Interleukin-2 tyrosine kinase (ITK), a BTK/TEC type tyrosine kinase, is critical for efficient signaling downstream of the T cell receptor. Itk is directly phosphorylated and activated by Lck. Subsequently, Itk activates phospholipase C-gamma1, leading to calcium mobilization and extracellular signal-regulated kinase/mitogen-activated protein kinase activation. Itk contains five domains in addition to the catalytic domain: pleckstrin homology, Tec homology which contains a proline-rich region, Src homology 3, and Src homology 2.Synonyms: EMT, Kinase EMT, LYK, T-cell-specific kinase, Tyrosine-protein kinase Lyk