Bim and Bmf coregulate thymocyte apoptosis in response to stress, but only Bim appears critical for the developmentally programmed death of thymocytes. (A) Representative dot plots from flow cytometric analysis of single cell suspensions of thymocytes from 7- to 9-week-old mice of the indicated genotypes stained with CD4- and CD8-specific antibodies. (B) Sorted CD4⁺CD8⁺ thymocytes from 7- to 9-week-old mice of the indicated genotypes were placed in culture and incubated in the absence or presence of the indicated cell death inducers. Cell viability was assessed over time by AnnexinV/propidium iodide (PI) staining and flow cytometric analysis (Annexin V⁻/PI⁻ cells were considered alive). Data are presented as means ± SEM of ≥4 independent experiments and 4 to 8 animals per genotype. Significant differences by ANOVA (P < .05) at individual time points ^&between WT and Bim^−/−, ^#between WT and DKO, and ^§between Bim^−/− and DKO cells. Due to differences in spontaneous cell death in culture, specific drug-induced killing was calculated using the formula (induced apoptosis − spontaneous cell death)/(100 − spontaneous cell death) (%).