In vitro systems for exposure of lung cells to NO2 and O3

In vitro studies of the effects of NO2 and O3 require development of methods for separation and culture of those lung cells that experience in vivo exposure, and also the design and construction of systems for controlled exposure of the cells to known concentrations of the gases. Separation of lung cell types has been accomplished by enzymatic dispersal of lung tissue and centrifugation of the mixed cells on media of various densities in order to separate the cells on the basis of buoyant density or sedimentation rate. The application of centrifugal elutriation has enabled separation of type II alveolar cells and Clara cells with a high degree of purity. Alveolar macrophages and endothelial cells have also been obtained in good yield. Exposure of cultured cells to test atmospheres requires precise control of pollutant levels, close contact of cells and gas without an intervening layer of medium, capability for prolonged exposure, and maintenance of sterile conditions, so that recovered cells can be cultured further or studied for other biological activity. Systems which meet these criteria include roller bottle cultures, petri dish cultures on rocker platforms, cell cultures on cellulose filters fed by perfusion of medium from the side opposite the cells, and cells grown in dishes with gas-permeable film bottoms. Systems that rely on solution of the gases in the overlaying medium do not resemble exposure conditions in vivo, and may not be suitable for studying effects of the poorly soluble oxidant gases. The cell exposure systems have not been used extensively for studies of the effects of pollutants on freshly isolated specific lung cell types. Such studies should be encouraged.