CCR4 is now known to be selectively expressed in Th2 cells. Since the bronchial epithelium is recognized as an important source of mediators fundamental to the manifestation of respiratory allergic inflammation, we studied the expression of two functional ligands for CCR4, i.e., macrophage-derived chemokine (MDC) and thymus- and activation-regulated chemokine (TARC), in bronchial epithelial cells. The bronchial epithelium of asthmatics and normal subjects expressed TARC protein, and the asthmatics showed more intense expression than the normal subjects. On the other hand, MDC expression was only weakly detected in the asthmatics, but the intensity was not significantly different from that of normal subjects. Combination of TNF-α and IL-4 induced expression of TARC protein and mRNA in bronchial epithelial A549 cells, which was slightly up-regulated by IFN-γ. The enhancement by IFN-γ was more pronounced in bronchial epithelial BEAS-2B cells, and a maximum production occurred with combination of TNF-α, IL-4, and IFN-γ. On the other hand, MDC was essentially not expressed in any of the cultures. Furthermore, expressions of TARC protein and mRNA were almost completely inhibited by glucocorticoids. These results indicate that the airway epithelium represents an important source of TARC, which potentially plays a role via a paracrine mechanism in the development of allergic respiratory diseases. Furthermore, the beneficial effect of inhaled glucocorticoids on asthma may be at least in part due to their direct inhibitory effect on TARC generation by the bronchial epithelium.

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Several lines of evidence have suggested that a CXC chemokine receptor 4 (CXCR4)/stromal cell-derived factor-1 [SDF-1; CXC chemokine ligand 12 (CXCL12)] pair is involved in baseline trafficking of leukocytes into extravascular tissues and that modulation of surface CXCR4 expression may represent an alternative mechanism for control of cell-specific biological responses to SDF-1/CXCL12. We explored the regulation of CXCR4 expression by cytokines in polymorphonuclear neutrophils (PMNs). No significant surface expression of CXCR4 in freshly isolated PMNs was detected, but expression became apparent gradually during incubation. SDF-1α/CXCL12 initiated Ca2+ mobilization and migratory responses in 20 h cultured PMNs. The surface CXCR4 expression was suppressed most potently by interferon-γ (IFN-γ). IFN-α, granulocyte-macrophage colony-stimulating factor (GM-CSF), and G-CSF also inhibited spontaneous CXCR4 expression. Real-time, quantitative PCR experiments revealed that a spontaneous increase and an IFN-γ-mediated decrease in surface CXCR4 paralleled changes in the CXCR4 mRNA level. These results on PMNs support the argument that the SDF-1 (CXCL12)/CXCR4 system is regulated by cell type-specific mechanisms.