Elevated expression of interleukin-9 mRNA in the bronchial mucosa of atopic asthmatics and allergen-induced cutaneous late-phase reaction: relationships to eosinophils, mast cells and T lymphocytes

Background Interleukin-9 is a T cell-derived Th2-type cytokine that has been linked to airway hyper-responsiveness. mucus hypersecretion and mast cell infiltration in animal models. We recently demonstrated the potential for IL-9 to act in human eosinophil development and survival. Objectives The aims of this study were: (i) to compare IL-9 mRNA expression in bronchial biopsies between atopic asthmatics and normal controls, (ii) to investigate kinetic expression of IL-9 mRNA in skin biopsies after allergen challenge; and (iii) to relate IL-9 expression to infiltration of eosinophils, mast cell and T lymphocytes in local tissue. Methods Bronchial biopsies were obtained from atopic asthmatics (n = 12) and normal non-asthmatics (n = 12) at baseline. Skin biopsies were obtained from atopic subjects (n = 11) at 1, 3, 6, 24, 48 and 72 h after allergen challenge. Diluent challenge sites at 24 h were used as controls. IL-9 mRNA was identified using the technique of in situ hybridization. The numbers of eosinophils, mast cells and T cells were evaluated by immunohistochemistry. Results The numbers of IL-9 mRNA-cells present in the bronchial mucosa were significantly greater in atopic asthmatics than those in normal controls (P = 0.003). The numbers of eosinophils, but not mast cells. were also significantly higher in asthmatics (P < 0.005). The numbers of IL-9 mRNA- cells present in the airway of asthmatics significantly correlated with the numbers of eosinophils (r = 0.623. P = 0.03), but not mast cells or T cells. Compared with diluent challenge, the numbers of IL-9 mRNA- cells were significantly elevated at all allergen-challenged sites in the skin. with maximal signals at 48 h (P < 0.005). At 72 h. the numbers of IL-9 mRNA(+) cells significantly correlated with the numbers of eosinophils (r = 0.707, P = 0.015). Conclusion Elevated expression of IL-9 in allergic inflammation may contribute to local eosinophil infiltration and survival in asthma and other allergic atopic diseases.