Superantigens as immunogens and tolerogens.

Superantigens are a family of proteins that are receiving a great deal of attention as a group of potent immunomodulatory molecules. They combine with MHC class II molecules to form the ligands that stimulate T cells via the V beta element of the T cell receptor. Two groups of superantigens have been described: those expressed endogenously such as the mouse mammary tumour virus (MMTV) and the exogenously derived products such as the Staphylococcal enterotoxins. Here we review the interactions between the superantigens and MHC class II molecules, the mechanisms of T cell activation, the role of superantigens in the induction of tolerance and their involvement in autoimmune diseases.