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      Epitope Mapping of Monoclonal Antibodies Directed to Aminopeptidase A and Their Relevance for Albuminuria in Mice

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          Abstract

          We have shown previously that injection of specific combinations of anti-aminopeptidase A monoclonal antibodies induces an acute massive albuminuria in mice. This albuminuria is neither dependent on systemic mediators of inflammation nor angiotensin II. In this study, we examined the contribution of two individual antibodies, the enzyme-inhibiting antibody ASD-37 and the non-enzyme-inhibiting antibody ASD-41, in the induction of albuminuria as well as the interactions between these two monoclonals. In addition, we have mapped the epitopes of both antibodies using in vitro coupled transcription/translation of specifically designed cDNA fragments followed by immunoprecipitation, and using peptide enzyme-linked immunosorbent assay in case of a continuous epitope. A single intravenous injection of 4 mg of either ASD-37 or ASD-41 did not induce albuminuria. This dose of ASD-37 did not completely inhibit enzyme activity. The combination of 4 mg ASD-37/41 (1:1 weight ratio) induced albuminuria and almost completely inhibited enzyme activity. Similar results were obtained with a combination of ASD-37/41 in a 1:39 or 39:1 weight ratio. Administration of 2 mg ASD-41 24 h before injection of 2 mg ASD-37 significantly enhanced albuminuria. The epitope of ASD-37 is located at the C-terminal end of aminopeptidase A, whereas the ASD-41 epitope is mapped near the enzyme active site. Our data suggest that ASD-41 modulates the binding of ASD-37 to its epitope and/or vice versa. As a consequence, ASD-37 and ASD-41 act synergistically, not only in inhibiting enzyme activity but also in inducing albuminuria.

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          Most cited references 13

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          Immunochemical quantitation of antigens by single radial immunodiffusion.

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            Families of zinc metalloproteases.

             John Hooper (1994)
            A scheme based on the zinc binding site [1992, FEBS Lett. 312, 110-114] has been extended to classify zinc metalloproteases into distinct families. The gluzincins, defined by the HEXXH motif and a glutamic acid as the third zinc ligand, include the thermolysin, endopeptidase-24.11, aminopeptidase, angiotensin converting enzyme, endopeptidase-24.15, and tetanus and botulinum neurotoxin families. The metzincins, defined by the HEXXH motif, a histidine as the third zinc ligand and a Met-turn, include the astacin, serralysin, reprolysin and matrixin families. The inverted zincin motif, HXXEH, defines the inverzincin family of insulin-degrading enzymes, the HXXE motif defines the carboxypeptidase family, and the HXH motif DD-carboxypeptidase.
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              Reactive oxygen species expose cryptic epitopes associated with autoimmune goodpasture syndrome.

              Goodpasture syndrome is an autoimmune disease of the kidneys and lungs mediated by antibodies and T-cells directed to cryptic epitopes hidden within basement membrane hexamers rich in alpha3 non-collagenous globular (NC1) domains of type IV collagen. These epitopes are normally invisible to the immune system, but this privilege can be obviated by chemical modification. Endogenous drivers of immune activation consequent to the loss of privilege have long been suspected. We have examined the ability of reactive oxygen species (ROS) to expose Goodpasture epitopes buried within NC1 hexamers obtained from renal glomeruli abundant in alpha3(IV) NC1 domains. For some hexameric epitopes, like the Goodpasture epitopes, exposure to ROS specifically enhanced recognition by Goodpasture antibodies in a sequential and time-dependent fashion; control binding of epitopes to alpha3(IV) alloantibodies from renal transplant recipients with Alport syndrome was decreased, whereas epitope binding to heterologous antibodies recognizing all alpha3 NC1 epitopes remained the same. Inhibitors of hydrogen peroxide and hydroxyl radical scavengers were capable of attenuating the effects of ROS in cells and kidney by 30-50%, respectively, thereby keeping the Goodpasture epitopes largely concealed when compared with a 70% maximum inhibition by iron chelators. Hydrogen peroxide administration to rodents was sufficient to expose Goodpasture epitope in vivo and initiate autoantibody production. Our findings collectively suggest that ROS can alter the hexameric structure of type IV collagen to expose or destroy selectively immunologic epitopes embedded in basement membrane. The reasons for autoimmunity in Goodpasture syndrome may lie in an age-dependent deterioration in inhibitor function modulating oxidative damage to structural molecules. ROS therefore may play an important role in shaping post-translational epitope diversity or neoantigen formation in organ tissues.
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                Author and article information

                Journal
                NEE
                Nephron Exp Nephrol
                10.1159/issn.1660-2129
                Cardiorenal Medicine
                S. Karger AG
                1660-2129
                2003
                May 2003
                17 November 2004
                : 94
                : 1
                : e25-e34
                Affiliations
                Departments of aPathology and bInternal Medicine, Division of Nephrology, University Medical Centre Nijmegen, Nijmegen, and cDepartment of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
                Article
                70816 Nephron Exp Nephrol 2003;94:e25–e34
                10.1159/000070816
                12806185
                © 2003 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 4, Tables: 1, References: 28, Pages: 1
                Product
                Self URI (application/pdf): https://www.karger.com/Article/Pdf/70816
                Categories
                Original Paper

                Cardiovascular Medicine, Nephrology

                Mouse, Aminopeptidase A, Monoclonal antibodies, Epitope, Albuminuria

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