Involvement of IL-9 in the bronchial phenotype of patients with nasal polyposis

Background: Nasal polyposis (NP) is frequently associated with asthma. In this disease, asymptomatic bronchial hyperresponsiveness (BHR) is thought to precede the development of asthma. IL-9 and its receptor have been reported as candidate genes for asthma and to be associated with BHR. Objective: The objective of this study was to assess the contribution of IL-9 to the pathogenesis of BHR in NP by comparing the expression of IL-9 and its receptor in bronchial biopsy specimens from three groups of patients with NP : NP without BHR, NP with asymptomatic BHR, and NP and BHR and asthma. Methods: Bronchial biopsy specimens were examined in terms of cellular infiltration and in terms of expression of IL-9 protein and mRNA as well as its receptor by using immunohistochemistry and in situ hybridization. Results: Patients with NP with asthma as compared with two other groups exhibited and an increased bronchial infiltration of basophils, eosinophils, and T cells that correlated with the asthma score. The two groups of patients with NP with BHR showed an increase in the expression of IL-9 mRNA at the epithelial level. These modifications were inversely correlated with the airway responsiveness to methacholine, producing a 20% fall in FEV1. There was a close association between IL-9(+) cells , IL-5 mRNA expression, and eosinophil infiltration that correlated with each other. Conclusions: These results suggest an important role for IL-9 in the pathogenesis of BHR and a causal relation between IL-9 and the development of bronchial eosinphilia in asthma.