BASAL CELLS IN HUMAN BRONCHIAL EPITHELIUM

The morphology and distribution of basal cells were investigated in adult human bronchial epithelium. In both smokers and non-smokers typical basal cells were more numerous than atypical basal cells, which were distinguished by their spindle-shaped nucleus, polar cytoplasm, and processes that extended along the basal lamina. The nucleus of the atypical basal cell was consistently closer to the muco-ciliary surface than was the nucleus of the typical basal cell. In cross-sections of bronchi the numbers of typical basal cells/mm epithelium were greatest in large airways; in smaller bronchi (i.e., generations 7-16) the frequency declined. The numbers of atypical basal cells/mm epithelium were similar throughout the bronchial tree. Throughout the bronchial tree both types of basal cells contributed to the maintenance of epithelial cohesion by providing desmosomal attachment for columnar cells. The importance of typical basal cells in this role was indicated by their greater numbers, which collectively presented a large surface for epithelial cell attachment by desmosomes. The surface presented by the cell body and processes of each atypical basal cell for attachment of columnar cells by desmosomes was extensive. If the basal cell is the most important progenitor of bronchial epithelium and the cell at risk in the development of lung cancer, the presence of more basal cells in upper airways, where many lung cancers originate, may be significant. The basal cell populations in larger bronchi are perhaps the greatest concentration of cells with proliferative capability and potential for neoplastic transformation in the human bronchial tree. (C) 1994 Wiley-Liss, Inc.