Tyk2 signaling is shared by both type I and III IFNs and its altered expression as well as some Tyk2 genetic variants have been implicated in the pathogenesis of numerous autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, diabetes, ulcerative colitis and Crohn's disease [33]. Here, TYK2 is linked to rheumatoid arthritis.