NITROGEN-DIOXIDE EXPOSURE ENHANCES ASTHMATIC REACTION TO INHALED ALLERGEN IN SUBJECTS WITH ASTHMA

We investigated whether exposure to a low level (490 mu g/m(3)) of nit rogen dioxide (NO2) affects bronchial responsiveness to allergen and e nhances allergen-induced increase in airway responsiveness to histamin e. Eighteen subjects with asthma and allergy to pollen were exposed at rest to either purified air or NO2 for 30 min followed 4 h later by a n allergen inhalation challenge. Responsiveness to histamine was measu red the day after. Lung function during NO2 exposure and allergen chal lenge was measured by plethysmography and after exposure by a portable spirometer hourly. The order of exposure to NO2 and air was randomize d and separated by at least 2 wk. The asthmatic reaction during the la te phase was enhanced by NO2, and peak expiratory flow after allergen challenge was on average 6.6% lower (p = 0.02) after NO2 than after ai r exposure. The number of subjects having a late asthmatic reaction (f all in FEV(1) > 15%) was seven after air and 10 after NO2 (NS). Periph eral blood samples were analyzed for differential cell counts before a nd after NO2/allergen and serum levels of eosinophil cationic protein (ECP). NO2 effect on lung function was neither associated with an incr ease in eosinophil numbers nor with ECP levels. NO2 did not affect lun g function before allergen challenge, early asthmatic reaction, and al lergen-induced increase in responsiveness to histamine. These results indicate that short exposure to an ambient level of NO2 followed sever al hours later by allergen inhalation enhances allergen-induced late a sthmatic reaction.