Current understanding of the role of tyrosine kinase 2 signaling in immune responses

Figure 3 Illustration of interleukin-12 and interleukin-23, as well as their receptors and downstream signaling pathways. IL-12 and IL-23 share the p40 subunit, while their receptors share the IL-12Rβ1 subunit. The binding of IL-12 to its receptor induces the activation of Jak2 and Tyrosine kinase 2 (Tyk2), which results in signal transducer and activator of transcription (STAT)4 phosphorylation. Activated STAT4 promotes the differentiation of naïve Th cells into Th1 cells, which subsequently produce IFN-γ that is required for the development of Th1 immune response. The binding of IL-23 to its receptor induces the activation of Jak2 and Tyk2, which results in STAT3 phosphorylation. IL-23 induces the expression of IL-17A, IL-17F, and/or IL-22 and stabilizes Th17 cells. STAT: Signal transducer and activator of transcription.