Interaction between various polymerized human albumins and hepatitis B surface antigen

Mapping of immunodominant B-cell epitopes and the human serum albumin-binding site in natural hepatitis B virus surface antigen of defined genosubtype

Twelve MAbs were generated by immunization of BALB/c mice with plasma-derived hepatitis B virus surface spherical antigen particles subtype ayw2 (HBsAg/ayw2 genotype D). Their epitopes were mapped by analysis of reactivity with plasma-derived HBsAg/ayw2 and HBsAg/adw2 (genotype A) in enzyme immunoassays and blots. Mapping was supported by nested sets of truncated preS2 proteins and preS2 peptides. Five antibodies were S domain-specific, seven were preS2-specific and 11 had a preference for genotype D. According to our data, group I of the three known epitope groups of preS2 has to be divided into IA and IB. Three preS2-specific MAbs forming the new group IA reacted with genotype D residues 3-15 which have not yet been described as an epitope region. IA antibodies strongly inhibited the binding of polymerized human serum albumin. Two antibodies (group II) reacted with the glycosylated N-terminal region of preS2 in plasma-derived HBsAg, but not with a preparation from transfected murine cells. One group III antibody was subtype-specific and reacted with the highly variable preS2 sequence 38-48. Only one antibody (group IB) mapped to the region (old group I) which was believed to be immunodominant and genotype-independent. Geno(sub)type-specific epitopes of preS2 are obviously the immunodominant components of natural HBsAg in BALB/c mice, but these epitopes may be masked by serum albumins in humans. The data may explain why it is difficult to detect anti-preS2 antibodies in human recipients of preS2-containing vaccines, in spite of the preS2 immunodominance in mice.

Evaluation of B and T-cell responses in chimpanzees immunized with Hepagene, a hepatitis B vaccine containing pre-S1, pre-S2 gene products

Approximately 5-10% of healthy young adults receiving the commercially available hepatitis B vaccine (either serum derived or recombinant) fail to mount an adequate immune response. This nonresponder rate has prompted the demand for more immunogenic vaccines. An alternative to the currently licensed hepatitis B vaccines is Hepagene, a novel recombinant hepatitis B vaccine containing S, pre-S1 and pre-S2 antigenic components, produced in the mouse C127I clonal cell line after transfection of the cells with genes encoding the three antigens. In this study, chimpanzees were immunized with Hepagene to study the humoral and cellular immune responses to this vaccine. Two out of the three animals immunized with this vaccine seroconverted 4 weeks after their first injection and all of the animals elicited high anti-HBs levels that were maintained for at least 28-30 weeks after their third immunization. The anti-HBs levels elicited in these animals protected them against an experimental challenge with HBV. Peripheral blood mononuclear cells (PBMCs) obtained from immunized animals could be stimulated in vitro by rHBsAg and peptides representing regions within all three of the viral envelope proteins. Additionally, an anti-id that mimics the a determinant in the S-region of HBsAg could also stimulate in vitro proliferation of PBMCs from these immune animals. These results indicate that this new recombinant HBV vaccine encoding all three of the surface antigen proteins is highly immunogenic is that it can stimulate strong cellular and humoral immune responses.

Spontaneous development of anti-hepatitis B virus envelope (anti-idiotypic) antibodies in animals immunized with human liver endonexin II or with the F(ab')2 fragment of anti-human liver endonexin II immunoglobulin G: evidence for a receptor-ligand-like relationship between small hepatitis B surface antigen and endonexin II

In a previous study, we have identified endonexin II (E-II) on human liver plasma membranes as a specific, Ca(2+)-dependent, small hepatitis B surface antigen (HBsAg)-binding protein. In this article, we describe the spontaneous development of anti-HBs antibodies in rabbits immunized with native or recombinant human liver E-II and in chickens immunized with the F(ab')2 fragment of rabbit anti-human liver E-II immunoglobulin G. Anti-HBs activity was not observed in rabbits immunized with rat liver E-II. Cross-reactivity of anti-E-II antibodies to HBsAg epitopes was excluded, since anti-HBs and anti-E-II activities can be separated by E-II affinity chromatography. The existence of an anti-idiotypic antibody is further demonstrated by competitive binding of human liver E-II and this antibody (Ab2) to small HBsAg, suggesting that Ab2 mimics a specific E-II epitope that interacts with small HBsAg. In addition, it was demonstrated that anti-HBs antibodies developed in rabbits after immunization with intact human liver E-II or in chickens after immunization with F(ab')2 fragments of rabbit anti-human liver E-II immunoglobulin G recognize the same epitopes on small HBsAg. These findings strongly indicate that human liver E-II is a very specific small HBsAg-binding protein and support the assumption that human liver E-II is the hepatitis B virus receptor protein.

Virological and serological aspects of hepatitis B and the delta agent

The hepatitis B virus (HBV) belongs to a group of viruses termed hepadnaviruses. The 3.2 kb genome encodes for a variety of proteins involved in viral replication (p-gene), transactivation (x-gene), or encodes for structural proteins (c- and s-genes). Several viral and non-viral functions determine the clinical course of HBV infection. The hepatitis D virus resembles a viroid and requires the HBV as a helper virus. The interaction between the viruses is not well understood. More information on the interaction between the human host and viruses is needed to help improve the treatment.

Three envelope proteins of hepatitis B virus: large S, middle S, and major S proteins needed for the formation of Dane particles

The infectious particles of hepatitis B virus are called Dane particles and consist of viral nucleic acid encapsulated within a core particle that is enveloped by virus-coded surface proteins. The major S protein constitutes a significant fraction of these surface proteins. In addition, there are two other related proteins (large S and middle S), but their role in envelope formation has not yet been elucidated. We modified the translation initiation codon ATG of each of the envelope proteins by site-directed mutagenesis and found that mutant genomes that did not produce one or two of these proteins were unable to form Dane particles. The particles released into the culture medium by such mutants did not carry DNA. Synthesis of virus-coded RNA still occurred normally, and core particles carrying DNA accumulated intracellularly. The DNA in such core particles was mostly in the double-stranded open circular form, in contrast to the normal situation in which the particles contain mostly RNA and its complementary single-stranded DNA or else contain linear DNA that is partially single stranded and otherwise duplex. The role of the large S and middle S proteins in the formation of Dane particles is discussed.

Expression and characterization of the preS1 peptide of hepatitis B surface antigen in Escherichia coli

The infectious particles of hepatitis B virus (HBV) contain 3 related surface antigens, i.e., small, medium, and large, all of which are encoded by one large open reading frame with multiple initiation codons. The large surface antigen (L-Ag) contains preS1, preS2, and S regions while both the middle and small surface antigens lack preS1. Several lines of evidence suggested that the preS1 region is involved in the binding of HBV to human hepatocytes as shown by its binding to HepG2 cells and isolated human hepatocyte membranes. To obtain large quantity of preS1 peptide, an expression vector was constructed containing a lac promoter, the 5' half of the beta-galactosidase gene, the Factor Xa tetrapeptide recognition sequence, and the coding region of preS1 plus preS2. This recombinant plasmid constitutively produced high concentration of a fusion protein in inclusion bodies in Escherichia coli. When the fusion protein was treated with Factor Xa, a peptide consisting of the N-terminal 91 amino acids of the preS1 region was released. This preS1 fragment purified by anion exchange chromatography was able to bind specifically to the isolated plasma membranes from human liver. Hence, this recombinant preS1 peptide can be used to identify and isolate hepatocyte receptors for HBV.

Significance of natural polymerized albumin and its receptor in hepatitis B infection of hepatocytes

Lack of information regarding the presence of native albumin polymer in serum and its structural similarity to the one produced by glutaraldehyde treatment casts doubt on the postulate that hepatitis B virus attachment to hepatocytes is mediated through polymerized albumin. We used a sandwich enzyme-linked immunosorbent assay with murine monoclonal antibodies raised against glutaraldehyde-polymerized albumin to detect native albumin polymer in human serum and its cross-reactivity with other albumin polymers. Presence of polymerized albumin receptor on the HepG2 cell was studied by radioreceptor assay. Purified hepatitis B virus and synthetic peptide analogous to part of pre-S2 sequence (120-145) were used to study polymerized albumin-dependent attachment of the virus to HepG2 cells. Antibodies raised against pre-S2 peptide were used to inhibit the pre-S2 and hepatitis B virus attachment to HepG2 cells. Glutaraldehyde-treated polymerized albumin was found to be immunologically cross-reactive with native albumin polymer. Its levels were found to be significantly raised in sera of patients with liver diseases. Polymerized albumin has specific saturable receptor on HepG2 cells with two classes of binding sites of different equilibrium dissociation constant (Kd1 = (16 +/- 9.6)pmol/L and Kd2 = (1,019 +/- 172)pmol/L. Albumin monomer was unable to compete for the polymerized albumin receptor sites on HepG2 cells. Anti-pre-S2 antibodies inhibit hepatitis B virus and pre-S2 binding to hepatocyte by 40% and 70%, respectively. Added extraneous polymerized albumin and the antibody against it did not interfere with virus attachment to HepG2 cells.

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).

Expression of pre-S2 region of hepatitis B surface antigen in Escherichia coli

We constructed a recombinant plasmid that can express the entire pre-S2 sequence of hepatitis B surface antigen (HBsAg) as a fusion protein in E. coli. The hybrid protein, which comprises the bacterial TrpLE protein and the pre-S2 sequence, was the prominent protein that was found in cell extracts. As determined by immune blot analysis, this protein reacted with human HBV convalescent sera, as well as with sera from animals immunized with either purified HBsAg or isolated polypeptides containing pre-S2. It bound specifically to 125I-polymerized human albumin cross-linked with glutaraldehyde but not to 125I-monomeric human albumin. A novel adjuvant formulation was used in place of Freund's adjuvant to immunize guinea pigs with the recombinant product. The antisera obtained from serial bleedings were found to react with HBsAg of both d and y subtypes. These antisera were also shown to react solely with HBsAg polypeptides which contain of HBsAg to solid-phase polymerized the binding of HBsAg to solid-phase polymerized human albumin.

Human liver plasma membranes contain receptors for the hepatitis B virus pre-S1 region and, via polymerized human serum albumin, for the pre-S2 region

Hepatitis B virus particles contain three related viral envelope proteins, the small, middle, and large S (surface) proteins. All three proteins contain the small S amino acid sequence at their carboxyl terminus. It is not clear which of these S proteins functions as the viral attachment protein, binding to a target cell receptor and initiating infection. In this report, recombinant hepatitis B surface antigen (rHBsAg) particles, which contain only virus envelope proteins, were radioactively labeled, and their attachment to human liver membranes was examined. Only the rHBsAg particles containing the large S protein were capable of directly attaching to liver plasma membranes. The attachment was saturable and could be prevented by competition with unlabeled particles or by a monoclonal antibody specific for the large S protein. In the presence of polymerized human serum albumin, both large and middle S protein-containing rHBsAg particles were capable of attaching to the liver plasma membranes. Small S protein-containing rHBsAg particles were not able to attach even in the presence of polymerized human serum albumin. These results indicate that the large S protein may be the viral attachment protein for hepatocytes, binding directly to liver plasma membranes by its unique amino-terminal (pre-S1) sequence. These results also indicate that polymerized human serum albumin or a similar molecule could act as an intermediate receptor, attaching to liver plasma membranes and to the amino acid sequence (pre-S2) shared by the middle and large S proteins but not contained in the small S protein.

In vitro immune responses to hepatitis B surface antigen (Pre-S2 and S) following remote infection by hepatitis B virus in humans

In this report we evaluate the human immune response to hepatitis B surface antigen (HBsAg) following remote infection with hepatitis B virus (HBV). HBsAg-reactive lymphocytes can be readily demonstrated in the peripheral blood of individuals with established immunity following infection with HBV. In vitro stimulation with small doses of plasma-derived HBsAg, yeast-derived HBsAg (S region) or pre-S2 peptide will induce specific IgG to HBsAg (anti-HBs) in the absence of a polyclonal increase in total IgG. The pre-S2 peptide will stimulate, in a T cell-dependent fashion, the in vitro production of anti-HBs with specificity for the S domain. This anti-HBs production is mediated by pre-S2-stimulated soluble T-cell factors. Peripheral blood mononuclear cells from individuals with established immunity proliferate to the yeast-derived HBsAg but not to the plasma-derived HBsAg or pre-S2 peptide. The chronic HBsAg carriers do not produce anti-HBs following stimulation with HBsAg regardless of the source or component of antigen used. Different study protocols failed to demonstrate HBsAg-specific responses in the peripheral blood mononuclear cells of chronic carriers.

Characterization of the binding sites for glutaraldehyde-polymerized albumin on purified woodchuck hepatocyte plasma membranes

Highly purified woodchuck hepatocyte plasma membranes demonstrated tight specific binding to glutaraldehyde-polymerized serum albumin immobilized on Sepharose macrobeads. This phenomenon was characterized in detail and used for recognition of the plasma membrane constituents involved in binding of the albumin polymer. The hepatocyte membrane-polyalbumin interaction was found to be ligand-specific, saturable, and time-dependent. Other characteristics of a specific receptor-ligand interaction were also noted, including a dependence on the temperature, pH, and ionic strength of the binding medium. Kinetic studies revealed the presence of two classes of binding sites for glutaraldehyde-polymerized albumin on purified membranes. The sites mediating the saturable high-affinity binding of polymer to hepatocyte membranes could not be solubilized by Triton X-100. Binding activity of Triton-insoluble membrane residues was inhibited by heat treatment and proteolysis, and was significantly suppressed by neuroaminidase digestion. These findings suggest a glycoprotein nature for the high-affinity binding sites and indicate that the corresponding receptors apparently are tightly associated with the plasma membrane matrix. In contrast, low-affinity binding of polymeric albumin was inhibited by both Triton X-100 and pronase, was resistant to neuraminidase, and was activated by lipase, suggesting that membrane lipids are important for the binding conduct. In conclusion, these results provide clear evidence that hepatocyte plasma membranes are endowed with at least two classes of chemically distinct binding components, which are able to specifically recognize serum albumin artificially modified by glutaraldehyde treatment. Therefore, they suggest that in vivo hepatocytes may perform a specific receptor-dependent uptake of ligands expressing glutaraldehyde-polymerized albumin specificity. This phenomenon may play an important role in the proposed participation of naturally modified human serum albumin as a bridge in the attachment and penetration into host hepatocyte of hepatitis B virus, which is known to possess a receptor that is specific for glutaraldehyde-cross-linked human serum albumin.

The interaction between native serum albumin and hepatitis B virus

Purified hepatitis B virus particles were obtained from HBeAg positive serum by sucrose gradient ultracentrifugation and sephadex G-200 gel filtration. These virions formed a precipitation line in counterimmune electrophoresis with anti-albumin antibody, but the reaction could be inhibited by anti-HBs. After two months at 4 degrees C, another precipitating line was formed under the same condition which could not be inhibited by anti-HBs and was, thus, due to free albumin. When that sample was incubated at 37 degrees C overnight, the line of free albumin disappeared. The virion bound albumin was monomeric in non-denaturing gel electrophoresis. These results suggest that a reversible binding between virion and albumin may occur in vivo and does not require chemical modification or cross-linking.

Characterization of purified hepatitis B surface antigen containing pre-S(2) epitopes expressed in Saccharomyces cerevisiae

The cloning and expression of the hepatitis B middle-protein surface antigen gene in the yeast Saccharomyces cerevisiae is described. A generalized expression vector carrying the yeast glyceraldehyde-3-phosphate dehydrogenase gene promoter was used. Expressed material, in the form of supramolecular particles, was purified and characterized. Severe proteolysis within the pre-S(2) region was observed for material expressed in a wild-type yeast host. This proteolysis was substantially reduced by utilization of a protease-deficient host. Immunoblotting of sodium dodecyl sulfate-polyacrylamide gels with several antibodies of differing specificity was performed to characterize the various protein species present. All species were analyzed by N-terminal sequencing after electroelution from gels. Carbohydrate staining of gels and glycosidase treatments of the purified antigen material indicated that full-length antigen was present in both glycosylated and unglycosylated forms. Glycosylation appeared to be of both asparagine-linked and threonine/serine-linked types. Site-directed mutagenesis was used to convert two arginine residues in the pre-S(2) region of the antigen to glutamine residues. The changes abolished reactivity with one polyclonal and two monoclonal antibodies specific for epitopes within the pre-S(2) region.

Uptake and metabolism of polymerized albumin by rat liver. Role of the scavenger receptor

Hepatitis B virus binds avidly to albumin polymers, which in turn may mediate viral attachment to liver cells. This hypothesis is critically dependent on prior results obtained using glutaraldehyde-polymerized human serum albumin as a model for naturally occurring albumin species. We used the perfused rat liver to characterize the uptake, cellular distribution, and metabolism of glutaraldehyde-polymerized human albumin. 125I-glutaraldehyde-polymerized human albumin was efficiently removed from the perfusate by the liver (29% extraction). However, few autoradiographic grains were located over hepatic parenchymal cells (6%). Instead, most glutaraldehyde-polymerized human albumin appeared to be removed by endothelial (59%) or Kupffer (31%) cells. Hepatic uptake was strongly inhibited by formaldehyde-treated monomeric albumin, a known ligand of the endothelial scavenger receptor for chemically modified proteins. After uptake, most glutaraldehyde-polymerized human albumin was rapidly degraded and released into the perfusate (74% within 60 min). This process was blocked by chloroquine and leupeptin, suggesting that it involves lysosomal acid hydrolases. We conclude that glutaraldehyde-polymerized albumin is efficiently cleared and degraded by the endothelial scavenger pathway. Glutaraldehyde-polymerized albumin therefore appears to be a poor model for predicting the hepatic handling of naturally occurring albumin species bound to hepatitis B virions. Even if viral particles were to follow this pathway, few would enter parenchymal hepatocytes.

Antibodies recognizing human serum albumin are not elicited by immunization with preS2 sequences of the hepatitis B virus envelope protein

Antibodies to the preS2 region of the hepatitis B virus (HBV) envelope protein and to human serum albumin (HSA) were allegedly detected at about the same level in sera of humans with acute or chronic hepatitis B [Hellström et al., 1986]. It was claimed that anti-HSA arises as a result of an immune response to the preS2 sequence and that it was involved in hepatocellular damage. Over 100 sera from animals and humans immunized with HBsAg containing preS2 sequences, or with synthetic peptides from the preS1, preS2, and S regions of the HBV env protein were assayed for anti-HSA. The results revealed the following: 1) Immunization with the native preS2 sequence or with unconjugated synthetic peptides derived from that sequence does not result in elicitation of anti-HSA. Therefore the alleged appearance of anti-HSA during hepatitis B cannot be directly related to an anti-preS2-specific immune response. 2) Some synthetic peptides, whether or not they were derived from the preS2 sequence, when linked to certain carriers, but not to others, elicited in rabbits an anti-HSA response, which was markedly lower than the response to the homologous peptide. These anti-HSA antibodies could be separated from anti-preS2-specific antibodies by affinity chromatography and did not recognize the synthetic peptide used for immunization. The use in active immunoprophylaxis of hepatitis B of unconjugated peptides from the preS2 sequence with proven high immunogenicity will avoid carrier/linker-mediated induction of antibodies not relevant to protection against HBV.

The isolation and purification of pre-S2 containing hepatitis B virus surface antigen by chemical affinity chromatography

A simple, rapid, and efficient method was developed to isolate and purify pre-S2 containing HBsAgs from the plasma of a single chronic carrier of HBsAg (adw) by ammonium sulfate fractionation, hydroxyapatite column chromatography, and polymerized human serum albumin-affinity column chromatography. About 500 micrograms of pre-S2 containing HBsAg was obtained from 140 mL of plasma containing 4,200 micrograms of HBsAg. Two purified pre-S2 containing HBsAgs were analyzed by SDS-polyacrylamide gel electrophoresis and their molecular weights were determined to be 31,000 and 68,000 respectively. No significant amount of HBsAg or its derivative was detected in the final product.

A cultured cell receptor for the small S protein of hepatitis B virus

Human hepatitis B virus (HBV) has not been passaged in established cell culture systems. To determine whether this inability results from the lack of a receptor, 30 cell lines were examined for their abilities to bind 125I-labeled recombinant hepatitis B virus surface antigen (rHBsAg) particles. These particles contained only the small surface (S) protein, which is also found in the envelope of infectious HBV particles. Only two cells lines, both derived from African green monkey kidney, were able to bind a large portion of the 125I-rHBsAg particles. Binding to one of these cell lines, Vero, was found to be specific by three criteria: it was competitively inhibited by nonradioactive particles, it was saturable, and it could be blocked by chimpanzee antiserum raised against the rHBsAg particles. Analysis of the binding data indicated a single major population of high affinity receptor sites: 2.7 X 10(5) sites/cell, Kd = 2.8 nM. Binding was not due to the covalently linked 125I tracer isotope because unlabeled particles also bound, as detected with a monoclonal antibody. Binding was not unique to this recombinant particle preparation since serum-derived particles also bound to Vero cells. These results indicate that the Vero cell line expresses a receptor for the small S protein of HBV and that the small S protein, alone, may function as the HBV attachment protein.

Interaction of natural and synthetic albumin polymers with hepatocytes

The hepatitis B virus binds avidly to albumin polymers which in turn may mediate the initial binding of viral particles to the liver cell. However, the interaction of albumin polymers with the liver remains poorly characterized, and the possibility that hepatic binding reflects an artifact of polymerization with glutaraldehyde has not been excluded. We therefore characterized the binding of 125I-labeled natural and synthetic albumin polymers to suspensions of rat hepatocytes. Saturable binding was demonstrated for all preparations of monomeric and polymeric albumin studied. Glutaraldehyde-polymerized albumin (mean polymerization number = 15) bound much more avidly than naturally occurring albumin polymers (mostly dimers and trimers) or monomeric albumin. Competition between monomer and synthetic polymer was not observed. Reduction of free aldehyde groups on the synthetic polymer decreased nonsaturable binding without affecting saturable binding. Autoradiography confirmed binding of polyalbumin to hepatic parenchymal cells. Glutaraldehyde-polymerized ovalbumin, a protein unrelated to serum albumin, also bound hepatocytes saturably. We conclude that hepatic binding of synthetic albumin polymers is not due to residual aldehyde groups on the polymer and is much more avid than for natural polymer. This difference may reflect the higher degree of polymerization or chemical modification of the synthetic polymer. The hepatic binding sites for synthetic polymer appear distinct from those previously described for monomeric albumin and may not be specific for albumin.

Interactions between hepatitis B virus and polymeric human albumin. I. Production of monoclonal anti-idiotypes (anti-anti-polymeric human albumin) which recognize hepatitis B virus surface antigen

In an attempt to characterize the polymeric human albumin (polyHSA) receptor expressed on hepatitis B virus and hepatocytes, we have used a human anti-polyHSA IgG to generate monoclonal anti-idiotypes (anti-Id) which bear the internal image of polyHSA and mimic its binding activity. Two monoclonal anti-Id antibodies, 63.14 and 70.F9, were strongly reactive in both radioimmunoassay and enzyme-linked immunosorbent assay (ELISA) with the F(ab')2 of the immunogen as well as with purified hepatitis B surface antigen (HBsAg) expressing various subtypes. The specificity of the binding of anti-Id to HBsAg was confirmed in direct ELISA and by Western blot analysis. These experiments also showed that the anti-Id bind to a site expressed on the major 24-kDa protein of HBsAg particles, and that this recognition is specifically inhibited by polyHSA. Experiments on cellular staining and radioimmunoprecipitation on HBsAg-positive and -negative cell lines showed that the anti-Id recognize intracellular HBsAg but not other liver cell proteins, including the putative polyHSA receptor. These data indicate, therefore, that the monoclonal anti-Id mimic the binding activity of polyHSA and recognize its binding site on the virus. The inability of both anti-Id to react with the hepatocyte surface suggests either the absence of a specific hepatic polyHSA receptor or the expression of one with a different configuration.

Failure to detect polyalbumin-binding sites on the woodchuck hepatitis virus surface antigen: implications for the pathogenesis of hepatitis B virus in humans

Binding sites for polymerized albumin on hepatitis B virus components were reported in human hepatitis B virus chronic carriers predominantly with active viral replication (HB e antigen positive). The presence of comparable albumin-binding sites in the woodchuck hepatitis virus (WHV) model was examined on WHV components obtained from woodchucks with active viral replication (DNA polymerase positive). Binding sites for polymerized woodchuck serum albumin were not detected on the intact WHV virion, on 22-nm woodchuck hepatitis surface antigen (WHsAg), or on WHsAg polypeptides. Woodchuck albumin was not detected in purified 22-nm WHsAg, and anti-albumin antibodies were not detected in WHV chronic-carrier woodchucks. Our results in the WHV model argue against a role for viral polyalbumin-binding sites in tissue- and host-specific virus infectivity.

Identification and chemical synthesis of a host cell receptor binding site on hepatitis B virus

Hepatitis B virus (HBV) has not yet been propagated in vitro, and knowledge concerning its reaction with receptors on target cells remained scant. We have located within the HBV envelope proteins a sequence mediating the attachment of HBV to human hepatoma HepG2 cells. A synthetic peptide analog (PLGFFPDHQLDPAFGANSNNPDWDFNP) is recognized by both cell receptors and anti-HBV antibodies and elicits antibodies reacting with native HBV. The synthetic peptide is a promising immunogen expected to elicit protective antibodies based on the concept of the attachment blockade pathway of virus neutralization. The approach described here, based on anti-peptide antisera and the binding of peptide analogs to cell receptors is generally applicable for the delineation of cell receptor binding sites on viruses with known gene sequences.

Antibody to the receptor for polymerized human serum albumin in acute and persistent infection with hepatitis B virus

The antibody against the receptor for polymerized human serum albumin was determined by radioimmunoassay. The method involved the inhibition by the test serum, absorbed with HBsAg particles without the receptor, on the binding of polymerized human serum albumin to HBsAg particles with the receptor fixed on a solid support. The amount of polymerized human serum albumin captured by the receptor on HBsAg was then determined by the radiolabeled monoclonal antibody directed to an epitope specific for polymerized human serum albumin. In acute infection, the antibody to the receptor for polymerized human serum albumin appeared in the early recovery phase while HBs antigenemia and elevated transaminase levels were still present, preceding the antibody to HBsAg (anti-HBs). The antibody was detected in 4 (1%) of 358 sera from asymptomatic carriers of HBsAg containing antibody to HBeAg, and in none of 67 sera containing HBeAg. Although the antibody was found in as many as 111 (74%) of 150 sera from blood donors who had presumably acquired anti-HBs after natural infection, it was not detected in any sera from 77 recipients of hepatitis B vaccine who had seroconverted for anti-HBs. On the basis of these observations, the determination of antibody to the receptor for polymerized human serum albumin helps in further understanding the immunity to hepatitis B virus.

Detection of pre-S1 proteins in serum and liver of HBsAg-positive patients: a new marker for hepatitis B virus infection

The presence of pre-S1 proteins in serum and liver of individuals with acute and chronic hepatitis B virus infection was investigated in Western blots using antibodies against a fusion protein, containing amino acids 20-120 of the pre-S region. Pre-S1 proteins were present in 20 of 38 HBsAg-positive sera. All sera positive for pre-S1 proteins were also positive for hepatitis B virus DNA indicating the presence of hepatitis B virions, and 16 of these sera were also positive for HBeAg. In five sera positive for hepatitis B virus DNA, pre-S1 proteins were not found. In an additional study, pre-S1 proteins could be detected in 4 of 6 patients with acute hepatitis B virus infection during the first 2 weeks after admission to the hospital. The presence of pre-S1 proteins showed a good correlation with the detection of hepatitis B virus DNA. After seroconversion from HBeAg to anti-HBe, both hepatitis B virus DNA and pre-S1 proteins were no longer detectable. Pre-S1 proteins were present in three liver tissue specimens from two patients with acute hepatitis B virus infection and from one patient with cirrhosis of the liver. The proteins were not found in the liver of two HBsAg-positive patients with hepatocellular carcinoma (primary liver carcinoma), negative for HBeAg. Pre-S1 proteins can be detected in serum, positive for hepatitis B virus DNA and in liver tissue of hepatitis B virus-infected individuals. The presence of these proteins appears to correspond with the presence of hepatitis B virus DNA, both markers indicating hepatitis B virus replication.