Lectin-Gold Histochemistry on Paraffin and Lowicryl K4M Sections Using Biotin and Digoxigenin-Conjugated Lectins.

A variety of staining reactions for the visualization of cellular and extracellular glycoconjugates at the light microscopic level are available that are based on the detection of carboxyl and sulfate groups or periodic acid reactive configurations (1,2). Starting in the late 1960s lectins have replaced many of these chemical staining reactions because of their high specificity for defined monoand oligosaccharidic sequences in both N- and o-glycosidic-linked oligosaccharide side-chains of glycoproteins and glycolipids. In order to be useful as histochemical reagents, lectins must be tagged with appropriate markers and those employed in immunocytochemistry have been used successfully (3-9) Horisberger and coworkers were the first to prepare lectins labeled with particles of colloidal gold and used them in scanning electron mrcroscopy (10) Subsequently, gold-labeled lectins were applied in transmission electron microscopy to study various aspects of cell surface expression and internalization of lectin-binding sites (5,8,11,12), as well as in postembedding labeling of Lowicryl K4M thin sections (13). Later, it was shown that gold-labeled lectins can be used to stain sections of paraffin-embedded tissues (14-16), as well as semithin sections of Epon (17) and Lowicryl K4M-embedded tissues (18,19), However, in order to achieve a visible pink staining, which is the natural color of particles of colloidal gold in transmitted visible light (20), highly concentrated lectin-gold complexes had to be used, thereby allowing the possibility of nonspecific staining. A major improvement resulted through the application of a photochemrcal silver reaction for signal amphfication (21-24), whrch permitted the use of lectins for light microscopy in concentrations as applied for electron microscopy (25,26).