REPAIR OF BRONCHIAL EPITHELIUM

Lesions of the respiratory epithelium can be related to a mucosal immu ne deficiency, secondary to physicochemical alterations of the mucus b arrier which normally protects the epithelium from the harmful action of inhaled irritants, bacteria and viruses. Lesions of the respiratory epithelium result in increased junctional permeability, partial desqu amation of epithelial cells, or even total exposure of the basement me mbrane. In vivo and in vitro models of lesions of the respiratory epit helium show that, in response to a lesion, the surface epithelium can be repaired by a number of mechanisms including: spreading, migration of basal epithelial cells, repair of tight junctions, transdifferentia tion phenomena and proliferation of basal and mucus-secreting cell. Ce lls of the surface epithelium are able to repair a lesion and restore functional integrity of the epithelium after intervals ranging from 48 to 72 hours according to the dimensions of the lesion. Various molecu les are directly involved in the repair process (especially constituen ts of the extracellular matrix and the corresponding integrins (fibron ectin and alpha(5) beta(1) integrins), epithelial matricial metallopro teinases (gelatinase B and stromelysin). During repair of the epitheli um, remodelling of the surface epithelium can induce the appearance of apical receptors to bacterial adhesins, thereby facilitating recurren ce of bronchial infection.