Interleukin-17A activation on bronchial epithelium and basophils: a novel inflammatory mechanism

Basophils are the accessory cell type for T-helper (Th) 2 induction and initiators in immunoglobulin E-mediated chronic allergic inflammation. Basophils and Th17 cells accumulate at the inflammatory sites, such as the airways of allergic asthmatic patients. We investigated the activation of interleukin (IL)-17A on the primary human basophils/KU812 basophilic cells and primary human bronchial epithelial cells/BEAS-2B bronchial epithelial cells. Cytokines, chemokines, adhesion molecules and intracellular signalling molecules were assayed by ELISA or flow cytometry. Co-culture of bronchial epithelial cells and basophils could significantly induce the release of IL-6, an epithelial inflammatory cytokine, and CCL2, a chemokine for basophils, esosinophils and monocytes. Such induction was synergistically enhanced by IL-17A, and direct interaction between these two cells was necessary for IL-17A-induced IL-6 and CCL2 release. Surface expression of intercellular adhesion molecule-1 on bronchial epithelial cells was also upregulated upon their interaction. The interaction of basophils and bronchial epithelial cells under IL-17A stimulation was differentially regulated by extracellular signal-regulated kinase, c-Jun N-terminal protein kinase, p38 mitogen-activated protein kinase and nuclear factor-kappa B pathways. These findings suggest a novel immunopathological role of Th17 cells and basophils in allergic asthma through the activation of granulocyte-mediated inflammation initiated by the direct interaction between basophils and bronchial epithelial cells.