CARBOHYDRATE-CARBOHYDRATE INTERACTIONS IN ADHESION

Cell-cell interactions play an important role in the development, main tenance, and pathogenesis of tissues. They are highly dynamic processe s which include migration, recognition, signaling, adhesion, and final ly attachment. Cells on their pathway to a final location have to pass and interact with their substratum formed of matrix and cell layers. Testing and recognition are important keys for the proper result of ti ssue formation. They can, however, also lead to diseases when they are misused in pathological situations, by microorganisms or malignant ce lls, for instance. Carbohydrates, which are the most prominent surface -exposed structures, must play an important role as recognition molecu les in such processes. The rich variability of carbohydrate sequences which cell surfaces can present to lectins, adhesion molecules, and ot her ligands creates a refined pattern of potential attachment sites. T he subtle control of the surface presentation density can provide vari ations in attachment strength. Not only the carbohydrate sequences but also the fact that carbohydrates can be branched while proteins canno t and that the oligosaccharide chains can be attached to the protein b ackbone in different densities and patterns will create yet more inter action possibilities.Maximal use of the combinatorial richness of carb ohydrate molecules would be made when carbohydrate sequences could int eract with other carbohydrate sequences. Such interactions have only v ery rarely been considered for biochemically and biologically relevant situations since they are difficult to measure. A few are known and w ill be summarized here with the hope that this wealth of possible chem ical interactions may be considered more and more by surface cell bioc hemists when analyzing fine tuning in cellular interactions. (C) 1996 Wiley-Liss, Inc.