(A) Percentage of cells in the G0 and G1 phases after stimulation with the increasing concentrations of GM-CSF (0.1 to 100 ng/mL) in the presence of 10 U/mL of EPO. Growth factor-deprived UT-7/GM cells were cultured under various conditions and obtained for the analysis of the cell cycle. (B) Effect of the increasing concentration of GM-CSF on the proliferation of UT-7/GM cells in the presence of a constant concentration of EPO. Cell proliferation of UT-7/GM was analyzed by MTT assay (see Materials and Methods). Cells were plated at a density of 10⁴/well in IMDM supplemented with 5% FCS and cultured with increasing concentrations of GM-CSF (0.01 to 10 ng/mL) in the presence of 10 U/mL of EPO. MTT reduction was measured after 3 days of culture. The values represent the mean ± SD from triplicate cultures. (C) Suppression by GM-CSF of EPO-induced erythroid differentiation in a dose-dependent manner. UT-7/GM cells were cultured with increasing concentrations of GM-CSF (0.01 to 10 ng/mL) in the presence of 10 U/mL of EPO. Two weeks later, the cells were obtained and stained with dianisidine as described in Materials and Methods. (D) Percentage of dianisidine-positive cells after stimulation with increasing concentrations of EPO. Cells were cultured with increasing concentrations of EPO (0.1 to 100 U/mL). Two weeks later, the cells were obtained and stained with dianidisine. (E) Percentage of cells in the G0 and G1 phases after stimulation with increasing concentrations of EPO. Growth-factor–deprived cells were cultured with increasing concentrations of EPO (0.1 to 100 U/mL) for the indicated periods and then harvested for the analysis of the cell cycle.