THU0034 AUTOREACTIVE B CELLS ESCAPE PERIPHERAL CHECKPOINT IN ANCA-ASSOCIATED VASCULITIS AND SJÖGREN’S SYNDROME

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 thenatural and pathological autoimmunityand 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 ELISPOTResults: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, Naturalauto-reactive Bcells are able to secrete only IgM isotype autoantibodies uponin vitrostimulation but not IgG class switched antibodies. In order to better understand what differentiates auto-reactive B cells and the mechanisms leading to pathological autoimmunity, agenomic analysisof the antibody repertoire as well as atranscriptional profilingof 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, SFRDisclosure of Interests:None declared