Epithelial Mediators

The bronchial epithelium has a number of mechanical functions including mucociliary clearance and protection against noxious agents. However, there is increasing evidence that it is a metabolically active tissue that may modulate the function of the underlying smooth muscle by metabolism and regulation of mediators and the production of relaxant, constrictor, or chemotactic factors. It is therefore possible that the epithelial abnormalities observed in asthmatics may lead, via several different mechanisms, to increased bronchial hyperresponsiveness (figure 2), which is a fundamental feature of asthma. However, it may not be necessary to invoke structural damage to explain derangement of epithelial function. It is possible that functional biochemical abnormalities may be present in epithelial cells, thereby producing bronchial hyperresponsiveness in the absence of histologic abnormalities. Further studies with bronchial epithelium, similar to those with vascular endothelium, are needed to clarify its role in the pathogenesis of asthma.