AO/EB staining of adherent RAW 264.7 cells revealed that DON exposure (1000 ng/ml, 6 h) induced significant apoptosis concurrent with rRNA degradation (Fig. 5A) . Because RAW 264.7 cells attach to the bottom of the cell culture plate under normal physiological conditions but detach during apoptosis, flow cytometry was additionally employed to measure apoptosis in adherent and suspended cells following DON treatment (Fig. 5B) . Both adherent and total populations contained markedly higher annexin V-positive cells (early apoptotic) (60 and 78%, respectively) than the control total cells (31%). Similarly, the percentage of annexin V/PI-double positive cells (late apoptotic) were much higher in adherent (4.8%) and total (10.8%) populations than that of the control (1.2%).