Figure 3: Knock down expression of APE1 promotes intracellular reactive oxygen species (ROS) production after photoirradiation. Intracellular ROS production was measured using DCFH-DA staining and assayed by flow cytometry. A549 cells received 4 kJ/m2 photoirradiation and were collected for ROS assay at 1, 2, and 4 hours after irradiation. ROS production at 2 hours after photoirradiation versus the HpD only control is shown in the histogram.