Inhibition of albumin binding to hepatitis B virions by monoclonal antibody to the preS2 domain of the viral envelope.

The binding of polyalbumin to hepatitis B virus (HBV)-associated envelope epitopes has been studied by means of a radioimmunoprecipitation technique. HBV particles were purified from the sera of chronic hepatitis B surface antigen (HBsAg) carriers and labelled through the endogenous HBV-DNA polymerase reaction. Human albumin, polymerized through glutaraldehyde cross-linking, was able to precipitate (100%) labelled HBV at concentrations of 31.2 and 62.5 micrograms/ml, in contrast to monomeric albumin (HSA). This event was further confirmed by immune electron microscopy. The addition of anti-HSA to the mixture HBV plus polyalbumin gave a 100% precipitation in a wide dilution range (15.6-500 micrograms/ml). The binding of polyalbumin (31.2 micrograms/ml) to virions was strongly inhibited (up to 98%) when preincubating with antibody to a glycosylation-dependent preS2 epitope on HBV. The same was accounted (up to 99%) for polyvalent IgG anti-HBs. However, antibodies to the group 'a' and subtype 'd' determinants, as well as anti-preS1 region antibodies, inhibited weakly polyalbumin binding to HBV. The binding site of the inhibitory antibody overlaps probably with neutralizing epitopes. Our findings support the hypothesis that albumin binding plays an important role in the viral life cycle.