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Airway Response to Low-Dose Allergen Exposure in Allergic Nonasthmatic and Asthmatic Subjects*: Eosinophils, Fibronectin, and Vascular Endothelial Growth Factor FREE TO VIEW

Marie-Eve Boulay, MSc; Louis-Philippe Boulet, MD, FCCP
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*From the Centre de Recherche, Hôpital Laval, Institut Universitaire de Cardiologie et de Pneumologie de l’Université Laval, Ste-Foy, Quebec, Canada.

Correspondence to: Marie-Eve Boulay, MSc, 2725 Chemin Ste-Foy, Sainte-Foy, Québec, Canada, G1V 4G5; e-mail: marie.eve.boulay@crhl.ulaval.ca

Chest. 2003;123(3_suppl):430S. doi:10.1378/chest.123.3_suppl.430S
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Low-dose allergen challenge (LDAC) is a potentially useful tool for studying the capacity of allergens to induce airway inflammation and remodeling in atopic subjects. To evaluate markers of inflammation (eosinophils) and remodeling (fibronectin, vascular endothelial growth factor [VEGF]) following repeated LDAC in nonasthmatic subjects with allergic rhinitis compared with mild allergic asthmatic subjects. Fourteen nonasthmatic subjects with allergic rhinitis and 11 stable mild allergic asthmatic subjects underwent spirometry and methacholine challenge, and blood and induced sputum (IS) with differential cell counts were obtained. Each subject underwent LDAC on 4 consecutive mornings with a relevant allergen. Spirometry, methacholine challenge, and blood and IS samplings were repeated 6 h after the second and fourth LDAC and 1 week later. Sputum eosinophil cationic protein, fibronectin, and VEGF were measured using radioimmunoassay and enzyme-linked immunosorbent assay.

Although there were no changes in FEV1 nor in the provocative concentration causing a 20% fall in FEV1 in either group, the mean percentage of eosinophils on IS was significantly increased in nonasthmatic subjects with allergic rhinitis on day 2 of LDAC and decreased in all but one subject on day 4, with a tendency to return to baseline levels 1 week later. In mild allergic asthmatic subjects, there was a nonsignificant trend for sputum eosinophils to increase on day 2; four subjects showed a decrease of eosinophils on day 4 of LDAC. There was a correlation between eosinophil cationic protein levels and eosinophil counts in nonasthmatic subjects with allergic rhinitis throughout the study. There were no variations in other sputum cells or blood inflammatory cells. VEGF was significantly increased in the group of allergic nonasthmatic subjects 1 week after challenge. Fibronectin levels did not vary significantly throughout the study. Repeated exposure to low doses of allergen can increase the percentage of eosinophils in IS of nonasthmatic subjects with allergic rhinitis without associated respiratory symptoms nor physiologic modifications. A reduction in eosinophilic response despite repeated exposure, more common in nonasthmatic subjects with allergic rhinitis, suggests an adaptation process that needs to be further evaluated. Growth factors involved in angiogenesis can increase after allergen exposure in nonasthmatic subjects with allergic rhinitis.

Abbreviations: IS = induced sputum; LDAC = low-dose allergen challenge; VEGF = vascular endothelial growth factor




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