Determinants of Allergen-Induced Asthma: Dose of Allergen, Circulating IgE Antibody Concentration, and Bronchial Responsiveness to Inhaled Histamine1–3

The relationships among bronchial responsiveness to allergen, bronchial responsiveness to histamine, and cutaneous sensitivity to allergen were examined in 25 asthmatic subjects. Bronchial responsiveness to allergen was determined by inhalation tests with 2-fold increasing doses of allergen extract, and was expressed as the provocative concentration producing an early asthmatic response with a 20 % decrease in the forced expiratory volume in one second (allergen PC20). Bronchial responsiveness to histamine was determined in a similar way and was expressed as histamine PC20. Cutaneous sensitivity to allergen was determined by duplicate prick skin tests with doubling concentrations of the same allergen extract used for inhalation, and was expressed as the concentration producing a mean wheal diameter of 2 mm. There was a poor correlation between histamine PC20 and cutaneous sensitivity to allergen (r = −0.03, p > 0.1). There was a good correlation between allergen PC20 and histamine PC20 (r = 0.52, p > 0.02) and a better correlation between allergen PC20 and cutaneous sensitivity to allergen (r = 0.60, p > 0.01). However, using multiple linear regression of allergen PC20 as a function of histamine PC20 and cutaneous sensitivity to allergen, there was an even better correlation (r = 0.78, p < 0.001). We used as an estimate of the severity of the allergic reaction in the airways the mean wheal diameter produced by the concentration of allergen extract that caused a 20 % or greater decrease in the forced expiratory volume in one second in the allergen inhalation test. A highly significant negative correlation was found between the mean wheal diameter and the histamine PC20 (r = −0.91, p < 0.001). The results indicate that bronchial responsiveness to inhaled allergen is dependent not only on allergen sensitivity, but also on the degree of nonallergic bronchial responsiveness to histamine.