Enhancement of macromolecular ligand binding by rabbit alveolar macrophages by mannose oligosaccharides and related compounds

When rabbit alveolar macrophages were incubated with 10 mM D-mannose, binding of macromolecular ligands containing D-mannose, such as bovine serum albumin modified with mannose (Man-BSA), was enhanced more than 100%, but was inhibited at higher concentrations [C.A. Hoppe and Y. C. Lee (1982) J. Biol. Chem. 257, 12831-12834]. This phenomenon was further investigated with ovalbumin-derived glycopeptide, Asn(GlcNA2,Man5), and with a wide variety of synthetic mannose oligosaccharides. The extent of enhancement is related to the fine structure of the oligosaccharide groups, but the results are complicated by concurrent inhibition exerted by these compounds. It appears that the more inhibitory a compound is, the less capable it is of exerting the enhancement effect. Thus, small mannose derivatives such as glycosides, including clustered mannosides based on tris(hydroxymethyl)aminomethane [Y. C. Lee (1978) Carbohydr. Res. 67, 509-514], and most of the biantennary mannose oligosaccharides were found to be effective in enhancing the binding of radiolabeled Man-BSA. Triantennary oligosaccharides, on the other hand, showed only a slight enhancement effect and a much stronger inhibitory effect. The effects of ligand size, valency, as well as the fine structure on enhancement are discussed.