Antibiotics induce apoptosis but not cell cycle suppression in B-cell progenitor populations. (A) BrdU incorporation was determined for Ctrl- and Abx-treated mice in the early B-cell progenitors, and pre–pro-B, pro–B, and pre–B cells, in the BM. (B) Proportion of annexin V–positive BM B-cell progenitor cells was determined in Ctrl- and Abx-treated mice. (C) Proportion of live cells and annexin V–positive cells from B220⁺ B cells in the peripheral blood. (D) Proportion of live cells and annexin V–positive cells from B220⁺ B cells in the spleen. (E) Proportion of cells positive for the fluorescent reporter (FAM) in the FLICA assay as a measure of caspase activity for quantification of cell apoptosis. For panel A, the Kruskal-Wallis test was used to test statistical significance between groups of interest; and for panels B-E, the Mann-Whitney U test was used. Data are displayed as ± SEM from 2 independent experiments. ∗P ≤ .05; ∗∗P ≤ .01; ∗∗∗P ≤ .001; ∗∗∗∗P ≤ .0001.