Hepatic expression patterns of the large and middle hepatitis B virus surface proteins in viremic and nonviremic chronic hepatitis B

The envelope of hepatitis B virus consists of large, middle, and small hepatitis B surface proteins. Recent data from in vitro studies suggest that intracellular expression and distribution of the three polypeptides may be variable. These observations in artificial expression systems prompted this analysis of the occurrence and distribution of the three hepatitis B surface proteins in the liver tissue of substantial viremic (hepatitis B virus DNA- and hepatitis B e antigen-positive) and low-viremic or nonviremic (hepatitis B virus DNA-negative, anti-hepatitis B e antigen-positive) carriers by specific monoclonal antibodies against large, middle, and small proteins. Patients with an active form of viral replication showed a prevalence of middle and small hepatitis B surface proteins in the liver. In nonviremic carriers, the large hepatitis B surface protein was the predominant intrahepatic antigen, a finding that was confirmed at the ultrastructural level by staining of the entire filaments of the viral envelope material in ground glass hepatocytes. The present data are thus consistent with observations in hepatitis B virus-transgenic mice and in transfected cell systems, suggesting that the different patterns of the envelope proteins in the liver may be due to different processing at the translational level.

Hepatocellular carcinoma and bladder cancer as complications following five years of chemotherapy for acute myeloblastic leukemia

Acute myeloblastic leukemia (AML) was diagnosed in a 54-year-old male, a chronic hepatitis B surface antigen (HBsAg) carrier, in June, 1983. Prompt remission was achieved, and maintenance and intensification chemotherapy were given for five years. He was readmitted in March, 1988 because of a mass in the liver and was diagnosed as having hepatocellular carcinoma (HCC). Curative right segmentectomy was performed in May, 1988. In December, 1988, transitional cell carcinoma of the bladder was discovered, and resected transurethrally. These secondary neoplasms, HCC and bladder cancer, were thought to be associated with the long-term chemotherapy given for the AML.

Polymerized albumin binding to serum in various liver diseases: its significance and relation to hepatitis B virus infection

Sensitive and specific enzyme-linked immunosorbent assays (ELISA) were developed to detect separately the binding of polymerized human serum albumin (PHSA) to its antibody (A-PHSA) and to the hepatitis B surface antigen (HBsAg). A-PHSA was not detected in normal serum, whereas more than one-third to about half of sera from patients with acute liver cell injury showed this antibody. Frequency of A-PHSA positivity was low in chronic liver diseases, being relatively higher in those with continuing liver injury. A-PHSA detection was not related to seropositivity for HBsAg. PHSA binding of HBsAg positive sera showed a higher frequency of positivity in chronic carriers than acute hepatitis B. Of 172 asymptomatic HBsAg carriers, PHSA binding was demonstrated in 25 (15%), the frequency being significantly high if HBeAg was also present (84%). Binding was infrequent in sera having anti-HBe (2.9%) and in those negative for both HBeAg and anti-HBe (2.7%). Binding of HBsAg to PHSA was significantly higher than to human serum albumin (HSA). Immunoblotting of separated HBsAg components showed PHSA binding specifically to the high molecular weight peptide. PHSA binding in HBsAg positive serum may indicate the latter's infectivity as detected in a study of maternal-fetal transmission, where it demonstrates 100% infectivity in HBsAg and HBeAg positive mothers. PHSA possibly mediates the attachment of the HBV to the hepatocyte and a competitive binding between A-PHSA with HBsAg for PHSA may modulate the course of HBV infection.

Synthesis and secretion of hepatitis B middle surface antigen by the methylotrophic yeast Hansenula polymorpha

The methylotrophic yeast, Hansenula polymorpha, has been developed as a host system for the synthesis of heterologous proteins. The middle surface antigen of hepatitis B virus (preS2-HBsAg) has been synthesized under the control of a methanol-regulated promoter derived from the methanol oxidase-encoding gene. The synthesized preS2-HBsAg protein was found to be secreted outside the cell membrane into the periplasm and further excreted into the culture medium following permeabilization of the cell wall with beta-1,3-glucanase (beta Glu). Cell cultures treated with beta Glu were able to continuously synthesize and secrete 22-nm particles of preS2-HBsAg into the medium for several days. The overall yield of antigen from treated cultures was found to be over threefold greater than that of untreated controls. The observation that complex supramolecular structures, such as the 22-nm particles of preS2-HBsAg, can be secreted by H. polymorpha and released into the medium, suggests the potential for these yeasts to be an alternative secretory host.

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.

Immune adherence of nascent hepatitis B surface antigen-antibody complexes in vivo in humans

Upon i.v. injection into humans, pre-formed immune complexes bind complement and adhere to complement receptor type I (CR1, CD35) on erythrocytes (immune adherence). However, in most circumstances antigen and antibody react in the presence of complement; such nascent immune complexes may have properties different from pre-formed immune complexes. To define whether nascent immune complexes would also adhere to erythrocytes in vivo in humans, we studied immune complexes that formed upon i.v. injection of radiolabelled hepatitis B surface antigen (HBsAg) into immunized volunteers (eight subjects with anti-HBsAb levels ranging from undetectable to 50 U/ml.; and three control non-immune individuals). Immune complexes formed immediately in the subjects with detectable levels of specific antibody, and the clearance rate of these immune complexes correlated with the anti-HBsAb level (r = 0.78, P < 0.01). A fraction of the circulating immune complexes bound to erythrocytes in the three individuals with the highest antibody level (8-15% at 10 min). The effect of CR1 number per erythrocytes was analysed in two subjects with similar antibody levels and immune complexes clearance rates: immune adherence was higher in the subject with more CR1 per erythrocytes. The same immune complexes model studied in vitro provided similar results: a fraction of nascent immune complexes bound to human erythrocytes; this immune adherence was observed only when immune complexes formed in the presence of antibody excess, and correlated with CR1 number per erythrocytes (r = 0.99, P < 0.01). Finally, adherence of nascent HBsAg-antibody immune complexes to platelets was demonstrated in rabbits. Although immune adherence involves only a small fraction of nascent immune complexes at any given time, it may be essential for the safe disposal of large nascent immune complexes.

[Using BPV transforming foci as selective markers to express HBsAg]

We constructed a plasmid pBMTHBR2 containing mouse MT promoter, entire HBsAg gene (preS and S gene), splicing signal from SV40 and complete BPV genome. Using calcium phosphate precipitation technique to transform C127 Cells and using BPV transforming foci as selective markers, we obtained transformed cell clones. The experiment shows that 57% of the cloned cell lines can secrete HBsAg continuously.

[Activation of the interferon system enzymes by recombinant alpha2-interferon in patients with chronic hepatitis B]

Treatment of patients suffering from chronic hepatitis B with recombinant leukocytic interferon (reaferon) increased the levels of circulating interferon and activated interferon-dependent enzymes such as 2-5A-synthetase and histone kinase. Activation of the enzymes was observed for 1 to 2 weeks. After that period it was maintained at the required levels with intramuscular administration of 1-3 million units of reaferon 2 or 3 times a week. In parallel with increasing of the levels of the interferon system enzymes there was observed a decrease in the level of aminotransferase. The reaction of the viral antigens to the treatment with reaferon was not the same: HBe antigen and antibodies to HBe antigen disappeared, the content of HBs antigen and antibodies to delta-interferon did not change.

Efficient expression of genetically engineered hepatitis B virus surface antigen P31 proteins in yeast

We have constructed plasmids that express modified hepatitis B virus surface antigen (HBsAg) P31-coding genes (M-P31c, d, e, f, and i) having various genetically engineered pre-S2 regions. The plasmids contain the GAPDH (gene coding for glyceraldehyde-3-phosphate dehydrogenase) promoter and the PGK (gene coding for 3-phosphoglycerate kinase) terminator, both isolated from sake brewing yeast, Saccharomyces cerevisiae Kyokai III. Expression levels of the modified HBsAg P31 proteins in yeast are greatly increased from 0.4% to 11.7% of total cell protein. However, the specific mRNAs are expressed at equal levels and the degradation rates of the modified P31 proteins do not vary significantly. Therefore, we considered that different expression levels of the modified P31 proteins are attributed to the changes of the post-translational efficiency. And it was suggested that the conformational stability of the N-terminal peptide (Met-1-Phe-46) in the endoplasmic reticulum membrane determines the expression level of modified P31 proteins.

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.

Binding of biotin to hepatitis B surface antigen: a possible pitfall in immunohistochemistry

We report on the binding of biotin, and hence of biotinylated antibodies and lectins, to ground glass hepatocytes and liver cell membranes in chronic hepatitis B viral infection. This binding is of low affinity, and was proved to be directed at the hepatitis B surface antigen, presumably at its disulfide bonds. To avoid false-positive results, this affinity should be considered in the interpretation of immunohistochemical stainings of hepatitis B virus-infected liver tissue with biotinylated reagents.

Urinary neopterin as a new biochemical marker for the monitoring of disease activity and prognosis in membranous nephropathy associated with hepatitis B surface antigenemia

In an attempt to find a parameter for the differentiation of membranous nephropathy with hepatitis B surface antigenemia (HBVMN) and other types of nephrotic syndrome (NS) in HBsAg (+) carriers, we measured the urinary neopterin in 20 HBVMN patients, other types of NS in HBsAg (+) carriers, asymptomatic HBsAg (+) carriers and HBsAg (-) controls, during the active nephrotic phase and in remission. The urinary neopterin excretion was found to be significantly elevated only in the HBVMN during NS or heavy proteinuria. It progressively decreased and corresponded with the amount of proteinuria. In patients with deteriorated renal function, initially, urinary neopterin excretion was significantly higher than in others and it remained significantly elevated during the follow-up period. In vitro when a patient's mononuclear cells were stimulated with lymphoblastoid cell line, the release of neopterin content in supernatant was increased during the acute phase. There was a significant correlation between supernatant and urinary neopterin level. These results suggest that urinary neopterin may be a new biochemical marker for the differential diagnosis of HBVMN and may be used to monitor the course of HBVMN and serve as a prognostic indicator. However, the specificity is not clear.

Secreted hepatitis B surface antigen polypeptides are derived from a transmembrane precursor

Hepatitis B surface antigen (HBsAg), the major coat protein of hepatitis B virus, is also independently secreted from infected cells as a lipoprotein particle. Secretion proceeds without signal sequence removal or cleavage of other segments of the polypeptide. We have examined the synthesis and transport of HBsAg in cultured cells expressing the cloned surface antigen gene. Our results show that HBsAg is initially synthesized as a integral membrane protein. This transmembrane form is slowly converted to a secreted lipoprotein complex in the lumen of the endoplasmic reticulum via a series of definable intermediates, after which it is secreted from the cell. This unusual export process shares many features with the assembly and budding reactions of conventional enveloped animal viruses. However, it differs importantly in its absence of a requirement for the participation of nucleocapsid or other viral proteins.

Influence of hepatitis delta virus superinfection on the clearance of hepatitis B virus (HBV) markers in HBV carriers in Japan

To elucidate the influence of hepatitis delta virus (HDV) superinfection on the clearance of hepatitis B virus (HBV) associated antigens in HBV carriers, we examined for antibody to hepatitis delta antigen (anti-HD) serial sera collected from 1,029 HBV carriers in Kure, Japan. Of the 242 HBV carriers with hepatitis B e antigen (HBeAg), 28 became seropositive for anti-HD, of whom 18 (64.3%) cleared HBeAg; 214 did not become seropositive for anti-HD, of whom 70 (32.7%) cleared HBeAg. Thus, HBeAg clearance was observed in a significantly higher proportion of HDV-superinfected carriers as compared with carriers without HDV infection (P less than 0.005). In the 56 HBV carriers who cleared hepatitis B surface antigen (HBsAg), anti-HD was detected in three cases with increased serum alanine aminotransferase activity preceding HBsAg clearance. The duration of anti-HD seropositive state was less than 5 years, and the titer of anti-HD was relatively low in every case. These data suggest that the HDV infection rate in Japan is higher than previously reported, that HDV superinfection can be one of the factors that induce the HBeAg clearance and HBsAg clearance in HBV carriers, and also that the most likely outcome of HDV superinfection in HBV carriers in Japan may be acute self-limited infection.

Variable efficacy of interferon-alpha treatment on growth of human hepatoma cell lines in vitro

Three human hepatoma cell lines, PLC/PRF/5, Mahlavu and Sk-Hep 1, two of which contain integrated HBV DNA, were grown in culture and treated with human alpha-IFN for up to 14 days. IFN treatment caused a varying suppression of cell growth of the three hepatoma cell lines. While doubling time and cloning efficiency were significantly reduced for all three hepatoma cell lines tested, 3[H]thymidine incorporation was markedly suppressed, in a dose-dependent fashion, only in treated PLC/PRF/5 cells but not in Sk-Hep 1 and Mahlavu cells. The inhibiting effect of interferon treatment on growth of PLC/PRF/5 cells in vitro was neutralized by antibodies to human IFN. IFN treatment caused a significant suppression of HBsAg and alpha FP secretion by PLC/PRF/5 hepatoma cells. This effect, while constant throughout the observation period for HBsAg, was cumulative for alpha FP secretion. Following discontinuation of treatment, suppression of PLC/PRF/5 hepatoma cell growth was rapidly reversed, and HBsAg and alpha FP secretion returned to their pretreatment levels. These experiments suggest that human alpha-IFN suppresses the growth of some human hepatoma cells in culture but that this effect is dependent on the continuous presence of IFN in the growth medium. Finally, the inhibitory effects of IFN on cell growth differed for the various hepatoma cell lines tested.

A block to the intracellular transport and assembly of hepatitis B surface antigen polypeptides in Xenopus oocytes

Hepatitis B surface antigen is the major protein of the virion envelope, and is also independently secreted from infected cells as a subviral particle composed exclusively of HBsAg and host-derived lipid. Similar particles are efficiently assembled and secreted by cultured mammalian cells transfected with the gene for HBsAg. In contrast to such cultured cells, Xenopus oocytes microinjected with HBsAg mRNA secrete less than 5% of newly synthesized HBsAg polypeptides. We have examined the HBsAg biosynthetic intermediates in such oocytes and provide evidence that the impaired secretion of HBsAg is due to a discrete block in the assembly of lipoprotein particles.

Interrupted replication of hepatitis B virus in liver tissue of HBsAg carriers with hepatocellular carcinoma

To search for events underlying reduction of peripheral viremia and integration of hepatitis B virus (HBV) DNA into the liver cell genome in long-term virus carriers with hepatocellular carcinoma, paired samples of liver and tumor tissue were analyzed by molecular hybridization and immunological methods. Most tumor tissues contained integrated viral DNA; in none was extrachromosomal HBV DNA detected. Integrated HBV DNS was also found in peritumor liver tissue in the majority of patients. However, liver of patients either with or without peripheral viremia also contained free HBV DNA and replicative intermediates. In three nonviremic patients with replicative HBV DNA in liver, viral core antigen expression was markedly reduced or absent, whereas viral envelope protein (surface antigen) expression was normal. In one case, replicative intermediates in liver were sensitive to DNase I digestion, indicating that viral DNA was not encapsidated in normal viral core particles. These results suggest that decreased or defective core antigen production can lead to reduced viremia associated with blocked virus assembly/secretion and accumulation of unencapsidated HBV DNA replicative intermediates in the liver cell. Accumulation of such HBV DNA molecular forms in the liver may lead to an increased propensity for HBV DNA to integrate into the host genome, which has been found with high frequency in hepatic neoplasms from patients infected with hepatitis B virus.

The Vero cell receptor for the hepatitis B virus small S protein is a sialoglycoprotein

The Vero (African green monkey kidney-derived) cell line is capable of binding recombinant hepatitis B surface antigen (rHBsAg) particles containing only the small surface (S) protein of hepatitis B virus (HBV). This binding activity appears to be due to a single major population of receptors (M. E. Peeples et al., Virology 160, 135-142 (1987]. Since infectious HBV particles also contain the small S protein, it is possible that the Vero cell receptor might also function as an HBV receptor. The initial physical characterization of this receptor is reported here. Treatment of Vero cells with each of four proteases reduced their binding activity by 70% or greater, indicating that the receptor is partially protein in nature. Binding activity was also reduced by pretreating cells with neuraminidase or low levels of sodium periodate, indicating that sialic acid also plays a major role in the receptor activity. Consistent with this interpretation, N-acetylneuraminic acid and N-acetylneuraminyl-lactose were able to competitively inhibit rHBsAg particle attachment to Vero cells. The protein nature of the Vero cell receptor was confirmed by the demonstration that chymotrypsin treatment which resulted in 70% loss of binding had little effect on the cell sialic acid content. Therefore, the Vero cell receptor for rHBsAg particles is a sialoglycoprotein.

Characteristics of a cell line (Tong/HCC) established from a human hepatocellular carcinoma

A continuous adherent cell line was established from a hepatocellular carcinoma of an HBsAg-positive Italian male. This cell line, designated Tong/HCC, has been grown in a hormone-supplemented medium for more than 18 months. The cell line secretes HBsAg, alpha-fetoprotein, albumin and alpha 1-antitrypsin. alpha-Fetoprotein production is enhanced by the addition of hydrocortisone and appears to be glucocorticoid concentration-dependent. The concentrates of the supernatant from the cell cultures and cell lysates were negative when tested for HBeAg. The cell culture medium was negative for hepatitis B virus DNA when tested by dot-blot hybridization. However, hepatitis B virus DNA was found to be integrated in the chromosomal DNA by Southern blot analysis. At least five different integration sites were identified, and no free hepatitis B virus DNA was observed. The modal chromosome number was 64, and a translocation on Chromosome 15 was consistently noted. HLA typing revealed sites for A3, Aw24, Bw34 and Cw1.

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.

Cell type specific expression of pre S 1 antigen and secretion of hepatitis B virus surface antigen. Brief Report

Production of the three hepatitis B surface (HBs) proteins was studied in a hepatoma cell line (PLC/PRF/5) and two HBs antigen secreting cell lines (HeLa and mouse L-cells), which had been transfected by a viral genome isolated by molecular cloning from PLC/PRF/5 chromosomal DNA. The DNA used for transfection contains the HBs-specific promoters and the enhancer which regulate the expression of HBs genes in the transfected cell lines. All three cell lines expressed well the small and middle HBs protein, but the larger pre S 1 containing protein was barely detectable in the L-cell. In vivo growth of the transfected HeLa cell as nude mouse tumour increased pre S 1 expression and suppressed secretion of HBsAg.

Pre-S encoded surface proteins in relation to the major viral surface antigen in acute hepatitis B virus infection

The role of pre-S encoded viral surface proteins in acute hepatitis B virus infection is still poorly understood. Binding sites for polymerized human serum albumin have been found to be encoded by the pre-s2 region of the hepatitis B virus genome. Recently, murine monoclonal antibodies against pre-s1 and pre-s2 encoded hepatitis B virus gene products were generated and used for their specific detection in serum. In sera from patients with acute hepatitis B, pre-s1 and pre-s2 antigen occurred in 16 of 20 and 15 of 20 patients, respectively. In the initial stage of the disease, pre-S gene products correlated with binding sites for polymerized human serum albumin, but not with hepatitis B surface antigen. Subsequently, pre-s1 and pre-s2 antigens were cleared from the serum of patients with acute hepatitis B before binding sites for polymerized human serum albumin and hepatitis B surface antigen. Possibly, the early clearance of pre-S markers can be of prognostic value in acute hepatitis B. The mechanisms of the early clearance of the pre-S antigens in acute hepatitis B remain to be elucidated. However, elimination by immunologic mechanisms appears likely.

Dissociation of hepatitis B surface antigen (HBsAg) from immobilised anti-HBsAg antibody in a two site immunoradiometric assay: its relevance to hook effect and recycled assay

The mechanism of the hook effect in a two site immunometric assay of hepatitis B surface antigen (HBsAg) was studied using a novel method. The results showed that HBsAg dissociated from immobilized anti-HBsAg at low as well as high doses of antigen (Ag). This probably was not due to lack of immobilized antibody (Ab) or dissociation of HBsAg non-specifically bound to the immobilized Ab. The dissociated Ag sequestered the labelled Ab in the second reaction and contributed to the decrease in percent binding (B%) of the assay and thus the hook effect. The dissociated Ag could contaminate the recovered pooled labelled Ab in recycled assay and give rise to high non-specific binding. Prolonged washing decreased the side reaction but also the B% of the assay.

Studies on HBsAg binding with polymerised human serum albumin by ELISA

A simple and sensitive ELISA was developed to characterize the interaction between polymerised human serum albumin (pHSA) and HBsAg, using pHSA-coated polyvinylmicrotitre plates as solid phase and anti-HBs-coupled HRPO as the conjugate. The interaction was found to be specific and dependent on the size of albumin polymer. pHSA-binding activity (pHSA-BA) was studied in both HBsAg-negative and HBsAg-positive sera from various liver diseases including acute viral hepatitis, fulminant hepatitis, cirrhosis of liver, chronic active hepatitis, and healthy HBsAg carriers. pHSA-BA was detected only in HBsAg-positive sera. Analysis of HBsAg-positive sera indicated pHSA-BA in high proportions of patients sera as compared to sera from healthy HBsAg carriers. pHSA-BA was detected both in the presence and absence of HBe markers, though the mean BA was relatively high in presence of HBeAg. The effect of human serum immunoglobulins (IgG, IgA, and IgM) on the BA was investigated and a correlation between pHSA-BA and HBsAg-IgM complex positivity in sera was established. Finally, the probable role of human serum IgM in facilitating the binding process was discussed.