5-FU treatment leads to defective reticulocyte exit from the BM into circulation. (A) Wild-type mice received 1 5-FU injection on day 0 (150 mg/kg) and mice were analyzed at various times during recovery (at 2, 4, 8, 12, and 16 days). BM cells were stained with anti-CD71 and anti-Ter119 antibodies (upper panels) and PB were stained with thiazole orange (lower panels) and analyzed by flow cytometry to characterize the distribution of either the CD71/Ter119 subsets of erythroid cells or to enumerate the absolute reticulocyte number, respectively. On each day, 4 to 5 mice were analyzed. (B) Changes in the absolute number of reticulocytes in the BM (1 femur + 1 tibia) and PB of 5-FU-treated or untreated (d0) mice. Data are shown as mean ± standard deviation and 4 to 5 mice were analyzed. (C) Histology of control and 5-FU-treated mice by H&E staining. Venous sinuses (marked with asterisks). Bar = 20 μm. (D) Changes in PB red blood cell counts in 5-FU-treated and untreated (d0) mice after a single 5-FU injection. Data are shown as mean ± standard deviation and 4 to 5 mice were analyzed. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; unpaired Student t test. H&E hematoxylin and eosin; n.s., not significant; RBC, red blood cell; Retic, reticulocyte; SSC, side scatter.