Effective allergen avoidance at high altitude reduces allergen-induced bronchial hyperresponsiveness.

We studied the effects of reduced allergen exposure on bronchial hypereactivity (BHR) in two groups of asthmatic children allergic to house dust mites (HDM) living at high altitude for 9 continuous mo. In the first group the serum levels of total and HDM-specific IgE showed significant decreases after 3 mo (p < 0.001 and p < 0.02, respectively) and after 9 mo (p < 0.001). Three months after returning home the total IgE levels had increased significantly (p < 0.001). The mean percentage fall in peak expiratory flow after exercise testing improved after 3 and 9 mo (p < 0.05), but it had deteriorated after 3 mo at home (p < 0.01). The methacholine PD20-FEV1 increased after 3 mo (p = 0.001) and further after 9 mo (p < 0.001), with a decrease after the 3-mo period at sea level (p = 0.01). In the second cohort there was a significant increase in HDM PD20-FEV1 after 6 and 9 mo (p < 0.001), with a slight decrease of magnitude of the allergen-induced late reaction. Histamine PD20-FEV1 significantly increased after 6 and 9 mo at high altitude, particularly in the challenges performed after the HDM bronchial provocation (p < 0.01). Our data demonstrate that allergen avoidance in asthmatic children not only decreases nonspecific BHR but also decreases allergen sensitivity, late allergen-induced bronchial reactions, and enhancement of BHR by allergen challenge.