Figure 9: Determination of Active TGF-β1 levels in mouse BAL fluid at various times post-initiation of repeated cycles of O2, IR or O2+IR exposure 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 doublehit combination of both challenges (O2+IR) followed by intermittent normoxia (21% pO2) for repeated cycles 3 times a week for 4 weeks. At 1,2,4,8,12,16 and 20 weeks post exposure, BAL fluid were collected. Active TGF-β1 levels were determined by ELISA. Data is represented as mean ± SEM. Letter a indicates p< 0.05 for each challenge condition cohort vs. untreated.