Lectin Histochemistry and CytochemistryLight Microscopy: AvidinBiotin Amplification on Resin-Embedded Sections

Within the last 25 yr, the study of glycans, their structures, and their drstribution in tissues has emerged from relative obscurity to become a major theme of molecular and cellular biology: “glycobiology” (1 ). Glycans are major components of cellular surfaces (2 ,3 ), extracellular matrices (4 ,5 ), and secretions (6 ), and play important roles in cell—cell and cell—matrix recognition and adhesion (7 ,8 ). They regulate the surface environment of cells by influencing the structure of water (6 ,9 ), by modulating diffusion, by sequestering metabohtes such as metal ions, by presenting various growth factors to their receptors (10 ,11 ), by acting as ligands in recognition-adhesion systems (11 –13 ), and by making major contributions to cell surface charge (2 ,14 ). In secretions, they are variously determinants of molecular folding (15 ), hydration, interaction, and targeting, and they serve in the mechanisms that monitor the aging of glycoconjugates in circulation (6 ,9 ,16 ,17 ). They are now implicated in mechanisms of molecular targeting and segregation within the endomembrane systems of cells (18 -20 ), in calcium transport in mitochondria (21 ), the handling of mRNA and its export from the nucleus, the regulation of transcription (19 ), and in then classical role as energy stores. In all of this, the association of anatomical or ultrastructural localization with biological function is of paramount importance. specific glycans occur in specific places (22 ,23 ). The challenge for the histochemist is to reconcile the achievement of sufficiently precise anatomical localization of glycans with the maximum of chemical information about their nature. The lectins have been the main means of accompllshing this, since their first application as fluorochrome-labeled probes to paraffin sections in the early 1970s (2 ,24 ). More recently, fluorescence has been largely supplanted by nonfluorescent disclosing systems, such as biotin-avidin-peroxidase and, though paraffin sections are still widely used, resin-embedding of specimens has proved advantageous in terms of resolution and economy of material at the light microscopic level.