Radiation induced secretion of surfactant from cell cultures of type II pneumocytes: an in vitro model of radiation toxicity.

The pathogenesis of pneumonitis and fibrosis secondary to lung irradiation is incompletely understood. The role of the type II alveolar epithelial pneumocyte in these processes has been under investigation. The type II pneumocyte has been shown in vivo to respond to radiation induced injury with release of pulmonary surfactant. The effect of irradiation on cell cultures of type II pneumocytes was studied to determine if this could be reproduced in vitro. Type II pneumocytes were found to release surfactant material with a threshold of radiation dose between 1000 and 1500 rad. This is similar to the dosage range over which the same effect has been demonstrated in vivo. Experimental results support the concept that the release of surfactant is not due to either cell disruption or non-specific release of phospholipid from cell membranes. Irradiation appears to trigger membrane receptor mediated surfactant release. In addition, irradiation abolishes the ability of cells to subsequently respond to a physiologic agonist, suggesting radiation induced damage to the secretory mechanism. These studies establish that surfactant release in response to irradiation in vivo is a direct effect on type II pneumocytes. Cell cultures of type II pneumocytes can serve as a laboratory model of lung cell radiation toxicity.