Abstract
Particulate sulphates, including sulphuric acid (H2SO4), are important components of the ambient aerosol in some areas and are regarded as air pollutants with potentially important human health effects. Challenge studies suggest little or no effect of H2SO4 exposure on lung function in asthmatic adults, although some epidemiological studies demonstrate an effect of acid species on symptoms in subjects with asthma. To date, the effect of H2SO4 on allergen responsiveness has not been studied. The effect of exposure to particulate H2SO4 on the early asthmatic response to grass pollen allergen has been investigated in 13 adults with mild asthma. After establishment of the provocative dose of allergen producing a 15% fall in forced expiratory volume in one second (FEVI) (PD15) for each subject, they were exposed to air, 100 microg m(-3) or 1,000 g x m(-3) H2SO4 for 1 h, double-blind in random order > or =2 weeks apart, through a head dome delivery system 14 h after each exposure subject underwent a fixed-dose allergen challenge (PD15). Ten subjects completed the study. The mean early asthmatic responses (maximum percentage change in FEV1 during the first 2 h after challenge) following air, 100 microg x m(-3) H2SO4, and 1,000 microg m(-3) H2SO4, were -14.1%, -16.7%, and -18.4%, respectively. The difference between 1,000 microg x m(-3) H2SO4 and air was significant (mean difference: -4.3%, 95% confidence interval (CI: -1.2-7.4%, p=0.013). The difference between air and 100 microg m(-3) H2SO4 approached significance (mean difference: -2.6%, 95% CI: 0.0-5.3%, p = 0.051). These results suggest that, at least at high mass concentration, sulphuric acid can potentiate the early asthmatic response of mild asthmatic subjects to grass pollen allergen, although the effect is limited.