CELL-ADHESION MOLECULES AND THE BRONCHIAL EPITHELIUM

The bronchial epithelium is the major barrier between the host and the provoking antigens in bronchial asthma. Recent studies have indicated that the epithelium is a truly stratified structure, with the superfi cial columnar cells depending on the underlying basal cells for anchor age. Only columnar cells are shed into bronchial lavage fluid. The epi thelium is more fragile in asthma and more cells are lost in clusters. Desmosomes appear to be the major structural adhesion mechanism at th e plane of cleavage between the columnar cells and the basal cells. Th e alpha(8)- and beta(4)-integrins, which contribute to hemidesmosomes and anchor cells to the underlying basement membrane, are expressed so lely by basal cells. The apical aspects of the columnar cells are seal ed by tight and intermediate junctions. There is constitutive expressi on of ICAM-1 and E-selectin in the vasculature of the bronchial mucosa , and ICAM is also present within the epithelium. These findings indic ate that the bronchial epithelium is a complex structure that, as a mu cosal surface, has constitutive expression of inflammatory cell adhesi on molecules to serve normal leukocyte traffic.