Figure 1.

Puma and Bim are rate limiting for γ-radiation–induced apoptosis of thymocytes in vivo. Animals of the indicated genotypes were exposed to the indicated doses of whole-body γ-radiation and killed 20 hours thereafter. Thymi were harvested and the single-cell suspensions stained with fluorescence-conjugated antibodies to CD4 and CD8 and analyzed by flow cytometry. (A) Representative dot blots of stained thymocyte suspensions from untreated or radiated animals of each genotype indicating the percentage of CD4^-8^-, CD4⁺8⁺, CD4⁺8^-, and CD4^-8⁺ cells. The lower proportion of CD4⁺8⁺ DP cells in the thymus of untreated mice that lack Bim or overexpress Bcl-2 is expected from previous studies.²³,³⁰ (B) Thymic cellularity of untreated or radiated animals was assessed using a hemocytometer and trypan blue staining. (C) The percentage of CD4⁺8⁺ DP cells and total thymic cellularity were used to calculate (D) the absolute number of CD4⁺8⁺ DP thymocytes in control and radiated animals. Bars represent means ± SE of 4 to 10 animals of each genotype and treatment regimen from at least 4 independent experiments. tg indicates transgenic. Statistically significant differences are as follows: (D) 2.5 Gy wt vs Puma^-/- (P < .001), 5.0 Gy wt vs Puma^-/- (P < .001), 2.5 Gy wt vs Bim^-/- (P = .003), 5.0 Gy wt vs Bim^-/- (P = .001), 2.5 Gy wt vs vav-BCL2 (P < .001), 5.0 Gy wt vs vav-BCL2 (P < .001).