Complement‐mediated cytotoxicity and inhibition of ligand binding to hepatocytes by woodchuck hepatitis virus–induced autoantibodies to asialoglycoprotein receptor

Hepadnavirus invasion in woodchucks has been identified as a potent inducer of autoantibodies against asialoglycoprotein receptor (anti‐ASGPR), a molecule essentially unique to hepatocytes that mediate clearance of desialylated serum proteins. We evaluated the possible pathogenetic importance of anti‐ASGPR triggered by woodchuck hepatitis virus (WHV), using anti‐ASGPR–reactive serum immunoglobulins (Igs) from five animals with different stages of WHV hepatitis or self‐limited WHV infection and isolated woodchuck hepatocytes or HepG2 cells as targets. The results revealed that WHV‐induced anti‐ASGPR can specifically inhibit asialoglycoprotein recognition by both homologous and heterologous liver cells, as tested in an asialofetuin (ASFN)‐binding radioassay. However, the extent of the interference significantly varied (from 85% inhibition to none) for anti‐ASGPR with similar titer from different animals, indicating a high degree of heterogeneity in the ASGPR epitope specificity and in the potential biological effects of these autoantibodies. The WHV‐triggered anti‐ASGPR also induced complement‐mediated hepatocytolysis in a microculture tetrazolium (MTT) assay, which ranged from 8.9% ± 0.3% to 33.6% ± 3.6% (mean ± SD) for different animals and target cell numbers. This cytopathic effect was strictly ASGPR‐specific, complement‐dependent, and was not related to the anti‐ASGPR ability to inhibit ligand‐hepatocyte binding. Our findings indicate that among pathways by which anti‐ASGPR autoimmunity could cause liver damage, hepadnavirus‐induced anti‐ASGPR might impair hepatocytes by both disrupting clearance of desialylated proteins and activation of the complement‐mediated cytolysis. These cytopathic effects might contribute to the pathogenesis, aggravate severity, and prolong recovery from liver injury in viral hepatitis.