BMP4 + SCF + hypoxia promotes the terminal differentiation (TER119⁺Draq5^low/−) spleen stress erythroid progenitors in vitro. Spleen cells were cultured in Epo at 20% O₂ or Epo + BMP4 + SCF at 2% O₂ (A-B) or in the indicated conditions (C) in liquid culture. (A). Viable cells were determined by trypan blue staining on the indicated days of culture. (B). Cells were stained on days 0 and 5 of culture for TER119 and Draq5. The top panel shows representative flow diagrams and the bottom panel shows the total number of Ter119⁺Draq5^low/− cells in the culture at days 0 to 5. (C). Cells were grown in the indicated conditions, and the total number of Ter119⁺Draq5^low/− cells in the culture is shown at day 4. The flow diagrams for this graph are presented in Figure S2. These data are representative of 3 independent experiments.