The proposed research is a continuation of ongoing studies concerning pulmonary cell renewal as related to tissue injury and repair. Three areas of study are proposed. In the first, we will determine if the proliferative response following injury is a quantitative measure of the amount of injury. This will be accomplished by correlating the proliferative response with morphometric measurements of the amount of tissue damage following exposure to NO2. In the second area, we will test the ability of dietary vitamin E and selenium to alter the amount of lung damage. This will be accomplished by quantitating the amount of injury following exposure to NO2 of rats with diets supplemented and deficient in these antioxidants. In the third area, we will determine if tolerance in the epithelium of rats exposed to NO2 is associated with increased turnover or accumulation of cells. This will be accomplished by measuring the proliferative response and differentiation of Type 2 cells to Type 1 cells and nonciliated bronchiolar cells to ciliated cells in the epithelium tolerant to NO2.