Apoptosis of erythroid progenitor cells by LY294002. Day 8 cells that contained 71% ± 5% erythroid progenitor cells were suspended at a concentration of 5 × 10⁵/mL in 1.0 mL serum-free medium supplemented with 2 U/mL EPO with (B) or without (A) 50 μmol/L LY294002. After incubation for 24 hours, cells were collected, washed twice, counterstained with PI and annexin V conjugated with FITC, and then analyzed using FACS Vantage.