We describe the first evidence that soluble asialoglycoprotein receptors (AGPR) are present in human serum and that they are quantifiable by an enzyme-linked immunosorbent assay (ELISA). An affinity chromatography gel immobilized with monoclonal antibodies (McAbs) against human liver AGPR was mixed with normal sera, and the bound fraction was analyzed both by sodium dodecyl sulfate polyacrylamide gel electrophoresis and by Western blot analysis. Immunoreactive bands corresponding to 35 to 40 kd were obtained, which were lower than those of liver AGPR (41 kd and 46 kd). Soluble AGPR in human serum was able to bind to D-galactoseimmobilized beads, indicating that the soluble AGPR remained ligand-binding activity. In order to quantify soluble AGPR, we established an ELISA using a monoclonal antibody (30220 McAb)-immobilized microplate and horseradish peroxidase-labeled F(ab' ) , of another monoclonal antibody (30201 McAb). Reproducibility of intraand interassay of the ELISA were 4% to 14% and 7% to 14%, respectively. Analytical recoveries ranged from 93% to 99%. The detection limit was estimated to be 0.1 pg/ L. By nonparametolic analysis, a median and a 90% tile of serum AGPR level obtained from 283 normal volunteers were 0.4 pgL and 2.4 pgL, respectively. (HEPATOLOGY 1995;21:383-388.)
The asialoglycoprotein receptor (AGPR) is a transmembrane glycoprotein that recognizes galactose and N-acetylgalactosamine residues of desialylated glycoproteins and is endocytosed into the hepatocytes as a ligand-receptor complex. 1-3 Immunohistochemical studies showed that AGPR is localized in both the cytosol and the cell surface of normal hepatocytes but not Abbreviations: AGPR, asialoglycoprotein; ELISA, enzyme-linked immunosorhant assay; McAh, monoclonal antibody; EDTA, ethylenediaminetetraacetic acid; PBS, phosphate-buffered saline; BCA, bicinchonic acid; BSA, bovine serum albumin; PHST, phosphate-buffered saline Tween-20; SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis.