Effect of Ozone on Allergic Airway Inflammation

ABSTRACT Background Exposure to O 3 has been associated with increased risk of exacerbations of asthma, but the underlying mechanisms are not well studied. We hypothesized that O 3 exposure would enhance airway inflammatory responses to allergen and the GSTM1 null genotype would modulate this enhancement. Procedures In a cross-over design, 10 asthmatic subjects (50% with GSTM1 null genotype) who had specific sensitization to Dermatophagoides pteronyssinus (DP) were exposed to 160 ppb O 3 or filtered air (FA) control for 4 h with intermittent exercise on two separate days at least three weeks apart. 20 h post-exposure, endobronchial challenge with DP allergen, and sham normal saline (NS) instillation, were performed in two separate lung lobes. Six h later, a second bronchoscopy was performed to collect bronchoalveolar lavage (BAL) fluid from the DP- and NS-challenged lobes for analyses of cellular and biochemical markers of inflammation. Multiple variable regression was used to compare cell and cytokine responses across the four exposure groups (FA-NS, O 3 -NS, FA-DP, O 3 -DP). Effect modification by GSTM1 genotype was assessed in stratified regressions. Main Findings BAL eosinophil and lymphocyte counts were increased in segments challenged with DP compared to segments that received sham challenges (p<0.01). DP challenge compared to sham challenge also caused a significant increase in BAL concentrations of the Th2 cytokines IL-4, IL-5, IL-10, and IL-13 (p<0.03 for all comparisons). O 3 exposure did not significantly affect BAL cells or cytokine levels although BAL neutrophil count with DP challenge was non-significantly higher after O 3 compared to after FA exposure (p<0.11). Compared to GSTM1-present subjects, GSTM1-null subjects had significantly reduced inflammatory responses including lower eosinophil (p<0.041) and IL-4 (p<0.014) responses to DP challenge after O 3 exposure. Conclusions O 3 appears to have mixed effects on allergen-induced airway inflammation. While O 3 did not cause a clear differential effect on airway cellular or cytokine responses to allergen challenge, those responses did appear to be modulated by the antioxidant enzyme, GSTM1, as evident by the attenuation of airway inflammatory responses to allergen after O 3 exposure in the absence of the gene. HIGHLIGHTS Ozone may increase risk of asthma exacerbation but the exact mechanisms are not clear. Susceptibility to ozone-induced airway inflammation may be associated with GSTM1 genotype. Ozone may enhance allergen-induced airway recruitment of neutrophils. The GSTM1 null mutation may decrease both eosinophil and cytokine allergic airway responses after O 3 exposure.