ANALYSIS OF CELLULAR AND BIOCHEMICAL-CONSTITUENTS OF INDUCED SPUTUM AFTER ALLERGEN CHALLENGE - A METHOD FOR STUDYING ALLERGIC AIRWAY INFLAMMATION

To determine whether analysis of the constituents of induced sputum pe rmits detection of changes provoked by aerosolized antigen challenge, we performed sputum induction (20-minute inhalation of aerosolized 3% saline solution) before and after aerosolized allergen challenge in ei ght subjects with asthma. Total cell counts and cell differentials of nonsquamous cells in induced sputum samples were determined after the samples were homogenized in dithiothreitol. Centrifugation of the enti re homogenized sputum sample yielded supernatant that could be analyze d for biochemical constituents. We found that the median percentage of eosinophils and neutrophils in induced sputum samples was significant ly higher 4 hours after allergen challenge than at baseline (12% vs 0. 5%, p < 0.05; 30.5% vs 7.5%, p < 0.05) and remained high 24 hours afte r challenge. Median levels of eosinophil cationic protein and histamin e in induced sputum supernatants were significantly higher 4 hours aft er challenge than at baseline (151.3 vs 39.8 ng/ml, p < 0.05; 19.4 vs 8.8 mu g, p < 0.05) and remained significantly higher 24 hours after c hallenge. Tryptase was detectable in sputum from seven of the subjects , and in these subjects, we found a trend toward an increase in median tryptase levels 4 hours after allergen challenge (4.4 vs 22 U/L, p = 0.09). We conclude that analysis of induced sputum after aerosolized a llergen challenge reveals changes in inflammatory cells and markers si milar to those reported in bronchoalveolar lavage fluid and that sputu m induction is a useful noninvasive method for studying allergic airwa y inflammation in asthma.