AIRWAY INFLAMMATION AFTER REMOVAL FROM THE CAUSAL AGENT IN OCCUPATIONAL ASTHMA DUE TO HIGH AND LOW-MOLECULAR-WEIGHT AGENTS

In order to determine 1) the features of airway inflammation after rem oval from exposure to high (HMW) and low (LMW) molecular weight agents 2) if there are any differences in the pattern of inflammation induce d by these two types of agents, we studied 18 subjects with a recently confirmed diagnosis of occupational asthma (OA) due to HMW (n=11) and LMW (n=7) agents. The duration of asthma symptoms varied from 2 to 10 8 months (mean 33 months), and withdrawal from exposure to the sensiti zing agent from 3 to 24 weeks (mean 10 weeks). All subjects underwent measurements of expiratory flow rates, methacholine inhalation tests, and a flexible bronchoscopy with bronchoalveolar lavage (BAL) and bron chial biopsies. Endoscopic findings were compared with a group of 10 n ormal subjects. At the time of the bronchoscopy, asthma symptoms were minimal in most subjects. Although 15/18 subjects had normal forced ex piratory volume in one second (FEV(1)>80% pred), all subjects had incr eased airway responsiveness to methacholine (provocation concentration producing a 20% fall in FEV(1)=0.2-10.0 mg.ml(-1)). BAL analysis show ed similar median percentages of the total number of cells and differe ntials in control subjects and those exposed to HMW and LMW agents. Br onchial biopsies showed that mean inflammatory cell count, both epithe lial and sub-epithelial, was similarity raised in OA subjects exposed to either HMW or LMW agents, compared to controls, except for epitheli al lymphocyte count. In contrast to the controls, bronchial biopsy of both groups with OA also showed other changes such as extensive epithe lial desquamation, ciliary abnormalities of the epithelial cells, smoo th muscle hyperplasia and subepithelial fibrosis. Bronchial biopsies f rom subjects with occupational asthma showed similar significant infla mmatory changes after withdrawal from exposure to either high or low m olecular weight sensitizing agent, even when symptoms were minimal.