ABSTRACT
Surfactant protein A (SP-A) binding to bovine alveolar macrophages was examined in order to characterize SP-A binding proteins on the cell surface and to isolate putative receptors from these cells that could be obtained in large amounts. Human SP-A, unlabeled or labeled with gold particles, was bound to freshly isolated macrophages and analyzed with ELISA or the transmission electron microscope. Binding of SP-A was inhibited by Ca2+ chelation, by an excess of unlabeled SP-A, or by the presence of 20 mg/ml mannan. We conclude that bovine alveolar macrophages expose binding sites for SP-A that are specific and that depend on Ca2+ and on mannose residues. For isolation of SP-A receptors with homologous SP-A as ligand we isolated SP-A from bovine lung lavage. SDS-PAGE analysis of the purified SP-A showed a protein of 32-36 kDa. Functional integrity of the protein was demonstrated. Bovine SP-A bound to Dynabeads was used to isolate SP-A binding proteins. From the fractionated and blotted proteins of the receptor preparation two proteins bound SP-A in a Ca2+-dependent manner, a 40-kDa protein showing mannose dependency and a 210-kDa protein, showing no mannose sensitivity.
Subject(s)
Macrophages, Alveolar/metabolism , Proteolipids/metabolism , Pulmonary Surfactants/metabolism , Receptors, Cell Surface/metabolism , Animals , Binding Sites , Cattle , Humans , Pulmonary Surfactant-Associated Protein A , Pulmonary Surfactant-Associated Proteins , Receptors, Cell Surface/isolation & purificationABSTRACT
The possible interaction of galactose/glucose-specific liver lectins with nonenzymatically glycated human serum albumin was analyzed. The binding activity of the asialoglycoprotein receptor on hepatocytes and of the corresponding lectin on Kupffer cells was determined using freshly isolated liver cells from Wistar rats. Nonenzymatically glucosylated or galactosylated human serum albumin (HSA) did not inhibit lectin binding in a competitive adhesion assay (less than 15% inhibition). In contrast, lactosylated HSA strongly interacted with the two liver lectins (more than 80% inhibition). Lectin binding increased with lactosylation reaching a maximum at 44-49 mol D-galactose bound per mol HSA. In conclusion, at least in certain cases, nonenzymatically glycated proteins may interact with endogenous lectins.
