Qualitative and quantitative aspects of labeling cell surface carbohydrates using lectins as probes

Lectins are proteins which bind mono- and oligosaccharides with great specificity. Many polysaccharides, glycoproteins and glycolipids which are important constituents of cell walls and surface membranes of prokaryotic and eukaryotic cells, contain sugar moieties with which lectins can interact. As a result lectins have been extensively used for the study of cell surface and membrane structure of their labeling. This paper reviews and evaluates the available methods for the preparation of fluorescent, electron-dense and radioactive lectin derivatives. The procedures involved in the visualization of lectin binding under light and electron microscopy are described. In addition, the methods for quantitative evaluation of the fluorescence on labeled cells and for analysis of the number of cell surface lectin binding sites using radioactively-labeled lectins are outlined. Examples are given for the application of fluorescent lectin derivatives for the detection of specific saccharide-containing molecules on the surfaces of living or fixed microbial cells and various normal and neoplastic cells. The use of lectins to demonstrate the dynamic nature of cell membranes and to detect changes in membrane structure or organization which occur or organization which occur during differentiation, development or after neoplastic transformation is discussed.