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:2303780, PubMed:25015819). Causes also the intoxication staphylococcal food poisoning syndrome (By similarity). Interacts with MHC class II molecules composed of alpha/HLA-DRA and beta/HLA-DRB1 chains (PubMed:8152483, PubMed:25015819). Interacts with T-cell receptor beta variable 19/TRBV19 (PubMed:9881971, PubMed:25015819). Lacks the zinc-binding site found in other members of this family, such as staphylococcal enterotoxin A, C2 and D, thus it possesses only one MHC class II binding site. Belongs to the staphylococcal/streptococcal toxin family.