Loss of the BH3-only protein Puma protects mast cells from apoptosis induced by cytokine deprivation. Survival of mast cells in the absence of cytokines was measured by staining with PI plus annexin V-FITC (A) MLMCs where ◇ indicates wild-type; ▵, Noxa^−/−; ×, Bad^−/−; and ○, Bid^−/−. N = 4-12 (B) CTLMCs where ◇ indicates wild-type; ▵, Noxa^−/−; ×, Bad^−/−; ○, Bid^−/−; and □, Bmf^−/−. N = 2-6 (C) MLMCs where ◇ indicates wild-type; −, vav-Bcl2; ●, Puma^−/−; ▴, Puma^+/−. N = 6 (D) CTLMCs where ◇ indicates wild-type; −, vav-Bcl2; ●, Puma^−/−; ▴, Puma^+/−. N = 3-4 and results are presented as mean (± SD). (E) Expression of Puma was determined by Western blotting of lysates from wt MLMCs and CTLMCs following cytokine deprivation for 10 hours. Probing for Erk or Actin served as a loading control. The results shown are representative of at least 3 independent experiments.