Epo dose-dependent increases in TUNEL-positive EPCs from EpoR-HM mice. Marrow preparations from EpoR-HM and wt-EpoR mice were cultured in the presence of Epo at 0, 0.1, or 1.6 U/mL. At 42 hours of culture, cells were processed through TUNEL reactions and stained for Ter119 expression. As compared with wt-EpoR controls, Ter119-positive EPCs from EpoR-HM mice had increased frequencies of TUNEL-positive cells (eg, 32.3% TUNEL-positive EpoR-HM EPCs versus 15.1% TUNEL-positive EPCs for wt-EpoR at 0.1 U/mL Epo). Percents are frequencies of TUNEL-positive cells among Ter119-positive EPCs.