Analysis of mast cell survival. (A,C) Survival of wild-type, Apaf-1^-/-, caspase-9^-/-, and Bcl2 transgenic mast cells in the absence of cytokines or (B) during treatment with 10 μg/mL etoposide. Cell viability was measured by exclusion of PI (A,B) or by staining with PI plus annexin V-FITC (C). (A-B)▪ indicates wild type; •, Apaf-1^-/-; ▴, caspase-9^-/-; and ○, vav-Bcl2. (D) Expression of caspases and the caspase inhibitor XIAP as determined by Western blotting of lysates from wild-type thymocytes (T) and wild-type fetal liver-derived mast cells (M). Probing for actin served as a loading control. (E) Cytokine-induced proliferation of wild-type, Apaf-^-/-, caspase-9^-/-, and Bcl2 transgenic fetal liver-derived mast cells following cytokine deprivation for 24 hours. Cells were enumerated 6 days after re-addition of cytokine or after 6 days of cytokine deprivation, and cell numbers are expressed relative to the initial number of cells in the culture. □ indicates no delay in re-addition; ▪, 24 hours delay; and ▦, cytokines never added. Graphs indicate mean ± SD (in panel A, n = 19, wild type; n = 4, Apaf-1^-/-;n = 4, caspase-9^-/-;n = 3, vav-Bcl2;in panel B, n = 11, wild type; n = 3, Apaf-1^-/-;n = 4, caspase-9^-/-;n = 3, vav-Bcl2;in panel E, n = 3 for all genotypes, except n = 4 for caspase-9^-/-).