Figure 1.

Epithelial differences between normal and diseased small airways. Ciliated, cuboidal epithelial cells constitute the majority of a normal bronchiolar epithelium. In a diseased SAE, however, these cell types undergo metaplasia and become a more squamous phenotype. Secretory goblet cells are found in small numbers within a normal SAE, but under diseased conditions, increase in prevalence. By contrast, the number of secretory club cells are reduced in a diseased SAE, compared to normal, with a subsequent reduction in the secretion of the protective protein, CC-16. Their proposed progenitor cell, the basal cell, is however present in greater abundance in a diseased epithelium, compared to normal.

Abbreviations: SAE, small airway epithelium; CC-16, club cell protein 16.