T cell-activating properties of an anti-Thy-1 monoclonal antibody. Possible analogy to OKT3/Leu-4.

We have identified a single rat monoclonal antibody, G7, that is a potent inducer of interleukin (IL-2) production from all functioning T cell hybridomas as well as from normal T cells. G7 is also mitogenic for normal T cells and is a very effective inducer of IL-2 receptor expression. On fluorescence-activated cell sorter analysis, G7 recognized a pan-T cell antigen. Immunoprecipitation studies demonstrated that G7 recognized a cell surface molecule of 28-32 kD that appeared to be identical to Thy-1 in coprecipitation studies. In addition, G7 precipitated a protein of 50 kD. The possible relationship of the putative molecular complex identified by G7 on murine cells to the molecular complex identified on human T cells with anti-T3 reagents is discussed. In addition, G7 should prove to be a very useful reagent for studying the early events of lymphocyte activation as well as an inducer of lymphokine-rich supernatants.