Pathogenesis of late asthmatic reactions induced by exposure to isocyanates

The importance of airways inflammation for the development of bronchial hyperresponsiveness and for exacerbation of asthma was investigated in subjects with occupational asthma. We examined subjects sensitized to isocyanates, a small molecular weight compound that causes occupational asthma. Studies in asthmatic subjects sensitized to toluene diisocyanate (TDI) demonstrated that late, but not early, asthmatic reactions induced by TDI were associated with an acute increase in bronchial responsiveness, and with a marked infiltration of neutrophils and a slight infiltration of eosinophils into the airways, both prevented by steroids. As the late asthmatic reactions and the increase in responsiveness induced by TDI were prevented by steroids, but not by indomethacin, we speculated that cell membrane phospholipid metabolites, which are inhibited by steroids but not by indomethacin, may be involved in TDI induced hyperresponsiveness. The results of these studies suggest that bronchial hyperresponsiveness and exacerbation of asthma may be related to inflammation of the airways and that cell membrane phospholipid metabolites may be involved.