Expression and generation of interleukin-8, IL-6 and granulocyte-macrophage colony-stimulating factor by bronchial epithelial cells and enhancement by IL-1 beta and tumour necrosis factor-alpha

Abstract

We have tested the hypothesis that the bronchial epithelium has the capacity to generate and release cytokines that could contribute to inflammatory events associated with inflammatory lung diseases. Messenger RNA (mRNA) for interleukin-6 (IL-6), IL-8 and granulocyte-macrophage colony-stimulating factor (GM-CSF) was identified in human bronchial epithelial cell primary cultures, characterized on the basis of staining for cytokeratin, using both in situ hybridization and Northern blotting. Using in situ hybridization we have shown that the majority of the cells expressed mRNA for IL-6 and IL-8, whereas fewer than 20% of cells expressed message for GM-CSF. The numbers of cells expressing message were increased by culture with tumour necrosis factor-alpha (TNF-alpha) (20 ng/ml, 24 hr). These observations were substantiated by Northern blotting, which showed that both TNF-alpha and IL-1 beta were able to induce a dose-dependent increase in IL-8-specific mRNA. Immunoreactive IL-6 and GM-CSF were detected and quantified in the culture supernatants by ELISA, and IL-8 by radioimmunoassay. The levels of immunoreactivity were increased by incubation of epithelial cells with either IL-1 beta or TNF-alpha for 24 hr. A transformed tracheal epithelial cell line (9HTEo-) expressed mRNA for IL-6, IL-8 and GM-CSF but, whereas levels of immunoreactive IL-6 in culture supernatants were comparable with those in primary cell cultures, levels of IL-8 were low and GM-CSF trivial. These observations indicate that the bronchial epithelium has the potential to be a major source of IL-8 and a number of other cytokines, and that production can be amplified substantially by IL-1 beta and TNF-alpha. The bronchial epithelium is ideally situated to modulate inflammatory and immunological events in and around the airways, and these observations suggest that it could contribute to promote and sustain inflammatory and immunological processes in inflammatory lung diseases such asthma.