Modulation of airway intraepithelial dendritic cells following exposure to steroids.

Recent studies from our laboratory have identified a network of constitutively class II major histocompatibility complex (MHC) (Ia)-bearing dendritic cells (DC) within the epithelium of the conducting airways of laboratory animal species and in humans. These studies have also demonstrated that the density of the DC network increases within the airway epithelium in response to inflammatory challenge. In the present report, we demonstrate that exposure of adult rats to inhaled steroids leads to a rapid but readily reversible decrease both in the number of airway intraepithelial DC, and in their surface Ia expression. Similar changes are also seen in response to high doses of systemic dexamethasone. In addition, we demonstrate that steroid inhalation reduces the rate of postnatal expansion of the airway intraepithelial DC network in rat pups, and prevents the rapid expansion of the DC network in adults which occurs during the acute inflammatory response following inhalation of microbial stimuli.