Activation of MHC class I-restricted CD8+ CTL by microbial T cell mitogens. Dependence upon MHC class II expression of the target cells and V beta usage of the responder T cells.

The T cell response to microbial T cell mitogens (MTM) such as enterotoxins from Staphylococcus aureus (SE) and the soluble mitogen from Mycoplasma arthritidis, resemble the minor lymphocyte stimulatory locus (Mls) response in several aspects. An important feature of the Mls response is it restriction to CD4+ cells. This study demonstrates that in contrast to Mls, the MTM response includes both CD4+ and CD8+ subsets. Both CD4+ and CD8+ cells expanded in IL-2 after stimulation with SEB showed preferential expression of T cell receptors bearing V beta 8 domains. Mouse and human target cells could be lysed in the presence of MTM both by MTM-stimulated CD8+ lymphocytes and by MHC class I-restricted CTL clones of defined Ag specificity. MTM-induced lysis required the expression of MHC class II, but not class I Ag, on the target cells. Inhibition studies of SEB and Ag-dependent cytolysis by CTL clones underlined the crucial role of CD3 and LFA-1 in both instances, but showed CD8 dependence only for AG-dependent cytolysis. Together these findings suggest important differences between the putative MTM-mediated interaction of TCR with MHC molecules and the classical TCR/MHC interaction involved in MHC-restricted Ag recognition.