Noxa ablation provides a survival advantage for activated B cells in vivo. (A) The concentration of immunoglobulins in the serum of 12-week-old naive mice (n = 6 per genotype; 1 of 2 experiments is shown). (B-D) Mice were infected intranasally with Influenza A and analyzed 10 days after infection. (Bi) FACS staining of splenic B cells 10 days after infection. Gated is for B220⁺ cells. (ii) Absolute numbers of GC B cells in (top) the spleen and (bottom) the draining (mediastinal, mLN) lymph node was analyzed by FACS. (iii) Representative pictures (100× enlarged) of immunostained splenic sections. B220⁺ (yellow) and PNA⁺ (purple) cells were stained. (C) Mice were infected with influenza and after 10 days injected intraperitoneally with BrdU. Two hours after injection, BrdU incorporation was analyzed by FACS. Histograms of FB and GC B cells in the spleen, stained intracellularly for BrdU are shown (n = 5 per genotype). (D) Direct ex vivo quantification of cells with active caspase-3 in FB and GC B cells, 10 days after influenza infection. (i) FACS plots of splenic B cells stained for cells with active caspase-3 using the Vybrant FAM caspase-3 assay. Gated is for GC B cells (B220⁺CD38^dimCD95⁺). (ii) Quantifications of B-cell subsets with active caspase-3 (n = 3-8 per genotype; 1 of 2 independent experiments with similar results is shown). Mean and SEM are shown (*P < 0,05, **P < .005; Student t test).