JAK1 and rheumatoid arthritis: Filgotinib inhibited Th1, Th2, and Th17 differentiation, and JAK1-dependent cytokines in a dose-dependent manner, including IL-2, IL-4, and IL-6, which plays vital pathological roles in chronic inflammation and autoimmune disorders.409 Filgotinib is mostly used for inflammatory and autoimmune diseases, including inflammatory bowel diseases, rheumatoid arthritis, PsA, and ankylosing spondylitis.410–412 In September 2020, the EU approved filgotinib for the treatment of moderate-to-severe RA patients who inadequately respond to one or more DMARD.