Impaired TCR-mediated apoptosis of activated WASp-deficient CD4⁺ T lymphocytes. (A) Specific cell death of activated CD4⁺ T cells from WT and WASp deficient mice restimulated with the indicated concentrations of plate-bound anti-CD3 mAb for 6 hours and measured by annexin V and PI staining. The data are average and SEM of 5 independent experiments with age- and sex-matched mice on the 129 backgrond. Apoptosis measurements were performed in triplicate for each sample. Results of unpaired t test comparisons of cell death at each dose of anti-CD3 are shown as *P < .05, **P < .005, ***P < .001. (B) Surface TCR, Fas on activated CD4⁺ T cells from WASp-deficient and control mice activated as in panel A. (C) Proliferation of WT and WASp-deficient T cells activated in the presence of exogenous IL-2 as in panel A measured by ³H-thymidine incorporation at 72 hours. (D) Cell death of WASp-deficient and control T-cell blasts after addition of the indicated concentrations of Mega-FasL (an oligomerized biologically active form of soluble FasL). (E) Viable cell number during IL-2 cytokine deprivation (cRPMI) or with IL-2 measured by trypan blue exclusion. (F) Cell viability measured by PI and DiOC of WASp-deficient and control CD4⁺ T cells during IL-2 cytokine withdrawal. (E-F) Data are representative of 2 independent experiments.