Growth arrest and apoptosis of πBCL₁ cells treated with external beam irradiation and MoAb. πBCL₁cells were either treated with 2 Gy external beam irradiation, or remained untreated, before being cultured for 72 hours in 24-well plates, which were either coated (or uncoated) with MoAb as indicated. The cells were then harvested after 72 hours, stained with PI to detect DNA content, and analyzed by flow cytometry. (A) Flow cytometry histograms for one typical experiment. The horizontal bars show the gated areas representing fragmented DNA (indicative of apoptosis). The percentage of DNA within each gate is shown. (B) Average (+SD) of three similar experiments to that in Fig 7A. The * indicates statistical significance (P < .01) over other combinations of MoAb and irradiation.