Upper airway inflammation in children exposed to ambient ozone and potential signs of adaptation

In order to investigate nasal inflammation and subsequent adaptation after ambient ozone exposure, nasal lavage (NL) fluid was collected from 170 schoolchildren on 11 occasions (time points) between March and October. Eosinophil cationic protein (ECP), albumin and leukocytes were quantified as markers of nasal inflammation. The highest half-hour outdoor O₃ concentration for each individual on the day prior to the NL was used as a measure of exposure (O₃indiv). To avoid confounding with exposure to common environmental allergens, the study population was restricted to children without sensitization to inhalant allergens. In the initial period of increased O₃ levels in May (time point 4), with a median O₃indiv of 135 μg·m^-3 (5th -95th percentile 100-184 μg·m^-3), the highest medians of all 11 leukocyte and ECP measurements were observed. The highest O₃indiv were observed in June at time point 7 (O₃indiv 173 μg·m^-3, 5th-95th percentile 120-203 μg·m^-3). Cross-sectional analysis of all 11 time points revealed no significant association of O₃indiv on the one hand and ECP, albumin and leukocyte levels on the other. A multivariable model estimated using generalized estimating equations showed a statistically significant association of O₃indiv and leukocytes and ECP as the dependent variable, when time points 1-4 were analysed (p<0.05). In the same model, this association diminished continuously when time points 5-11 were added stepwise, in spite of high O₃ exposure. Not even a tendency towards an O₃ effect could be recognized when time points 1-8 were considered. The results indicate: 1) acute inflammation of the nasal mucosa after the first increase in ambient ozone levels, with 2) a significant dose-dependent increase in leukocyte and eosinophil cationic protein levels, and 3) possible adaptation of the nasal mucosa in spite of constant high levels of ozone exposure in children during the summer season.