IL21 and rheumatoid arthritis: When RA synovial fibroblasts were cultured in media supplemented with IL-17, IL-21, or IL-22, TNF-α was upregulated; however, SKI306X reduced Th17 cytokine-induced TNF-α expression (Figure 1A), TNF-α production was increased upon IL-17 stimulation in culture media, and SKI306X reduced TNF-α production (Figure 1B).