CCL17/thymus and activation-regulated chemokine induces calcitonin gene-related peptide in human airway epithelial cells through CCR4

Background: Calcitonin gene-related peptide (CGRP) is a potent arterial and venous vasodilator. Increased airway epithelial cell expression of CGRP, together with increased CCL17 expression, was previously observed in a model of provoked asthma in atopic human subjects. Objective: We sought to determine whether CCL17 induces CCR4-dependent CGRP synthesis and secretion by human airway epithelial cells. Methods: Human airway epithelial cell lines (BEAS-2B and A549) and human primary airway cells were cultured with CCL17 or various other cytokines, and CGRP expression was measured by using RT-PCR, quantitative immunofluorescence, and enzyme immunoassay. CCR4 expression was determined in cultured cells by using flow cytometry and in bronchial biopsy specimens by using immunohistochemistry. Results: CCL17 induced a several thousand-fold increase in CGRP mRNA expression and released peptide product from BEAS-2B and A549 cells in a time-and concentration-dependent fashion. Concentration-dependent CCL17-induced release of CGRP by primary human airway epithelial cells was also observed. Under comparable conditions, CCL17 induced greater CGRP release from BEAS-2B cells than either IL-13, a cytokine mixture (TNF-alpha, GM-CSF, and IL-1), or CCL22. CCR4 was expressed by BEAS-2B and A549 cells and internalized after ligation with CCL17. CCL17-induced CGRP release was inhibited by a specific anti-CCR4 blocking antibody. Bronchial biopsy specimens obtained from healthy volunteers and asthmatic patients before and after provoked asthma all exhibited CCR4 staining of equivalent intensity, indicating that the receptor is constitutively expressed. Conclusions: CCL17-induced, CCR4-dependent release of CGRP by human airway epithelial cells represents a novel inflammatory pathway and a possible target in patients with asthma and allergic disease.