Dose- and time-dependent inhibition of day-5 ECFCs by IFNγ. Day-5 ECFCs were incubated in liquid medium with rhIFNγ from 0 to 1,000 U/mL. After 96 hours of incubation, the cells were collected and the number of cells was counted (A), or the cells were cultured with or without 1,000 U/mL rhIFNγ and harvested at the indicated times. (B) The number of total cells in each control without rhIFNγ was taken as 100% and was compared with that of the rhIFNγ groups. Each graph represents the mean from two experiments. The purity of the day-5 ECFCs, determined by plasma clot assay, was 54% ± 6% (A) and 56% ± 9% (B).