Specificity: This antibody reacts with a 180 kD glycoprotein of CD45 family, occurring on most thymocytes and activated T cells but only on the portion of the resting T cells. It reacts with most thymocytes, a subpopulation of resting cells within both the CD4 and CD8 subsets and mature activated T cells. This antibody shows no reactivity with normal B or natural killer cells, but reacts with granulocytes and monocytes. Though this antibody is useful to identify T-cell lymphomas and leukemia, rare staining with B cell lymphomas reported.