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43. Kongress der Deutschen Gesellschaft für Rheumatologie, 29. Jahrestagung der Deutschen Gesellschaft für Orthopädische Rheumatologie, 25. Wissenschaftliche Jahrestagung der Gesellschaft für Kinder- und Jugendrheumatologie

02.-05. September 2015, Bremen

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Extensive glycosylation of ACPA-IgG variable domains modulates binding to citrullinated antigens in rheumatoid arthritis

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  • Yoann Rombouts - Leiden University Medical Center, Department of Rheumatology, Leiden, The Netherlands
  • Annemiek Willemze - Leiden University Medical Center, Department of Rheumatology, Leiden, The Netherlands
  • J. J. B. C. van Beers - Nijmegen Center for Molecular Life Sciences and Institute for Molecules and Materials, Radboud University Nijmegen, Department of Biomolecular Chemistry, Nijmegen, The Netherlands
  • Jing Shi - Leiden University Medical Center, Department of Rheumatology, Leiden, The Netherlands
  • Priscilla Kerkman - Leiden University Medical Center, Department of Rheumatology, Leiden, The Netherlands
  • Janssen Georg - Leiden University Medical Center, Department of Immunohematology and Blood Transfusion, Leiden, The Netherlands
  • Peter van Veelen - Leiden University Medical Center, Department of Immunohematology and Blood Transfusion, Leiden, The Netherlands
  • Arnaud Zaldumbide - Leiden University Medical Center, Department of Molecular Cell Biology, Leiden, The Netherlands
  • Rob Hoeben - Leiden University Medical Center, Department of Molecular Cell Biology, Leiden, The Netherlands
  • Leendert Trouw - Leiden University Medical Center, Department of Rheumatology, Leiden, The Netherlands
  • Tom Huizinga - Leiden University Medical Center, Department of Rheumatology, Leiden, The Netherlands
  • Manfred Wuhrer - Leiden University Medical Center, Center for Proteomics and Metabolomics, Leiden, The Netherlands
  • René Toes - Leiden University Medical Center, Department of Rheumatology, Leiden, The Netherlands
  • Hans Ulrich Scherer - Leiden University Medical Center, Department of Rheumatology, Leiden, The Netherlands

Deutsche Gesellschaft für Rheumatologie. Deutsche Gesellschaft für Orthopädische Rheumatologie. Gesellschaft für Kinder- und Jugendrheumatologie. 43. Kongress der Deutschen Gesellschaft für Rheumatologie (DGRh); 29. Jahrestagung der Deutschen Gesellschaft für Orthopädische Rheumatologie (DGORh); 25. wissenschaftliche Jahrestagung der Gesellschaft für Kinder- und Jugendrheumatologie (GKJR). Bremen, 02.-05.09.2015. Düsseldorf: German Medical Science GMS Publishing House; 2015. Doc52.09 - ER.08

doi: 10.3205/15dgrh050, urn:nbn:de:0183-15dgrh0502

Published: September 1, 2015

© 2015 Rombouts et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at http://creativecommons.org/licenses/by/4.0/.

Outline

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Introduction: Antibodies against citrullinated antigens (ACPA) are highly relevant diagnostic and prognostic biomarkers in rheumatoid arthritis. Previous studies have indicated that the citrulline-specific immune response differs from conventional B cell responses by generating polyclonal, cross-reactive antibodies of mostly low-avidity. The present study was undertaken to characterize the molecular make-up of ACPA and its potential functional consequences in the context of RA.

Methods: Serum components of RA patients were fractionated by size exclusion chromatography and analysed for the presence of ACPA-IgG by ELISA. In addition, ACPA-IgG and non-citrulline-specific IgG were affinity purified from RA patient serum and synovial fluid and analysed by gel electrophoresis. Electrophoresis bands were excised and subsequently analysed by HPLC and mass-spectrometry. Recombinant monoclonal ACPA with variations in ACPA molecular structure were used to study binding affinity by surface plasmon resonance.

Results: ACPA-IgG from RA patients were found to have a higher molecular weight as compared to other IgG molecules, including antibodies against recall antigens and other autoantibodies. This higher molecular weight was explained by the overrepresentation of N-linked glycans in the variable domain (Fab region) of ACPA-IgG. Structural analysis of these glycans demonstrated that ACPA-IgG Fab glycans are complex-type biantennary N-glycans that differ from the conventional Fc-linked N-glycans by a high degree of sialylation, galactosylation, and fucosylation together with the presence of bisecting N-acetylglucosamine. Using recombinant ACPA-IgG monoclonal antibodies with and without Fab-glycans, we observed that Fab-glycans modulate binding affinity of ACPA-IgG for citrullinated antigens. Finally, lectin-immunoblotting showed that ACPA Fab-glycans can bind to sialic acid-binding immunoglobulin-type lectins.

Conclusion: This study describes a novel molecular feature of the citrulline-specific immune response in RA. ACPA-IgG, in contrast to non-citrulline-specific IgG, are highly glycosylated in the variable region, which modulates recognition of citrullinated antigens. Moreover, ACPA-IgG linked Fab glycans can be the target of specific lectins, suggesting functional features potentially involved in ACPA-mediated pathogenetic effects. Finally, this finding points to aberrations in the selection/maturation of ACPA-expressing B cells and, thus, could further elucidate our understanding of basic disease mechanisms in RA.