IL21 and rheumatoid arthritis: In RA, filgotinib decreased the serum levels of multiple cytokines, Th1-related cytokines (IL-2, IFN-γ, and IL-12), Th2-related cytokines (IL-4, IL-5, and IL-13), and Th17-related cytokines (IL-1β, IL-6, IL-17A, IL-21, and IL-23) at 12 weeks [23].