Lectin--digoxigenin conjugates: a new hapten system for glycoconjugate cytochemistry

We report the use of a novel hapten system for lectin cytochemistry. Various lectins conjugated to the steroid hapten digoxigenin (DIG) and monospecific anti-digoxigenin antibodies were applied for the light and electron microscopic detection of glycoconjugates in tissue sections. Both IgG and Fab' anti-DIG antibodies were complexed to particles of colloidal gold and compared to commercially available alkaline phosphatase and horseradish peroxidase conjugated Fab' as general second step reagents. The three different markers performed equally well on paraffin sections whereas the gold-labeled antibodies were superior reagents for semithin and ultrathin sections of Lowicryl K4M embedded tissues. In conjunction with the latter marker, no pretreatment to abolish endogenous enzyme activity was necessary. At the light microscope level, gold signal amplification by the photochemical silver reaction was required. DIG, in contrast to biotin, does not occur in animal tissues thus eliminating the need for blocking reactions prior to lectin incubation. Compared to affinity techniques using glycoprotein-gold complexes as second step reagent the DIG hapten system required smaller amounts of lectins. The staining patterns were indistinguishable from those obtained in other lectin-gold techniques and the specificity of the labeling could be demonstrated in sugar inhibition tests.