Evidence for receptor-mediated binding of glycoproteins, glycoconjugates, and lysosomal glycosidases by alveolar macrophages.

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Abstract
Rat alveolar macrophages bind glycoproteins and synthetic glycoconjugates (neoglycoproteins) that have mannose, N-acetylglucosamine or glucose in the exposed, nonreducing position. Galactose-terminal glycoproteins are not bound. Binding of radiolabeled ligands to cells is nearly completely impaired by the presence of an excess of yeast mannan. Binding is temperature sensitive and proceeds optimally at pH 7.0. Prior treatment of the cells with trypsin severely decreases their capacity to bind ligands. An inhibition assay was developed, using radioiodinated glucose-albumin conjugate, agalacto-orosomucoid, .beta.-glucuronidase and RNase B as ligands. Various glycoproteins are effective inhibitors of ligand binding, including horseradish peroxidase, agalacto-orosomucoid, .beta.-glucuronidase, ovalbumin, agalcto-fetuin and RNase B. RNase A and asialo-fetuin are ineffective as antagonists. There may be a cell surface receptor on alveolar macrophages that binds glycoproteins having terminal sugars with the mannose or glucose configuration.