Enhanced sensitivity to receptor-mediated cell death by sub-lethal irradiation is apoptotic.

<p>Kinetics of dead and apoptotic cells were analyzed by annexin V–PE/7AAD staining of cells and flow cytometry. A–F. WiDr tumor cells were mock-irradiated (0 Gy) or irradiated with 5 or 10 Gy and re -cultured for 72 h. Cells were harvested and incubated with the indicated concentrations of Fas crosslinking antibody CH11 (A–C) or IgM isotype control antibody (D–F) for 5 h. Percent of apoptotic cells are represented in the upper left quadrant as Annexin-V⁺ and 7AAD⁻. B. Induction of apoptosis (Annexin-V⁺ and 7AAD⁻) following Fas receptor signaling in SW620 cells 120 h post-IR. Cells were treated with 1 µg/ml of CH11 mAb for 5 h. C. Induction of apoptosis (Annexin-V⁺ and 7AAD⁻) following TRAIL receptor signaling in HCT116 cells 72 h post-IR. Cells were incubated with 100 ng/ml of recombinant TRAIL protein for 5 h. Experiment was repeated 3 times with similar results.