Tracheobronchial epithelium of the sheep: IV. Lectin histochemical characterization of secretory epithelial cells

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Abstract
Conventional histochemical characterization of the mucus secretory apparatus is often difficult to reconcile with the biochemical analysis of respiratory secretions. This study was designed to examine the secretory glycoconjugates in airways using lectins with biochemically defined affinities for main sugar residues of mucus. We used five biotinylated lectins—DBA (Dolichos biflorus) and SBA (Glycine max) for N-acetyl galactosamine (gaINAc), BSAI (Bandeiraea simplicifolia) and PNA (Arachis hypogea) for galactose (gal), UEA I (Ulex europeus)—for detection of fucose (fuc) in HgCl2 -fixed, paraffin-embedded, serially sectioned trachea, lobar and segmental bronchi and bronchioles of nine sheep. Lectins selectively localized the carbohydrate residues in lumminal secretions, on epithelial cell surfaces, and in secretory cells. Inp proximal airways, the major carbohydrate residues in luminal secretions, cell surfaces, goblet cells, and glands were fuc and gal-NAc. PNA reacted mainly with apical granules of < 10% of goblet cells, and gal residues were only detected in some of the mucous cells and on basolateral cell surfaces. Distal airways contained sparse secretion in the lumen, mucous cells containde weakly reactive fuc and gal-NAc, and the epithelial surfaces of Clara cells contained gal. Sugars abundant in the airway secretions were also the major component of cells in glands. We conclude that there is a correlation between specific sugar residues in secretory cells, glycocalyx, and luminal secretions in proximal and distal airways. This suggests that lectins may be used to obtain information about airway secretory cell composition from respiratory secretions.