Selective stimulation of human T cells with streptococcal erythrogenic toxins A and B

Streptococcal exotoxins have been implicated in the pathogenesis of a toxic shock-like syndrome and scarlet fever. Previous studies have demonstrated that these toxins are potent stimulators of human T cells and have structural homology to staphylococcal enterotoxins. In the current study, we investigated the mechanism by which streptococcal erythrogenic toxins type A (SPEA) and B (SPEB) activate T cells and compared it with anti-CD3 and the known "superantigen" staphylococcal enterotoxin B. SPEA was found to selectively activate T cells bearing V beta 8, V beta 12, and V beta 14, whereas SPEB selectively activated T cells bearing V beta 2 and V beta 8. Furthermore, fibroblasts transfected with MHC class II molecules were capable of presenting SPEA and SPEB to purified T cells. The T cell response to these toxins, however, was not MHC-restricted. Although the streptococcal exotoxins stimulated both CD4+ and CD8+ T cells, SPEA but not SPEB stimulated the CD4+ T cell subset proportionately more than the CD8+ T cell subset. Our results indicate that SPEA and SPEB, like the staphylococcal enterotoxins, are superantigens and suggest a mechanism by which they may mediate particular systemic syndromes associated with streptococcal infections.