Determinants of airway responses to cat allergen: Comparison of environmental challenge to quantitative nasal and bronchial allergen challenge

Background: Why allergic subjects may have asthma or rhinitis on allergen exposure remains unclear. Objective: This study was carried out to compare airway responses during environmental allergen challenge (EAC) with quantitative allergen provocation challenges of the upper and lower airways. Methods: Thirteen subjects with allergy to cats underwent EAC to cats. Lower airway responses during EAC were compared with bronchoprovocation with allergen. Nasal mucosal challenge with allergen-soaked disks were compared with EAC nasal responses. Nonspecific bronchial reactivity was assessed with methacholine; allergen sensitivity was assessed by skin prick tests, RAST, and end-point skin titration. Results: During EAC, the maximal fall in FEV₁ ranged from 6% to 57% (median, 18%) and correlated closely with allergen bronchoprovocation PD₂₀ (Spearman's correlation coefficient [R(s)] = - 0.85, p < 0.0002). EAC asthmatic responses and allergen bronchoprovocation correlated with methacholine PD₂₀ (R(s) = -0.85, p = 0.0002 and R(s) = 0.83, p = 0.0004, respectively). Nasal provocation and EAC nasal responses correlated with each other but not with lower airway responses. On the basis of EAC and allergen bronchoprovocation responses, seven participants with asthma were identified. This group was significantly more sensitive to inhaled methacholine but was similar to the nonasthmatic group in IgE- mediated sensitivity and nasal responses. Conclusions: The lower respiratory tract is less responsive to allergic and nonallergic stimuli in persons with allergic rhinitis. In persons with asthma during EAC, the response to nebulized cat allergen is also abnormal and correlates closely with their abnormal responsiveness to nonimmunologic stimuli.