Immunological aspects of infections part 20

BACTERIAL SUPERANTIGENS

Among the toxins secreted by bacteria is a special group from the streptococcal and staphylococcal family of toxins called superantigens (SAg). Instead of binding to the specific antigen receptor known for most antigens, these toxins bind to the lateral surface of both the T-cell receptor and the MHC. Thus, in contrast to a conventional  peptide antigen, which stimulates only one in 10(4) to 10(8) T cells, the superantigen may bind up to approximately 1:50 T cells. The result is a veritable explosion of cytokines resulting in high fever, hypotension, and multiorgan shock. Death often occurs within 24 hours of the release of these toxins. The most widely studied superantigens are produced by Staphylococcus aureus and group A streptococcus. These superantigens bind the T cell receptor at its β region, and that exact Vβ region is different for each superantigen.