Carbohydrate Antigens

Cornells PJ Glaudemans, Chief, Section on Carbohydrates, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA

Copyright © 1998 Elsevier Ltd. All Rights Reserved.

Carbohydrates, containing n asymmetric carbon atoms, can exist in 2" stereoisomeric forms. A common hexose possesses a priori four asymmetric carbon atoms (C-2, -3, -4 and -5) and thus can exist in 16 stereoisomeric forms (i.e. d-glucose, L-glucose, d-mannose, L-mannose, etc.). Each of these isomers can occur in either a six-membered (pyranose) or five-membered (furanose) ring form. When a hexose is in the ring form, the C-l aldehyde function also becomes asymmetric, and the 1-hydroxyl group can assume either the a or the (3 configuration, thereby doubling the number of possible isomers. In total, a hexose can thus occur in an oligo- or polysaccharide in 64 different ways. This enormous capability for diversity makes carbohydrates very versatile as nature's alphabet for recognition in biological events, including immunology. Bacteria, viruses and mammalian cells nearly always have polysaccharides as capsular or cell wall material, and/or have glycolipids and glycoproteins on, or in, their walls, and these wall components or capsules often dictate the ensuing cascade of biological events in which they participate.

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