Bronchoprovocation: Effect on priming and desensitization phenomenon in the lung

Priming, or increased sensitivity to antigen, has not been demonstrated in the lung and could play a role in asthmatic symptomatology during seasonal pollen exposure. It is also an important consideration in the design of any experimental protocol requiring serial bronchoprovocations with antigen. Thirteen patients with a history of asthma symptoms during the pollen season and a positive skin test to ragweed extract were selected. Patients were given bronchial challenge out of season on 4 successive days with stepwise inhalations of antigen, and airways conductance was monitored in the body plethysmograph. Antigen dose-response curves were drawn, and the cumulative dose required for a 35% reduction in specific airway conductance was calculated and designated Provocation Dose (PD₃₅). No regular trend toward either priming or desensitization was noted. The daily changes in antigen sensitivity did not correlate with daily variation of baseline pulmonary function. To determine if there was any priming due to natural exposure to pollen, 9 patients were brought back and rechallenged during the pollen season with no significant increase in bronchial sensitivity to ragweed extract. The PD₃₅ method provides figures useful for comparing dose-response curves and shows a one-log variation from day to day. Any evaluation by bronchial challenge of antigen sensitivity or drug efficacy must take into account such variation.