CROSS-REACTING EPITOPES BETWEEN STAPHYLOCOCCUS AUREUS ENTEROTOXINS A AND E

Abstract

The staphylococcal enterotoxins (SEs) are a family of serologically defined, low molecular mass proteins (26-30 kDa) produced by strains of Staphylococcus aureus. The SEs (designated SEA, SEB, SEC₁, SEC₂, SEC₃, SED, SEE, SEG, SEH and SEI), commonly cause food poisoning in the form of emesis and diarrhea in man, but are also implicated in the pathogenesis of toxic shock-like illness. SEA and SEE are structurally homologous and share common epitopes, although none of these epitopes have been clearly defined in the literature. Twenty antibodies were made in mice against SEA. It was found that one of these antibodies, 1G6, was also reactive to SEE, but not any other SE or toxic shock syndrome toxin-1 (TSST-1). This antibody was used as a tool to identify and characterize a cross-reacting epitope between SEA and SEE. Competition enzyme-linked immunosorbent assay (ELISA) using the whole toxins showed that 1G6 did recognize and compete with SEA and SEE. Using internal deletion mutants of SEA, a possible cross-reacting epitope was localized to the carboxy terminus of the molecule. Competition ELISAs utilizing linear peptides of the C-terminus of these molecules, also showed competition, although this was very weak. Peptide immunizations however, revealed that this region did not elicit an active immunity, although passive protection experiments with 1G6 did show some protective efficacy.