Normal Fas-induced apoptosis but defective AICD in T-cell blasts from the patient. (A) Fas-mediated apoptosis was induced in T-cell blasts from 3 healthy controls and from the patient using different concentrations of anti-Fas mAb. Results are mean ± SD on T-cell blasts from 3 healthy controls or in 3 experiments performed with T-cell blasts from the patient. (B) Day 6 T-cell blasts from healthy controls or from the patient, as indicated, were incubated at 2 × 10⁶ cells/mL during 12 hours with control medium, 5 μg/mL PHA (left panel), or different concentrations of PHA (0.1-5.0 μg/mL) (right panel), always in the presence of 30 UI/mL IL-2. Left panel: Cell death was estimated by trypan blue and PI staining, with identical results, and results are the mean ± SD of triplicate determinations on cells from 4 healthy controls or in 4 different experiments performed with T-cell blasts from the patient. *P = .011. Right panel: In one experiment, ΔΨm was determined by DiOC₆³  staining and flow cytometry.