Interleukin 4 receptors on human bronchial epithelial cells. An in vivo and in vitro analysis of expression and function.

Asthma is considered a Th2-like disease, characterized by locally increased levels of interleukin (IL) 4. The bronchial epithelium plays an important role in the initiation and perpetuation of inflammatory reactions within the airways. However, little is known about the presence of IL-4 receptors on human bronchial epithelial cells, or the effects of IL-4 on these cells. In this report, definitive evidence of IL-4 receptor expression on human bronchial epithelial cells using several methods is presented. IL-4 receptor expression on human bronchial epithelial cells in vivo was demonstrated using in situ hybridization and immunohistochemistry. No difference in IL-4 receptor protein expression was observed between bronchial biopsies of healthy subjects compared to allergic asthmatics. Cultured human bronchial epithelial cells also expressed IL-4 receptor mRNA and protein (as determined by RT-PCR analysis and flow cytometry, respectively). IL-4 receptor protein expression by bronchial epithelial cells could be increased by stimulation with PMA+calcium ionophore, whereas IL-1beta and IL-6 decreased IL-4 receptor expression. A cyclic AMP analogue and IL-4 had no effect. Finally, it is shown that the IL-4 receptor is functionally active as IL-4 stimulates the release of IL-8, monocyte chemoattractant protein 1, and particularly IL-1 receptor antagonist by human bronchial epithelial cells. It is concluded that human bronchial epithelial cells express IL-4 receptors both in vivo and in vitro. Stimulation of human bronchial epithelial cells by IL-4 may result in the release of both pro- and anti-inflammatory mediators known to be upregulated in asthmatic airways.