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International audience; The innate B cell (IBC) population is heterogeneous and involved in the primary immune response. IBC functions include a high ability to produce natural antibodies with IgM isotype, the elimination of apoptotic cells, and a capacity to be cognate help to T cells. Among IBC subsets, B-1 cells and marginal zone B cells are the main producers of IgM, act as rapid immune responders that may relocate to follicular lymphoid and differentiate to cytokine and antibody-secreting cells shortly after infection. IBCs functions are highly dependent on their localization site and the nature of their B cell receptor repertoire, suggesting a high plasticity range of different immune responses. In this review, we will describe the nature and functions of the different innate-like B cell subsets, first in mice and then in humans. Besides this, we will emphasize the strong ability of these cells to undertake different protective functions from the first line of defense against pathogens to the regulatory role of the broader immune response.

Background: Sjogren’s syndrome (SS) is a chronic systemic autoimmune disease, characterized by mouth and eye dryness, due to irreversible destruction of glandular tissue by infiltrated lymphocytes. It is now well established that B cells play a key role in the physiopathology of SS. Indeed, B cells exhibit various signs of hyperactivity and produce excessive amounts of pro-inflammatory cytokines and immunoglobulins (Ig), especially IgG type-antibodies (Abs) (Kroese et al.,2014). Currently, it is suggested that the interleukin (IL)-21 (Wang et al., 2018) and IFNα (Yao et al., 2013), promote the generation of autoreactive IgG-producing plasma cells (PC). On the other side, some studies highlight the protective role of IgM producing cells in autoimmunity through enhanced efferocytosis and immune-regulatory properties (Ehrenstein and Notley, 2010). Objectives: This study aims to understand the influence of IL21 and IFNα on the B cell differentiation and the subsequent functional responses of the cells according to their maturation stage. Moreover, this will also enable a further understand of the contribution of these cytokines to the pathogenesis of SS. Methods: We established in vitro models to study the differentiation of different B cell subsets in a T-independent (TI) and T-dependent (TD) manner, under different cytokine stimulations. Naive, switched memory, unswitched memory and CD27-negative memory B cells were isolated from peripheral blood of healthy controls (HC) and SS patients and thereby cultured in those different conditions. After three days of culture, the expression of surface markers and transcription factors was analysed by flow cytometry and molecular identity was further determined by transcriptional analysis. Additional functional assay was also performed to measure Abs and cytokine secretion. Results: First results on HC suggest that switched memory B cells differentiate into IgG and IgA-secreting plasmablasts (PB), when stimulated in a TI manner. This process is highly increased in presence of IFNα. Unswitched memory B cells mostly become PB able to secrete IgM and IL10. IL21 and IFNα oppose distinct effector functions. IL21 promote activation of B cells with an upregulation of the surface marker CD11c and T-bet transcription factor. Transcriptomic studies are still in progress to further define the molecular profile of those distinct effector B cells. Preliminary results on SS patients suggest that B cell differentiation is altered with a biased ratio between activated cells and PB. Conclusion: This work will allow us a better understanding of the heterogeneity of the distinct effector B cells and their involvement in SS pathogenesis. References [1] Ehrenstein, M. R. & Notley, C. A. The importance of natural IgM: scavenger, protector and regulator. Nature Reviews Immunology10, 778–786 (2010). [2] Kroese, F. G. M. et al. B-cell hyperactivity in primary Sjogren’s syndrome. Expert Rev Clin Immunol10, 483–499 (2014). [3] Wang, S. et al. IL-21 drives expansion and plasma cell differentiation of autoreactive CD11chiT-bet+ B cells in SLE. Nat Commun9, 1758 (2018). [4] Yao, Y., Liu, Z., Jallal, B., Shen, N. & Ronnblom, L. Type I interferons in Sjogren’s syndrome. Autoimmun Rev12, 558–566 (2013). Disclosure of Interests: None declared

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