Heterogeneity of human T4+ inducer T cells defined by a monoclonal antibody that delineates two functional subpopulations.

A monoclonal antibody termed anti-T4 that detected approximately 60% of peripheral blood T lymphocytes was shown to define the human inducer population. In the present study, we characterized three additional monoclonal antibodies, anti-T4A, anti-T4B, and anti-TQ1, that were reactive with a similar percentage of T lymphocytes. Anti-T4A, anti-T4B, and anti-T4 delineated identical cell populations, while those defined by anti-TQ1 differed in several respects: 1) Anti-TQ1 stained a minority (less than 7%) of thymocytes, whereas the other antibodies stained a majority (80%); 2) Anti-TQ1 reacted with 70 to 85% of T4+ lymphocytes, but also stained 50% of T cells within the T4- (T8+) cytotoxic/suppressor subset; 3) The antigen defined by anti-TQ1 was not restricted in its expression to T cells; it defined a fraction of normal B and null lymphocytes as well as non-T cell lines. In vitro studies indicated that the subpopulations of T4+ T lymphocytes delineated by anti-TQ1 were functionally distinct. Although T4+TQ1+ and T4+TQ1- T cells proliferated in an equal fashion to soluble antigen and alloantigen, only the T4+TQ1+ subset was responsible for maximal proliferation in autologous MLR. This T4+TQ1+ subset contained a population of lymphocytes reactive with the previously defined JRA autoantibody. In contrast, the T4+TQ1-, but not the T4+TQ1+, subset provided the majority of T cell help for B cell immunoglobulin production in a pokeweed-driven system. We conclude that the subpopulation of T4+ inducer cells responsible for maximal helper activity in T-B interactions is restricted to a minor subpopulation of T4+ lymphocytes.