TIA-1 (T-cell intracytoplasmic antigen) is a 15 kDa cytoplasmic granule-associated protein, expressed in lymphocytes processing cytolytic potential. TIA-1 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 thought to be derived from the carboxyl terminus of the 40 kDa product by proteolytic processing.

The expression of TIA-1 has been studied in anaplastic large cell lymphomas (ALCL), NK-cell lymphomas, peripheral T-cell lymphomas, T-cell lymphocytosis, B-cell lymphomas and lymphoblastic leukemia, and Hodgkin’s lymphoma, etc. Studies show that 60 to 70% of anaplastic large cell lymphomas react with TIA-1. TIA-1 also reacts with most large granular lymphocytic leukemias, 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 and pulmonary angiocentric lymphomas of T-or NK-phenotype. All B-cell lymphomas, Hodgkin’s and lymphoblastic leukemias are negative for TIA-1.^1-5