Ozone exposure increases eosinophilic airway response induced by previous allergen challenge

We investigated whether exposure to ozone (O-3) 24 hours after an allergen challenge test would increase airway eosinophilia induced by allergen in subjects with mild asthma with late airway response. Twelve subjects with mild atopic asthma participated in a randomized, single-blind study. Subjects underwent allergen challenge 24 hours before a 2 hour exposure to O-3 (0.27 ppm) or filtered air. Pulmonary function was monitored during the allergen challenge and after the exposure to O-3 or air. Six hours later, induced sputum was collected. After 4 weeks, the experiment was repeated with the same subjects. Allergen induced a comparable late airway response in both challenges. O-3 exposure induced a significant decrease in FVC, FEV1, and vital capacity, and was associated with a significant increase in total symptom score compared with air exposure. The percentage of eosinophils, but not the percentage of neutrophils, in induced sputum was significantly higher after exposure to O-3 than after exposure to air (p = 0.04). These results indicate that O-3 exposure after a late airway response elicited by allergen challenge can potentiate the eosinophilic inflammatory response induced by the allergen challenge itself in subjects with mild atopic asthma. This observation may help explain the synergistic effect of air pollution and allergen exposure in the exacerbation of asthma.