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. In turn, this ternary complex activates a large number of T-lymphocytes initiating a systemic release of pro-inflammatory cytokines (PubMed:24194959). Causes also the intoxication staphylococcal food poisoning syndrome (PubMed:20394711). Binds 1 zinc ion per subunit. The zinc ion is necessary for the toxin interaction with MHC class II. Interacts with host MHC class II molecules composed of alpha/HLA-DRA and beta/HLA-DRB1 chains (PubMed:24194959). Interacts with host T-cell receptor beta variable TRBV7-9 (PubMed:24194959, PubMed:26147596, PubMed:27180909). Belongs to the staphylococcal/streptococcal toxin family.