Ozone and nitrogen dioxide are significant outdoor and indoor air pollutants that can cause lung damage. Both are termed oxidant gases because the oxygen atoms they contain react with a variety of lung components and produce injury. Dr. Bruce Freeman and colleagues at the University of Alabama, Birmingham examined oxidant injury to alveolar epithelial cells and tested whether supplementing the levels of antioxidants would modify the cells' resistance to damage. The investigators exposed cultures of rabbit alveolar epithelial cells to air or to 95% oxygen (hyperoxia) to study how these exposures affected the levels of antioxidants. To test whether supplementing levels of antioxidants in the alveolar cells would protect against hyperoxic injury, the investigators packages antioxidant enzymes and the antioxidant vitamin E in microscopic lipid membranes, called liposomes, and added them to the cells. They also instilled liposomes into rabbits\' lungs, exposed the rabbits to air or 100% oxygen, and then evaluated changes in the levels of antioxidant enzymes in the lungs.