TSST-1-induced AICD. T cells from healthy controls were activated with either anti-CD3 or TSST-1 as described in “Fas and activation-induced cell death sensitivity.” (A) Day 9 activated lymphocytes were double stained for CD3 and TCR-Vβ2 expression or for CD95 expression (gray histograms). One representative experiment of 5 is shown. The proportion of CD4⁺ T cells is not significantly different in anti-CD3-activated (61.4% ± 19.1%) vs TSST-1-activated (58.5% ± 11.9%) blasts (data not shown). Numbers on the plots are percentages of total cells. (B) T cells were reactivated (2°) at day 9 after initial stimulation (1°) by plate-bound anti-CD3 (░) or soluble TSST-1 (■) for 18 hours. At the same time, sensitivity to Fas-induced apoptosis was assessed using cross-linked agonistic anti-CD95 (APO1.3) mAb (□). Apoptosis was determined as described in “Apoptosis detection.” Values are the means (± [SEM]) of duplicated determinations of 5 independent experiments with 5 unrelated donors. ns indicates not significant; **P < .005; and ***P < .001.