Objective: To study the effects of different disease modifying anti-rheumatic drugs (DMARDs) on different events mediated by IL-15-activated lymphocytes.
Methods: Peripheral blood lymphocytes (PBL) were isolated from healthy donors and activated with IL-15 after exposure to different DMARDs: leflunomide, cyclosporin A, methotrexate, mycophenolic acid, FK-506, sulphasalazine and sodium aurothiomalate. The expression of different surface molecules on the PBL was then determined by flow-cytometry. Cells were also co-cultured with the monocytic cell line THP-1 and the TNF concentration in the supernatant was measured after 24 h using an immunoenzyme assay. The effect of the aforementioned drugs on IL-17 production by IL-15-activated PBL was also studied.
Results: Treatment of PBL with leflunomide, cyclosporin A and FK-506 inhibited the IL-15-induced expression of both CD54 and CD69 by PBL, as well as TNF production in co-cultures of activated-PBL and THP-1 cells. The down-regulation of CD54 and CD69 in PBL was correlated with the inhibition of TNF production. Likewise, leflunomide, cyclosporin A and FK-506 all inhibited IL-17 production in IL-15-activated PBL. Interestingly, the effect of leflunomide was not reverted by the presence of uridine in the medium. In addition, leflunomide inhibited the phosphorylation of STAT6 in vitro.
Conclusion: Inhibition of the JAK/STAT pathway may represent an additional effect of leflunomide in chronic polyarthritis since it impairs certain events that control proinflammatory TNF and IL-17 cytokine production.