FACS analyses of splenic erythroblasts at different maturation stages from naive or P chabaudi AS–infected mice, either untreated or treated with 10 units of rmEPO per day for 3 days. Erythroblasts at different maturation stages were identified by double staining with PE-conjugated anti-TER119 and FITC-conjugated anti-CD71 antibodies in naive mice (A), naive mice treated with EPO (B), infected mice (C), and infected mice treated with EPO (D). Region I: The CD71^highTER119^low population represents proerythroblasts, the least mature type of the erythroblasts. Region II: The CD71^highTER119^high population represents basophilic erythroblasts. Region III: The CD71^low-medTER119^high population represents polychromatic and orthochromatic erythroblasts, the mature Hb-producing cells. Region IV: CD71^medTER119^– represents the nonerythroblast population that expresses CD71. Values represent frequencies of splenocytes in each region. Data are means ± SEM of 3 to 5 mice per group. When 2 sets of data are labeled with superscripts of different lowercase letters, it indicates that these 2 sets of data are statistically different (P < .05). Similar results were obtained in 2 independent experiments.