Study objectives: The purpose of this study was to examine the effects of NO2, a major component of air pollution, on airway eosinophilic inflammation and bronchial hyperreactivity, using a mouse model of asthma.
Setting and subjects: BALB/c mice (eight mice per experimental group) were studied in a basic research laboratory at the University of Iowa.
Interventions: Using a standard murine model of asthma, BALB/c mice were sensitized to ovalbumin (OVA) by intraperitoneal (IP) injections (days 1 and 7) and were challenged with aerosolized OVA (days 13 and 14). Some mice were exposed to NO2 (2 ppm) in an exposure chamber for 24 h before undergoing OVA aerosol challenge. A control group was exposed to OVA alone.
Measurements and results: The outcomes assessed included airway inflammation, bronchial hyperreactivity to inhaled methacholine, and goblet cell hyperplasia. We found that NO2 exposure modestly increased airway neutrophilia but not airway eosinophilia in OVA-exposed mice. These mice exhibited epithelial damage and loss of epithelial mucin. Surprisingly, nonspecific bronchial hyperreactivity (ie, enhanced pause index) was not increased, although baseline smooth muscle tone was increased (p < 0.05) in the mice exposed to NO2.
Conclusions: These data indicate that relatively short-term (24 h) exposure to NO2 causes epithelial damage, reduced mucin expression, and increased tone of respiratory smooth muscle. Reduced mucin production may be a mechanism of injury following long-term exposure to inhaled NO2. Despite enhancing epithelial damage in OVA-exposed mice, NO2 exposure does not otherwise alter the expression of allergen-induced airway responses.