The T Cell-Specific CXC Chemokines IP-10, Mig, and I-TAC Are Expressed by Activated Human Bronchial Epithelial Cells

Abstract

Recruitment of activated T cells to mucosal surfaces, such as the airway epithelium, is important in host defense and for the development of inflammatory diseases at these sites. We therefore asked whether the CXC chemokines IFN-induced protein of 10 kDa (IP-10), monokine induced by IFN-γ (Mig), and IFN-inducible T-cell α-chemoattractant (I-TAC), which specifically chemoattract activated T cells by signaling through the chemokine receptor CXCR3, were inducible in respiratory epithelial cells. The effects of proinflammatory cytokines, including IFN-γ (Th1-type cytokine), Th2-type cytokines (IL-4, IL-10, and IL-13), and dexamethasone were studied in normal human bronchial epithelial cells (NHBEC) and in two human respiratory epithelial cell lines, A549 and BEAS-2B. We found that IFN-γ, but not TNF-α or IL-1β, strongly induced IP-10, Mig, and I-TAC mRNA accumulation mainly in NHBEC and that TNF-α and IL-1β synergized with IFN-γ induction in all three cell types. High levels of IP-10 protein (>800 ng/ml) were detected in supernatants of IFN-γ/TNF-α-stimulated NHBEC. Neither dexamethasone nor Th2 cytokines modulated IP-10, Mig, or I-TAC expression. Since IFN-γ is up-regulated in tuberculosis (TB), using in situ hybridization we studied the expression of IP-10 in the airways of TB patients and found that IP-10 mRNA was expressed in the bronchial epithelium. In addition, IP-10-positive cells obtained by bronchoalveolar lavage were significantly increased in TB patients compared with normal controls. These results show that activated bronchial epithelium is an important source of IP-10, Mig, and I-TAC, which may, in pulmonary diseases such as TB (in which IFN-γ is highly expressed) play an important role in the recruitment of activated T cells.