TIA1 is a member of an RNA binding protein family and possesses nucleolytic activity against cytotoxic lymphocyte (CTL) target cells. It has been suggested that this protein may be involved in the induction of apoptosis as it preferentially recognizes poly(A) homopolymers and induces DNA fragmentation in CTL targets. The major granule-associated species is a 15- kDa protein that is thought to be derived from the carboxyl terminus of the 40- kDa product by proteolytic processing. TIA-1 (T-cell intracytoplasmic antigen) monoclonal antibody reacts with a 15 kDa cytoplasmic granule-associated protein, expressed in lymphocytes processing cytolytic potential. The expression of TIA-1 was studied in CD30+ anaplastic large cell lymphomas (ALCL), NK cell lymphomas and peripheral T-cell lymphomas and T cell lymphocytosis, B-cell lymphomas and lymphoblastic leukemia, Hodgkin's etc. Studies showed that 60 to 70 % of anaplastic large cell lymphoma reacted with TIA-1. Studies also indicate that TIA-1 reacts with most large granular lymphocytic leukemia's, hepatosplenic T-cell lymphomas, intestinal T-cell lymphomas, NK-like T-cell lymphomas, NK-cell lymphomas, nasal T/NK-cell lymphomas, subcutaneous T-cell lymphomas, pulmonary angiocentric lymphomas of T or NK phenotype. The author's concluded from TIA-1 studies that anaplastic large-cell lymphomas are cytotoxic T-or NK-cell neoplasms. All B-cell lymphomas, Hodgkin's and lymphoblastic leukemias were negative for TIA-1.Synonyms: Nucleolysin TIA-1, RNA-binding protein TIA-1, TIA1 cytotoxic granule-associated RNA binding protein, p15-TIA-1, p40-TIA-1