ITA, a Vertebrate Homologue of IAP That Is Expressed in T Lymphocytes

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Abstract
Apoptosis plays a crucial role in both the development and the control of the immune system. During T lymphocyte development, thymocytes undergo apoptosis as part of the process of elimination of self-reactive clones. Mature T cells also undergo apoptosis following antigen-stimulated proliferation as part of a mechanism that controls the immune response. Apoptosis also provides a defense mechanism against viruses whereby the rapid death of virus-infected cells reduces virus spread. Viruses, on the other hand, often express proteins that inhibit apoptosis of their host cells, thereby enhancing their infectivity. We have isolated a novel gene, ita (inhibitor of T cell apoptosis), which is a vertebrate homologue of the viral apoptosis inhibitor IAP. Expression of ita appears to be restricted to cells of the T lymphocyte lineage, and high levels of ita mRNA are induced within 4–8 hr of T cell activation. Immunohistologic studies show that medullary and cortical thymocytes express detectable levels of ITA. ITA is a 69 kDa protein that contains a C-terminal ring-finger motif that is found in several oncogenic proteins and N-terminal repeat elements that have only been reported in other apoptosis inhibitors. These findings suggest that ITA may play a role in controlling apoptosis in T cells.