Radiation-induced strain differences in mouse alveolar inflammatory cell apoptosis

Whole-thorax irradiation results in the development of the diffuse inflammatory response alveolitis in C3H/HeJ (C3H) mice and a milder alveolitis with fibrosis in C57BL/6J (B6) mice. In this study, we investigate if this mouse strain difference in response to radiation is due to differences in lung inflammatory cell apoptosis. Mice of the C3H and B6 strains were given a radiation dose of 18 Gy to the thorax and the animals were sacrificed at 11 or 18 weeks following exposure or when they were moribund. Active caspase-3 staining was used to identify apoptotic cells in the alveolar space of histological lung sections from the mice. The apoptotic index of B6 mice was greater than that of C3H mice at 11 weeks postirradiation (17.8% of airspace cells vs. 7.8%, p = 0.028) and in mice sacrificed because of illness (27.3% vs. 14.4%, p = 0.036). No C3H mice survived to the later time point. The inflammatory cells undergoing apoptosis in the mouse lungs were morphologically consistent with alveolar macrophages. We ...