Background:Rheumatoid arthritis (RA) is an autoimmune disorder in which Th17 cells, B cells and inflammatory cytokines (1-3) contribute to joint tissue damage, however the role of specific myeloid populations to immunopathogenesis of RA remains unclear.Objectives:To address this question, we studied transcriptional, phenotypical and functional characteristics of monocytes (Mo), CD1c+ and CD141+ conventional dendritic cells (cDC) from RA patients.Methods:Frequencies and maturation patterns of Lin-CD14-HLADR+ plasmacytoid (CD11c-), CD1c+ and CD141+ cDC (CD11c+) subsets and CD14+ Mo from n=25 RA patients at baseline were analyzed by multicolor flow cytometry. In addition, longitudinal studies on the evolution of these populations after treatment initiation were conducted on a smaller group of RA patients. Moreover, CD1c+ and CD141+ cDC subsets and total Mo were sorted from the peripheral blood from n=4 untreated RA and healthy individuals and the synovial fluid from n=3 RA and chondrocalcinosis patients. Differential transcriptional patterns within each population were analyzed by RNAseq. Functional validation of targets were performed in vitro with cDC subsets isolated form the synoviual fluid of RA patients. Finally, silencing of expression of NLRC4 and NLRP3 on CD1c+cDCs was performed with specific siRNAs.Results:Both CD1c+ (p=0.0001) and CD141+ (p=0.0008) cDCs were significantly depleted from the blood and enriched in the synovial fluid from untreated RA patients, but proportions of CD1c+ cDCs were more significantly recovered after treatment initiation and associated with improved clinical parameters. In addition, specific increased expression levels of the IgG-Fc receptor CD64 on CD1c+ cDC was associated with higher DAS28 (p=0.0002). Moreover, differential transcriptional patterns of circulating CD1c+cDCs from RA patients were characterized by genes linked to toll-like receptor, Fc-receptor, inflammasome pathways and elevated CCR2 expression (p=0.016), while CD141+cDCs transcribed interferon-related genes. Importantly, CCR2+ CD64Hi CD1c+cDCs from the synovial fluid from RA patients transcribed proinflammatory cytokines such as IL1-β, CCL3 and IL-8, actively expressed the inflammasome mediator caspase 1 and were more effective activating pathogenic IFNγ+IL-17+ CD4+ T cells in vitro than CD141+ cDC (p=0.0019). These functional profiles could be artificially induced stimulating CD1c+ cDCs with dsDNA in the presence of IgGs and was dependent on caspase 1 and the NLRC4 inflammasome.Conclusion:Our data provides novel insights about specific activation and functional patterns on CD1c+cDC contributing to RA pathogenesis and identifies new sensors that could represent novel therapeutic target to treat RA.References:[1]Alvandpur N, Tabatabaei R, Tahamoli-Roudsari A, Basiri Z, Behzad M, Rezaeepoor M, et al. Circulating IFN-gamma producing CD4+ T cells and IL-17A producing CD4+ T cells, HLA-shared epitope and ACPA may characterize the clinical response to therapy in rheumatoid arthritis patients. Human immunology. 2020.[2]Nistala K, Adams S, Cambrook H, Ursu S, Olivito B, de Jager W, et al. Th17 plasticity in human autoimmune arthritis is driven by the inflammatory environment. Proceedings of the National Academy of Sciences of the United States of America. 2010;107(33):14751-6.[3]Chapuy-Regaud S, Nogueira L, Clavel C, Sebbag M, Vincent C, Serre G. IgG subclass distribution of the rheumatoid arthritis-specific autoantibodies to citrullinated fibrin. Clinical and experimental immunology. 2005;139(3):542-50.Disclosure of Interests:None declared
Dendritic cells, T cells and their interaction in rheumatoid arthritis