Nitrogen dioxide compromises defence functions of the airway epithelium

The effect of nitrogen dioxide (NO2) exposure on airway epithelial defence functions, such as ciliary activity, mucociliary transport velocity and jun ctional barrier function, remains to be elucidated. Our study investigates the effect of 24-h exposure to 3.0 ppm of NO2 on the airway epithelial defe nce functions in the healthy rabbit. Fifty-two healthy rabbits were exposed to 3.0 ppm of NO2 (NO2 group) or pure air (control group) for 24 successiv e hours in exposure chambers. After completion of the exposure sequence, th e ciliary activity in the trachea was examined by a photoelectric method, t he mucociliary transport velocity in the trachea by an endoscopic method an d epithelial permeability of the trachea to fluorescein isothiocyanate-dext rans (FD-70s; molecular weight: 70,000 daltons) by an in vitro tracheal sac method. In the NO2 group, all epithelial defence functions, including cili ary activity, mucociliary transport velocity and epithelial permeability we re significantly inferior to those in the control group. Although there was considerable overlap in the parameters examined between the two groups, ap proximately two-thirds of the animals were susceptible to 24-h exposure to 3 ppm of NO2. Dysfunction of both the junctional barrier and the mucociliar y system could allow easier entry of allergen molecules to the airway paren chyma, where immunocomponent cells exist. NO2 might be involved to some ext ent in the clinical manifestation of airway allergic disorders through epit helial dysfunction.