TYK2 and Autoimmunity: As an essential intracellular component of the autoimmune-related cytokine (e.g., IL23, IL12, and type I IFN) pathways, TYK2 mediates the downstream events following cytokine/receptor activation, and thus plays pivotal roles in these cytokine-associated autoimmune disorders and inflammatory pathogenesis (2, 28–32).