POS0388 INTERLEUKIN 40 (IL-40) IS UP-REGULATED IN RHEUMATOID ARTHRITIS (RA) AND ASSOCIATED WITH DISEASE ACTIVITY, LEVELS OF AUTOANTIBODIES AND CHEMOKINES
Authors: A. Navrátilová, L. Andres Cerezo, H. Hulejova, V. Becvar, D. Tegzová, M. Olejárova, D. Veigl, K. Pavelka, J. Vencovský, L. Šenolt
Journal: Annals of the Rheumatic Diseases (2021)

Background: Interleukin 40 (IL-40) is newly identified B cell - associated cytokine implicated in humoral immune responses and in B cell development. As B cells play a pivotal role in autoimmunity, we aimed to investigate the function of IL-40 in rheumatoid arthritis (RA). Objectives: The aim of our study was to determine the function of IL-40 in RA. Methods: IL-40 expression in the synovial tissue was determined by immunohistochemistry and immunofluorescence (n=4-5). IL-40 was analysed in the serum/synovial fluid of patients with RA (n=69), systemic lupus erythematosus (SLE; n=69), osteoarthritis (OA; n=44), and in healthy controls (HC; n=25). Given the association of IL-40 with B cells, we analysed the effect of rituximab therapy on the serum IL-40 in 19 patients with RA after 16 and 24 weeks of the therapy. The clinical activity of patients with RA was assessed according to the 28 joint count Disease Activity Score (DAS28). Levels of C-reactive protein (CRP) and autoantibodies were measured by routine laboratory techniques. In vitro experiments were performed in RA synovial fibroblasts (n=9). Levels of cytokines and inflammatory mediators were determined in serum, synovial fluid and supernatants using ELISA or multiplex immunoassay. Results: IL-40 was overexpressed in RA synovial tissue compared to OA, particularly by synovial fibroblasts and immune cells such as B and T lymphocytes, macrophages and neutrophils. The levels of IL-40 were significantly higher in the synovial fluid of RA patients compared to OA (33.2 (6.6-68.9) vs. 0.7 (0.1-2.4) ng/ml; p&lt;0.0001). In addition, IL-40 was increased in the serum of RA patients compared to SLE, OA or HC (4.8 (1.7-24.9) vs. 1.4 (1.0-1.9), 1.6 (0.6-3.1) or 1.5 (0.7-2.7) ng/ml; p&lt;0.0001 for all) and decreased after 16 (p&lt;0.01) and 24 weeks (p&lt;0.001) in a subgroup of rituximab treated patients with RA. IL-40 levels in RA patients correlated with autoantibodies rheumatoid factor (IgM) and anti-citrullinated protein antibody (ACPA) in the serum (p&lt;0.0001 and p&lt;0.01) as well as in the synovial fluid (p&lt;0.0001 and p&lt;0.001). IL-40 in RA synovial fluid was also significantly associated with DAS28 (p&lt;0.05), synovial fluid leukocyte count (p&lt;0.01), number of swollen joints (p&lt;0.05) and neutrophil attractants IL-8 (p&lt;0.01) and MIP-1α (p&lt;0.01). RA synovial fibroblasts exposed to recombinant IL-40 increased secretion of IL-8 (p&lt;0.01), MCP-1 (p&lt;0.05) and MMP-13 (p&lt;0.01) compared to unstimulated cells in in vitro conditions. Conclusion: Our results show for the first time that IL-40 is elevated in RA and decreases following B-cell depletion therapy. The association of IL-40 with autoantibodies and chemokines may imply its potential involvement in RA development. Moreover, IL-40 up-regulates the secretion of chemokines and MMP-13 by synovial fibroblasts, indicating its role in the regulation of inflammation and tissue destruction in RA. Acknowledgements: Supported by MHCR 023728 a SVV 260 523 Disclosure of Interests: None declared