Mechanism of Action of Steroids on Inflammation

Schleimer, Robert

Abstract

The overall aim of this project is to advance our understanding of the importance in allergic inflammation of resident cells in the airways, i.e. macrophages and epithelial cells, and their responses to glucocorticoids. We have recently found that macrophages within the airways express increased cell surface phenotypic markers of activation in asthmatics compared to normals and rhinitics using recently developed technologies. These cell surface markers, which include adhesion molecules and receptors for immunoglobulins and other ligands, are also increased following antigen challenge of allergic individuals. We will determine whether glucocorticoids regulate macrophage activation in human airways by monitoring the expression of activation markers in vivo after antigen challenge in allergic subjects on placebo or inhaled glucocorticoid. In vitro studies will focus on the effects of glucocorticoids on the expression of these surface markers as well as on gene expression in general. Another centrally important resident airway cell type, the epithelial cell will be the focus of studies on the regulation of glucocorticoid function in the airways. We have recently found that human airways epithelial cells can metabolize cortisol to form cortisone (which is inactive). To study this metabolic pathway in vivo in the airways we have developed a sensitive gas chromatography/mass spectrometry assay. Studies in BAL fluids indicate that endogenous cortisol is actively metabolized in the lungs. We will determine whether the metabolism of cortisol in the airways differs among patient groups including asthmatics, rhinitics, and normals by assessing cortisol and cortisone levels in BAL fluids. The effect of antigen challenge on endogenous metabolism of cortisol will also be assessed. RT PCR and Northern blot assays will be used to investigate any changes in the expression of the 11beta hydroxysteroid dehydrogenase enzyme which is responsible for cortisol metabolism. We have devised a strategy to discover new genes relevant to allergic diseases and glucocorticoid action. DNA differential display will be used with alveolar macrophages and airway epithelial cells for the identification of genes whose expression is induced by cytokines and inhibited by glucocorticoids. We believe these criteria will lead us to novel genes likely to be involved in inflammation. candidate genes will be rapidly sequenced through a collaboration with industry and functional studies will follow the identification of genes of interest. The studies outlined in this proposal are expected to further advance our knowledge of the function of the two most ubiquitous cell types at the mucosal surface, macrophages and epithelial cells. Results of these studies are likely to have significant relevance to the understanding and therapeutic management of allergic diseases.