Ozone inhalation induces exacerbation of eosinophilic airway inflammation and hyperresponsiveness in allergen-sensitized mice

Background: Ozone (O-3) exposure evokes asthma exacerbations by mechanisms that are poorly understood. We used a murine model to characterize the effects of O-3 on allergic airway inflammation and hyperresponsiveness and to identify factors that might contribute to the O-3-induced exacerbation of asthma. Methods: BALB/c mice were sensitized and challenged with Aspergillus fumigatus (Af). A group of sensitized and challenged mice was exposed to 3.0 ppm of O-3 for 2 h and studied 12 h later (96 h after Af challenge). Naive mice and mice exposed to O-3 alone were used as controls. Bronchoalveolar lavage (BAL) cellular and cytokine content, lung function [enhanced pause (P-enh)], isometric force generation by tracheal rings and gene and protein expression of Fas and FasL were assessed. Apoptosis of eosinophils was quantified by FACS. Results: In sensitized mice allergen challenge induced a significant increase of P-enh and contractile force in tracheal rings that peaked 24 h after challenge and resolved by 96 h. O-3 inhalation induced an exacerbation of airway hyperresponsiveness accompanied by recurrence of neutrophils and enhancement of eosinophils 96 h after allergen challenge. The combination of allergen and O-3 exposure inhibited Fas and FasL gene and protein expression and eosinophil apoptosis and increased interleukin-5 (IL-5), granulocyte-macrophage-colony stimulating factor (GM-CSF) and G-CSF protein levels. Conclusions: O-3 affects airway responsiveness of allergen-primed airways indirectly by increasing viability of eosinophils and eosinophil-mediated pathological changes.