[Experimental study of the pathogenesis of radiation pneumonitis]

Radiation pneumonitis is a well-recognized complication of therapeutic thoracic irradiation that is occasionally fatal. However, its pathogenesis remains unclear. In this report, to define the mechanism of radiation pneumonitis, bronchoalveolar lavage findings and nitroblue tetrazolium reduction of alveolar macrophages were studied and compared with histopathological findings following 40 Gy X-ray irradiation to the right hemithorax of rats. The total number of cells was significantly increased and the percentage of alveolar macrophages was significantly decreased at 28 days after irradiation. At that time, the percentages of lymphocytes and neutrophils were increased and acute inflammatory changes had appeared histopathologically. Nitroblue tetrazolium reduction of alveolar macrophages was significantly increased at 21 days after irradiation. This shows that activation of alveolar macrophages occurs before the completion of radiation pneumonitis, and it is suggested that these activated alveolar macrophages play a major role in the pathogenesis of radiation pneumonitis.