The role of basal cells in attachment of columnar cells to the basal lamina of the trachea

The mechanism by which basal cells play a role in attachment of airway epithelium to the basal lamina has not been determined. Our hypothesis is that basal cells form a structural bridge between columnar cells and the basal lamina via hemidesmosomes, the cytoskeleton, and desmosomes. To evaluate this hypothesis, we determined the percentage of the columnar cell surface area associated with attachment to the basal lamina and the basal cell in tracheal epithelia of different heights. Tracheas from mice, hamsters, rats, bonnet monkeys, cats, and sheep were prepared for electron microscopy by standard techniques. The height of the epithelia ranged from 8.6 microns in the hamster to 56.8 microns in the sheep. The number of basal cells/100 microns ranged from 3.4 in the hamster to 21.4 in the sheep. The percentage of the basal lamina covered by basal cells increased from 32.6 in the hamster to 94.7 in the sheep. In the shorter epithelia of the hamster, 32% of the columnar cell attachment to the basal lamina was indirect through basal cells, and in the taller epithelia of the sheep, 92% of the columnar cell attachment was by this means. Conversely, the percentage of columnar cell surface in contact with the basal lamina decreased from 67.4% in the hamster to 5.3% in the sheep. These data demonstrate that basal cells play a role in attachment of columnar epithelium to the basal lamina by presenting a surface area for cell-to-cell attachment, thus acting as a bridge between columnar cells and the basal lamina.