Figure 2.

Cytokines and molecular mediators modulated by the Janus kinase (JAK) and tyrosine kinase (TYK2) system. The JAK/TYK2 system regulates the expression of numerous cytokines, growth factors, and hormones, resulting in a transcriptional crossroads of immune function and the inflammatory process. These kinases (i.e., JAK and TYK) interact with several transcription factors, namely those of the signal transducer and activator of transcription (STAT) family, which, through intranuclear translocation processes, regulate the gene expression of molecules that are part of the signalling pathway that combinations among all the mediators previously exposed determine. According to a simplified scheme (top of figure), activation of the membranous receptor complex consisting of the various combinations of JAK and TYK family members (bottom part of the figure) by binding of a ligand, which may be, for example, a cytokine or a transcription factor (1), which results in downstream activation, mainly by phosphorylation processes of STAT family members (2), which in turn are activated intranuclearly by acting as transcription factors and modulating gene expression of several genes coding for crucial molecules in the inflammatory process (3). Note: IL: interleukin; EPO: erythropoietin; GM-CSF: granulocyte–macrophage colony-stimulating factor; G-CSF: granulocyte-colony stimulating factor; TPO: thyroperoxidase; GH: growth hormone; LEP: leptin; OSM: oncostatin M; IFN: interferon.