INFLUENCE OF SENSITIZATION AND ALLERGEN PROVOCATION PROCEDURES ON THEDEVELOPMENT OF ALLERGEN-INDUCED BRONCHIAL HYPERREACTIVITY IN CONSCIOUS, UNRESTRAINED GUINEA-PIGS

THE effects of different sensitization and allergen provocation regime ns on the development of allergen-induced bronchial hyperreactivity (B HR) to histamine were investigated in conscious, unrestrained guinea-p igs. Similar early and late phase asthmatic reactions, BHR for inhaled histamine after the early (6 h) as well as after the late reaction (2 4 h), and airway inflammation were observed after a single allergen pr ovocation in animals sensitized to produce mainly IgG or IgE antibodie s, respectively. Repeating the allergen provocation in the IgE-sensiti zed animals after 7 days, using identical provocation conditions, resu lted in a similar development of BHR to histamine inhalation. Repetiti on of the allergen provocation during 4 subsequent days resulted in a decreased development of BHR after each provocation, despite a signifi cant increase in the allergen provocation dose necessary to obtain sim ilar airway obstruction. The number of inflammatory cells in the bronc hoalveolar lavage was not significantly changed after repeated provoca tion, when compared with a single allergen provocation. Finally, we in vestigated allergen-induced bronchial hyperreactivity by repetition of the sensitization procedure at day 7 and 14 (booster), followed by re peated allergen provocation twice a week for 5 weeks. Surprisingly, no BHR to histamine could be observed after either provocation, while th e number of inflammatory cells in the bronchoalveolar lavage fluid aft er 5 weeks was enhanced compared with controls. These data indicate th at both IgE and IgG sensitized guinea-pigs may develop bronchial hyper eactivity after a single allergen provocation. Repeated allergen expos ure of IgE sensitized animals causes a gradual fading of the induced h yperreactivity despite the on-going presence of inflammatory cells in the airways, indicating a mechanism of reduced cellular activation.