Analysis of the mitogenic effects of toxic shock toxin on human peripheral blood mononuclear cells in vitro

It has been shown previously that the staphylococcal enterotoxins A and B are T-cell mitogens and also cause inhibition of murine plaque-forming cells generated in vitro. Similarly, toxic shock toxin, a 24,000-MW protein produced by toxic shock-associated strains of Staphylococcus aureus, is mitogenic and inhibits the generation of both murine and rabbit plaque-forming cells. In this study, an analysis of the T-cell response to toxic shock toxin was performed. Human peripheral blood mononuclear cells responded to toxic shock toxin over a broad dosage range (1 ng/ml to 5 μg/ml) with maximum proliferation at day 4 (96 hr) of culture. Heat treatment (100°C for 60 min) of toxic shock toxin attenuated its mitogenic effects by only a small amount, and this attenuation could be reversed with increasing concentration of the toxin. By cytofluorography, both untreated and toxic shock toxin-treated small lymphocytes manifested normal percentages of OKT3 +, OKT11 +, OKT4 +, OKT8 +, HLA DR + , and Leu-7 + cells. However, toxic shock toxin-induced blasts were 99% OKT11 + and expressed the receptor for interleukin 2 (89%–100% TAC +). Approximately 85% of the blasts were OKT4 +, and 25% of the blasts were OKT8 +. Proliferation of purified, double-rosetted T cells was enhanced monotonically by the addition of irradiated “non-T” cells. Irradiated, monocyte-enriched non-T cells were 2.5 times more potent than unfractionated non-T cells in producing quantitatively similar proliferation by toxic shock toxin-stimulated, autologous T cells. In addition, preincubation of non-T cells for 24 hr with toxic shock toxin, followed by extensive washing and irradiation, induced substantial proliferation by unexposed, autologous T cells. These data show that toxic shock toxin is mitogenic for T cells and requires accessory cells for maximal activity. Further, this substance appears to induce both a subset of OKT4 + (Class II MHC-restricted) and OKT8 + (Class I MHC-restricted) blasts.