Demonstration of bronchial eosinophil activity in seasonal allergic rhinitis by induced plasma exudation combined with induced sputum

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Abstract
BACKGROUND Patients with seasonal allergic rhinitis may develop bronchial hyperresponsiveness during the active disease period. Eosinophil activation may occur in the bronchial mucosa and may be reflected by increased sputum levels of eosinophil cationic protein (ECP), especially when ECP binding proteins such as α2-macroglobulin pass through the lamina propria and across the epithelium into the airway lumen. A study was therefore undertaken to determine histamine airway responsiveness (FEV1) and bronchovascular responsiveness (exudation of α2-macroglobulin) to histamine in subjects with seasonal allergic rhinitis, and to explore whether sputum ECP levels are increased by the use of induced exudation followed by induced sputum. METHOD Eleven patients with seasonal allergic rhinitis were examined before and during a birch pollen season. Sputum was induced by inhalation of 4.5% saline twice before and twice during the pollen season. Histamine inhalations were given before the second of each pair of sputum inductions at increasing concentrations until FEV1 was reduced by 20%. Sputum levels of α2-macroglobulin and ECP were determined as indices of bronchial exudation of plasma and activation of bronchial eosinophils, respectively. RESULTS Bronchomotor responsiveness increased during the pollen season (median difference in the reduction of FEV1 9% (95% confidence interval (CI) –3 to 26)) but histamine induced exudation of plasma was not increased. Baseline sputum levels of α2-macroglobulin and ECP did not increase. Histamine induced exudation of α2-macroglobulin was associated with increased sputum levels of ECP exclusively during the pollen season (median difference 8.2 ng/ml (95% CI 0.4 to 562.0)). CONCLUSION Bronchial hyperresponsiveness in seasonal allergic rhinitis may not be associated with bronchovascular exudative hyperresponsiveness. Sputum levels of ECP were increased only during the season, and only after induced exudation (potentially moving ECP to the mucosal surface). It is suggested that the combined method of induced exudation and induced sputum may significantly improve the yield of some markers of inflammation in sputum samples.