[Stimulation of the immune system by microbial "superantigens"]

The enterotoxins and the toxic-shock-syndrome toxin-1 of Staphylococcus aureus, the erythrogenic toxins of Streptococcus pyogenes as well as a still uncharacterized exoprotein of Mycoplasma arthritidis belong to a family of exotoxins, that have in common a potent mitogenic activity for T lymphocytes of several species. These proteins stimulate CD4(+)- and CD8+ T-lymphocytes by cross-linking the T-cell-antigen receptor with MHC-class-II molecules on accessory or target cells. They are functionally bivalent molecules having distinct interaction sites for variable parts of the T-cell receptor and for nonpolymorphic parts of MHC-class-II molecules. Due to their preferential action on T cells expressing certain V beta-parts of the T-cell receptor the designation "superantigens" has been proposed. The mechanism of T-cell stimulation has apparently been conserved in evolution and has been adapted to the host's T-cell-receptor repertoire. The T cells stimulating activity apparently contributes to the pathogenesis of certain infectious diseases. Noteworthy, mice express endogenous "superantigens" that have similar properties.