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

TLDR

Prior work using a heteroantiserum to the T(H2) membrane component identified two distinct human T‑cell subsets that together constitute the majority of erythrocyte‑rosette‑forming cells. This study aimed to generate monoclonal antibodies that recognize surface determinants unique to each of those two T‑cell subsets. The authors produced the antibodies and evaluated their ability to block effector T‑cell–mediated cytolysis in vitro in the absence of complement. The resulting antibodies, alphaLeu‑2a/2b and alphaLeu‑3a/3b, bound separate thymocyte and ERF‑C populations, with alphaLeu‑2a potently inhibiting cytotoxic killing while alphaLeu‑2b had weaker effects; none of the antibodies reacted with sIg⁺ leukemic cells or normal B cells, thereby defining two distinct Leu‑2 (T(H2)+) and Leu‑3 (T(H2)−) T‑cell subpopulations.

Abstract

In prior studies a heteroantiserum to a surface membrane component termed T(H2) was used to define two subsets of human T cells (T(H2) (+) and T(H2) (-)), which were found to express distinct sets of activities in 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 alphaLeu-2a and alphaLeu-2b, which seem to define the same surface antigen identified by the original T(H2) 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 alphaLeu-3a and alphaLeu-3b, reacted with the same subpopulation of thymocytes (78-89%) and peripheral blood ERF-C (47-78%) but, unlike alphaLeu-2a and alphaLeu-2b, did not exhibit cross-blocking; i.e., labeling cells with alphaLeu-3a did not inhibit the subsequent binding of alphaLeu-3b. T cells reactive with alphaLeu-2a were shown to be unreactive with alphaLeu-3a, indicating that two separate subpopulations of T cells, Leu-2 (formerly T(H2) (+)) and Leu-3 (T(H2) (-)) 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) alphaLeu-2a abolished the killing by cytotoxic T cells of allogeneic phytohemagglutinin-stimulated blasts, (ii) inhibition of killing by alphaLeu-2b was markedly less than inhibition by alphaLeu-2a, and (iii) other antibodies, including alphaLeu-1, alphaLeu-3a, and alphaLeu-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.