POS0413 COMPREHENSIVE IMMUNE PROFILING OF PERIPHERAL BLOOD IN PSORIATIC ARTHRITIS (PsA) PATIENTS: EXPANSION OF INTERMEDIATE MONOCYTES AND DECREASED T REG AND CD8 T CELLS

Background: Psoriatic arthritis (PsA) is a heterogeneous inflammatory arthritis that develops in a subset of patients with psoriasis. According to the current paradigm, cells of the innate and adaptive immunity interact with resident tissue fibroblasts mounting an inflammatory response via complex cytokine networks in the skin and joints in which type 1 and type 17 T cells play a dominant role. The abundance and relative contribution of other peripheral blood immune cells to disease pathogenesis as well the molecular signature of peripheral blood mononuclear cells and tissue fibroblasts remain ill defined. Objectives: To comprehensively characterize immune cell subsets driving inflammation in the peripheral blood of patients with active PsA and their impact on psoriatic skin fibroblasts. Methods: Peripheral blood was collected from PsA patients (n=31) and age-/sex-matched healthy individuals (HI) (n=9), after informed consent. Psoriatic skin biopsies were acquired from a subset of 5 patients and 3 HI. All patients fulfilled the CASPAR criteria for the diagnosis and displayed peripheral polyarthritis of moderate- to high-disease activity. Patients’ demographic and clinical data were recorded at time of sampling. Disease activity was assessed using the Disease Activity Index for Psoriatic arthritis (DAPSA) score. Skin psoriasis activity indices, enthesitis and dactylitis were also recorded. Peripheral blood mononuclear cells (PBMCs) were isolated by ficoll density gradient centrifugation. Flow cytometry was performed using a BD FACS-Aria-III and analyzed using FlowJo software. The antibody staining panel utilized aimed at the identification of the following immune cell subsets: Monocyte subsets (HLA-DR+ CD14+/- CD16+/-), Plasmacytoid dendritic cells (HLA- DR+ CD123+), T helper (CD4+), cytotoxic T (CD8+), regulatory T (CD4+ CD25+ CD127-) and B cells (CD19+). Statistical analyses were performed using GraphPad Prism software. Differences between groups were compared using unpaired T test for parametric data; Mann-Whitney and Kruskal Wallis tests for non-parametric data. The level of significance was set at P Results: 9 males and 22 females PsA patients are included (mean age 50 years and the mean disease duration 19.2 years for skin disease and 5.9 years for arthritis). The mean DAPSA score was 43.4, suggestive of high disease activity, while 8 (26%) patients displayed clinical enthesitis at time of sampling. Flow cytometry analysis revealed aberrancies in peripheral blood immune cell populations. More specifically, PsA patients displayed a significant increase in intermediate monocyte subset (HLA-DR+ CD14+ CD16+) compared to HI with patients with clinical enthesitis demonstrating a more exaggerated expansion of intermediate monocytes compared to patients without enthesitis. A trend towards increased patrolling monocytes (HLA-DR+ CD14- CD16+) was also noted although this did not reach statistical significance. In contrast, both regulatory T cells and cytotoxic CD8+ T cells were significantly decreased probably due to their selective migration at the sites of inflammation. RNA-seq from whole blood and skin fibroblasts from affected skin are in progress. Conclusion: These data demonstrate significant expansion of intermediate monocytes -more pronounced in the enthesitis affected individuals- and decrease in T regulatory cells and T cytotoxic cells in PsA peripheral blood. Increased antigen presentation and co-stimulation mediated via intermediate monocytes in combination with their proangiogenic properties may contribute to disease pathogenesis References: [1]Veale, D. J. & Fearon, U. The pathogenesis of psoriatic arthritis. The Lancet (2018) doi:10.1016/S0140-6736(18)30830-4. Disclosure of Interests: None declared