Reversible and irreversible airway inflammation and fibrosis in mice exposed to inhaled ovalbumin

Objective and design: We examined the reversibility of several changes in the lungs and airways of mice immediately after exposure to ovalbumin aerosol and after a period of recovery breathing clean air. Methods: Mice were exposed for 1, 2, 4, 6, 8, or 10 weeks, with recovery in clean air for 1-3 weeks. Results: Airway collagen content, exhaled NO, airway mucous cell hyperplasia, and lung lavage inflammatory cell content increased upon exposure to ovalbumin aerosol. All parameters except airway fibrosis decreased partially or completely to control values with recovery in clean air. Conclusions: Airway mucous cell hypertrophy and hyperplasia appear to be completely reversible after recovery in clean air, while exhaled NO and airway inflammation appear to be mostly reversible, except for persistence of lymphocytes in the lung lavage fluid. Airway fibrosis appears to be reversible when mice are exposed to ovalbumin aerosol for periods of up to 4 weeks of exposure, but becomes irreversible after 6 or more weeks of exposure.