Bronchial epithelium: morphology, function and pathophysiology in asthma

Human bronchial epithelium has a number of mechanical functions, including mucociliary clearance and protection against noxious agents. Bronchial epithelial cells are also able to release a variety of mediators, including cytokines, chemokines, growth factors, and arachidonic acid metabolites, which are able to regulate the recruitment, activation, and differentiation of inflammatory cells. They also modulate the function of the underlying smooth muscle cells by the release or metabolism of bronchoactive mediators. Finally, bronchial epithelial cells may control inflammatory reactions by the release of anti-inflammatory mediators or by the inactivation of pro-inflammatory mediators. Morphological or functional abnormalities of the bronchial epithelium may contribute to the initiation, perpetuation and prolongation of inflammatory processes and thereby to the pathogenesis of asthma. In this review, the morphology of the bronchial epithelium, its function with regard to host defense, and its immunological potential will be reviewed. Alterations associated with asthma will be emphasized.