UCSF

Background

Exposure to ozone (O₃) is associated with increased risk of exacerbations of asthma, but the underlying mechanisms are not well studied.

Objective

We sought to determine whether O₃ exposure would enhance airway inflammatory responses to allergen and the GSTM1-null genotype would modulate this enhancement.

Methods

In a crossover design, 10 asthmatic participants (5 with GSTM1-null genotype) who had specific sensitization to Dermatophagoides pteronyssinus (DP) were exposed to 160 ppb O₃ or filtered air (FA) control for 4 hours on 2 separate days at least 3 weeks apart. At 20 hours after exposure, endobronchial challenge with DP allergen, and sham normal saline (NS) instillation, were performed in separate bronchi. Six hours later, a second bronchoscopy was performed to collect bronchoalveolar lavage (BAL) from the DP- and NS-challenged segments for analyses of inflammatory biomarkers. Linear regression compared cell and cytokine responses across the 4 exposure groups (FA-NS, O₃-NS, FA-DP, O₃-DP). Effect modification by GSTM1 genotype was assessed in stratified regressions.

Results

BAL eosinophil counts were increased in segments challenged with DP compared to sham-challenged segments (P < .01). DP challenge compared to sham also caused a significant increase in BAL concentrations of the T_H2 cytokines IL-4, IL-5, IL-10, and IL-13 (P < .03 for all comparisons). O₃ exposure did not significantly affect BAL cells or cytokine after DP challenge. Compared to GSTM1-present participants, GSTM1-null participants had significantly lower eosinophil (P < .041) and IL-4 (P < .014) responses to DP challenge after O₃ exposure.

Conclusions

While O₃ did not cause a clear differential effect on airway inflammatory responses to allergen challenge, those responses did appear to be modulated by the antioxidant enzyme, GSTM1.