Itk (IL-2 Inducible T-cell Kinase), also known as Emt or Tsk, is a member of the Tec family of kinases, containing PH, SH3, SH2, and kinase domains. It is primarily expressed in T cells and certain B cells, where it regulates T cell activation, differentiation, and cytokine production through T cell receptor (TCR) signaling. Itk participates in cellular immune responses by activating PLCγ1 and downstream Ras/MAPK, NF-κB, and NFAT signaling pathways. The gene expression specificity and functional activity of Itk are crucial for T cell function, and its mutations or functional dysregulation are associated with immunodeficiency and autoimmune diseases, making it a potential target for immunotherapy.