Staphylococcal enterotoxin that activates the host immune system by binding as unprocessed molecules to major histocompatibility (MHC) complex class II and T-cell receptor (TCR) molecules via their alpha domain, in particular TRAV27. In turn, this ternary complex activates a large number of T-lymphocytes initiating a systemic release of proinflammatory cytokines. Causes also the intoxication staphylococcal food poisoning syndrome. The illness characterized by high fever, hypotension, diarrhea, shock, and in some cases death.