Injury of lung alveolar cells by lysolecithin

Lysolecithin derived from the dipalmitoyl lecithin of lung surfactant is a potential cytotoxic and mitogenic agent for alveolar epithelial cells. In order to examine this prospect experimentally we introduced lysolecithin into lungs of mature mice in concentrations between 0.02 and 5.0 mg/ml. Electron microscopy demonstrated that lysolecithin at concentrations above 0.1 mg/ml lysed type I cell processes and cell bodies, whereas type II cells were more resistant and were not usually lysed in mice given 1 mg/ml of lysolecithin. Autoradiography based on the incorporation of tritiated thymidine was used to identify proliferating type II cells. With high concentrations of lysolecithin (0.1–1.0 mg/ml), increased labeling of type II cells was observed. Low concentrations (less than 0.1 mg/ml) did not stimulate type II cell labeling. We conclude that the type I cell is not unusually resistant to the lytic effect of lysolecithin, that the type II cell is more resistant than the type I cell, and that levels of lysolecithin which are not grossly injurious are not clearly mitogenic for type II cells.