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

Quantitation of large, middle and small hepatitis B surface proteins in HBeAg-positive patients treated with peginterferon alfa-2a

BACKGROUND & AIMS

Hepatitis B virus (HBV) contains three viral surface proteins, large, middle and small hepatitis B surface protein (LHBs, MHBs, SHBs). Proportions of LHBs and MHBs are lower in patients with inactive vs active chronic infection. Interferon alfa may convert hepatitis B e antigen (HBeAg)-positive chronic hepatitis B (CHB) to an inactive carrier state, but prediction of sustained response is unsatisfactory. The aim of this study was to test the hypothesis that quantification of MHBs and LHBs may allow for a better prognosis of therapeutic response than total hepatitis B surface antigen (HBsAg) concentration.

METHODS

Hepatitis B surface proteins were measured before and during peginterferon alfa-2a therapy in serum from 127 Asian patients with HBeAg-positive CHB. Sustained response was defined as HBeAg seroconversion 24 weeks post-treatment.

RESULTS

Mean total HBs levels were significantly lower in responders vs nonresponders at all time points (P < .05) and decreased steadily during the initial 24 weeks treatment (by 1.16 vs 0.86 ng/mL in responders/nonresponders respectively) with unchanged relative proportions. Genotype B had a two-fold higher proportion of LHBs than genotype C (13% vs 6%). HBV DNA, HBeAg, HBsAg and HBs protein levels predicted response equally well but not optimally (area under the receiver operating characteristic curve values >0.70).

CONCLUSIONS

Hepatitis B surface protein levels differ by HBV genotype. However, quantification of HBs proteins has no advantage over the already established HBsAg assays to predict response to peginterferon alfa-2a therapy in HBeAg-positive patients.

Interaction between hepatitis B surface proteins and monomeric human serum albumin

HBsAg is known to bind to human serum albumin polymerized by glutaraldehyde, human serum albumin has been found in preparations of HBsAg by several investigators. However, it is not yet known whether natural human serum albumin binds to hepatitis B virus under physiological conditions. We studied the binding between natural or recombinant HBsAg and monomeric human serum albumin by immunological, biochemical and biophysical methods. The binding capacity of 20-nm HBs spheres was variable but ranged up to six molecules HSA/sphere. A reversible binding site for human serum albumin was exclusively localized in the preS2 domain, whereas the S domain was inactive in vitro. Human serum albumin copurified with HBsAg of human origin during gel chromatography or sucrose-gradient centrifugation. This human serum albumin was monomeric in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The preS2-bound part of the human serum albumin could be removed from HBsAg by high-salt, such as CsCl centrifugation, but another part could only be removed by treatment with a disulfide cleaving reagent. Most of this covalently bound human serum albumin was retained at the HBsAg particle after complete cleavage of medium-sized HBs protein with trypsin. This indicates a second way in which albumin binds irreversible to cysteine(s) of the small HBs protein (SHBs, P24 and GP27).

Identification of an attachment site for human liver plasma membranes on hepatitis B virus particles

The surface antigen of hepatitis B virus (HBsAg) exposes three protein domains: preS1, preS2, and S. In a previous study we have shown that preS1 sequences expressed in transfected yeast cells bind specifically to plasma membranes of human liver. In this study we show that purified virus particles from a virus carrier bind also specifically to such membranes. Subviral HBsAg filaments which are rich in preS1 bind well too, while HBsAg 20-nm particles which contain small amounts of preS1 bind to a much lesser degree. The binding can be inhibited by a monoclonal antibody which recognizes a sequential epitope between amino acids 27 and 49 of the preS1 domain.