A, induction of caspase 3/7 activity after a single dose of ionizing radiation. MOC1 cells were irradiated and cultured for 12 hours before caspase 3/7 detection reagent added. Representative photomicrographs at 20× magnification. TNFα (100 ng/mL) used as positive control. Quantification from 10 HPFs per condition. B, induction of apoptosis and necrosis after a single dose of ionizing radiation. MOC1 cells were irradiated, cultured for 24 hours, harvested, and immediately stained and analyzed via flow cytometry. Late apoptosis/necrosis defined as annexin V and 7AAD double positive; early apoptosis as annexin V positive but 7AAD negative. Representative results from one of at least three independent experiments are shown. **, p,0.01; ***, p<0.001.