Histochemical reactivity of peanut lectin-horseradish peroxidase conjugate

A peanut lectin-horseradish peroxidase (PL-HRP) conjugate has been applied to histochemical staining of paraffin sections of various mouse organs. The PL-HRP conjugate has selectively reacted with secretory bodies, the Golgi zone, and the apical cell surface in various cell types. Some positive sites, including lingual and tracheal serous glands, Brunner's glands, and the brush border of the proximal straight nephron, contained periodic acid-Schiff (PAS)-positive glycoconjugate with no affinity for basic reagents. The stored secretion in these sites was interpreted as containing neutral glycoprotein with terminal galactose residues which could, in part at least, account for the PAS reactivity. Duodenal goblet cells, which exhibited basophilia attributable to sulfate esters, also bound PL-HRP. As the binding was affected by prior sialidase digestion, the secretory glycoprotein in the duodenal goblet cells was judged to contain oligosaccharides with sulfate esters and terminal galactose uncapped by sialic acid. All sites known from their basophilia to form sialomucin failed to stain with the PL-HRP conjugate, but consistently gained reactivity following sialidase digestion and were inferred, therefore, to possess glycoproteins with oligosaccharide side chains containing subterminal galactose and terminal sialic acid. Lingual mucous glands, known to secrete a mucosubstance with basophilic properties indicative of the presence of sulfate esters but not sialic acid, stained with PL-HRP only after sialidase digestion and, accordingly, were reinterpreted as containing both sulfate esters and terminal galactose-sialic acid dimers. Staining of gastric surface epithelium demonstrated a srongly PAS-reactive neutral glycoprotein, and that of goblet cells in the cecum disclosed PAS-positive sulfated glycoprotein. The latter two sites lacked PL-HRP affinity without or with prior sialidase treatment and apparently possessed neither terminal galactose residues nor galactose-sialic acid dimers. PL-HRP affinity was observed exclusively in the Golgi cisternae of some epithelial cells, thus indicating that galactose occurs transiently as a terminal residue in this site. A few histologic sites, such as pancreatic and gastric zymogen cells and renal tubules, were devoid of both PAS reactivity and basophilia indicative of the presence of complex carbohydrate but stained strongly with the PL-HRP conjugate by means which are not understood. Galactose in the PL-HRP solution blocked or reversed the PL-HRP binding in most of the structures with an affinity for the conjugate, supporting the conclusions that the reagent is specific for galactosyl residues.