Release of Interleukin-8, Interleukin-6, and Colony-stimulating Factors by Upper Airway Epithelial Cells: Implications for Cystic Fibrosis

Abstract

Abstract Cystic fibrosis (CF) is characterized by a dramatic neutrophil recruitment and repeated Pseudomonas infections in the lungs. To evaluate cytokine releasability by airway epithelial cells in the context of CF, we studied primary nasal epithelial cells isolated from the upper airways and continuous epithelial cell lines from normal and CF subjects. Relatively low levels of interleukin (IL)-8, IL-6, and granulocyte/macrophage colony-stimulating factor (GM-CSF) were produced spontaneously by primary epithelial cells (< 50 pg/106 cells) and higher levels of colony-stimulating factor-1 (CSF-1) (1 to 2 ng/106 cells). Cells were stimulated with substances that are likely to be present in the inflamed lungs of CF patients—namely, the proinflammatory monokines IL-1 and tumor necrosis factor-α (TNFα) as well as neutrophil elastase and bacterial products from Pseudomonas (mucoid exopolysaccharide [MEP] and rhamnolipids). Both IL-1 and TNFα induced a dose-dependent release of IL-6 (5 to 10 ng/106 cells) and GM-CSF (2 to 3 ng/106 cells) by primary epithelial cells from eight normal volunteers. The TNFα/IL-1-stimulated GM-CSF release was blocked by the addition of 1 µM dexamethasone, whereas basal CSF-1 release was unaffected. Neutrophil elastase was a potent inducer of IL-8 and GM-CSF both in primary epithelial cells and in cell lines. Dexamethasone (1 µM) did not inhibit elastase-induced IL-8 release in either normal or CF epithelial cells. Rhamnolipids and MEP were found to stimulate the copious release of IL-8, GM-CSF, and IL-6 from epithelial cells, in a steroid-sensitive fashion. Epithelial cell lines from normal and CF subjects secreted very similar amounts of cytokines upon exposure to the various stimuli. We conclude from the above that: (1) proinflammatory cytokine release by epithelial cells is induced with leukocyte products and Pseudomonas bacterial products; (2) elastase induces IL-8 release in a manner unaffected by steroid treatment; (3) CSF-1 release occurs constitutively, and its spontaneous release may be related to a maintenance function for this cytokine; and (4) continuous epithelial cell lines obtained from CF subjects do not have an aberrant cytokine secretion profile. These results have implications in CF, where high levels of elastase, monokines, Pseudomonas rhamnolipids, and MEP are generated in the inflamed lungs of CF patients.