Appearance of erythroid progenitors cultured in EPO and EST on day 7 and day 14. (A) Representative fields of Giemsa-stained erythroid cells. Identical magnification (× 63) was used for all the microscopic fields to demonstrate the decrease in erythroblast size associated with terminal differentiation. (B) Flow cytometric analyses of cells simultaneously stained with anti-transferrin receptor (CD71) and anti-glycophorin A (GPA) antibodies. The percentage in the right upper quadrant of each panel describes the population staining positive for GPA and CD71. (C) Summary of cell-cycle analyses. Bars with standard deviation denote mean percentage values for G₀/G₁ (▦), S (▪), and G₂/M (□) populations from experiments performed on 3 separate donors.