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The effect of exposure to sulphuric acid on the early asthmatic response to inhaled grass pollen allergen

¹ Heartlands Research Institute, Heartlands Hospital, Birmingham, UK. ² Division of Environmental Health and Risk Management, University of Birmingham, Edgbaston, Birmingham, UK

CORRESPONDENCE: J.G. Ayres, Heartlands Hospital, Bordesley Green East, Birmingham, B9 5SS, UK. Fax: 44 1217720292

Keywords: air pollution, allergen, challenge study, particles, sulphuric acid

Received: October 16, 2000
Accepted June 11, 2001

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 (FEV₁) (PD₁₅) for each subject, they were exposed to air, 100 µg·m^–3 or 1,000 g·m^–3 H₂SO₄ for 1 h, double-blind in random order 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 µg·m^–3 H₂SO₄, and 1,000 µg·m^–3 H₂SO₄, were –14.1%, –16.7%, and –18.4%, respectively. The difference between 1,000 µg·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 µg·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.