[Superantigens and antigen recognition of T lymphocytes]

Superantigens are antigens which can stimulate T cells bound to MHC molecules. The conventional foreign antigens are recognized by the T cell within the MHC peptide binding groove. Superantigens differ from conventional antigens. They bind with high affinity to class II MHC molecules outside the antigen binding groove in the absence of antigen processing. The MHC class II/superantigen complexes on antigen presenting cells trigger the proliferation of T cells expressing the TcR-VB gene products. Superantigens can amplify or suppress immune responses. To date, two main groups of superantigens have been described, namely endogenous and exogenous superantigens. Exogenous superantigens are microbial toxins and other protein products. Endogenous superantigens are the products of unlinked genetic loci in mice the best known of which are the murine retroviral gene products. Toxins of S. aureus and S. pyogenes are the best known exogenous superantigens, implicated in Toxic Shock Syndrome.