HEPATITIS-B VIRUS - SPECIFIC BINDING AND INTERNALIZATION OF SMALL HBSAG BY HUMAN HEPATOCYTES

Previously, we identified human liver endonexin II (EII) present on hu man hepatocyte plasma membrane as a specific hepatitis B surface antig en (HBsAg) binding protein. We also showed the spontaneous development of anti-idiotypic (anti-HBsAg) antibodies in rabbits immunized with E II and in chicken immunized with the F(ab')(2) fragment of rabbit anti -EII IgG. These findings suggest the existence of a receptor-ligand re lationship between EII and HBsAg. In the present study, we demonstrate that small HBsAg conjugated to 10 nm colloidal gold also binds specif ically to human hepatocytes. Invagination of the coated pit region at the HBsAg binding sites on the human hepatocyte plasma membrane result s in the internalization of the HBsAg-gold particles. The binding and consequently the internalization of HBsAg is inhibited by anti-EII or anti-idiotypic (anti-HBsAg) antibodies. These findings indicate that E II is directly involved in the binding acid uptake of hepatitis B enve lope proteins.