Thymus-dependent membrane antigens in man: Inhibition of cell-mediated lympholysis by monoclonal antibodies to T H 2 antigen

In prior studies a heteroantiserum to a surface membrane component termed TH2 was used to define two subsets of human T cells (TH2 + and TH2 - ), which were found to express distinct sets of activitiesin vitro . In the present studies we prepared monoclonal antibodies to surface determinants that are restricted to T cells belonging to each of these two subsets. Two antibodies, termed αLeu-2a and αLeu-2b, which seem to define the same surface antigen identified by the original TH2 antiserum, reacted with 57-84% of thymocytes and 22-46% of the erythrocyte-rosette-forming cells (ERF-C) in peripheral blood. Two other monoclonal antibodies, termed αLeu-3a and αLeu-3b, reacted with the same subpopulation of thymocytes (78-89%) and peripheral blood ERF-C (47-78%) but, unlike αLeu-2a and αLeu-2b, did not exhibit cross-blocking; i.e., labeling cells with αLeu-3a did not inhibit the subsequent binding of αLeu-3b. T cells reactive with αLeu-2a were shown to be unreactive with αLeu-3a, indicating that two separate subpopulations of T cells, Leu-2 (formerly TH2 + ) and Leu-3 (TH2 - ) T cells, were thereby defined. These two T cell subsets make up the subpopulation of ERF-C (80-95%) previously defined by a monoclonal antibody to a T cell membrane antigen (Leu-1) that has a thymus-dependent distribution on normal lymphocytes but is expressed by some surface-immunoglobulin-positive (sIg+ ) leukemic lymphocytes. None of the Leu antibodies reported here reacted with sIg+ , Leu-1+ leukemic cells, nor did they react with normal hematopoietic cells or lymphoid cells that had surface markers characteristic of B cells. Studies of the blocking effects of Leu antibodies on killing in cell-mediated lympholysis by effector T cells were carried out in the absence of complement. These experiments established the following points: (i ) αLeu-2a abolished the killing by cytotoxic T cells of allogeneic phytohemagglutinin-stimulated blasts, (ii ) inhibition of killing by αLeu-2b was markedly less than inhibition by αLeu-2a, and (iii ) other antibodies, including αLeu-1, αLeu-3a, and αLeu-3b, had little or no effect on killing in cell-mediated lympholysis. The relevance of these findings to prior studies done in the mouse and in man are discussed.