FIG. 1.

Histological sections of proximal and distal conducting airways. (size bar: 200 µm.) Inset: Higher magnification of epithelial layer. (size bar: 50 µm.) A, Naïve rat section with the proximal bronchiolar epithelium with a single layer of epithelium with a uniform underlying basement membrane. B, Two days after SM exposure, the epithelium was patchy with areas of complete epithelial denudation and flattened, squamous-appearing epithelium without cilia. C, Two weeks after exposure, areas of proximal epithelium appeared with persistent areas of denudation and metaplastic, squamous epithelium. The surrounding mesenchyme was disorganized with significant inflammatory infiltrates. D, One month after SM injury, the epithelial layer of the proximal bronchioles was still not restored with epithelial sloughing (black arrow).