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:9551975). In addition, induces B-cell proliferation and differentiation in the presence of T-cells (PubMed:8621894). Causes also the intoxication staphylococcal food poisoning syndrome (PubMed:17306397). A zinc-binding site contributes directly to formation of the homodimer. Homodimer; zinc-dependent (PubMed:9003758). Interacts with MHC class II molecules composed of alpha/HLA-DRA and beta/HLA-DRB1 chains (PubMed:9003758, PubMed:9551975). Belongs to the staphylococcal/streptococcal toxin family.