Antigenic conversion from HBcAg to HBeAg by degradation of hepatitis B core particles

Replication-competent infectious hepatitis B virus vectors carrying substantially sized transgenes by redesigned viral polymerase translation

Viral vectors are engineered virus variants able to deliver nonviral genetic information into cells, usually by the same routes as the parental viruses. For several virus families, replication-competent vectors carrying reporter genes have become invaluable tools for easy and quantitative monitoring of replication and infection, and thus also for identifying antivirals and virus susceptible cells. For hepatitis B virus (HBV), a small enveloped DNA virus causing B-type hepatitis, such vectors are not available because insertions into its tiny 3.2 kb genome almost inevitably affect essential replication elements. HBV replicates by reverse transcription of the pregenomic (pg) RNA which is also required as bicistronic mRNA for the capsid (core) protein and the reverse transcriptase (Pol); their open reading frames (ORFs) overlap by some 150 basepairs. Translation of the downstream Pol ORF does not involve a conventional internal ribosome entry site (IRES). We reasoned that duplicating the overlap region and providing artificial IRES control for translation of both Pol and an in-between inserted transgene might yield a functional tricistronic pgRNA, without interfering with envelope protein expression. As IRESs we used a 22 nucleotide element termed Rbm3 IRES to minimize genome size increase. Model plasmids confirmed its activity even in tricistronic arrangements. Analogous plasmids for complete HBV genomes carrying 399 bp and 720 bp transgenes for blasticidin resistance (BsdR) and humanized Renilla green fluorescent protein (hrGFP) produced core and envelope proteins like wild-type HBV; while the hrGFP vector replicated poorly, the BsdR vector generated around 40% as much replicative DNA as wild-type HBV. Both vectors, however, formed enveloped virions which were infectious for HBV-susceptible HepaRG cells. Because numerous reporter and effector genes with sizes of around 500 bp or less are available, the new HBV vectors should become highly useful tools to better understand, and combat, this important pathogen.

A micromolar pool of antigenically distinct precursors is required to initiate cooperative assembly of hepatitis B virus capsids in Xenopus oocytes

Assembly of hepatitis B virus capsid-like (core) particles occurs efficiently in a variety of heterologous systems via aggregation of approximately 180 molecules of a single 21.5-kDa core protein (p21.5), resulting in an icosahedral capsid structure with T = 3 symmetry. Recent studies on the assembly of hepatitis B virus core particles in Xenopus oocytes suggested that dimers of p21.5 represent the major building block from which capsids are generated. Here we determined the concentration dependence of this assembly process. By injecting serially diluted synthetic p21.5 mRNA into Xenopus oocytes, we expressed different levels of intracellular p21.5 and monitored the production of p21.5 dimers and capsids by radiolabeling and immunoprecipitation, by radioimmunoassay, or by quantitative enzyme-linked immunosorbent assay analysis. The data revealed that (i) p21.5 dimers and capsids are antigenically distinct, (ii) capsid assembly is a highly cooperative and concentration-dependent process, and (iii) p21.5 must accumulate to a signature concentration of approximately 0.7 to 0.8 microM before capsid assembly initiates. This assembly process is strikingly similar to the assembly of RNA bacteriophage R17 as defined by in vitro studies.

Stability of the recombinant hepatitis B core antigen

The recombinant gene for hepatitis B core antigen (HBcAg) was cloned and expressed, and the protein was purified from Escherichia coli cultures. Purified HBcAg was tested for the effects of various physical and chemical agents on its immunoreactivity by a paramagnetic particle-based enzyme immunoassay. Recombinant HBcAg retained its immunoreactivity when heated at 70 degrees C for 60 min but was inactivated at 85 degrees C in 10 min. It was stable between pHs 5 and 10.5 but not at pHs 2 and 13.5. Treatment with sodium dodecyl sulfate (SDS), ethanol, and methanol caused a significant loss in HBcAg reactivity. The proteolytic enzymes papain and bacterial protease (type VIII from Bacillus licheniformis) degraded HBcAg significantly, but trypsin and chymotrypsin did not. The effect of combined SDS and 2-mercaptoethanol on recombinant HBcAg was an immediate loss in immunoreactivity, followed by rapid recovery to about 50% of the initial level. This level was maintained for 24 to 48 h and was followed by an almost total loss of HBcAg in about 120 h.

Characterization of hepatitis B virus capsid particle assembly in Xenopus oocytes

Little is known about the assembly of the 28-nm nucleocapsid or core particle of hepatitis B virus. Here we show that this assembly process can be reconstituted in Xenopus oocytes injected with a synthetic mRNA encoding the hepatitis B virus capsid protein (p21.5). Injected oocytes produce both a nonparticulate p21.5 species (free p21.5) and capsid particles. We describe rapid and simple methods for fractionating these species on a small scale either with step gradients of 10 to 60% (wt/vol) sucrose or by centrifugation to pellet the particles, and we characterize the oocyte core particles. Free p21.5 exhibits chemical and physical properties distinctly different from those of particles. Free p21.5 is partially cleaved by proteinase K, whereas core particles are almost completely resistant to cleavage. This suggests that the carboxyl-terminal protamine region, the main target for proteases within p21.5, is exposed in free p21.5 but faces the interior of the p21.5 core particle. Finally, pulse-chase experiments demonstrated that free p21.5 can be chased almost quantitatively into core particles, establishing that free p21.5 is fully competent to form particles and represents an assembly intermediate on the pathway for core particle formation. However, core particle assembly appears very dependent on p21.5 concentration and is rapidly compromised if the p21.5 concentration is lowered. The advantages of oocytes for studying assembly are discussed.

Human and murine B-cells recognize the HBeAg/beta (or HBe2) epitope as a linear determinant

The complete amino acid (aa) sequence of the hepatitis B virus (HBV) core protein (HBcAg), deduced from the genome of the HBV ayw subtype, was synthesized as decapeptides with five overlapping aas. The peptides were tested for reactivity with monoclonal antibodies (mAbs) to the beta (or HBe2) epitope of hepatitis B e antigen (HBe/b mAbs; 57/8, 78/3, 141/158 and 141/207). Cross-competition between the mAbs with a mAb to the HBe/alpha epitope (or HBe1) and an anti-HBc mAb showed that all the HBe/b mAbs specifically inhibited human anti-HBe/b binding. Screening the HBc/e peptides showed that all anti-HBe/b mAbs recognized a peptide covering the residues 126-135. Three of the mAbs, 78/3, 141/152 and 141/207, had a less restricted reactivity than the other two, suggesting the recognition of the HBe/b as a discontinuous determinant. Fine mapping of the region aa 126-135 was performed by synthesizing decapeptides with nine overlapping aas, covering residues aa 121-140. All mAbs, except 78/3, reacted with the linear sequence TPPAYR, at residues 128-133. An additional set of peptides was synthesized, where the six aas within the epitope 128-133 were substituted in turn by the other 19 possible aas. By this approach, the essential aas for mAb 57/8 were found to be the sequence of PPA at residues 129-131, and for mAb 141/158 the sequence PP-Y, at residues 129, 130 and 132, respectively. Human recognition of the linear HBe/b epitope was investigated by using a peptide covering residues 121-140 (p 33). Thirty-one sera from chronic carriers of HBsAg, of which seven were positive for HBeAg and the remaining 24 for anti-HBe, were investigated. Of the sera with HBeAg, two had low levels of anti/-HBe/b in the p 33 assay. Out of the sera with anti-HBe, eight were positive in the p 33 EIA. Thus, murine monoclonals and human sera may recognize the HBe/b epitope as a linear determinant residing around aa 130.

Characterisation of a linear binding site for a monoclonal antibody to hepatitis B core antigen

The complete amino acid (aa) sequence of the hepatitis B virus (HBV) core protein (HBcAg), ayw subtype, was synthesized as decapeptides with five overlapping aas. The peptides were tested for reactivity with monoclonal antibodies (mAbs) to HBcAg (35/312, 37/275, and 7/275). All the mAbs specifically inhibited human anti-HBc by cross competition in assays for anti-HBc and anti-HBe. The mAb 35/312 recognised a peptide covering residues 76-85 of the HBcAg sequence. The other two mAbs did not react specifically with any linear peptide, suggesting discontinuous epitopes for these mAbs. The linear sequence EDPASR at residues 77-82 was found to constitute the epitope for mAb 35/312 when fine mapping the binding site. The most essential aas for mAb 35/312 were found to be the DP at residues 79-80, when peptides were synthesized where the aas at 77-83, were substituted by the other 19 aas. Since the mAb 35/312 inhibits the binding of human anti-HBc positive sera, which are known to recognise an SDS labile epitope, the sequence 77-82 might be a part of a larger discontinuous epitope. Alternatively the mAb 35/312 blocks the binding of human anti-HBc by steric hindrance.

Comparison of class and subclass distribution of antibodies to the hepatitis B core and B e antigens in chronic hepatitis B

The IgG subclasses IgM and IgA1 of antibodies to hepatitis B core antigen (anti-HBc) and hepatitis B e antigen (anti-HBe) were assayed in sera from 82 patients with chronic hepatitis B utilising class/subclass-specific enzyme immunoassays (EIA). The solid-phase was either recombinant hepatitis B core antigen (rHBcAg) or rHBcAg converted to HBeAg by addition of 0.1% SDS with remaining HBcAg antigenicity blocked with monoclonal anti-HBc. Anti-HBc IgG1 was detected in 81 sera at a geometrical mean titre (GMT) of 296,110 x divided by 2.9. Anti-HBc IgG2 was not detected in any of the sera, and anti-HBc IgG3 and IgG4 were detected in 50 and 37 sera, respectively. Anti-HBc IgM and IgA1 were both significantly correlated to the presence of HBV DNA. The predominant antibody to HBeAg was found to be IgG1, being detected in 45 sera with a GMT of 1,035 x divided by 3.3. Anti-HBe IgG2 was not detected in any serum, while anti-HBe IgG3 and IgG4 were found in 8 and 23 sera, respectively. Anti-HBe IgG1, IgG3, and IgG4 were mainly detected in sera positive for anti-HBe in RIA (Abbott). No patient was found positive for anti-HBe IgA1 or IgM. Thus, in contrast to HBcAg, HBeAg does not trigger a persistent IgM and IgA1 response in chronic hepatitis B. The levels of anti-HBe IgG1 and IgG3 were much lower than the levels of anti-HBc IgG1 and IgG3. The presence of anti-HBe IgG4 was significantly correlated to that of anti-HBc IgG4.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of cytoplasmic and nuclear particles of hepatitis B virus

The properties of hepatitis B virus (HBV) core particles from liver tissue of two patients with acute HBV infection were investigated. Cores were isolated from cytoplasm and nuclear fractions by centrifugation and two thirds of the cores were located in the cytoplasm. In all properties examined cores isolated from the cytoplasm or nucleus were the same. The cores had a density of 1.38 g/ml and had the same DNA and protein content when analyzed by Southern blotting and by Western blotting with C-specific antisera. Cores from both subcellular fractions had endogenous polymerase activity. We conclude that core particles with identical properties are found in both the cytoplasm and nucleus of cells during acute infection.

Synthesis of hepatitis B virus e antigen in E. coli

Hepatitis B virus core antigen (HBcAg) gene was deleted at some unique restriction enzyme sites, or at random, and inserted into the expression plasmids of E. coli which had the tryptophan promoter. E. coli transformants with the plasmids, synthesized materials with many kinds of antigenicity of HBcAg, HBeAg, or both HBcAg and HBeAg. HBeAg-specific material smaller than native HBeAg was produced in a stable condition.

Intra- and extracellular distribution and immunochemical characterization of hepatitis B virus nucleocapsid proteins produced by a human hepatoma cell line transfected with cloned viral DNA

Hepatitis B virus (HBV)-related antigens produced by the human hepatoma cell line (HB611 cell), which had been transfected with a cloned HBV DNA and established as a stable producer of HBV (T. Tsurimoto, A. Fujiyama, and K. Matsubara, 1987, Proc. Natl. Acad. Sci. USA 84, 444-448), were investigated immunochemically and morphologically. All HBV-related antigens, HBV surface (HBsAg), e (HBeAg), and core (HBcAg), were semiquantitatively examined by the respective reversed passive hemagglutination assay (RPHA). RPHAs for HBcAg and for HBeAg were characterized as reacting only to the core particles and to the free form of nucleocapsid proteins, respectively. The amounts of HBsAg and nucleocapsid protein in culture medium were roughly related to the number of viable cells. The amount of core particles was, instead, proportional to the number of dead cells. Relative amounts of HBsAg, core particles, and nucleocapsid proteins in culture medium, cell surface, and cell lysate were determined and it was found that HBsAg and nucleocapsid proteins were effectively secreted into culture medium but core particles were not. Molecular species of nucleocapsid proteins were identified to be p17 and p18 (HBeAg polypeptides) in the culture medium and HBeAg polypeptides and p21.5 (HBcAg polypeptide) in the cytosol fraction. The p21.5 was preferentially found in the nuclear fraction.

A signal peptide encoded within the precore region of hepatitis B virus directs the secretion of a heterogeneous population of e antigens in Xenopus oocytes

Using synthetic hepatitis B virus (HBV) mRNAs, we have shown that expression of HBV core-antigen gene sequences in Xenopus oocytes leads to the stable accumulation of 21-kDa cytoplasmic core protein (P21). In contrast, expression of precore plus core sequences leads mainly to the secretion of a heterogeneous population of proteins ranging in size from 15 to 22 kDa that collectively display viral e antigen (HBeAg) activity. We demonstrate that the precore region contains a cleavable 19 amino acid signal peptide that targets the precore proteins to the secretory pathway. The initial product of translocation (P22) is further processed during migration through the secretory pathway, apparently by a series of cleavage events at the arginine-rich carboxyl terminus, to yield multiple proteins of 15-18 kDa (P15-P18) that are secreted along with some P22. Our results indicate that serum HBeAg is generated by a signal peptide-mediated secretion event dependent on precore sequences.

Mechanisms of liver cell damage in acute hepatitis B

Markers of hepatitis B viral infection and the evolution of immune response to these were compared with serum alanine aminotransferase (ALT) levels in adult male and non-pregnant and pregnant female patients with acute hepatitis B from the time of onset of disease to the seventh week. In the adult male and non-pregnant female patients, the peak ALT levels of about 360 IU/litre, seen at the time of onset, gradually declined during the course of the disease. Significantly, even in the seventh week, the median ALT level was abnormal (80 IU/litre). In contrast, the disease was mild in pregnant patients and the ALT levels declined rapidly, returning to normal by the third week. Markers associated with HBV replication, i.e., serum HBV-DNA and HBeAg, declined early in the course of the disease in both groups. The anti-HBc-IgM and anti-HBe responses were well evolved early in the course of the disease in both groups. HBsAg was present in the serum in large amounts (1-1.5 X 10(4) AU/100 microliter) early in the course of the disease and remained so up to the seventh week. Even the pregnant patients who had recovered clinically by the fourth week continued to have HBsAg in their sera in large amounts in spite of normal ALT levels. LMI and LTT responses to HBsAg, which were practically absent in the first week, gradually increased to a peak during the fourth week and remained elevated up to the seventh week in adult male and non-pregnant female patients. In contrast, LMI response to HBsAg was absent in pregnant patients with acute hepatitis B even up to the fourth week Thus, continued liver cell necrosis after the fourth week, as indicated by raised ALT levels, may be associated with T cell responses to HBsAg.

Virological significance of HBeAg subtypes (HBeAg/1 and HBeAg/2) in patients with type B hepatitis

In order to establish the virological significance of HBeAg subtypes (HBeAg/1 and HBeAg/2) during hepatitis B virus infection, HBsAg, HBeAg and hepatitis B virus DNA in serum and HBcAg in liver were determined quantitatively in relation to the detection of HBeAg subtypes in agar gel diffusion. Thirty-eight chronic HBsAg carriers with HBeAg, including 16 non-specific reactive hepatitis, 8 chronic persistent hepatitis, 11 chronic active hepatitis and 3 liver cirrhosis, who were seen at Tohoku University Hospital from 1983 to 1985, were examined. Significantly larger amounts of HBsAg, HBeAg and hepatitis B virus DNA in serum and HBcAg in liver were found in patients positive for both HBeAg/1 and HBeAg/2 in serum than in those positive for only HBeAg/1 or negative for both subtypes. These results suggest that the presence of HBeAg/2 in serum may reflect the occurrence of active viral replication. When the detection pattern of HBeAg subtypes was examined during serial follow-up for at least 1 year, three groups of patients were classified with respect to the presence of HBeAg/2, i.e., Type I, consistently positive for HBeAg/2; Type II, consistently negative for HBeAg/2, and Type III, intermittently positive for HBeAg/2. More than 80% of Type I patients were histologically diagnosed having as nonspecific reactive hepatitis, while more than 80% of Type II and III patients had more progressive liver diseases such as chronic persistent hepatitis, chronic active hepatitis and liver cirrhosis. These results suggest that the serial examination of HBeAg subtypes in serum may be important for more detailed evaluations of type B hepatitis.

5'-terminal sequences influence the segregation of ground squirrel hepatitis virus RNAs into polyribosomes and viral core particles

To determine which of the major ground squirrel hepatitis virus RNAs serve as mRNAs and which serve as templates for reverse transcription of the genome, we analyzed the subcellular distribution of these RNAs in livers of infected ground squirrels. Both major classes of viral RNA, the 2.3- and 3.5-kilobase (kb) classes, are unspliced, are polyadenylated at a common position, and display heterogeneous 5' ends that can encode proteins with different amino termini (G.H. Enders, D. Ganem, and H. Varmus, Cell 42:297-308, 1985). Both of the 2.3-kb RNAs, which encode surface antigens, appear to be predominantly associated with polyribosomes. Of the three 3.5-kb RNAs, the two longer, which can encode a protein initiated from the first methionine codon in the core antigen gene, appear to be predominantly associated with polyribosomes, and a minority of the shortest 3.5-kb RNAs, which can encode a protein initiated from the second methionine in the core antigen gene, appears to be associated with polyribosomes. This last RNA is instead found predominantly within viral core particles, consistent with evidence that indirectly implicates it in two steps of viral DNA synthesis (C. Seeger, D. Ganem, and H.E. Varmus, Science 232:477-484, 1986). None of the other viral RNAs is detectably packaged into cores. These findings provide independent evidence that the shortest 3.5-kb RNA is the template for synthesis of the viral genome and reveal a novel selectivity in viral RNA packaging.

Immunochemical characterization of hepatitis B e antigen subtypes, HBeAg/1 and HBeAg/2, in sera of hepatitis B virus carriers

The interrelation between HBeAg subtypes, HBeAg/1 and HBeAg/2, in sera was examined immunochemically. The detection of HBeAg subtypes in immunodiffusion (ID) depended upon the amount of HBeAg determined by reversed passive haemagglutination (RPHA), ie, the titres of HBeAg in sera positive for both HBeAg/1 and HBeAg/2, positive for only HBeAg/1 and negative for both HBeAg/1 and HBeAg/2 were 2(9.8) +/- 1.5, 2(7.0) +/- 1.6, and 2(5.6) +/- 1.3, respectively. When the sera belonging to the latter two groups were concentrated up to 2(10) RPHA titre, the precipitin line corresponding to that of HBeAg/2-anti-HBeAg/2 was visualized in ID. Monoclonal anti-HBeAg antibody that absorbed only the precipitin line of HBeAg/1-anti-HBeAg/1 in ID was prepared for the characterization of HBeAg subtypes. A linear correlation (r = 0.91) between titres of HBeAg determined by the RPHA cells prepared with monoclonal and polyclonal antibodies was found in almost all HBeAg-positive sera. The reactivities of this monoclonal anti-HBeAg antibody to both HBeAg/1 and HBeAg/2 were demonstrated in affinity chromatography experiments using a Sepharose 4B column conjugated with this antibody. These results suggest that both HBeAg/1 and HBeAg/2 are constantly present in HBeAg-positive sera and that they are closely associated. Based upon these results, a hypothetical model for the elucidation of the immunological relationship between HBeAg/1 and HBeAg/2 is proposed.

Expression of hepatitis B virus core antigen gene in Saccharomyces cerevisiae: synthesis of two polypeptides translated from different initiation codons

Two recombinant plasmids were constructed that allow expression of the hepatitis B core (HBc) antigen gene in the yeast Saccharomyces cerevisiae under the control of the repressible acid phosphatase promoter. One plasmid was designed to produce polypeptide I, which consists of 183 amino acids, and the other plasmid was designed to produce polypeptide II, which has an additional 29-amino-acid sequence at the amino terminus of polypeptide I. The viral genome may code for either one or both of these two polypeptides, depending upon the selection of initiation codons. Both polypeptides produced in yeast cells reacted with anti-HBc antibody and were assembled into spherical particles approximately 27 nm in diameter. Particles made of polypeptide I were stable, whereas those made of polypeptide II readily dissociated when exposed to high salt levels. The antigenicity of the HBc (as defined by its reactivity to anti-HBc antibody in the reversed passive hemagglutination assay) disappeared as the particle dissociated, leaving materials that sedimented slowly and that reacted to anti-hepatitis B e antibody. These observations strongly suggest that native viral cores are mostly (if not all) made of polypeptide I, because it is reasonably stable, and that the N-terminal portion of this polypeptide has some, but not a profound, influence on the assembly of polypeptides into particles.

Human and monoclonal antibodies to hepatitis B core antigen recognise a single immunodominant epitope

Monoclonal antibodies were raised against hepatitis B core antigen (HBcAg) synthesized in Escherichia coli. They identified a single immunodominant determinant on both liver-derived and E. coli-derived HBcAg. Cross-inhibition studies demonstrated that HBsAg-containing human sera which contained antibodies to HBcAg (anti-HBc) together with either hepatitis B e antigen (HBeAg) or its antibody (anti-HBe) essentially only recognised the same single determinant as the murine antibodies. The identification of a single dominant HBcAg determinant may be important if future hepatitis B virus vaccines contain HBcAg.

Demonstration of a firm association between hepatitis B surface antigen proteins bearing polymerized human albumin binding sites and core-specific determinants in serum hepatitis B viral particles

Hepatitis B viral particles (HB-VP) were purified from sera of chronic hepatitis B surface antigen (HBsAg) positive carriers by consecutive isopycnic and rate-zonal sedimentation in sucrose gradients. Their immunological properties [HBsAg, hepatitis B core antigen (HBcAg) and hepatitis B e-antigen (HBeAg) activities] were examined by a radioimmunoassay based upon the classical "sandwich principle". A double antibody specificity radioimmunoassay (DAS-RIA) was then developed to determine whether envelope proteins (HBsAg) with binding activity for polymerized human serum albumin (pHSA-BA) were associated with core-specific antigenicities (HBc/HBeAg). An e-antigen activity cosedimenting with intact HB-VP (negative for HBcAg reactivity) was detected in association with HBsAg and receptors for pHSA. The presence of HBcAg-specific determinant(s) on HBeAg molecules was also indicated by DAS-RIA. So, we postulated that such hepatitis B virion (HBV) specific molecules are involved in immune complexes with anti-HBc as antibodies in sera of patients with chronic HBV infection. To define the significance of these molecular forms in HB-VP morphogenesis, we studied the effects of a mild treatment with a chaotropic salt, NaSCN, on HB-VP-rich fractions (DNA polymerase positive). A small mol. wt HBeAg derived from HB-VP by dissociating treatment was detected. We found that core-specific determinants (HBe/HBcAg) were bound to large surface proteins (HBsAg) with pHSA-BA and therefore probably contained the pre-S sequence. The selective release from HB-VP of such molecular forms, which could be a product of the major S-region transcript, suggests that they may be components of complete virions.

Detection of two forms of HBeAg (free-and IgG-bound HBeAg) in patients with HBe antigenemia using staphylococcus bearing protein A

Protein A-bearing Staphylococcus aureus organisms (STA) were used to separate free HBeAg from IgG-bound HBeAg. Free HBeAg was detected in the supernate while IgG-bound HBeAg could be liberated from the pellets using MgCl2 or a glycine buffer. HBeAg was determined by radioimmunoassay and the results expressed as patient's cpm/normal control's cpm ratio (S/N ratio). This ratio was demonstrated to be proportionate to the antigen concentration and used as a titer of HBeAg. Sera of 40 HBsAg-negative healthy volunteers and 82 HBeAg-positive patients who were either asymptomatic HBsAg carriers or had various diseases including chronic persistent hepatitis (CPH), chronic active hepatitis (CAH), and renal disease undergoing hemodialysis, were tested for free HBeAg and IgG-bound HBeAg. Patients with CAH from two different countries were compared. Free HBeAg was detected in all patients but one, IgG-bound HBeAg was detected with similar prevalences (from 56% to 67%) in HBsAg asymptomatic carriers, hemodialysis patients, CPH and Italian CAH patients. In contrast, all CAH patients from New York, who had frequently been exposed to HBV infection, had detectable levels of IgG-bound HBeAg, with the highest S/N ratios observed in the study, and frequently showed an unfavorable outcome. In AVH due to HBV and delta agent co-infection, IgG-bound HBeAg was detected in two of four patients only in the initial stage of the disease. The data reported indicate that a separate determination of free- and IgG-bound HBeAg may have clinical value.

The HBV HBX gene expressed in E. coli is recognised by sera from hepatitis patients

We have cloned the X gene (HBx) and the HBc antigen (HBc Ag) gene of human hepatitis B virus (HBV) in Escherichia coli as fusion products with beta-galactosidase. Both HBV genes are expressed in E. coli strain CSR 603. Expression is detected by u.v. irradiation of the bacteria, metabolic labelling and electrophoresis of the labelled extracts on SDS-polyacrylamide gels. The HBc Ag protein produced in bacteria can be recognised by anti-HBc sera and peptides derived from the protein are also recognised by anti-HBe sera. The HBx protein is recognised by some, but not all, sera which are anti-HBe positive. HBx Ag is also recognised by a woodchuck antibody similar to anti-HBe (anti-WHe). These results constitute the first proof that the open reading frame X is a true viral gene and is expressed during HBV (and WHV) infection and that an HBx/anti-HBx system, which may have important biological implications, can exist in parallel with the classic HBe/anti-HBe system.

Quantitation of hepatitis B virus (HBV) core antigen in serum in the presence of antibodies to HBV core antigen: comparison with assays of serum HBV DNA, DNA polymerase, and HBV e antigen

A quantitation procedure for hepatitis B core antigen (HBcAg) in serum without prior removal of antibodies to HBcAg is described. The virus nucleoprotein core was released from hepatitis B virus (HBV) particles by treatment with Nonidet P-40 detergent and allowed to form immune complexes with homologous antibodies to HBcAg present in the sera of HBV-infected individuals. After precipitation with 2.0% polyethylene glycol-1.5% Tween 20, the HBcAg immune complexes were dissociated by treatment with 3 M KSCN and then adsorbed onto polystyrene beads in the presence of the SCN- ions. Thereby, HBcAg and antibodies to HBcAg were linked independently of each other to the matrix, and the core antigen could be quantitated directly by incubation of the beads with 125I-labeled anti-HBc. Even in the presence of an excess of antibodies to HBcAg in the polyethylene glycol precipitates, HBcAg could be detected without appreciably affecting the sensitivity. The assay proved to be specific for core determinants and exhibited excellent reproducibility. The application of the HBcAg assay in 185 hepatitis B e antigen-positive sera revealed HBc antigenemia in 99% of the sera containing hepatitis B e antigen at titers of greater than or equal to 1:256 and 43% of the sera with lower hepatitis B e antigen levels. However, only in 6 of the 34 HBcAg-negative sera could HBV DNA be detected by blot hybridization. When correlated with HBV-associated DNA polymerase (DNAP) activity, HBc antigenemia was found in all DNAP-positive sera (n = 95) and in 39% of the hepatitis B e antigen-positive sera without detectable DNAP activity (n = 44). Of the DNAP-negative sera with HBc antigenemia, 94% contained HBV DNA, whereas in the absence of HBcAg, HBV DNA could be detected only in 3 of 27 DNAP-negative sera. With regard to sensitivity, the HBcAg assay appeared to be less sensitive than the hybridization technique, but more sensitive than the DNAP assay.

HBc and HBe antigenicity and DNA-binding activity of major core protein P22 in hepatitis B virus core particles isolated from the cytoplasm of human liver cells

Highly purified hepatitis B virus core particles were obtained in large amounts from the cytoplasm of infected human liver cells. This DNA polymerase-negative core preparation had only hepatitis B core antigen-specific antigenicity and showed a surprising stability. Two forms of a single protein of 22,000 molecular weight, P22, were resolved electrophoretically; the slower moving species, P22a, appeared to be a reduced form of the protein, and the faster moving species, P22b, could have represented a conformational isomer containing an intramolecular disulfide bond(s). The immunological properties and DNA-binding activity of the reduced form, P22a, were examined following separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by transfer onto nitrocellulose membranes (Western blotting). We found that the hepatitis B virus C gene protein shared the antigenic site responsible for both hepatitis B core and e antigen reactivity. We also demonstrated that the core protein(s) bound specifically the genomic hepatitis B virus DNA in comparison with a plasmid DNA (pBR322). This last observation was further substantiated by a radioimmunological method. P22a was also found to be phosphorylated in vitro by the endogenous protein kinase activity, copurified with the hepatitis B core antigen particles. These findings suggest that P22 is a multifunctional protein which is incorporated into core particles within the cytoplasm of the host cell before DNA encapsidation. A critical role of this protein in hepatitis B virus assembly is suggested.

Adsorption properties of different hepatitis B virus related antigens (HBsAg, HBcAg, HBeAg) on octanohydrazide-Sepharose 4B

Chromatography of plasma containing hepatitis B virus and partially purified viral antigens on a hydrophobic gel derivative (octanohydrazide-Sepharose 4B) revealed that HbsAg and HbcAg were adsorbed to the gel in 0.75 mol/l ammonium bicarbonate and eluted by a detergent, Berol. HBeAg in a purified HBcAg preparation from human liver, but not HBeAg in plasma, was bound to the gel. Furthermore, HBeAg in the HBcAg preparation, but not HBeAg in plasma, lost its antigenic reactivity in the presence of Berol, indicating that the two HBeAgs were present in different molecular configurations. However, HBeAg could be released from HBV (HBcAg) and form a component which sedimented slowly and was immune-reactive in the presence of the detergent. The results contribute to knowledge of the interrelationship between hepatitis B-related antigens and indicate that chromatography on hydrophobic gel derivatives can be used not only for the purification (and removal) of HBsAg but also of HBcAg.

Isolation and characterization of liver-derived hepatitis B e antigen

Two subpopulations of hepatitis B e antigen (HBeAg) were isolated from a human liver infected with hepatitis B virus. HBeAg extracted from liver homogenate subsequent to treatment with buffered 3 M NaSCN or 0.5 M MgCl2 banded at the density of 1.13 g/cm3 in CsCl and was polydispersed on gel filtration. In contrast, HBeAg released with phosphate-buffered saline (PBS) was detected mainly at a density of 1.20 g/cm3 in a CsCl gradient and consisted of low molecular weight species on gel chromatography. Polypeptides of 40,000 and 45,000 daltons were found in NaSCN and PBS-released HBeAg preparations, respectively. The results are interpreted as suggestive that liver HBeAg is a dimer of the major core particle polypeptide in different physicochemical forms.

Characterization of RNA transcripts and virally coded proteins synthesized in mouse fibroblasts transfected with hepatitis B DNA: HBeAg synthesis in HBcAg-negative cells with active core-antigen genes

A line of mouse cells expressing hepatitis B virus (HBV) surface and 'e' antigens identical in their physico-chemical properties to antigens from patients infected with HBV was isolated after transfection of 3T3 cells with cloned HBV DNA. The studies reported here indicate that the cells contain uninterrupted copies of the entire HBV genome which are unmethylated on CCGG sites and have no gross deletions or rearrangements. The entire core region is transcribed into polyadenylated RNAs large enough to serve as messengers for production of viral core antigen (HBcAg) yet no HBcAg can be detected. This suggests that the cells produce a primary translation product copied from the HBcAg messenger which either cannot assume the proper configuration for display of HBcAg determinants or is rapidly converted to HBeAg by proteolysis.

Circular dichroism and biochemical properties of the hepatitis B virus core antigen

The hepatitis B virus (HBV) core antigen was purified by mild procedures, including hydroxyapatite column chromatography, with care taken to avoid the degradation of the particles. Circular dichroism (CD) of the HBV core particles in saline showed low intensities of negative ellipticities in the region dominated by amide bond absorption. Acid treatment of the particles induced a remarkable change in the CD spectrum, with the appearance of a positive extremum at about 208 nm. The amino acid composition and the COOH-terminal residue of the isolated core polypeptide (Mr 21,000-21,500) were shown to be essentially the same as those of the polypeptide deduced from the nucleotide sequences which had been proposed for the HBV core antigen by other laboratories. We failed to detect any NH2-terminal dansyl-derivatives from the core polypeptide by the dansyl-Edman method. We also showed by the method of fluorescein polarization that the core polypeptide conjugated with fluorescein isothiocyanate has an affinity for serum albumin. This may indicate a state of disassembled or non-assembled core polypeptide in sera.

Core particles of hepatitis B virus and ground squirrel hepatitis virus. II. Characterization of the protein kinase reaction associated with ground squirrel hepatitis virus and hepatitis B virus

The recently described protein kinase activity in hepatitis B virus core antigen particles (Albin and Robinson, J. Virol. 34:297-302, 1980) has been demonstrated here in the liver-derived core particles of ground squirrel hepatitis virus. Both protein kinase activities were initially associated with DNA polymerase-positive heavy core particles in CsCl density equilibrium gradients and shifted to polymerase-negative cores during the course of purification. The major core-associated polypeptide of each virus was the dominant species labeled. A variable number of other polypeptide species were also labeled by this reaction. Tryptic peptide mapping of both major and minor phosphorylated polypeptides of each virus resulted in similar patterns, suggesting that many of the sites of phosphorylation were the same in the components of each core particle. Hydrolysis of these phosphorylated core particles revealed a major phosphoamino acid as serine and a minor phosphoamino acid as threonine. The products of the protein kinase reaction in both human hepatitis B and ground squirrel hepatitis virus core particles, then, share many characteristics. The possible function(s) of this protein kinase activity is discussed in the light of similarly characterized activities in other animal viruses.

Electron microscopy of human hepatitis B virus cores by negative staining-carbon film technique

The ultrastructure of the nucleocapsid component of human hepatitis B virus (core particle) was studied by negative staining-carbon film technique. Using this method an improved image of core particles was obtained in respect of resolution and contrast. Two-dimensional crystalline arrays of core particles were formed in vitro. Under these arrays the distance between the particle centers was 28.3 nm, corresponding to the capsid diameter, when analyzed through optical diffraction patterns. Positively stained images of these arrays revealed that core particles contain an electron-dense center of nucleoid-like area about 21 nm in diameter. The capsid surface rarely exhibited small capsomeres, ie, small spheres or ring-like structures measuring 4.0-4.2 nm. From the dimension of these structures and the analysis by Markham's rotational technique, it was suggested that each of these capsomeres is an individual subunit (monomer) and 180 of these subunits build up the core particle capsid according to the icosahedral symmetry (T = 3), but not clustering into distinct morphological features.

Enzyme-linked immunosorbent assay for detection of antibody to the hepatitis B surface antigen-associated delta antigen

A blocking enzyme-linked immunosorbent assay (ELISA) was developed for specific detection of antibody to the hepatitis B surface antigen-associated delta antigen. The sensitivity of ELISA was intermediate between that of previously described immunofluorescence and radioimmunological assays for anti-delta. Performance of ELISA was simple and required only ordinary and inexpensive laboratory equipment.

The conversion of hepatitis B core antigen synthesized in E coli into e antigen

The antigen (HBeAg) of hepatitis B virus (HBV) is a polypeptide of 17-20,000 daltons closely associated with the core antigen (HBcAg) of Dane particles, from which it is released by a variety of disruptive procedures. HBeAg could be a unique component of HBV core particles or a derivative of HBcAg. To resolve this question immunodiffusion experiments were carried out with preparations of HBcAg synthesized in E coli carrying a recombinant plasmid from which the HBcAg, but no other HBV gene, was expressed. HBcAg was converted into HBeAg by proteolytic degradation under dissociating conditions, thus confirming at the molecular level that HBeAg is a component of HBcAg. This offers a new route to the detection of HBeAg and antibodies to the antigen.

Prevalence of Williams e1 antigen in comparison with e2 antigen in hepatitis B antigen carriers and patients in hemodialysis unit

The prevalence of both e1 and e2 antigens in 1,158 sera of asymptomatic HBsAg carriers, carriers in hemodialysis units, and HBsAg-negative blood donors was examined. The detection rate of e1 antigen was as high as 80% in asymptomatic carriers, 95% in hemodialysis patients, and even 13.1% in HBsAg-negative donors. All of the e1 antigen-positive specimens in such HBsAg-negative sera were found to have both or either anti-HBs and anti-HBc, suggesting the past history of Hepatitis B virus (HBV) infection of the donors. In the HBsAg-positive serum, the detection rate of e2 antigen (17%) was lower than that of e1 (80%), and all sera having e2 antigen were positive for e1 antigen. The titers of HBsAg, HBcAg, and anti-HBc in e2 antigen-positive sera were higher than that of sera detecting only e1 antigen. The appearance of e1 antigen and e2 antigen in the course of post-transfusion hepatitis B was studied with five cases. Retrospective study showed that three of them each received one unit of HBsAg-positive blood, and the other two received HBsAg-negative blood but with high-titered anti-HBc. In four cases out of five, in which e2 antigen was detected during the course of infection, the initial detection of e2 antigen occurred at or just before the elevation of liver enzyme levels. On the other hand, e1 antigen was detected relatively early after transfusion, and the time of onset. Moreover, the detection period of e1 antigen persisted longer, even after the disappearance of HBsAg antigenemia. These two separate studies suggest that not only e2 antigen but also e1 antigen are associated with the infection of HBV, but they are distinct from each other; the e2 antigen may have the properties of a signal of the viral activity in the patient as suggested by many others, but e1 antigen does not seem to bear such diagnostic values.