IL-2-inducible T cell kinase is a member of the protein kinase superfamily, Tyr protein kinase family, and TEC subfamily. It contains 1 Btk-type zinc finger, 1 PH domain, 1 protein kinase domain, 1 SH2 domain, and 1 SH3 domain. As an intracellular kinase expressed in T-cells, IL-2-inducible T cell kinase contains both SH2 and SH3 domains which are often found in intracellular kinases. It is thought to play a role in T-cell proliferation and differentiation. It regulates the development, function, and differentiation of conventional T-cells and nonconventional NKT-cells. IL-2-inducible T cell kinase also plays an essential role in the regulation of the adaptive immune response. Effects in IL-2-inducible T cell kinase are the cause of lymphoproliferative syndrome EBV-associated autosomal type 1 (LPSA1). LPSA1 is a rare immunodeficiency characterized by extreme susceptibility to infection with Epstein-Barr virus (EBV). Inadequate immune response to EBV can have a fatal outcome. Clinical features include splenomegaly, lymphadenopathy, anemia, thrombocytopenia, pancytopenia, recurrent infections. There is an increased risk of lymphoma.