SPC and COX2 expression in lung tissue sections. Panel A: Percent of pro-SPC-expressing cells expressing COX2. Nearly all pro-SPC-positive AEC2 cells express COX2, except within highly cellularized regions detected within 12.5-Gy irradiated animals at 24 weeks. Panel B: Percent of total cells expressing COX2. A significant decrease in the numbers of COX2-positive cells was observed at 16 and 24 weeks in the 12.5-Gy exposure group. In contrast, at 10 Gy, no significant reduction in COX 2 expression as compared to controls was observed. At 24 weeks, COX2 expression was lower within the 12.5-Gy group as compared to the 0- and 10-Gy-exposed animals of similar age. Panel C: Percent of total cells dual labeled for pro-SPC and COX2. A significant decrease in the number of dual positive cells as a percent of total cells was observed at 16 weeks postirradiation after 12.5 Gy, with a further decrease at 24 weeks, which was similarly maintained at 32 weeks. In contrast, no significant difference between the number of dual-labeled cells was observed between the 10-Gy exposure and controls. At 24 and 32 weeks, the number of dual-labeled cells was significantly higher in the 10-Gy group as compared to 12.5 Gy. *P ≤ 0.05 by one-way ANOVA, and Tukey after hoc analysis. Panel D: Representative images showing expression of pro-SPC (green) and COX-2 (red) co-localized (yellow) to DAPI (blue) stained nuclei. Co-localization of pro-SPC, COX2, and DAPI (yellow) expression is reduced in 10- and 12-Gy irradiated animals compared to age matched controls, and noticeably reduced in 12.5 Gy irradiated lungs at 24 and 32 weeks compared to 32-week controls.