Epo-responsive erythroblast subsets in bone marrow and spleen. Wild-type mice were injected with a single dose of Epo (50 mg/kg) or an equal volume of saline, and followed for up to 96 hours. Bone marrow and spleen cells were freshly isolated and analyzed. The results of 7 independent experiments were pooled. Each data point is the mean ± SEM of 2 to 9 mice. Each experiment contained mice of a single sex or an equal number of females and males. There was no significant difference between the Epo response of male and female mice. (A-C) Epo caused a transient increase in spleen weight (A), hematocrit (B), and in the proportion of Ter119⁺ cells in both bone marrow (Ci) and spleen (Cii). (D-E) Examples of flow cytometric histograms of bone marrow (D) and spleen (E) cells labeled with Ter119 and CD71 antibodies and analyzed as illustrated in Figure 1. There is a clear increase in the proportions of the ProE and Ery.A subsets in both tissues, with a moderate increase in Ery.B. (F) Changes in the relative frequencies of erythroblast subsets within the Ter119⁺ compartment in bone marrow or spleen, following Epo injection or a control saline injection. Data were analyzed as illustrated in panels D-E, and mean values for data pooled from 7 experiments are presented.