B-CELL SUBSETS IN PERIPHERAL BLOOD ACROSS DISEASE PHASES OF PSORIATIC ARTHRITIS AND THEIR CORRELATION WITH SYNOVIAL TISSUE FEATURES

D. Bruno, B. Tolusso, C. DI Mario, S. Perniola, D. Somma, L. Petricca, A. Chiricozzi, M. R. Gigante, A. D’amore, M. Kurowska-Stolarska, S. Alivernini, E. GremeseUniversity of Verona, Department of Medicine, Verona, Italy Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Division of Clinical Immunology, Rome, Italy Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Immunology Research Core Facility – Gemelli Science and Technology Park (GSTeP), Rome, Italy University of Glasgow, Research Into Inflammatory Arthritis Centre Versus Arthritis (RACE), Glasgow, United Kingdom Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Division of Rheumatology, Rome, Italy Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Division of Dermatology, Rome, Italy Università Cattolica del Sacro Cuore, Division of Dermatology, Rome, Italy Università Cattolica del Sacro Cuore, Division of Rheumatology, Rome, Italy Università Cattolica del Sacro Cuore, Division of Clinical Immunology, Rome, Italy  Background Psoriatic Arthritis (PsA) has been historically considered as a T-cell driven disease, with the role of B-cells generally under investigated since common seronegativity. However, over the years new insights have come to light on B-cells in PsA, focusing on the presence of ectopic lymphoid structures as well as on the presence of specific anti-carbamylated/citrullinated cathelicidin LL37 antibodies in psoriatic SF and plasma. Objectives The aim of the study was to examine the frequencies of distinct peripheral blood (PB) B-cell subsets in across different disease phases, evaluating their potential correlation with synovial tissue (ST) heterogeneity in terms of inflammatory degree and microanatomical organization. Methods 150 patients fulfilling the CASPAR criteria for PsA were recruited (81 naive to cDMARDs or bDMARDs, 45 c- and/or b-DMARDs resistant and 24 in clinical and US sustained remission, respectively) and underwent US-guided ST biopsy and PB withdrawal. 22 patients with psoriasis (PsO) and arthralgia were included as comparison group. All ST FFPE specimens were routinely processed and stained with H&E and classified by a pathologist, blinded to clinical characteristics, using a H&E based semiquantitive score (KSS) integrated with the presence/absence of lymphocytes, plasmacells, granulocytes and myxoid degeneration, respectively. [1] Frequencies of PB B-cell subpopulations were determined by FACS using the CD27/IgD classification as follows: naïve B-cells (CD27IgD), IgM memory (CD27IgD), switched memory (CD27IgD ), late memory (CD27 IgD ), plasmablasts (CD27CD38) and plasmacells (CD138). Results In PsA cohort, the distribution of synovitis score was significantly different among patients with distinct disease phases (ANOVA p<0.001). In particular, KSS was contingent on disease phase being significantly lower in PsA in remission (2.04 ± 1.39) compared to naive (3.20 ± 1.77, p=0.02) and resistant PsA (3.78 ± 2.22, p<0.001), while there was no significant difference between remission PsA and at risk PsO group in terms of synovial hyperplasia, stromal density, and lymphocyte infiltrate respectively. ST of c- and/or b-DMARDs resistant PsA was enriched of plasmacells than remission PsA (p=0.03). Considering B-cell subpopulations, PB of c- and/or b-DMARDs resistant PsA was enriched of plasmablasts and plasmacells compared to PsO at risk of PsA development (p=0.01 for plasmablasts and p=0.001 for plasmacells, respectively). Conversely, c- and/or b-DMARDs resistant PsA showed, at PB level, lower rates of switched memory and naïve B-cells compared to PsO at risk of PsA development (p= 0.02 for switched memory and p=0.039 for naive, respectively). Finally, stratifying PsA based on KSS category, remission PsA with persistent high grade synovitis (KSS ≥ 5) showed lower rates of PB plasmablasts compared to remission PsA with low grade or without residual synovial inflammation (p=0.045). Conclusion Disease state across PsA course significantly impacts PB B-cell subsets distribution mirroring ST residual inflammation at the time of sustained disease remission and supporting the tight dynamic connection between PB and ST environments. Reference [1]Alivernini S et al. Arthritis & Rheumatology 2021 Acknowledgements: NIL. Disclosure of Interests None Declared. Keywords: Synovium, Biomarkers, Remission DOI: 10.1136/annrheumdis-2023-eular.5841Citation: , volume 82, supplement 1, year 2023, page 739Session: Psoriatic arthritis - clinical aspects (other than treatment) (Poster View)