Superantigens: interaction of staphylococcal enterotoxins with MHC class II molecules.

We have shown that the staphylococcal enterotoxins and TSST specifically bind to MHC class II molecules. This binding to class II molecules is a prerequisite for the function of these bacterial exotoxins as T cell mitogens in vitro. While SEA bound all class II molecules tested with respect to isotype and allotype, the other enterotoxins were limited in binding by the class II isotype. In contrast to conventional antigen, the nature of enterotoxin interactions with MHC enables them to stimulate class I-restricted CD8+ T cells, most likely due to the ability of SEs to engage the T cell receptor based solely on V beta usage. Finally, in addition to activating adjacent T cells, the enterotoxins and TSST can evoke responses from the class II-bearing cells to which they bind. Enterotoxin/TSST effects on cells that bear class II molecule "receptors", in addition to their induction of T cell hormones such as interleukin-2 and interferon-gamma, provide possible explanations for some of the symptomatology seen with these bacterial exotoxins and also implicate MHC class II molecules as signal-transducing receptors.