A 21-mer synthetic peptide of toxic shock syndrome toxin 1, TSST-1[58-78], activates T cells by binding to MHC class II and by an MHC unrestricted xenostimulatory pathway.

Toxic shock syndrome toxin-1 (TSST-1) is a "superantigen" which binds to MHC class II molecules and induces a polyclonal stimulation of T cells. In this communication by using a FACS technique and a 21-mer synthetic peptide from the primary sequence of TSST-1 (KGEKVDLNTKRTKKSQHTSEG), designated TSST-1(58-78), we demonstrated binding of the peptide only to cells bearing MHC class II. The proliferative effect of TSST-1(58-78) on human T cells was shown to be inhibited much more by anti-HLA-DR than by anti-HLA class I antibody. Furthermore, human monocytes were able to present TSST-1(58-78) to a mouse VSV specific T cell clone by a xenostimulatory mechanism. These data indicate this peptide to contain an active site of the TSST-1 holotoxin.