Cell surface molecules involved in early events in T-cell mitogenic stimulation by staphylococcal enterotoxins.

We tested the mitogenic response to staphylococcal enterotoxin (SE) type A and SE type B in spleen cells from five strains of mice and found consistent and significant differences among the strains. We chose to study the mitogenic responses of two of these strains, C58BL/6J and BALB/cJ, in greater detail. We investigated the effects of specific monoclonal antibodies to cell surface determinants on SE-induced mitogenesis. Monoclonal antibodies against Ia (class II major histocompatibility complex) determinants blocked SE-induced mitogenesis. Both I-A and I-E molecules can participate in the stimulation, and in BALB/cJ mice which express both types of class II molecules both must be blocked to prevent mitogenesis. Mitogenesis was not inhibited by monoclonal antibodies specific for class I major histocompatibility complex antigens or monoclonal antibodies specific for Mac-1, Lyt-1, or Lyt-2 cell surface proteins. Monoclonal antibodies specific for the T-cell surface antigens L3T4 and T3 also substantially inhibited SE-induced mitogenesis. This implicates participation of the T-cell antigen receptor complex in stimulation induced by the SEs. Elimination of L3T4+ helper-inducer T cells abolished the mitogenic response of spleen cells to SE. Reconstitution of L3T4-depleted spleen cells with L3T4+ T cells showed that the level of the mitogenic response was directly proportional to the number of L3T4+ cells added. Elimination of Lyt-2+ cells resulted in a 50% decrease in the response to SEs. These results indicate that L3T4+ T cells are required for the mitogenic response to SE, but both L3T4+ and Lyt 2+ T cells participate in SE-induced mitogenesis. Our results suggest that both Ia and the T-cell antigenic receptor complex are involved in SE-induced mitogenesis.