SAT0003 Synovial tissue cd1c+ dendritic cells in rheumatoid arthritis express high levels of the epigenetic regulator of inflammation, microrna-155 and inflammatory cytokines
Authors: A. Elmesmari, S. Alivernini, B. Tolusso, L. Bui, D. Vaughan, M.R. Gigante, F. Federico, G. Ferraccioli, E. Gremese, I.B. McInnes, M. Kurowska-Stolarska
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Dendritic cells (DCs) direct the immune response against pathogens while maintaining self-tolerance by instructing T/B cells in lymphoid organs and peripheral tissues. However, their aberrant activation can lead to chronic inflammation and autoimmunity. Based on the distinct transcriptomics, function and distribution, DCs can be broadly categorised as plasmacytoid and myeloid (conventional) DCs. Based on recent single cells sequencing and secretome data, can be divided into CD141<sup>+</sup> DCs (DC1), DC2_A (DC2) defined as "CD1c<sup>high</sup>CD32B<sup>high</sup>CD36<sup>neg</sup>CD163<sup>neg"</sup> and DC2_B (DC3) defined as "CD1c<sup>low</sup>CD32B<sup>neg</sup>CD163<sup>high</sup>CD36<sup>high</sup>." In addition, populations of CD1c<sup>-</sup>CD141<sup>-</sup>CD16<sup>+</sup> DC (named DC4), that shares some gene expression with CD16<sup>+</sup>monocyte and inflammatory DC (infDC). Most to date studies on Rheumatoid Arthritis patients investigated DCs in circulation or in synovial fluid (SF). This provided important insight into epigenetic changes in DC-precursors before they enter synovial tissue, <i>e.g.</i> RA blood CD1c<b><sup>+</sup></b>have deregulated microRNA-34a driven epigenetic control of anti-inflammatory Axl pathway<sup>2</sup> or into the influence of inflammatory milieu on DCs, respectively. However, neither (peripheral blood) PB or SF are major sites for DC regulated T/B cell activation; instead, DCs control immune responses in the appropriate structures of lymph organs and tissues. <h3>Objectives</h3> In this study, we sought to investigate myeloid DCs in synovial tissue with the prospect of better understanding their role in driving autoimmunity in RA. <h3>Methods</h3> We developed a flow cytometry sorting strategy to characterise the phenotype of distinct myeloid DC subsets in multiple biological compartments (PB, SF and synovial tissue). Synovial tissue (ST) biopsies (RA n=9; Psoriatic arthritis n=3) were digested with liberase prior the analysis. Peripheral blood DCs (RA n=19, Psoriatic arthritis n=16, healthy donors n=12), and SF DC (n=3) were used as comparators. Synovial tissue, SF and PB DCs were sorted and microRNAs, pro-inflammatory and regulatory cytokine expression analysed by amplified qPCR. In addition, DCs were mapped in synovial tissue in RA (n=8), PsA (n=7) and control non-inflammatory OA (n=5) by immunohistochemistry. <h3>Results</h3> Myeloid DCs are scarce in control non-inflammatory OA synovial tissues and their number increased substantially in PsA and RA tissues. Phenotyping data revealed that all myeloid DC subsets can be present in inflamed RA and PsA synovium. However, CD1c<sup>+</sup> DC populations (DC2/DC3) were the most abundant in RA synovial tissues and the gene expression analysis of CD1c<sup>+</sup> sorted from RA synovial biopsies showed an increase in the expression of epigenetic regulator of inflammatory response miR-155 and IL-6, TNF and IL-23 as compared to circulating cells. <h3>Conclusions</h3> CD1c<sup>+</sup>DCs from RA synovial tissues had epigenetically regulated activated phenotype (miR-155 and miR-34a<sup>2</sup>) that through the production of cytokines could maintain tissue activation of autoreactive Th1 and Th17 cells and contribute to inflammation. <h3>References</h3> [1] Villani AC, et al. Science2017. doi:10.1126/science.aah4573 [2] Kurowska-Stolarska M, et al. Nat Commun2017. doi:10.1038/ncomms15877 <h3>Disclosure of Interest</h3> None declared