Linker for activation of T cells (LAT), a novel immunohistochemical markerfor T cells, NK cells, mast cells, and megakaryocytes - Evaluation in normal and pathological conditions

LAT (linker for activation of T cells) is an integral membrane protein of 3 6-38 kd that plays an important role in T cell activation. Using a rabbit p olyclonal antibody generated against the cytosolic portion of LAT, we inves tigated the immunohistochemical expression of LAT in normal and pathologica l hematolymphoid tissues. LAT reacts with human T cells in paraffin section s, including decalcified bone marrow trephines, LAT appears early in T cell s at the thymocyte stage and before TdT expression in embryos, and is expre ssed in peripheral lymphoid tissues, without restriction to any T cell subp opulations. in addition to T cells, natural killer (NK) cells (evaluated wi th now cytometry), megakaryocytes and mast cells are also LAT-positive, whe reas B cells and other myeloid and monocytic derived cells are negative. Te sted on a total of 264 paraffin-embedded tissue biopsies, LET reacted with the great majority (96.8%) of T/NK-cell neoplasms, covering the full range of T cell maturation. Although antibodies to both LAT and CD3 had a similar ly high sensitivity in the staining of T/NK-cell lymphomas, when used in co njunction, they successfully identified a higher number of cases (98.4%). A typical megakaryocytes from different hematological disorders, as well as m ast cells in mastocytosis were also LAT-positive, but all neoplasms of B ce ll origin, Hodgkin's lymphomas, and several nonlymphoid malignancies were n egative. These data indicate that the anti-LAT antibody may be of value to diagnostic histopathologists for the identification of T cell neoplasms.