Bronchial Response to High and Low Molecular Weight Occupational Inhalant Allergens

PURPOSE: Occupational asthma may be induced by high- or low-molecular weight allergens (HMWA or LMWA, respectively). The study was conducted to compare the pattern of bronchial response in 200 HMWA-induced asthmatics (n = 130) and LMWA-induced asthmatics (n = 70). METHODS: The study participants underwent a single-blind, placebo-controlled specific inhalation challenge (SIC) with workplace allergens, accompanied by evaluation of non-specific bronchial hyperresponsiveness (NSBHR) with methacholine before and after the SIC. RESULTS: A single early bronchial response more frequently occurred in HMWA-induced asthmatics than in LMWA-induced asthmatics (86.2% vs. 20%). An isolated late bronchial response or atypical patterns were more frequently observed in LMWA-induced asthmatics than in LMWA-induced asthmatics (45.7% vs. 3.8% or 34.3% vs. 10%, respectively). Baseline NSBHR before SIC was more often detected in LMWA-induced asthmatics than in HMWA-induced asthmatics (81.4% vs. 54.6%), and the median value of the provocation concentration of methacholine was relevantly lower in these patients before and after SIC. A significant 3-fold increase in NSBHR after SIC was observed more often in LMWA-induced asthmatics than in HMWA-induced asthmatics (82.8% vs. 66.1%). In addition, compared to LMWA-induced asthmatics, HMWA-induced asthmatics were older, were more frequently active smokers, showed lower level of NSBHR, and more frequently continued their work in harmful occupational exposure. CONCLUSIONS: The results of this study suggest that HMWA-induced asthmatics may have milder clinical courses and that there is a possibility of job continuation despite asthma exacerbation requiring medical surveillance.