A monoclonal antibody to rat asialoglycoprotein receptor that recognizes an epitope specific to its major subunit

We previously developed three mouse monoclonal antibodies (MoAbs) identifying the domain-specific plasma membrane proteins of rat hepatocytes. Based on the results of immunohistochemical and immunoblot analysis, one of them, clone 8D7, likely recognizes the rat asialoglycoprotein receptor (ASGPR), which consists of three polypeptide subunits: rat hepatic lectin (RHL)-1, RHL-2 and RHL-3. In this study, we examined the reactivity of MoAb 8D7 with these subunits in order to identify specifically the protein it recognizes. RHL-1 and RHL-2/3 were expressed in COS-1 mammalian kidney cells transfected with cloned cDNAs. Reactivity of MoAb 8D7 with these proteins was examined by flow cytometry, immunoblotting, and an immunofluorescence staining. By flow cytometry, MoAb 8D7 reacted with cell surface proteins on the COS-1 cells transfected with RHL-1 cDNA but not with RHL-2/3 cDNA. By immunoblotting, the antibody recognized proteins (molecular weights 45 and 96 kDa) in RHL-1-expressing cells but not in the RHL-2/3 cDNA-transfected cells. Immunoreactive staining with MoAb 8D7 was observed on the cell surface and in the cytoplasm of RHL-1-transfected COS-1 cells but not in cells expressing RHL-2/3. These findings indicate that MoAb 8D7 recognizes a subunit-specific epitope on RHL-1 of rat ASGPR.