Receptor-mediated pinocytosis of mannose glycoconjugates by macrophages: Characterization and evidence for receptor recycling

125I-Mannose-BSA is taken up by alveolar macrophages by receptor-mediated endocytosis. Uptake is macrophage-specific and does not occur in polymorphonuclear leukocytes. Binding (4°C) and uptake (37°C) of 125I-Man-BSA are time- and ligand concentration-dependent [K uptake = 40 nM; K d (4°C) = 10 nM]. When adjusted for ligand degradation, ligand uptake is linear with time. Binding saturates at 60 min and requires Ca ++. Following binding, ligand remains on the cell surface where it can be released by EGTA and trypsin. Internalization of prebound ligand occurs very rapidly ( t 1 2