Staphylococcal enterotoxin-dependent lysis of MHC class II negative target cells by cytolytic T lymphocytes

The enterotoxins of Staphylococcus aureus (SE) are extremely potent activators of human and mouse T lymphocytes. In general, T cell responses to SE are MHC class II dependent (presumably reflecting the ability of SE to bind directly to MHC class II molecules) and restricted to responding cells expressing certain T cell receptor beta-chain variable (TCR V beta) domains. Recently we demonstrated that CD8+ CTL expressing appropriate TCR V beta could recognize SE presented on MHC class II-bearing target cells. We now show that MHC class II expression is not strictly required for T cell recognition of SE. Both human and mouse MHC class II negative target cells could be recognized (i.e., lysed) in a SE-dependent fashion by CD8+ mouse CTL clones and polyclonal populations, provided that the CTL expressed appropriate TCR V beta elements. SE-dependent lysis of MHC class II negative targets by CTL was inhibited by mAb directed against CD3 or LFA-1, suggesting that SE recognition was TCR and cell contact dependent. Furthermore, different SE were recognized preferentially by CTL on MHC class II+ vs MHC class II- targets. Taken together, our data raise the possibility that SE binding structures distinct from MHC class II molecules may exist.