Differentiation antigens in human T-cell activation: Evidence that anti-VH antibodies react with a membrane structure on human T Lymphocytes distinct from the antigens detected by monoclonal antibodies of the OKT and Leu series

The effect of a panel of monoclonal antibodies and heteroantibodies on T-cell proliferation in various assay systems has been examined. The antibodies tested were directed against T-cell differentiation antigens, HLA-DR antigens, and structures defined by an anti-human V_H antiserum. As the test cell system highly purified subpopulations of T-cell growth factor (TCGF)-dependent T-cell lines activated either by mitogen or antigen were used. A survey of the data indicates the following: (1) Mitogenic and antigenic triggering of T lymphocytes are mediated through partly different membrane structures. (2) Antigenic stimulation by purified protein derivative (PPD) as well as polyclonal activation induced by OKT3/anti-Leu 4 monoclonal antibodies can be inhibited by heteroantibodies raised against human immunoglobulin V_H fragments thus pointing to a possible connection between the antigens detected by these antisera. (3) There does not seem to be differences between the two major subpopulations of T lymphocytes (i.e., helper/inducer and suppressor/cytotoxic cells) as to how they respond to antigens or mitogens in the investigated assay systems. (4) A clear distinction was found between T blasts specific for PPD and allogeneic cells as compared to cytotoxic T cells (CTL), as the T4 and T8 antigens seem to be functionally important for antigen recognition among CTL but not for the blasts proliferating in response to PPD and allogeneic cells. (5) An inhibitory effect of OKT3/anti-Leu 4, OKIal, and anti-HLA-DR on TCGF-dependent growth was detected, possibly indicating a steric relationship between these antigens and TCGF receptors on mitogen-induced T blasts. (6) Soluble factors obtained after incubating adherent cells with OKIal and anti-HLA-DR antibodies seemed to have an inhibitory effect on overall T-cell proliferation stressing the importance of studying the T-cell activation process at different levels in these kinds of experiments. (7) The results further suggest a complexity in the build up of antigen receptors on the various T-effector cells, perhaps also involving receptors for growth factors, HLA-DR antigens, and receptors for the latter.