OP0208 Synovial tissue of ra patients in remission contains a unique population of regulatory macrophages
Authors: A Elmesmari, S Alivernini, B Tolusso, D Vaughan, G Di Sante, L Petricca, E Gremese, G Ferraccioli, IB McInnes, M Kurowska-Stolarska
Journal: Annals of the Rheumatic Diseases (2017)

<h3>Background</h3> The majority of RA treatments target inflammation or the adaptive immune response. Partial- or non-response is common and only a minority have sustained remission. There is a knowledge gap in understanding the mechanisms that could reinstate synovial homeostasis in RA. Tissue macrophages may have a role in this process; they are present in healthy synovium and aid resolution of the inflammation in experimental models of RA. However, little is known about the regulatory properties of human synovial tissue macrophages. <h3>Objectives</h3> Our hypothesis is that healthy and RA synovium in remission contain macrophages with anti-inflammatory/repair properties and identifying the effector pathways that drive their function could facilitate therapeutic restoration of synovial homeostasis in RA. <h3>Methods</h3> We developed a flow cytometry sorting strategy for harvesting tissue-resident macrophages obtained from digested synovial biopsies of RA patients (n=21, including in remission n=5; and active RA n=16). Cells were labelled with cell lineage-specific antibodies; then macrophages were gated based on their expression of CD64<sup>pos</sup>CD11b<sup>pos</sup>MHCII<sup>pos</sup>Lineage<sup>neg</sup>. The potential homeostatic/repair macrophage was preliminary identified by the presence of CD206 marker. CD206<sup>pos</sup> and CD206<sup>neg</sup> macrophages were sorted using a FACS Aria III and RNAseq performed to characterise their functional signature. In some experiment, macrophages were seeded on collagen-coated plates and production of TNFa evaluated. <h3>Results</h3> All synovial tissue macrophages from RA in remission were CD206<sup>pos</sup> whereas a substantial number of synovial macrophages from active RA tissue were CD206<sup>neg</sup>. Gene expression analyses and functional assays suggest that these populations represent distinct phenotypes in the activation spectrum. CD206<sup>neg</sup> macrophages have high expression of microRNA-155, which drives production of inflammatory mediators <i>e.g.</i> TNFa. In contrast, CD206<sup>pos</sup> macrophages showed regulatory properties characterised by increased expression of soluble (<i>e.g.</i><i>IL10, TGFB</i>), surface (<i>e.g.</i><i>IL4/14R, TGFBR1/2</i>) and cellular (<i>e.g.</i><i>SHIP1, TAM, SMAD2, STAT6</i>) inhibitors of inflammatory activation, and increased expression of repair markers (<i>e.g. ARG2 and CCL18</i>). <h3>Conclusions</h3> We propose therefore that anti-inflammatory/repair macrophages may be present in human synovial tissues in remission representing a hitherto unnoticed regulatory tissue mechanism. <h3>References</h3> Smolen JS, Aletaha D, McInnes IB. Rheumatoid Arthritis. Lancet Volume 388, Issue 10055, 22–28 October 2016, Pages 2023–2038. Misharin AV et al. Non-classical Ly6C(-) monocytes drive the development of inflammatory arthritis in mice. Cell Rep. 2014;9:591. Kurowska-Stolarska M, Alivernini S et al. MicroRNA-155 as a pro-inflammatory regulator in clinical and experimental arthritis. PNAS 2011;108:11193. Elmesmari A, McInnes IB, Kurowska-Stolarska M. MicroRNA-155 regulates monocyte chemokine and chemokine receptor expression in Rheumatoid Arthritis. Rheumatology (Oxford). 2016 Nov;55(11):2056–2065. Epub 2016 Jul. 13. <h3>Disclosure of Interest</h3> None declared