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.
Diao
J
J
Division of Basic Medical Sciences, Faculty of Medicine, Health Sciences Centre, Memorial University of Newfoundland, St. John's, Canada.
Churchill
N D
ND
Michalak
T I
TI
D000818:Animals; D037263:Asialoglycoprotein Receptor; D001323:Autoantibodies / Q000276:immunology*; D003167:Complement Activation; D003165:Complement System Proteins; D003602:Cytotoxicity, Immunologic; D006509:Hepatitis B / Q000276:immunology*; D017919:Hepatitis B Virus, Woodchuck / Q000276:immunology*; D008024:Ligands; D008099:Liver / Q000276:immunology* / Q000473:pathology / Q000821:virology*; D008392:Marmota; D011956:Receptors, Cell Surface / Q000276:immunology*
D037263:Asialoglycoprotein Receptor; D001323:Autoantibodies; D008024:Ligands; D011956:Receptors, Cell Surface; D003165:Complement System Proteins