TYK2 and psoriasis: After binding to its receptor, IL-23, an important cytokine in psoriasis, promotes the formation of the JAK1/JAK2/TYK2 complex, followed by STAT3/STAT4 phosphorylation and dimerization and translocation into the nucleus, binds to the corresponding target gene promoter, and induces the expression and secretion of cytokines such as IL-17, IL-21, IL-22, and IFN-γ (75).