title: Endocytosis of hepatitis B immune globulin into hepatocytes inhibits the secretion of hepatitis B virus surface antigen and virions.
abstract: Hepatitis B immunoglobulin is used for prophylaxis against hepatitis B virus (HBV) and is thought to act by neutralization of virions and hepatitis B virus surface antigen (HBsAg)-containing particles in circulation. Using a panel of hepatocyte-derived cell lines, the present study investigated in vitro whether HBs-specific immunoglobulin G (IgG) is internalized in hepatocytes and whether it interacts with HBsAg in the cells. By immunoelectron microscopy and immunoblotting, human IgG and FcRn receptor for IgG were demonstrated on cellular membranes and in cytoplasmic extracts, irrespective of the HBsAg status of the cells. Furthermore, HBsAg and anti-HBs were shown to be colocalized in the same cellular compartment by two-color confocal microscopy. Endocytosis of HBs-specific IgG caused intracellular accumulation of HBsAg in a dose-dependent manner and inhibited the secretion of HBsAg and HBV virions from the cells. These effects were not observed with F(ab)(2) fragments or nonimmune IgG as controls. The specificity of intracellular HBsAg- anti-HBs interaction was further investigated in cells transfected with HBV genomes expressing wild-type HBsAg or immune escape HBsAg (with a G145R mutation). Monoclonal anti-HBs markedly reduced the secretion of wild-type HBsAg, while the secretion of mutant HBsAg was not affected. These results suggest that HBs-specific IgG binds to hepatocytes and interacts with HBsAg within the cells. This may be relevant for the selection of surface antibody escape mutations.
authors.affiliation: Institute of Hepatology, Department of Medicine, University College London, London WC1E 6HX, United Kingdom.
authors.forename: Ralf
authors.initials: R
authors.lastname: Schilling
authors.forename: Samreen
authors.initials: S
authors.lastname: Ijaz
authors.forename: Michail
authors.initials: M
authors.lastname: Davidoff
authors.forename: Jia Yee
authors.initials: JY
authors.lastname: Lee
authors.forename: Stephen
authors.initials: S
authors.lastname: Locarnini
authors.forename: Roger
authors.initials: R
authors.lastname: Williams
authors.forename: Nikolai V
authors.initials: NV
authors.lastname: Naoumov
mesh_terms: D001483:Base Sequence; D017931:DNA Primers; D004705:Endocytosis; D006514:Hepatitis B Surface Antigens / Q000276:immunology*; D006515:Hepatitis B virus / Q000276:immunology / Q000502:physiology; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014771:Virion / Q000276:immunology*; D014779:Virus Replication
chemical_list: D017931:DNA Primers; D006514:Hepatitis B Surface Antigens; D007136:Immunoglobulins; C045213:hepatitis B hyperimmune globulin