Because RA PBMC include several cell types in addition to T cells, some inflammatory cytokines released from macrophages and other lymphocytes might have affected the production of IL-17 from T cells. To evaluate the effects of inflammatory cytokines released by activated PBMC, we tested the effects of several cytokines and chemokines on IL-17 production. We detected an increase in IL-17 level after stimulation with IL-15 (10 ng/ml), whereas with IL-1β (10 ng/ml), TNF-α (10 ng/ml), IL-18 (10 ng/ml) or TGF-β (10 ng/ml) the levels in IL-17 were unchanged (Fig. 2a). When treated with MCP-1 (10 ng/ml) or IL-6 (10 ng/ml), significant upregulations of IL-17 proteins were observed (62 ± 42 and 50 ± 10 versus 31 ± 11 pg/ml, respectively; P < 0.05), whereas none was observed with IL-8 (10 ng/ml), MIP-1α (10 ng/ml) or MIP-1β (10 ng/ml) (Fig. 2b).