AIRWAY RESPONSE OF ASTHMATIC SUBJECTS TO INHALED ALLERGEN AFTER EXPOSURE TO POLLUTANTS

Background - Recent studies have suggested that air pollutants resulti ng from vehicle exhaust emissions and burning of fossil fuels, either in combination or individually, may enhance the airway response of ast hmatic subjects to inhaled allergen. It was hypothesised that the airw ay response to inhaled allergen after exposure to a combination of 400 ppb nitrogen dioxide (NO2) and 200 ppb sulphur dioxide (SO2) is incre ased 24-48 hours after exposure. Methods - Thirteen mild atopic asthma tic volunteers were exposed for six hours to a single exposure of air and three exposures of the combination of 400 ppb NO2 +200 ppb SO2 in randomised order, and then challenged with increasing concentrations o f Dermatophagoides pteronyssinus allergen either immediately after exp osure to air, or immediately, 24 hours or 48 hours after exposure to t he combination of the two pollutants, until a 20% fall in forced expir atory volume in one second (FEV(1)) was recorded. Results - Exposure t o 400 ppb NO2 +200 ppb SO2 significantly decreased the dose of D ptero nyssinus allergen required to produce a 20% fall in FEV(1) (PD(20)FEV( 1)) at all times after exposure when compared with air. The mean perce ntage changes in allergen PD(20)FEV(1) immediately, 24 hours, and 48 h ours after exposure to 400 ppb NO2 +200 ppb SO2 were -37% (95% confide nce intervals (CI) -50 to -23), -63% (CI -75 to -51), and -49% (CI -75 to -28.8), respectively, when compared with the PD(20)FEV(1) after ai r exposure and were significant at all time points studied. The allerg en PD(20)FEV(1) at 24 hours after exposure to the combination of the t wo pollutants was also found to be significantly lower when compared w ith that immediately after exposure to the two pollutants. Conclusion - These results demonstrate that exposure to a combination of NO2 and SO2, at concentrations which can be encountered during episodes of inc reased outdoor and indoor air pollution, enhances the airway response to inhaled allergen in asthmatic subjects. This effect persists over a period of 24-48 hours and is maximal 24 hours after exposure to these air pollutants.