Noxa ablation provides a survival advantage for activated B cells in vitro. B cells were purified from mouse spleens and stimulated in vitro with anti-IgM/LPS alone (−IL4) or in combination with 20 ng/mL IL-4 (+IL4). Representative results from one of at least 4 independent experiments are shown. (A) Quantification of apoptotic cell numbers (% annexin V⁺/DNAdye⁺ cells) in the CD38⁺GL7⁺ and CD38^dimGL7⁺ (latter are not present in cultures without IL4) populations is shown after 2 days of stimulation (n = 3 per genotype). (B) FACS plots of B220⁺CD38^dimGL7⁺ cells stained with annexin V and DNA dye after 2 days of stimulation with anti-IgM/LPS and IL-4. (C) CFSE dilution of B220⁺CD38^dimGL7⁺ cells after 2 days of stimulation with anti-IgM/LPS and IL-4. (D) Concentration of soluble IgG1 in the supernatant of cell cultures, determined by ELISA (n = 3 per genotype). Mean and SEM are shown (**P < .005; Student t test)