Interleukin-2 inducible T-cell kinase (Itk, Emt or Tsk) is a member of the non-receptor protein tyrosine kinases. Family members of Itk include Tec, Btk, Rlk and Bmx and are all defined by a common structure: an amino-terminal PH domain, a Tec-homology domain and a SH3 and SH2 domain followed by a carboxy-terminal kinase domain. Tec, Rlk and Itk are expressed in T cells and activated in response to T cell receptor (TCR) engagement.