Effect of nitrogen dioxide on ovalbumin-induced allergic airway disease in a murine model

The effect of exposure to irritant air pollutants on the development of allergic airway disease is poorly understood. This study examines the effects of the lower respiratory tract irritant, NO(2), on the outcome of ovalbumin (OVA)-induced allergic airway disease. Male and female C57Bl/6 mice were sensitized by weekly intraperitoneal (ip) OVA injections for 3 wk followed by daily 1-h OVA aerosol inhalation challenge for 3 or 10 d. Initially, mice were exposed daily for 3 d to air or 0.7 or 5 ppm NO(2) for 2 h following each OVA aerosol challenge. OVA exposure resulted in pronounced lower airway inflammation, as evidenced by a significant increase in bronchoalveolar lavage (BAL) total cellularity and eosinophil levels. BAL eosinophil levels were significantly lower in OVA-NO(2) compared to OVA-air animals. The reduction was similar at both NO(2) exposure concentrations. In a subsequent study, sensitized animals were exposed for 3 or 10 d to aerosolized OVA followed by air or 0.7 ppm NO(2). BAL eosinophils were again reduced at 3 d by OVA-NO(2) exposure compared to OVA-air mice. At 10 d the eosinophilia was virtually abolished. This reduction in OVA-induced cellular inflammation by NO(2) was confirmed by histopathological analysis. Contrary to expectations, exposure to NO(2) during the aerosol challenge to OVA dramatically diminished the outcome of allergic disease in lungs as measured by airway cellular inflammation.