Viral superantigens.

Viral superantigens bind several alleles and isotypes belonging to the MHC class II and subsequently activate particular T cell families via the varia ble portion of the beta chain of TCR. As a result, a superantigen bridges M HC and TCR molecules, leading to activation of T and B cells. The T expansi on of various TCR V beta subsets is triggered on the basis of their V beta specificity, but not on their antigenic specificity. The best known superan tigens are bacterial endotoxins produced by Staphylococcus aureus. However, viruses such as mouse mammary tumor or rabies viruses encode superantigens too. The ability of superantigens to break the barriers of MHC restriction and to activate large numbers of T and B cells has led to the hypothesis t hat superantigens may activate autoreactive T and B cells to initiate or wo rsen autoimmune diseases such as diabetes, multiple sclerosis, or psoriasis . (C) 2000 Editions scientifiques et medicales Elsevier SAS.