Figure 4: Kinetics of inflammatory cell activation and oxidative damage in (Panel A) Mice were exposed to 100% O2 for 8 hours only (O2), 0.25 Gy total body ionizing gamma irradiation (IR) only, or a double-hit combination of both challenges (O2+IR) followed by 16 hours of normoxia (21% pO2) for a single cycle. Whole blood was collected and leukocyte analysis of MPO, CD41, and CD18 was performed using flow cytometry. (Panel B) Separate cohorts of mice (n=5-15 / group) were exposed to 100% O2 for 8 hours only (O2), 0.25 Gy total body ionizing gamma irradiation (IR) only, or a double-hit combination of both challenges (O2+IR) followed by intermittent normoxia (21% pO2) for repeated cycles 3 times a week for 4 weeks. Mice were sacrificed at weeks 1, 2, and 4 weeks (early) and 8, 12, 16, and 20 weeks (chronic). Oxidative modification of lung tissues was measured by determining MDA levels in lung. Data is represented as mean fold change from untreated at each respective time point ± SEM. Letter a indicates p< 0.05 for all challenges vs. untreated at each respective time point. Letter b indicates p< 0.05 for O2+IR vs. O2 at each respective time point. Letter c indicates p< 0.05 for O2+IR vs IR at each respective time point.