PS exposure of NB4 and APL cells. Cells were costained with PI and either FITC–annexin V or FITC-lactadherin. (A) The cells were incubated with indicated concentrations of DNR for 24 hours. Percentage of annexin V/lactadherin-binding cells was analyzed by flow cytometry. After treatment with 1μM DNR, ∼ 75% of NB4 cells and 80% of APL cells were positive for lactadherin. (B) The plasma membrane of APL cells displayed green fluorescence when stained by FITC–annexin V (left) or FITC-lactadherin (right). Cell nuclei displayed red fluorescence when labeled by PI. Co-stained areas appeared yellow. Scale bars represent 10 μm.