Differentiation of primary human erythroblasts in culture. CD34⁺-derived erythroid progenitors were differentiated into erythroblasts and reticulocytes after flow cytometry sorting for transferrin receptor (CD71)–positive cells. (A) Flow cytometry analysis for glycophorin A (gypA) and CD71 on days 10, 14, and 16 of culture. Day 10 (i), day 14 (iii), and day 16 (v) cells were at least 95% positive for erythroid cells. Panels ii, iv, and vi are isotype controls to show antibody specificity. (B) Hematoxylin/benzidine staining of day 10 polychromatic erythroblasts, day 14 early orthochromatic erythroblasts, and day 16 enucleating/reticulocytes. All populations contained hemoglobin (brown staining). Bar represents 20 μm.