THU0034 AUTOREACTIVE B CELLS ESCAPE PERIPHERAL CHECKPOINT IN ANCA-ASSOCIATED VASCULITIS AND SJÖGREN’S SYNDROME
Authors: N. Chriti, M. Boudigou, E. Porchet, J. O. Pers, S. Hillion, D. Cornec
Journal: Annals of the Rheumatic Diseases (2020)

Background: B cells play a central role in many autoimmune diseases (AIDs) including ANCA-associated vasculitis (AAV) and primary Sjögren’s syndrome (pSS). Most of the research that has been conducted on AID has focused on the production, secretion, and pathogenicity of auto-antibodies, but little is known on the characteristics of autoreactive B cells in humans. Objectives: This study aims at characterizing circulating autoantigen (PR3 ou SSA)-specific B-cells in patients with AAV and pSS compared to healthy subjects to better understand their role in the natural and pathological autoimmunity and define the mechanisms leading to the breakdown of self-tolerance in patients with AID. Methods: First, we developed a new flow-cytometry method to detect circulating auto-reactive B cell based on the specificity of their B-cell receptor (BCR). To study surface phenotype of specific B cells by flow cytometry, blood samples were collected from patient with PR3-ANCA AAV, pSS and from healthy subjects. Functional analysis of antigen-specific B cells was also elicited by in vitro analysis of their capacity to secrete immunoglobulins against SSA or PR3 antigens by ELISPOT Results: Phenotype analysis showed that antigen-specific B cells in patients have a memory phenotype compared with healthy controls ( 5 to 9% are IgG-expressing memory B cells ). It suggests that in AID, theses auto-reactive cells are able to differentiate into IgG isotype-switched cells and escape peripheral tolerance checkpoint but not in healthy subjects. Interestingly, Natural auto-reactive B cells are able to secrete only IgM isotype autoantibodies upon in vitro stimulation but not IgG class switched antibodies. In order to better understand what differentiates auto-reactive B cells and the mechanisms leading to pathological autoimmunity, a genomic analysis of the antibody repertoire as well as a transcriptional profiling of these cells by single-cell RNA seq is ongoing to understand further the differences of these autoreactive B cells between healthy subjects and patients with AIDs. Conclusion: We developed a technology to identify and isolate antigen-specific B cells from the peripheral blood of patients with AID. Our results suggest that autoreactive B cells escape peripheral tolerance checkpoint and are able to differentiate into IgG isotype-switched cells in patients with AIDs but not in healthy subjects. References: [1]D. Cornec, A. Berti, A. Hummel, T. Peikert, J.-O. Pers, et U. Specks, « Identification and phenotyping of circulating autoreactive proteinase 3-specific B cells in patients with PR3-ANCA associated vasculitis and healthy controls », J. Autoimmun. , vol. 84, p. 122–131, 2017 [2]P. F. Kerkman et al., « Identification and characterisation of citrullinated antigen-specific B cells in peripheral blood of patients with rheumatoid arthritis », Ann. Rheum. Dis., vol. 75, no 6, p. 1170‑1176, juin 2016, doi: 10.1136/annrheumdis-2014-207182. Acknowledgments: with support of vasculitis foundation, CSL Berhing, SFR Disclosure of Interests: None declared