IL-21 plays a critical role in the activation and proliferation of Th17 cells and follicular helper T (Tfh) cells and further mediates several inflammatory processes in RA pathogenesis and progression.28 IL-21 could inhibit IL-2 production and impair Treg homeostasis,29 while IL-2 could improve these effects. The gene discussed is IL21; the disease is rheumatoid arthritis.