AID^−/− B cells show increased proliferation and decreased apoptosis when stimulated ex vivo. (A) B220⁺ cells were harvested from the spleens of age-matched WT and AID^−/− mice. Cells were incubated with CFSE, and proliferation was monitored daily for 96 hours in response to BCR/CD40 engagement. CFSE dilution plots are shown for the 3 replicates 96 hours after stimulation. Stimulated cells were also monitored for apoptosis through the measurement of annexin V binding (B) and caspase 3 activation (C). Representative plots are shown for BCR/CD40-stimulated WT and AID^−/− B cells at 96 hours after stimulation. Statistics represent comparisons between WT and AID^−/− cells over time. Data are mean ± SD of n = 3 mice per genotype.