Magnitude of late asthmatic response to allergen in relation to baseline and allergen-induced sputum eosinophilia in mild asthmatic patients

Background: Late asthmatic response (LAR) to allergen challenge is a validated method for studying the pathogenesis of and new treatments for asthma in the laboratory. Objective: To evaluate the relationship between the magnitude of allergen-induced LAR and clinical and biological determinants, including sputum and blood eosinophil percentages and eosinophil cationic protein concentrations. Methods: Thirty-eight untreated mild asthmatic patients (mean age, 21.2 years) were selected for the presence of allergen-induced early asthmatic response (EAR) and LAR. Each patient measured methacholine responsiveness (provocation dose that caused a decrease in forced expiratory volume in 1 second of 20% [PD20FEV1]) at baseline, differential blood cell counts and eosinophil cationic protein levels in blood and induced sputum, and serum neutrophil chemotactic activity at baseline and 24 hours after allergen challenge. Results: A correlation was found between LAR (as area under the curve [AUC]) and sputum eosinophil percentages at baseline (r = 0.51; P = .001) and 24 hours after allergen challenge (r = 0.44; P < .007). Furthermore, we found significant correlations between AUC LAR and AUC EAR, baseline methacholine PD20FEV1, baseline blood eosinophil percentages, and baseline serum neutrophil chemotactic activity. A stepwise multiple regression analysis showed that the stronger determinants of AUC LAR were baseline sputum eosinophilia and AUC EAR. Conclusion: Baseline sputum eosinophilia and functional findings are determinants of the magnitude of allergen-induced LAR.