Effect of whole-body irradiation on phagocytic activity of rat alveolar macrophages

The phagocytic activity of rat alveolar macrophages was studied in vitro for up to six weeks after whole-body gamma irradiation (7.5 Gy). Ingestion of fluorescent latex microspheres was evaluated using both microscopic examination and flow cytometric quantitation. After a transient decrease on first day post-irradiation, a slight increase in the phagocytic ability was observed from day 14 to day 28, with a maximum on day 21. From day 35 onwards, phagocytic capacities returned approximately to those of the controls. The percentage of phagocytic cells (cells having ingested one microsphere or more) increased by 75 per cent on day 21 after irradiation and the phagocytic index (percentage of phagocytic cells X the average number of ingested microspheres per cell) increased by 250 per cent while at the same time, the number of recovered alveolar cells decreased by 37 per cent. The augmentation of phagocytic capacities after irradiation was particularly characterized by an increase in the percentage of cells ingesting more than five microspheres. Flow cytometric studies showed a significant increase in mean cell size on day 21 post-irradiation. The augmentation of the phagocytic activity was not found when macrophages from control rats were incubated with serum or alveolar lavage fluid from an irradiated donor. Augmentation of phagocytic capacity was also observed after 8.5 Gy but no effect could be observed after 6.5 Gy.