Histochemical properties of the respiratory tract epithelium in different species.

The comparative composition of secretory components and cell surface moieties is described in this review on epithelial cells of the respiratory tract in mouse, rat, and humans. The discussion concerns mainly the nature of the carbohydrate-rich secretory substances and glycocalyx components present in the various types of epithelial cells in the 3 species. Older methods for characterizing acid groups and vicinal glycols of the complex carbohydrates and more recent methods for identifying specific terminal and internal sugars with labeled lectins are outlined, including techniques for both light and electron microscopic examination. Knowledge derived from the application of these methods is detailed for the surface glycocalyx of secretory cells lining the proximal and distal airways and alveoli, as well as for the glycocalyx of ciliated cells and membranous pneumocytes in each species. Histochemically derived knowledge of the composition of substances in secretory granules of surface epithelial cells is also summarized. The review concerns as well the nature of secretory products in serous and mucous cells of the glands in the lamina propria of trachea and bronchi. The available data delineate major differences between serous cell secretions compared with mucous cell secretions as well as differences between species for each cell type. In addition, ABO blood group dependent differences have been demonstrated in the human glands.