Stimulation of mannose-binding activity in the rabbit alveolar macrophage by simple sugars

Mammalian alveolar macrophages are known to bind glycoconjugates with terminal D-mannosyl residues (Stahl, P. D., Rodman, J. S. Miller, M. J., and Schlesinger, R. H. (1978) Proc. Natl. Acad. Sci. U. S. A. 75, 1399-1403). Although macromolecules containing D-mannosyl residues, such as bovine serum albumin modified with 2-imino-2-methoxyethyl 1-thio-alpha-D-mannopyranoside (mannose-BSA) (Lee, Y. C., Stowell, C. P., and Krantz, M. J. (1976) Biochemistry 15, 3956-3963), were very potent inhibitors of 125I-mannose-BSA binding to macrophages, the monosaccharides D-mannose, L-fucose, N-acetyl-D-glucosamine, and D-glucose doubled to tripled the binding of 125I-mannose-BSA to intact rabbit lung macrophages at 2 degrees C. The monosaccharide concentration required for maximum stimulation and the extent of stimulation were dependent on the number of D-mannosyl residues attached to the BSA ligand. The lower the number of D-mannosyl residues coupled to BSA, the smaller the effect by D-mannose and the lower the D-mannose concentration at which it occurred. Equilibrium binding analysis indicated that the apparent affinity of cell surface receptor for ligand increased from Kd = 1.0 nM to Kd = 0.3 nM under conditions of maximal stimulation of 125I-mannose43-BSA binding.