Response of mouse lung air-blood barrier to X-irradiation: ultrastructural and stereological analysis.

Male mice of the Balb/c strain were exposed, at an age of three months, to a single dose of 10 or 20 Gy on the right hemithorax. At 3, 4, 6, 9 and 12 months after exposure, lungs were processed for electron microscopy following a standardized procedure in order to allow stereological analysis. By this method, the arithmetical mean thickness and, the air-blood barrier mean thickness in the lung parenchyma was shown to increase quickly with time by oedemization and fibrinization of the septal space. The ratio endothelium/epithelium surfaces (SI/SE) gradually decreased by reduction of both surfaces but this was more marked for Si. The endothelium and epithelium were both highly damaged. Quantitative results indicate that damage to the epithelial cells and mainly to type II, appear at the same time as damage to the endothelium. From the time lapse quantitation it is not possible to determine which one plays the predominant role in the radiation pneumonitis. The strong reaction of the basement membrane and mainly of the interstitial cells could play a decisive role in the evolution of the illness.