ROLE OF A CARBOXY-TERMINAL SITE OF TOXIC-SHOCK-SYNDROME TOXIN-1 IN ELICITING IMMUNE-RESPONSES OF HUMAN PERIPHERAL-BLOOD MONONUCLEAR-CELLS

Staphylococcus aureus toxic shock syndrome toxin 1 (TSST-1) is involve d in the pathogenesis of toxic shock syndrome and perhaps other staphy lococcal diseases. Recently, the C-terminal part of the TSST-1 toxin h as been shown to be responsible for mitogenic activity in animal model s. We studied the role of the C-terminal structural unit of TSST-1 wit h regard to proliferation, cytokine release (tumor necrosis factor alp ha [TNF-alpha], interleukin-6 [IL-6], and IL-8), mRMA expression for I L-6, IL-8, IL-10, TNF-alpha and CD40 ligand (CD40L), synthesis of immu noglobulin E (IgE), IgA, IgG, and IgM CD23 expression, and soluble CD2 3 (sCD23) release from human peripheral blood mononuclear cells (PBMC) . For this purpose, we used the recombinant wild-type TSST-1 (p17) mut ant toxin Y115A (tyrosine residue modified to alanine) and toxin H135A (histidine residue modified to alanine). Unmodified toxin p17 and mut ant toxin Y115A, at a concentration below 5 ng, to a lesser degree, in duced a strong proliferation. Toxin p17 followed by toxin Y115A was th e most pronounced inducer for mRNA expression for IL-10 and CD40L and cytokine generation (mRNA and protein) for TNF-alpha, IL-6, and IL-8. Mutant protein H135A failed to activate human PBMC. Bath toxins p17 an d, to a lesser degree, Y115A significantly suppressed IL-4- and anti-C D40-induced synthesis of all four Igs as well as IL-4-induced CD23 exp ression and sCD23 release. Mutant toxin H135A failed to do so. Thus, o ur data show that a region in the C terminus of TSST-1 is responsible not only for mitogenic activity but also for additional immunomodulati ng biological activities of TSST-1. More specifically, histidine resid ue H135A of the 194-amino-acid toxin appears to be critical for the ex pression of biological activities in a human in vitro model.