Activation of human T lymphocytes II. Involvement of the T3 antigen in polyclonal T cell activation by mitogenic lectins and oxidation.

The effect of monoclonal antibodies against the T cell surface antigens T3 and T4 on accessory cell-dependent mitogen-induced proliferation of human antigen-specific T4+ T lymphocyte clones and purified peripheral blood T cells was studied. To avoid the Fc receptor-dependent mitogenic effects of the OKT3 antibodies, monocytes were replaced by Epstein-Barr virus-transformed B lymphoblastoid cells as accessory cells. Monoclonal antibody OKT3 but not OKT4 inhibited the response of both T lymphocyte clones and purified T cells to mitogenic lectins and oxidation. The inhibition was not due to nonspecific effects of the monoclonal antibodies since it affected only the initial triggering but not the proliferation of activated T cells and it could be overcome by higher concentrations of lectin indicating a competition between OKT3 antibody and lectin. Furthermore, OKT3 antibody at the same concentration that was inhibitory in this system was mitogenic in the presence of Fc receptor-bearing monocytes. Surface modulation of T3 but not of T4 antigens led to unresponsiveness to a mitogen pulse given directly after modulation. These findings suggest that antigen-specific and mitogen-induced T cell triggering are due to interaction with the same receptors of the T lymphocyte.