The effect of prolonged exposure to NO₂ from birth on airways responsiveness in rabbits sensitized at birth

Our aim was to determine whether daily exposure to 4 ppm nitrogen dioxide (NO2) from birth until 3 months of age influenced the development of airways hyperresponsiveness and atopic sensitivity in immunized rabbits. Littermate New Zealand White (NZW) rabbits were immunized within 24 h of birth by i.p. injection of house dust mite antigen in AI(OH)(3) gel, and exposed to either ambient air or 4 ppm NO2 for 2 h . day(-1), 5 days . week(-1). At 3 months, bronchoalveolar lavage (BAL) and serum samples were obtained. Airways responsiveness was measured as the provocative concentrations (mg . ml(-1)) of histamine or methacholine required to elicit a 50% increase in airway resistance (RLPC50) and a 35% decrease in dynamic compliance (CdynPC35). There were no differences in total cell or differential cell counts recovered in BAL fluid between control and NO2 exposed animals. Airways responsiveness did not differ between groups of animals (histamine RLPC50 values: air (n=15) versus NO2 (n=13), respectively, 9.98+/-1.32 versus 16.43+/-1.45 mg . ml(-1); CdynPC35 values: 16.60+/-1.44 versus 14.95+/-1.43 mg . ml(-1); methacholine RLPC50 values: air (n=14) versus NO2 (n=12), respectively, 2.18+/-1.51 versus 2.21+/-1.32 mg . ml(-1); CdynPC35 values: 2.64+/-1.41 versus 2.85+/-1.31 mg . ml(-1)). There was no difference in sensitization between groups of animals exposed to air or NO2, evaluated either by cutaneous responsiveness to intradermal antigen, or serum immunoglobulin E (IgE) levels assessed by the passive cutaneous anaphylaxis (PCA) reaction. We conclude that daily inhalation of 4 ppm NO2 during the first three months of life does not affect airways responsiveness and atopic status of rabbits sensitized at birth. The lack of influence of NO2 in this model may be related to the i.p. route of immunization.