TYK2/JTK1

TYK2 (tyrosine kinase 2, also called JTK1) is the fourth Janus kinase, discovered as the first kinase partner of the interferon-alpha/beta receptor and now known to pair with receptors for type I interferons, interleukin-12 and -23, and IL-10-family cytokines. Through STAT1, STAT2, STAT3 and STAT4, TYK2 shapes antiviral immunity, T-helper-1 differentiation and inflammatory interleukin-17 responses. Genome-wide association studies repeatedly link TYK2 variants to autoimmune diseases including psoriasis, lupus and inflammatory bowel disease. Unlike other JAK inhibitors that bind the active site, the allosteric TYK2 inhibitor deucravacitinib targets the pseudokinase (JH2) domain and is approved for moderate-to-severe plaque psoriasis, validating pseudokinase-directed pharmacology and TYK2's central role in inflammatory skin disease.