently demonstrated that IgA1 secreted by EBV-immortalized IgA1-producing cells from peripheral blood cells of IgAN patients was mostly polymeric and had galactosedeficient O-linked glycans, characterized by a terminal or sialylated N-acetylgalactosamine. This immortalized cells from IgAN also showed decrease in β1,3-galactosyltransferase activity and an increase in N-acetylgalactosamine-specific β2,6-sialyltransferese activity, suggesting premature sialylation leading to aberrant IgA1 glycosylation in IgAN. Although the functional significance of the changes in IgA1 glycosylation remain imprecisely understood, it has been shown that they are associated with the development of autoantibodies against the altered IgA1 hinge region, suggesting that IgA1 itself could be an endogenous antigen in IgAN.28,29 Furthermore, under-glycosylated IgA has a tendency to self-aggregate and is capable of binding to human mesangial cells.30,31 In this regard, the HIGA mouse (high IgA levels), which is an inbred strain established by Muso et al.32,33 by selective mating of the spontaneous IgAN-prone ddY mouse also displays abnormal glycosylation of serum IgA.34 It is also worth noting autoimmune prone (NZW × C57BL/6) F1 mice that overexpress human Bcl-2 in B cells display IgA hyperglobulinemia and develop a fatal glomerulonephritis with glomerular deposition of under-glycosylated and sialylated IgA.28 There are significant differences in the structure of IgA between animals and human. For example, all non-primate species lack a hinge region analogous to human IgA1, and the control of IgA production is different in the two species. Rodents do not have monomeric IgA as in human. However, these experimental findings suggest that aberrant glycosylation of serum IgA may be involved in the induction of IgAN in both mice and humans. This notion has been reinforced by the recent work of Nishie et al.29 They demonstrated that mice lacking β-1,4-galactosyltransferase-I spontaneously developed IgAN and had increased serum polymeric IgA levels. This enzyme transfers galactose to the terminal N-acetylglucosamine of N- and

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O-linked glycans in a β-1,4 linkage, and these transgenic mice displayed complete absence of β4 galactosylation and sialylation of the IgA N-glycans. On the other hand, several studies with animal models also suggested other endogenous antigens for IgA-IC formation in this disease. For example, studies in patients with IgAN have shown an increased binding of circulating IgA to the Fcα receptor (CD89), despite downregulation of monocyte CD89 expression.35 Based on these findings, Monteiro et al.36 generated transgenic mice overexpressing human CD89 on monocytes/macrophages and found that these mice developed IgAN in association with the appearance of large IgA-IC in the circulation. These IgA-IC were found to contain IgA complexed with soluble CD89. Fibronectin (Fn) and collagen co-deposition with IgA in glomerulus and high levels of plasma IgA-Fn complexes have been found in patients with IgAN.37 In this regard, it is interesting that two independent uteroglobin (UG)-deficient mouse models display a number of features characteristic of human IgAN including high serum IgA-Fn complex levels.38 Uteroglobin is a steroid-inducible cytokine-like protein with immunomodulatory and anti-inflammatory properties and a high affinity for Fn. In wild-type mice UG forms Fn-UG heterodimers and thereby prevents both Fn self-aggregation and IgA-Fn association.39 Coppo et al.40 could not however demonstrate a fall in circulating levels of UG in IgAN despite the presence of increased IgA-Fn complexes and the presence of UG in IgA-Fn complexes in IgAN patients.

Major Site and Responsible Cells for Nephritogenic IgA Production The major site of pathogenic IgA production in IgAN remains uncertain, although previous studies suggest that mucosal type pIgA1 may be partly derived from the BM.13,41,42 Imasawa et al.43 reported that transfer of BM from wild-type mice attenuated glomerular lesions in HIGA mice, conversely when wild-type mice were transplanted with HIGA BM they developed mesangial IgA deposition and glomerulonephritis. The authors suggested that IgAN may in part be a disorder of stem cell function. The ddY mouse is a well-known model of spontaneous IgAN, which was first described by Imai et al.44 These mice develop glomerulonephritis with striking deposition of IgA in the mesangium.45,46 As the ddY mouse is not an inbred strain, studies using this mouse and the HIGA mouse must take into account the wide variability in onset of spontaneous IgAN. Indeed, serum IgA levels do not correlate with the

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severity of glomerular injury.47 We recently reported that ddY mice can be classified into three groups, early-onset (∼20 weeks; 35%), late-onset (∼40 weeks; 35%) and quiescent groups (30%) by grading of glomerular lesions and IgA deposition on serial biopsies.48 Serum levels of IgA were not different in the three groups and did not correlate with the degree of glomerular IgA deposition. A genome-wide association analysis of early-active and quiescent mice indicated that the susceptibility to murine IgAN is partly regulated by specific loci syntenic to the IGAN1 gene, a known candidate gene of human familial IgAN.48 These results suggest that in this model of IgAN disease susceptibility may be regulated, at least in part, by the same genes involved in development of human IgAN and supports the use of this “grouped ddY mice” model for examining the pathogenesis of IgAN.47 We have now inbred the early-onset mice and have ddY mice that almost universally develop an IgAN phenotype (nearly 100%, our unpublished data). Using this model, we have confirmed that transfer of BM from these early onset mice to wild-type control mice results in the development of IgAN.49 By contrast, BM transfer from quiescent or wild-type control mice to early-onset ddY mice abrogates glomerular injury and the mesangial deposition. These findings suggest that the BM may be a reservoir of memory cells capable of synthesizing IgA with a propensity for mesangial deposition and triggering of glomerulonephritis. These BM located cells appear to be essential for the continuous delivery of pathological IgA. Are these cells responsible for the nephritogenic IgA production reserved only in BM? To approach the possibility that these cells are disseminated to other lymphoid tissues, we transferred whole spleen cells from ddY mice into SCID mice. Not only BMT but also the cell transfer could reconstitute the murine IgAN in SCID mice, suggesting that responsible cells may be also localized, at least, in spleen (Nakata et al., paper in preparation).

Mucosal Immune Priming in the Generation of Nephritogenic IgA The association of episodic macroscopic hematuria with mucosal infections in IgAN is suggestive of changes to the mucosal immune system, which may include changes in antigen handling in this disease.18 The results of immunization studies in IgAN support this notion. Mucosal

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immunization with neoantigen results in impaired mucosal and systemic IgA responses but normal IgG and IgM responses,50,51 suggesting that in IgAN there is mucosal hyporesponsiveness to mucosal neoantigens. By contrast, systemic and mucosal immunization with recall antigens results in exaggerated systemic IgA responses with increased and prolonged production of specific IgA.11,12,52,53 These results suggest that patients with IgAN respond excessively to recall antigens. From these clinical observations we hypothesize that in IgAN there may be impaired elimination of mucosal antigens due to aberrant local mucosal IgA responses. This results in accumulation of antigen and enhanced antigenic stimulation of B cells with an increase in immunologic memory for IgA1 production in the mucosa and perhaps the BM or other lymphoid tissues. This increase in IgA1-committed memory cells may explain the excessive IgA responses reported following exposure to recall antigens and be responsible for the synthesis of nephritogenic IgA1 in IgAN.18 If this hypothesis is correct then there must be continuous antigenic challenge and activation of the IgA immune system driving the synthesis of nephritogenic IgA and the development of IgAN. It is likely that common microbial and food or food-borne antigens play a role in this process. In 1983, Emancipator et al.54 elegantly demonstrated a pathogenic relationship between prolonged mucosal antigenic exposure, formation of circulating IgA-IC and the development of glomerulonephritis. The authors orally immunized Balb/c mice with protein antigens and found a significant increase in specific-IgAproducing plasma cells in the lamina propria of bronchial and intestinal mucosa coupled with a rise in circulating antigen-specific IgA and mesangial deposits of IgA and J chain. Coppo et al.55 argued that altered mucosal processing of food antigens such as gliadin, a lectin present in gluten, might be involved in the induction of this disease. High serum levels of IgA anti-gliadin have been reported in patients with IgAN.56–58 They also demonstrated that mice orally immunized with gliadin or ovalbumin developed glomerular injury with intense glomerular IgA deposition including anti-gliadin IgA antibodies.59 In addition to intrinsic food antigens, food-borne-microbial contaminants may also provide an antigenic stimulus in IgAN. Pestka et al.60–63 demonstrated that mice fed meal contaminated with deoxynivalenol developed increased levels of serum IgA, circulating IgA-IC, mesangial IgA deposition and hematuria, all clinical features of human IgAN.

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Koyama et al.64 suggested that microbial superantigens may play a key role in the pathogenesis of glomerulonephritis associated with methicillin-resistant Staphylococcus aureus (MRSA) infection. The abnormalities seen in these patients were similar to those seen in IgAN.64,65 They also found similar increases in specific T cell-receptor subsets in both patients with post-MRSA infection glomerulonephritis and IgAN66 and localization of S. aureus cell envelope antigen in the glomeruli of IgAN patients.67 Based on these clinical findings, they experimentally reproduced this glomerulonephritis very similar to IgAN in mice immunized subcutaneously with S. aureus antigens.68 Other groups have also demonstrated the development of experimental IgAN following oral immunization with Hemophilus parainfluenzae (HPI) antigens69 and associated with glomerular deposition of outer membranes of HPI antigens.70 In addition to the bacterial infection, viral infection also links to IgAN-like glomerulonephritis, such as Aleutian disease by parvovirus infection.71,72 Furthermore, Jessen et al.73 experimentally induced murine IgAN by mucosal viral infection with Sendai virus (SeV). Moreover, in this SeV-induced IgAN model, Th2-prone mice develop more severe nephritis with acute renal insufficiency than Th1-prone mice.74 Cytokine profiles by splenocytes from each Th1 and Th2 prone under SeV stimulation in vivo and in vitro were clearly different, suggesting that innate immune responses may be involved in this viral model. However, amplitudes of cytokines and PGE2 production by SeV-stimulated mesangial cells from each Th1 and Th2 prone were also different,75 suggesting that innate responses in not only mucosa but also renal resident cells should be carefully discussed. Considered together, these studies suggest that exogenous antigens derived from fungi, bacteria and viruses could play a key role in the development of IgAN. It remains unclear however how all of these microbe-related antigens precisely interact with the IgA immune system (or the inflammatory cascade) to trigger disease. Growing evidence from studies of innate immunity may provide a clue. Toll-like receptors (TLRs) are a family of pathogen-recognition molecules that discriminate self from non-self (pathogens) and activate suitable defence mechanisms.76 TLRs on antigen-presenting cells also initiate and modulate adaptive immunity during infection.77 We recently found overexpression of TLR9, which binds unmethylated CpG dinucleotides (CpG DNA) of bacteria and viruses, mainly on tonsillar plasmacytoid dendritic cells

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(pDC) of some patients with IgAN (Kano et al., paper in preparation). The same patient group with high TLR9 expression underwent a rapid and successful therapeutic response to combined tonsillectomy and steroid pulse therapy, suggesting that tonsillar TLR9 activation may be an important factor in the pathogenesis of IgAN. To investigate this further we maintained “grouped ddY mice”47 under conventional conditions and specific pathogen-free conditions. Interestingly, ddY mice reared under conventional conditions developed more severe glomerular injury with higher serum IgA levels and enhanced splenic TLR9 expression. Nasal challenge with CpG DNA worsened glomerular injury in these mice and was associated with greater mesangial IgA deposition and higher serum IgA levels,78 suggesting that TLR9 binding may represent a final common pathway of immune activation for abovementioned exogenous antigens in IgAN. Importantly, CpG DNA alone may enhance serum levels of IgA/IgG IC and thereby promote mesangial IgA deposition and glomerular injury. In this regard, we found that single nucleotide polymorphism (SNP) of TLR9 and its signaling molecule MyD88 significantly links to the severity of glomerular damage in Japanese IgAN patients.

Extent of Aberrant Mucosal Priming and Disruption of Immune Tolerance in IgAN If mucosal priming by common antigens is important in driving the development of IgAN then what are the factors responsible for the excessive IgA responses seen in IgAN? These same factors probably underlie the excessive systemic IgA responses seen with recall antigens.18 Oral tolerance is an important immune mechanism to avoid excessive immune responses to common oral antigens including food antigens and common microorganisms. Therefore, disruption of mucosal tolerance with a Th2-dominant immune phenotype has been discussed in the risk of IgAN.79–81 In 1990, Gesualdo et al.82 provided experimental data suggesting the possible involvement of impaired oral tolerance in the pathogenesis of IgAN. Inhibition of oral tolerance in orally immunized mice by parenteral administration of cyclophosphamide or estradiol given alone or in combination aggravated the nephritis and was associated with enhanced production of systemic IgG and IgM antibodies. Which factors might be involved in disruption of mucosal tolerance in IgAN? It is likely that cellular immunity plays a significant role in

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this process. Signaling through the lymphotoxin (LT) and LIGHT pathways play critical roles in regulating gene expression crucial for innate and adoptive defences against pathogens, and may contribute to the development of immune tolerance.83 Transgenic studies have shown that dysregulation of LIGHT signaling results in disturbance of T cell homeostasis and ultimately the breakdown of peripheral tolerance.84 LIGHT transgenic mice develop T cell-mediated intestinal inflammation and profound dysregulation of pIgA production. These changes are accompanied by dominant mesangial IgA deposition and glomerular lesions, highlighting the direct contribution of T cell-mediated mucosal immunity to development of IgAN.85 A number of studies have suggested that IgAN is a Th2-biased disease. However, there is also evidence for a Th1 bias in IgAN. Clinical studies to investigate this in human subjects are problematic because of difficulties with the timings of sample collection. In light of this we studied GATA3 transgenic mice. GATA3 is a transcription factor that specifically regulates the Th2 immune response. We crossed GATA3 transgenic mice with mice transgenic for the ovalbumin (OVA)-specific T cell receptor (TCR) gene. This double transgenic mouse was then exposed to repeated mucosal or parenteral OVA challenges. Only repeated mucosal antigen challenge in Th2biased mice resulted in mesangial deposition of, presumably underglycosylated, IgA and glomerular lesions. Indeed, only mucosally immunized GATA3/OVA TCR double transgenic mice had high serum levels of OVA-specific IgA. Analysis of cytokine expression by splenic cells and Peyer’s patch cells suggested that mesangial IgA deposition was linked to disruption of systemic Th1 tolerance in the Th2-biased mucosa.86 These findings suggest that mucosal antigen challenge in a Th2-biased host may induce dysregulation of systemic tolerance, followed by excessive systemic IgA responses, mesangial IgA deposition and glomerular injury.

Conclusions Insights from experimental animal studies discussed in this chapter suggest that patients with IgAN have an impaired mucosal immune system with dysregulation of both innate and cellular immunity. These changes may be closely linked to abnormal priming and subsequent dissemination of cells responsible for the nephritogenic IgA under a disruption of

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mucosal tolerance. These findings may provide important clues for the future treatment strategies.

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15. van den Wall Bake AW, Daha MR, van Es LA. (1989) Immunopathogenetic aspects of IgA nephropathy. Nephrologie 10: 141–145. 16. van Es LA, van den Wall Bake AW, Stad RK, et al. (1995) Enigmas in the pathogenesis of IgA nephropathy. Contrib Nephrol 111: 169–175; discussion 175–176. 17. Kunkel EJ, Butcher EC. (2003) Plasma-cell homing. Nat Rev Immunol. 3: 822–829. 18. Suzuki Y, Tomino Y. (2007) The mucosa-bone-marrow axis in IgA nephropathy. Contrib Nephrol 157: 70–79. 19. Gómez-Guerrero C, Suzuki Y, Egido J. (2002) The identification of IgA receptors in human mesangial cells: in the search for “Eldorado”. Kidney Int 62: 715–717. 20. Rifai A, Small PA, Teague PO, Ayoub EM. (1979) Experimental IgA nephropathy. J Exp Med 150: 1161–1173. 21. Rifai A, Millard K. (1985) Glomerular deposition of immune complexes prepared with monomeric or polymeric IgA. Clin Exp Immunol 60: 363–368. 22. Chen A, Wong SS, Rifai A. (1988) Glomerular immune deposits in experimental IgA nephropathy: a continuum of circulating and in situ formed immune complexes. Am J Pathol 130: 216–222. 23. Isaacs K, Miller F, Lane B. (1981) Experimental model for IgA nephropathy. Clin Immunol Immunopathol 20: 419–426. 24. Isaacs K, Miller F. (1982) Role of antigen size and charge in immune complex glomerulonephritis. I. Active induction of disease with dextran and its derivatives. Lab Invest 47: 198–205. 25. Hiki Y, Odani H, Takahashi M, et al. (2001) Mass spectrometry proves under-O-glycosylation of glomerular IgA1 in IgA nephropathy. Kidney Int 59: 1077–1085. 26. Allen AC, Bailey EM, Brenchley PE, et al. (2001) Mesangial IgA1 in IgA nephropathy exhibits aberrant O-glycosylation: observations in three patients. Kidney Int 60: 969–973. 27. Suzuki H, Moldoveanu Z, Hall S, et al. (2008) IgA1-secreting cell lines from patients with IgA nephropathy produce aberrantly glycosylated IgA1. J Clin Invest 118: 629–639. 28. Marquina R, Díez MA, López-Hoyos M, et al. (2004) Inhibition of B cell death causes the development of an IgA nephropathy in (New Zealand white × C57BL/6)F(1)-bcl-2 transgenic mice. J Immunol 172: 7177–7185. 29. Nishie T, Miyaishi O, Azuma H, et al. (2007) Development of immunoglobulin A nephropathy-like disease in beta-1,4-galactosyltransferase-I-deficient mice. Am J Pathol 170: 447–456. 30. Tomana M, Novak J, Julian BA, et al. (1999) Circulating immune complexes in IgA nephropathy consist of IgA1 with galactose-deficient hinge region and antiglycan antibodies. J Clin Invest 104: 73–81.

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31. Mestecky J, Suzuki H, Yanagihara T, et al. (2007) IgA nephropathy: current views of immune complex formation. Contrib Nephrol 157: 56–63. 32. Muso E, Yoshida H, Takeuchi E, et al. (1996) Enhanced production of glomerular extracellular matrix in a new mouse strain of high serum IgA ddY mice. Kidney Int 50: 1946–1957. 33. Muso E, Yoshida H, Takeuchi E, et al. (1997) Selective breeding for high serum IgA levels from noninbred ddY mice: isolation of a strain with an early onset of glomerular IgA deposition. Nephron 76: 201–207. 34. Kobayashi I, Nogaki F, Kusano H, et al. (2002) Interleukin-12 alters the physicochemical characteristics of serum and glomerular IgA and modifies glycosylation in a ddY mouse strain having high IgA levels. Nephrol Dial Transplant 17: 2108–2116. 35. Grossetête B, Launay P, Lehuen A, et al. (1998) Down-regulation of Fc alpha receptors on blood cells of IgA nephropathy patients: evidence for a negative regulatory role of serum IgA. Kidney Int 53: 1321–1335. 36. Launay P, Grossetête B, Arcos-Fajardo M, et al. (1999) Fc alpha receptor (CD89) mediates the development of immunoglobulin A (IgA) nephropathy (Berger’s disease). Evidence for pathogenic soluble receptor-Iga complexes in patients and CD89 transgenic mice. J Exp Med 191: 1999–2009. 37. Baldree LA, Wyatt RJ, Julian BA, et al. (1993) Immunoglobulin A-fibronectin aggregate levels in children and adults with immunoglobulin A nephropathy. Am J Kidney Dis 22: 1–4. 38. Zheng F, Kundu GC, Zhang Z, et al. (1999) Uteroglobin is essential in preventing immunoglobulin A nephropathy in mice. Nat Med 5: 1018–1025. 39. Zhang Q, Mosher DF. (1996) Cross-linking of the NH2-terminal region of fibronectin to molecules of large apparent molecular mass. Characterization of fibronectin assembly sites induced by the treatment of fibroblasts with lysophosphatidic acid. J Biol Chem 271: 33284–33292. 40. Coppo R, Chiesa M, Cirina P, et al. (2002) In human IgA nephropathy uteroglobin does not play the role inferred from transgenic mice. Am J Kidney Dis 40: 495–503. 41. Harper SJ, Allen AC, Pringle JH, et al. (1996) Increased dimeric IgA producing B cells in the bone marrow in IgA nephropathy determined by in situ hybridisation for J chain mRNA. J Clin Pathol 49: 38–42. 42. Sakai O. (1997) IgA nephropathy: current concepts and feature trends. Nephrology 3: 2–3. 43. Imasawa T, Nagasawa R, Utsunomiya Y, et al. (1999) Bone marrow transplantation attenuates murine IgA nephropathy: role of a stem cell disorder. Kidney Int 56: 1809–1817. 44. Imai H, Nakamoto Y, Asakura K, et al. (1985) Spontaneous glomerular IgA deposition in ddY mice: an animal model of IgA nephritis. Kidney Int 27: 756–761.

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45. Tomino Y, Nakamura T, Ebihara I, et al. (1991) Altered steady-state levels of mRNA coding for extracellular matrices in renal tissues of ddY mice, an animal model for IgA nephropathy. J Clin Lab Anal 5: 106–113. 46. Shimizu M, Tomino Y, Abe M, et al. (1992) Retroviral envelope glycoprotein (gp 70) is not a prerequisite for pathogenesis of primary immunoglobulin A nephropathy in ddY mice. Nephron 62: 328–331. 47. Suzuki H, Suzuki Y, Yamanaka T, et al. (2005) Genome-wide scan in a novel IgA nephropathy model identifies a susceptibility locus on murine chromosome 10, in a region syntenic to human IGAN1 on chromosome 6q22-23. J Am Soc Nephrol 16: 1289–1299. 48. Gharavi AG, Yan Y, Scolari F, et al. (2000) IgA nephropathy, the most common cause of glomerulonephritis, is linked to 6q22-23. Nat Genet 26: 354–357. 49. Suzuki H, Suzuki Y, Aizawa M, et al. (2007) Th1 polarization in murine IgA nephropathy directed by bone marrow-derived cells. Kidney Int 72: 319–327. 50. de Fijter JW, Eijgenraam JW, Braam CA, et al. (1996) Deficient IgA1 immune response to nasal cholera toxin subunit B in primary IgA nephropathy. Kidney Int 50: 952–961. 51. Roodnat JI, de Fijter JW, van Kooten C, et al. (1999) Decreased IgA1 response after primary oral immunization with live typhoid vaccine in primary IgA nephropathy. Nephrol Dial Transplant 14: 353–359. 52. Layward L, Allen AC, Hattersley JM, et al. (1993) Elevation of IgA in IgA nephropathy is localized in the serum and not saliva and is restricted to the IgA1 subclass. Nephrol Dial Transplant 8: 25–28. 53. Leinikki PO, Mustonen J, Pasternack A. (1987) Immune response to oral polio vaccine in patients with IgA glomerulonephritis. Clin Exp Immunol 68: 33–38. 54. Emancipator SN, Gallo GR, Lamm ME. (1983) Experimental IgA nephropathy induced by oral immunization. J Exp Med 157: 572–582. 55. Coppo R, Basolo B, Rollino C, et al. (1986) Mediterranean diet and primary IgA nephropathy. Clin Nephrol 26: 72–82. 56. Kumar V, Sieniawska M, Beutner EH, et al. (1988) Are immunological markers of gluten-sensitive enteropathy detectable in IgA nephropathy? Lancet 2: 1307. 57. Fornasieri A, Sinico RA, Maldifassi P, et al. (1987) IgA-antigliadin antibodies in IgA mesangial nephropathy (Berger’s disease). Br Med J 295: 78–80. 58. Rostoker G, Laurent J, André C, et al. (1988) High levels of IgA antigliadin antibodies in patients who have IgA mesangial glomerulonephritis but not coeliac disease. Lancet 1: 356–357. 59. Coppo R, Mazzucco G, Martina G, et al. (1989) Gluten-induced experimental IgA glomerulopathy. Lab Invest 60: 499–506.

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60. Yan D, Rumbeiha WK, Pestka JJ. (1998) Experimental murine IgA nephropathy following passive administration of vomitoxin-induced IgA monoclonal antibodies. Food Chem Toxicol 36: 1095–1106. 61. Pestka JJ. (2003) Deoxynivalenol-induced IgA production and IgA nephropathy-aberrant mucosal immune response with systemic repercussions. Toxicol Lett 140–141: 287–295. 62. Shi Y, Pestka JJ. (2006) Attenuation of mycotoxin-induced IgA nephropathy by eicosapentaenoic acid in the mouse: dose response and relation to IL-6 expression. J Nutr Biochem 17: 697–706. 63. Hinoshita F, Suzuki Y, Yokoyama K, et al. (1997) Experimental IgA nephropathy induced by a low-dose environmental mycotoxin, nivalenol. Nephron 75: 469–478. 64. Koyama A, Kobayashi M, Yamaguchi N, et al. (1995) Glomerulonephritis associated with MRSA infection: a possible role of bacterial superantigen. Kidney Int 47: 207–216. 65. Satoskar AA, Nadasdy G, Plaza JA, et al. (2006) Staphylococcus infectionassociated glomerulonephritis mimicking IgA nephropathy. Clin J Am Soc Nephrol 1: 1179–1186. 66. Muro K, Yamagata K, Kobayashi M, et al. (2002) Usage of T cell receptor variable segments of the beta-chain in IgA nephropathy. Nephron 92: 56–63. 67. Koyama A, Sharmin S, Sakurai H, et al. (2004) Staphylococcus aureus cell envelope antigen is a new candidate for the induction of IgA nephropathy. Kidney Int 66: 121–132. 68. Sharmin S, Shimizu Y, Hagiwara M, et al. (2004) Staphylococcus aureus antigens induce IgA-type glomerulonephritis in Balb/c mice. J Nephrol 17: 504–511. 69. Yamamoto C, Suzuki S, Kimura H, et al. (2002) Experimental nephropathy induced by Haemophilus parainfluenzae antigens. Nephron 90: 320–327. 70. Suzuki S, Nakatomi Y, Sato H, et al. (1994) Haemophilus parainfluenzae antigen and antibody in renal biopsy samples and serum of patients with IgA nephropathy. Lancet 343: 12–16. 71. Porter DD, Larsen AE, Porter HG. (1980) Aleutian disease of mink. Adv Immunol 29: 261–286. 72. Portis JL, Coe JE. (1979) Deposition of IgA in renal glomeruli of mink affected with Aleutian disease. Am J Pathol 96: 227–236. 73. Jessen RH, Emancipator SN, Jacobs GH. (1992) Experimental IgA-IgG nephropathy induced by a viral respiratory pathogen. Dependence on antigen form and immune status. Lab Invest 67: 379–386. 74. Yamashita M, Chitalacharuvu SR, Kobayashi N, et al. (2007) Analysis of innate immune responses in a model of IgA nephropathy induced by Sendai virus. Contrib Nephrol 157: 159–163.

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75. Kobayashi N, Baqheri N, Nedrud JG, et al. (2003) Differential effects of Sendai virus infection on mediator synthesis by mesangial cells from two mouse strains. Kidney Int 64: 1675–1684. 76. Akira S, Takeda K, Kaisho T. (2001) Toll-like receptors: critical proteins linking innate and acquired immunity. Nat Immunol 2: 675–680. 77. Akira S, Takeda K. (2004) Toll-like receptor signaling. Nat Rev Immunol 4: 499–511. 78. Suzuki H, Suzuki Y, Ichiei N, et al. (2008) Potential role of Toll-like receptor-9 for progression of IgA nephropathy. J Am Soc Nephrol (in press). 79. Johnson RJ, Hurtado A, Merszei J, et al. (2003) Hypothesis: dysregulation of immunologic balance resulting from hygiene and socioeconomic factors may influence the epidemiology and cause of glomerulonephritis worldwide. Am J Kidney Dis 42: 575–581. 80. Hurtado A, Johnson RJ. (2005) Hygiene hypothesis and prevalence of glomerulonephritis. Kidney Int Suppl S62–S67. 81. Suzuki Y, Tomino Y. (2008) Potential immunopathogenic role of the mucosabone marrow axis in IgA nephropathy: insights from animal models. Semin Nephrol 28: 66–77. 82. Gesualdo L, Lamm ME, Emancipator SN. (1990) Defective oral tolerance promotes nephritogenesis in experimental IgA nephropathy induced by oral immunization. J Immunol 145: 3684–3691. 83. Gommerman JL, Browning JL. (2003) Lymphotoxin/light, lymphoid microenvironments and autoimmune disease. Nat Rev Immunol 3: 642–655. 84. Wang J, Fu YX. (2004) The role of LIGHT in T cell-mediated immunity. Immunol Res 30: 201–214. 85. Wang J, Anders RA, Wu Q, et al. (2004) Dysregulated LIGHT expression on T cells mediates intestinal inflammation and contributes to IgA nephropathy. J Clin Invest 113: 826–835. 86. Yamanaka T, Tamauchi H, Suzuki Y, et al. (2005) Glomerular IgA deposition through Th2-dominant mucosal immune responses. J Am Soc Nephrol 16: 210A (Abstract).

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Chapter 27

Future Prospects for IgA Nephropathy Richard J. Glassock

The Past In the four decades that have elapsed since the first description of IgA nephropathy (IgAN), by Berger and Hinglais, in a brief two-page report,1 much has been learned about this enigmatic disorder. We now recognize how frequent a condition it really is in the developed world; we appreciate its potential for progression to end-stage renal disease (ESRD); we glimpse the outlines of its pathogenesis; we have methods to identify groups of patients having a better or worse prognosis; we have crude tools to manipulate its natural course; and we understand the risks for recurrence of the same disease in renal allografts. Yet, we have every reason not to be satisfied with this progress as impressive as it has been. We still lack the means to reliably identify subjects at risk for developing the disease; we are only at the beginning of an era of non-invasive diagnosis, our prognostic tools are limited when applied to individual patients, our treatments are largely empiric and evidencebased efficacy and safety recommendations are not buttressed by largescale, long-term randomized trials, and prevention of a recurrence of the original disease in renal transplants is not yet possible. Perhaps the most glaring deficiency of the past is our inability to determine the etiology of the common, sporadic form of the disorder, even though we are coming closer to an understanding of pathogenesis at the molecular and cellular level.2,3 Projecting a future for IgA nephropathy is fraught with hazards, not the least of which is the possibility of an unexpected 403

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404 ✦ R. J. Glassock

breakthrough from an unsuspected source. Nevertheless, at some risk, I shall try to peer into the dimly lit future and create some scenarios that may well come to pass before IgA nephropathy reaches its 50th birthday, in 2018, just a decade from now.

Diagnosis of IgA Nephropathy Presently, a renal biopsy is required for the accurate diagnosis of IgA nephropathy and its separation from other disorders have a somewhat similar clinical presentation (such as thin basement membrane nephropathy, Alport syndrome, resolving post-infectious glomerulonephritis, mesangio-proliferative glomerulonephritis, and IgM nephropathy). It seems likely that in the not too distant future a non-invasive diagnosis of IgA nephropathy will be possible. This will likely come from an extension of current studies showing increased levels of under-galactosylated IgA1 in the circulation.4 Urinary proteomics also shows great promise for non-invasive diagnosis of IgAN.5 Skin biopsy and analysis of alpha chains of type IV collagen in tissue specimens is emerging as a way to establish the diagnosis of X-linked Alport syndrome or autosomal recessive Alport syndrome in patients with hematuria without resorting to a renal biopsy.6 The clinical separation of IgA nephropathy from thin basement membrane nephropathy membrane nephropathy in patients with isolated microscopic dysmorphic hematuria will likely remain a problem. IgA nephropathy and thin basement membrane nephropathy can also co-exist in the same patient. Perhaps assessment of low levels of albumin excretion and/or examining the ratio of serum IgA to C3 concentrations may permit a more accurate “pre-biopsy” differentiation of these disorders, which have greatly different prognostic implications.7 However, even if an accurate and reliable means of non-invasively diagnosing IgA nephropathy emerges, renal biopsy will remain as an important tool for rational decision making with regards to treatment and perhaps also for prognosis. However, as will be discussed below, the role of conventional renal pathology in prognostication for IgA nephropathy remains in doubt. The emerging methods for precise non-invasive diagnosis of IgA nephropathy, if simple and inexpensive, will be a boon to epidemiological studies of large numbers of “at risk” subjects. Until then, we must rely on renal biopsy to provide the diagnosis necessary for epidemiological studies. This reliance on renal biopsy

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Future Prospects for IgA Nephropathy ✦ 405

for identification of “propositi” is fraught with hazards, as the frequency of “diagnosable” IgA nephropathy in any population must depend on the indications for renal biopsy itself (unless a study is done to perform renal biopsy in apparently healthy individuals, which is not likely). One might infer that the frequency (incidence or prevalence) of IgA nephropathy diagnosed in any given population would be directly related to: (i) the frequency of the performance of renal biopsy (non-transplant) for diagnosis of primary renal disease in the population as a whole, and (ii) to the existence of “screening” programs directed at identification of urinary abnormalities in asymptomatic persons.

Pathogenesis and Etiology of IgA Nephropathy The rudimentary outlines of a likely pathogenetic process operating in the sporadic forms of IgA nephropathy are already known. Central to these hypotheses is the appearance in the circulation of an aberrantly glycosylated (under-galactosylated and over-sialylated) form of IgA1 secreted by a sub-population of B-cells.2,3 Tbe subsequent development of an autoantibody response (IgG or IgA or both) to the “neo-antigens” exposed on this aberrant molecule (see Chapters 12 and 13 for details) results in the formation of circulating immune complexes which then deposit in the glomeruli (and other tissues), most likely by receptormediated events, and thereby evoke injury. Spontaneous aggregation of the aberrant IgA molecule is an alternate way for the formation of “complexes” which can deposit in tissues. IgA deposition alone in glomeruli is largely insufficient for the development of the full-blown syndrome leading to clinical recognition of IgA nephropathy. Indeed somewhere between 4% and 16% of the “normal” population have mesangial dominant or co-dominant IgA deposition, most often without any outward clinical signs of disease.8–14 We will soon know whether these “normal” subjects (who may also be relatives of subjects with overt IgA nephropathy) also have elevated levels of under-galactosylated IgA1 or have B-cells that are destined to secrete such abnormal IgA1 upon stimulation. This may provide some clues concerning the recognition of “at risk” individuals, an important step in a long-term goal of prevention of IgA nephropathy. The relative roles of the genetic milieu and of the environment and will likely continue to be a principal focus of future research in IgA

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nephropathy. Already at least four or five “IgA nephropathy” genetic loci have been identified in family studies of the form of the disease which aggregates among closely related individuals. (The current status is described in Chapter 3.) Whole genome scanning and identification of single nucleotide polymorphisms (SNP) associated with IgA nephropathy, in various ancestral populations, will likely shed much new light on the predisposition to the disorder, both in its “benign” and “progressive” forms. I would not be very optimistic that such genetic studies will be able to develop a “diagnostic” test for sporadic IgA nephropathy, but they will almost certainly aid in the early identification of potentially treatable and “progressive” forms of the disease and thus facilitate clinical trials of therapy. The specific role of unique environmental agents (such as bacteria or viruses) seems rather limited in the primary forms of IgA nephropathy, although non-specific inter-current infections may act as “triggers,” setting in motion a generic cascade of pathogenetic events, possibly including exaggerated synthesis of the offending aberrantly glycosylated IgA1. I doubt that the future hold much promise for identification of a specific and unique environmental “trigger” for the expression of the clinical picture of classical sporadic IgA nephropathy. Latent viral infection, with late onset expression of disease, is always a possibility, but the evidence for this process is presently lacking in IgA nephropathy. The elucidation of the etiology of the sporadic forms of IgA nephropathy is will continue to lag behind progress in identifying pathogenetic mechanisms. Several pathways may exist for induction of the disease. The “spontaneous” generation of a clone of semi-immortal B cells destined to secrete an abnormal IgA1 molecule seems to be distinct possibility and the identification of a genetic basis for such a transformation should be within the reach of current technology. An environmental “trigger,” such as a bacteria or virus, might also be involved, as mentioned above. Such an event might lead to a “microenvironment” (e.g. cytokines/chemokines/B cell mitogenic factors) for maturing B cells that favors deviation of their production machinery toward an abnormally glycosylated IgA1. The influence of T cells (particularly the Th2 subset), and their secretory products, in this process is likely to be much clearer in the future as a result of intensive research being conducted in this area and the growing sophistication of research in cytokines, chemokines and growth factors, as outlined in Chapter 18. This is likely

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to be a very fruitful area of research and may yet yield new avenues for therapy. Developments in the understanding of etiology and pathogenesis of IgA nephropathy, including the specific roles of genes and environmental pathogens and their interaction will be central to the progress in prevention and treatment of the disorder. If the molecular events underlying the conversion of a resting pre-B or B cells to a mature plasma cell secreting a pathogenic under-galactosylated IgA protein can be unraveled, it is not too far fetched to imagine that specific “designer” therapies will follow.

Prognostication in IgA Nephropathy The development of accurate methods to determine prognosis of IgA nephropathy is a key element for progress in treatment of the disorder. Clinical trials depend more and more on the accurate estimation of event rates for clinically significant end points (i.e. doubling of the baseline serum creatinine, end-stage renal disease, dialysis, transplantation or death) in the placebo or comparator arm of the trial design. Presently there are many such prognostic tools (indices, formulas, scoring systems) validated in groups of patients from particular regions of the world.15–17 Not all of these indices include pathology as a component of the evaluation of prognosis. In addition, they do not always agree on the prediction which is made by use of the tool and they are mainly applicable to groups of patients rather than to individual patients. Taken together, they explain only about 50% of the variability in prognosis of IgA nephropathy patients. Undoubtedly, even in their present rudimentary form these tools do have value for the design of clinical trials of therapy. Hopefully, studies in progress will finally clarify the true role of renal pathology in prognostication, over and above simple clinical clues.18 However, I would speculate that a new era in renal pathology will overtake the conventional approach to morphologic estimation of prognosis. I foresee the increasing use of new tissue markers of prognosis, such as can be obtained by special immunohistochemical studies for examining deposition of specific proteins (such as fibroblast specific protein-1), in-situ hybridization studies for cytokine expression, microdissection for mRNA and RNAi expression and studies of infiltration of renal tissue with immune cells carrying specific markers (such as

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GMP-17+ T cells).19 This new wave of “modern” renal pathology will likely replace the older approaches to morphology and will offer new avenues for more accurate prognostication based on tissue biopsy, even in “early” disease before progression to renal insufficiency has occurred. If these techniques provide reliable “early” indicators of progression, then renal biopsies will become a more widely accepted tool for the identification of IgA nephropathy even at the “isolated hematuria” stage. Urinary markers of progressive disease are also likely to be increasingly described and validated.20 I would predict that authentication of the predictive accuracy of surrogate markers of clinically significant events (such as ESRD), as currently exemplified by quantification of proteinuria and renal pathology, will continue to be a focus of clinical research for some time to come.

Treatment of IgA Nephropathy An honest appraisal of the available studies of therapy in IgA nephropathy would include the words “promising,” “controversial,” “inadequately designed,” and “too short-term.” Indeed, most of the trials used to support “evidence-based” treatment regimens are relatively small (less than 100 subjects), of short-term nature (usually much less than five years) and employ agents selected empirically based on their ability to interfere with immune responses or harmful hemodynamic or pathophysiological events (such as glomerular capillary/systemic hypertension or proteinuria)21 (see also Chapters 21–25). While real progress has no doubt been made, in terms of reducing the rate of progression of disease, no therapy for IgA nephropathy is truly “curative.” Eventually palliative therapy must give way to more effective modification of the fundamental disease processes, based on specific molecular or cellular events (so-called “designer” drug therapy). This approach has been very successful in oncology and I predict that it will become increasingly successful in IgA nephropathy as well, but only slowly and with great difficulty. One of the main obstacles is the high degree of unexplained variability in prognosis and the very indolent nature of the disease. These facts will make design and execution of randomized controlled trials a real challenge and may also discourage interest in investment in

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clinical trials by the bio-pharmaceutical industry, despite the frequency with which IgA nephropathy occurs in the general population. It is also very probable that pharmaco-genomics will make significant modification to the therapeutic approaches to IgA nephropathy in the not too distant future. The ability to rapidly and inexpensively identify individuals who are more or less likely to have a favorable response to therapy or who are at risk for a serious side effect of therapy is already on the horizon, and has been illustrated with work on the ACE gene polymorphisms in diabetic nephropathy.22 Some therapies, currently in wide use, such as tonsillectomy, parenteral immunoglobulins, antiplatelet agents, dietary modifications and combined ACEi and ARB need more rigorously designed, prospective controlled trials in order to fully validate their utility in the therapy IgA nephropathy.

The Future — A Summary The future prospects for IgA nephropathy appear bright but the path ahead is daunting. Clearly, a focus on the fundamental genetic, molecular and cellular events involved in the disease will bring forth novel approaches to diagnosis, prognosis, and therapy. It is logical to presume that diagnosis and prognosis will focus more and more on “early” disease, before irreversible kidney damage has occurred. Sophisticated studies of serum, urine and lymphoid and renal tissue will be employed to refine and improve the accuracy of this part of the process. Treatment regimens will become more “designer drug”based aimed at cure rather than just palliation. The response to therapy and/or the occurrence of treatment-emergent adverse events will be predictable by pharmaco-genomic analysis. However, it does not seem probable that eradication of IgA nephropathy will occur though application of preventative measures directed towards “at-risk” populations, at least in the time frame of this speculative contribution. Nevertheless, the future is glowing with prospects favoring a much better understanding and eventual control of this enigmatic disease that is diagnosed in as many as 200,000 individuals in the world each year and which may affect as many as 300,000,000 people in the world (if glomerular IgA deposition in asymptomatic, apparently normal individuals is considered as a “disease”).

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References 1. Berger J, Hinglais N. (1968) Intercapillary deposits of IgA-IgG. J Urol Nephrol (Paris) 74: 694–695. 2. Barratt J, Smith AC, Molyneux K, Feehally J. (2007) Immunopathogenesis of IgA nephropathy. Semin Immunopathol 29: 427–443. 3. Suzuki H, Moldoveanu Z, Hall S, et al. (2008) IgA1 secreting cell lines from patients with IgA nephropathy produce aberrantly glycosylated IgA1. J Clin Invest 118: 629–639. 4. Moldoveanu Z, Wyatt RJ, Lee JY, et al. (2007). Patients with IgA nephropathy have increased serum galactose-deficient IgA1 levels. Kidney Int 71: 1148–1154. 5. Haubitz M, Wittke S, Weissinger EM, et al. (2005). Urine protein patterns can serve as diagnostic tools in patients with IgA nephropathy. Kidney Int 67: 2313–2320. 6. Tryggvason K, Patrakka J. (2006) Thin basement membrane nephropathy. J Am Soc Nephrol 17: 813–822. 7. Shen P, He L, Jiang Y, Wang C, Chen M. (2007). Useful indicators for performing renal biopsy in adult patients with isolated microscopic hematuria. Int J Clin Pract 61: 789–794. 8. Curschellas E, Landmann J, Durig M, et al. (1991) Morphologic findings in “zero-hour” biopsies of renal transplants. Clin Nephrol 36: 215–222. 9. Varis J, Rantala I, Pastyernak H, et al. (1993) Immunoglobulin and complement deposition in glomeruli of 756 subjects who had committed suicide or met with a violent death. J Clin Pathol 46: 607–610. 10. Suzuki K, Honda K, Tanabe K, et al. (2003) Incidence of latent mesangial IgA deposition in renal allograft donors in Japan. Kidney Int 63: 2286–2294. 11. Sinniah R. (1983) Occurrence of mesangial IgA and IgM deposition in a control necropsy population. J Clin Pathol 36: 276–279. 12. Waldherr R, Rambausek M, Duncker WD, Ritz E. (1989) Frequency of mesangial IgA deposits in a non-selected autopsy series. Nephrol Dial Transplant 4: 943–946. 13. Rosenberg H, Martinez P, Vaccarezza A, Martinex L. (1989) A morphologic study of 103 kidneys donated for renal transplantation. Rev Med Chil 117: 1344–1350. 14. Rosenberg HG, Martinez PS, Vaccarezza AS, Martinez LV. (1990) Morphological findings in 70 kidneys of living donors for renal transplant. Pathol Res Pract 186: 619–624. 15. Bartosik LP, Lajoie G, Sugar L, Cattran DC. (2001) Predicting progression in IgA nephropathy. Am J Kidney Dis 38: 728–735.

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16. Berthoux FC, Mohey H, Afiani A. (2008) Natural history of IgA nephropathy. Semin Nephrol 28: 4–9. 17. Wakai K, Kawamura T, Endoh M, et al. (2006) A scoring system to predict renal outcome in IgA nephropathy: from a nationwide prospective study. Nephrol Dial Transplant 21: 2800–2808. 18. Cook HT. (2008) Interpreting renal biopsies in IgA nephropathy. In: IgA Nephropathy Today (ed.) Tomino Y. Contrib Nephrol 157: 44–49. 19. van Es LA, de Heer E, Vieminbg LJ, et al. (2008) GMP-17 positive T-lympocytes in renal tubules predict progression in early stage of IgA nephropathy. Kidney Int 73: 1426–1433. 20. Torres DD, Rossini M, Manno C, et al. (2008) The ratio of epidermal growth factor to monocyte chemotactic peptide-1 in the urine predicts renal prognosis in IgA nephropathy. Kidney Int 73: 327–333. 21. Barratt J, Feehally J. (2006) Treatment of IgA nephropathy. Kidney Int 69: 1934–1938. 22. Jacobsen PK, Tarnow L, Parving H-H. (2006) Time to consider ACE insertion/ deletion genotypes and individual renoprotective treatment for diabetic nephropathy. Kidney Int 69: 1293–1295.

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Index

α2,6-linked sialic acid, 198 α2,6-sialyltransferase, 198 αβ T cell, 199 γβ T cell, 199

angiotensin (Ang) II receptor, 291 type 1 (ATR1), 291, 322 type 2 (ATR2), 291, 324 angiotensin converting enzyme (ACE), 290 gene deletion polymorphism, 300 gene polymorphism, 332 gene insertion/deletion (I/D), 299 therapeutic efficacy, 300 angiotensin converting enzyme inhibitor (ACEi), 295, 321, 324, 330 angiotensinogen (AGT) gene, 299 M235T, 299 angiotensin receptor blocker (ARB), 321, 330 an overlapping syndrome of IgA nephropathy and lipoid nephrosis, 4 anti-angiogenic factor thrombospondin-1 (TSP-1), 60 anticoagulant, 351 antigen-antibody dependent immune complex, 226 antigen-antibody independent immune complex, 230 antioxidant, 349 antiplatelet agent, 351

1,3-beta-galactosyltransferase, 198 3-hydroxy-3-methylglutaryl Co-enzyme A (HMG-CoA) reductase inhibitor, 358 5-aminosalicylic acid, 354 aberrant glycosylation, 180, 197 aberrantly glycosylated (undergalactosylated and oversialylated) form of IgA1, 405 activated T cell, 58 activation induced cytidine deaminase, 195 aldosterone breakthrough, 291, 331 alpha-tocopherol, 350 Alport syndrome, 404 alternative and lectin pathway, 213 alternative pathway of complement, 238 ancestral difference, 9 factor, 16 angiotensin (Ang) II, 290 specific binding, 292

413

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414 ✦ Index

anti-Thy 1.1 model of mesangioproliferative glomerulonephritis, 256 apoptosis, 293 APRIL, 230 asialoglycoprotein receptor (ASGP-R), 217 aspirin, 351 association study, 24 ATR1 antagonist, 295 ATR1 gene, 299 A1166C, 299 at-risk population, 409 autoantigen, 197 autoimmune disease, 130, 180 azathioprine, 342 bacterial antigen, 228 BAFF, 230 B cell, 164, 194 Bcl-2, 75 biomarker, 239 B lymphocyte stimulator protein, 169 caldesmon, 60 CD4+ Th cell, 195 CD5+ B cell, 197 CD5-positive B cell, 372 CD8+ cytotoxic T lymphocyte, 199 CD20-positive B cell, 59 CD44, 63, 271 CD80/CD86, 58 CD86, 274 cellular immunity, 395 chemokine, 58, 271 receptor, 271 chronic kidney disease (CKD) stage 1, 381 stage 2, 381 stage 3, 381 stage 4, 381

chymase, 293 chymase-positive mast cell, 294 c-Jun amino terminal kinase (JNK), 273, 279 class II antigen, 372 clearance of IgA1 immune complex, 181 clinical course, 151 outcome, 93 presentation, 108 remission, 375 coeliac disease, 127 combination therapy, 330 complement, 91, 213 activation, 237 production, 237 connective tissue growth factor, 256 continuous antigenic challenge, 393 corticosteroid, 143, 340 corticosteroid plus cyclophosphamide +/− Azathioprine, 143 counterbalance of ATR1 by ATR2, 296 Crohn’s disease, 128 cyclin-dependent kinase (CDK) inhibitor, 73 cyclophosphamide, 340, 351 cyclosporin, 342 ddY mouse, 391 grouped, 395 delayed-type hypersensitivity, 277 dendritic cell, 166 dermatitis herpetiformis, 127 designer drug therapy, 408 dietary modification, 353 dilazep, 353 dipyridamole, 351, 379

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Index ✦ 415

disialyl-T antigen, 198 disodium cromoglycate, 354 docosahexanoic acid (DHA), 355 donor type, 152 eicosapentanoic acid (EPA) 355 electron microscopy, 46 end-stage renal failure (ESRF), 113 environmental antigen, 10 epidemiology, 9 epithelial-to-mesenchymal transition, 255 E-selectin, 270 evidence-based treatment regimen, 408 ezrin, 74 familial IgAN, 26 family study, 21 Fcα/µ receptor, 217 FcαRI/CD89, 163 Fc-gamma receptor, 201 Fc receptor for IgA (FcαRI, also known as CD89), 214, 271, 276 fibrinolytic, 351 fibroblastic-specific protein-1 (FSP-1), 60, 89 fish oil, 355 focal infection theory, 370 food antigen, 226 galactose, 198 galactose-deficient IgA1, 179, 232 galactose-deficient O-glycan, 180 genes with susceptibility to IgA nephropathy, 28 genetic factor, 154 genetic variant associated with progression of IgAN, 29 genome-wide association (GWA) study, 24

geographic variability, 10 glomerular capillaritis, 380 glomerular capillary basement membrane (GCBM), 46 glomerular epithelial protein 1 (GLEPP1), 74 glomerular filtration barrier, 69 glomerulo-podocytic cross-talk, 76 glomerulo-podocytic-tubular axis, 77 glomerulosclerosis, 39, 42 glomerulo-tubular cross-talk, 57, 76, 297 glucocorticoid, 310 antiapoptotic effect on podocyte, 310 mechanism of action, 310 receptor, 309 gluten-free diet, 354 glycosylation, 164 glycosyltransferase, 164 GMP-17-positive cytotoxic T cell, 59 graft survival, 151 gut associated lymphoid tissue, 196 haplotype, 23 Helicobacter pylori, 371 hematuria, 108 Hemophilus parainfluenzae, 371 Henoch-Schönlein purpura, 131 heparin, 351 hepatitis B virus (HBV), 124, 228 hepatocyte growth factor (HGF), 59 HIGA mouse, 390 hinge region, 179 histological grading, 44 human immunodeficiency virus (HIV) infection, 124 human leukocyte antigen (HLA), 153

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416 ✦ Index

hyaline arteriosclerosis, 43 hypertension, 86 IgA abnormally glycosylated, 212 class switching, 195, 200 IgA1, 162 IgA2, 162 immune complex, 389 monomeric (mIgA), 162 nephritogenic, 389 polymeric (pIgA), 162, 372 polymeric receptor (pIgR), 217 receptor, 76 secretory (SIgA), 162 sialylated, 390 under-glycosylated, 390 IgA cell/IgG cell ratio, 372 IgA-containing immune complex, 177 IgA nephropathy Berger’s disease, 1, 2 clinical feature, 3 different nomenclature, 3 down-regulation of ATR1, 295 genetic loci, 406 history, 1 progression, 238, 239 secondary, 37, 122 severity and poor outcome, 237 tonsil, 371 IgA nephropathy in children, 139, 140, 144 crescentic (rapidly progressive), 142 genetic loci, 406 mizoribine, 144 Mycophenolate Mofetil, 144 natural history, 140

prognosis, 140 treatment option, 141 IgA1-positive follicular dendritic cell, 372 IgM nephropathy, 404 immune complex, 183 tolerance, 395 immunofluorescence examination, 45 immunofluorescent tagging of antibody, 2 immunomodulatory therapy, 339 infection, 122 inflammatory bowel disease, 126 innate immunity, 394 intercellular adhesion molecule-1 (ICAM-1), 270 interleukin (IL) IL-1, 272 IL-6, 344 IL-8, 244 IL-10, 165 interstitial fibrosis, 89 intestinal permeability, 353 intravenous corticosteroid, 314 immunoglobulin, 345 J-chain, 212 mRNA-positive IgAbearing cell, 372 latency-associated protein (LAP), 252 latent IgA deposition from donor kidney, 154 leflunomide, 345 light chain, 212 κ-chain, 212 λ-chain, 212, 244 linkage analysis, 22

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Index ✦ 417

linked loci, 26 3p24-p23 loci, 27 4q26-q31, 27 6q22-q23, 27 17q12-q22, 27 liver disease, 4, 125 local C3, 237 lod score, 23 long-term prognostic index, 3 crescent, 3 glomerulosclerosis, 3 hypertension, 3 medial hyperplasia of blood vessel, 3 proteinuria, 3 low-antigen content diet, 354 lymphoepithelial symbiosis, 372 macrophage, 58, 268 macrophage migration inhibitory factor (MIF), 245, 270 male:female ratio, 108 malignancy, 129 mannose-binding lectin (MBL), 165, 238, 239 marker for progressive graft dysfunction, 155 mass screening program, 139 matrix metalloproteinase (MMP), 61 membrane attack complex (C5b-9), 237 mesangial deposit, 177 hypercellularity, 40 sclerosis, 39 mesangio-proliferative glomerulonephritis, 256, 404 meta-analysis, 340 metabolic syndrome, 48, 130 minimal change nephropathy overlapping on IgAN, 47

mismatch, 153 mitogen-associated protein kinase, 298 mizoribine, 345, 379 monocyte chemoattractant protein-1 (MCP-1), 244, 271 receptor, 278 monosialy-T antigen, 198 mucosa-bone marrow axis, 387 mucosal inflammation, 4 murine model, 292 Mycophenolate Mofetil, 343 myofibroblast, 60 N-acetylgalactosamine, 198 N-acetylneuraminic acid, 198 natural history, 113 nephrin, 71, 74 nephritogenic, 183 nephrotic-range proteinuria, 4 nestin, 74 neutrophil infiltration, 244 NF-κB, 310 nitric oxide, 273 NKG7+/CD8+ intraepithelial lymphocyte, 202 “normal” population have mesangial dominant or co-dominant IgA deposition, 405 O-glycosylation, 163, 164, 231 O-linked glycan, 179 omega-3 polyunsaturated fatty acid, 355 osteopontin, 271 percutaneous renal biopsy, 2 peritubular capillary network, 60 pharmaco-genomics, 409 pharyngeal mucosal infection, 369 pharyngitis, 369

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418 ✦ Index

phenytoin sodium, 359 plasma exchange, 345 plasmapheresis, 345 platelet-derived growth factor (PDGF), 58, 245 isoform, 248 receptor (PDGFR), 248 podocyte, 69 apoptosis, 71 podocytopathy, 74 podocytopenia, 73 point of no remission, 380 point of no slowing, 380 positional cloning, 23 post-infectious glomerulonephritis, 404 pre-diabetes, 48 prednisolone, 379 pregnancy, 86 primary T nodule, 372 T lymphocyte, 372 prognostic marker, 84 tool, 407 prognostic factor age, 85 gender, 85 prognostication, 404 progression, 116 proliferative activity, 73 properdin, 237 prorenin, 291 receptor, 291 protein kinase C pathway, 298 proteinuria, 58, 87, 322 proto-oncogene, 75 P-selectin, 270 randomized controlled trial, 5, 340, 379, 382 ratio of Bax/Bcl-2, 75 ratio of serum IgA to C3, 404

recurrence disease, 151 graft loss, 151 of mesangial IgA deposit, 149 rate, 150 risk factor, 152 renal allograft survival, 151 biopsy, 14, 38 survival, 3 survival rate, 374 transplantation, 149 renin, 290 renin-angiotensin system (RAS), 290, 322 gene polymorphism, 299 local, 290 retransplant, 156 rheumatic disease, 131 risk factor, 116, 322 risk of progression to end-stage renal disease, 374 Rituximab (anti-CD20), 345 routine protocol biopsy, 150 saturation analysis, 292 screening program, 405 secreted protein acidic and rich in cysteine (SPARC), 74 serum IgA/C3 ratio, 238 sialoadhesin (Siglec 1, also known as CD169), 203, 274 sialylation, 212 skin biopsy, 404 Smad, 252 somatic hypermutation, 195 Staphylococcus aureus cell envelope antigen, 371 MRSA infection, 124, 229 steroid pulse therapy, 375, 379 striped fibrosis, 42

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Index ✦ 419

Study of Heart and Renal Protection (SHARP), 359 synpharyngitic gross hematuria, 379 synpharyngitic macroscopic hematuria, 85 systematic screening of urine, 9 Th1-prone mouse, 394 Th2-prone mouse, 394 Th1/Th2 polarization, 201 thin basement membrane nephropathy, 404 Toll-like receptor (TLR), 278, 394 tonsillectomy, 142, 372, 374, 375, 382 efficacy, 372 indication, 379 tonsillectomy plus steroid pulse therapy, 375, 379, 380 at a relatively early stage, 380 indication, 381 traditional Chinese medicine, 360 transferrin (Tf) receptor (TfR or CD71), 217 transforming growth factor-beta (TGF-β), 59, 217, 249 Transmission Disequilibrium Test (TDT), 24 treatment, 324, 330 goal, 381

trimetazidine, 353 damage, 297, 322 fibrosis, 39, 256 injury, 55 tubulointerstitial damage, 297, 322 fibrosis, 39, 256 injury, 55 tumor necrosis factor-alpha (TNF-α), 57, 73, 76, 245, 297 receptor-1 (TNF-R1), 77 receptor-2 (TNF-R2), 77 twin study, 22 type 2 diabetes, 130 tyrosine kinase, 246 ulcerative colitis, 129 under-galactosylated IgA1, 404 under-glycosylated pIgA1, 388 urinary marker, 91 of progressive disease, 408 urokinase, 351 vascular cell adhesion molecule-1 (VCAM-1), 270 vascular endothelial growth factor (VEGF), 60, 73, 254 vasculitide, 131 VH-D-JH segment 194 viral antigen, 227 vitamin E, 350 warfarin, 351, 379

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