Objective: We sought to determine whether nitrogen dioxide (NO2) can enhance airway inflammation after allergen challenge in asthmatic subjects.
Methods: Fifteen house-dust-mite (HDM)-sensitive asthmatic subjects were exposed for 3 hours to filtered air or 0.4 ppm NO2, followed by inhalational challenge with HDM allergen. Markers of inflammation were measured in sputum at 6 hours and 26 hours after allergen challenge.
Results: After exposure to NO2, eosinophil concentration decreased significantly in the 6-hour postallergen sputum. No significant NO2-related difference was observed for other variables.
Conclusions: Our results suggest that, in most asthmatic individuals, multi-hour exposure to a high ambient concentration of NO2 does not enhance the inflammatory response to subsequent inhaled allergen as assessed by cell distribution in induced sputum. Because the decrease in airway eosinophils has been reported in previous animal studies, future research should be directed toward the mechanism of this effect.