IL-17 receptor and its functional significance in psoriatic arthritis

To delineate the functional significance of IL-17 Receptor (IL-17RA) and characterize the IL-17 producing T cell (T _h17) subpopulation in psoriatic arthritis (PsA). Mononuclear cells from blood and synovial fluid (SF) were obtained from PsA (n = 20), rheumatoid arthritis (RA, n = 20) and osteoarthritis (OA, n = 20) patients. Synoviocytes (FLS) were isolated from the synovium of RA (n = 5), PsA (n = 5) and OA (n = 5) patients. IL-17RA expression in FLS was identified by western blotting (WB) and flowcytometry. T lymphocytes derived from the SF of these patients were studied to identify and phenotype the T _h17 cells. The functional significance of IL-17RA was determined by evaluating its regulatory role on the production of proinflammatory cytokines and endopeptidase. IL-17RA expression was found to be significantly higher in FLS of RA (15.7% ± 4.9) and PsA (4.5% ± 0.9) in comparison to OA (1.14% ± 0.9). Western blot analyses showed that the relative intensity (RI) of IL-17RA protein was higher in RA and PsA compared to OA (Fisher exact, P < 0.01). A significant enrichment of IL-17-producing CD4+ T cells (7.9% ± 2.8) was observed in the SF of PsA patients compared to that of OA patients (P < .001). Compared to OA-FLS, recombinant IL-17 induced higher levels of IL-6, IL-8, and MMP-3 production in PsA-FLS. Blockage of IL-17RA with an anti-IL-17RA antibody inhibited the production of IL-6, IL-8, and MMP-3. This is the first report to demonstrate the functional significance of IL-17RA in PsA. Results of this study support the hypothesis that IL-17RA blocking antibodies have the potential to be a therapeutic option for psoriatic arthritis.