The virus of hepatitis, type B (first of two parts)

Exosomes as Conduits: Facilitating Hepatitis B Virus-Independent Hepatitis D Virus Transmission and Propagation in Hepatocytes

A number of research studies, including ours, have spotlighted exosomes as critical facilitators of viral dissemination. While hepatitis B virus (HBV) transmission through exosomes has been studied, the focus on its satellite virus, the hepatitis delta virus (HDV), has been unexplored in this context. HDV, although being a defective virus, can replicate its genome autonomously within hepatocytes, independently of HBV. Investigations on Huh7 cells revealed an intriguing phenomenon: the HDV proteins, S-HDAg and L-HDAg, are transmitted between cells without a complete viral structure. Detailed analysis further revealed that the expression of these proteins not only bolstered exosome secretion but also ensured their enrichment within these vesicles. Our experimental approach utilized transfection of various plasmids to examine the role of HDV RNA and proteins in the process. One salient finding was the differential propagation of the HDV proteins S-HDAg and L-HDAg, suggesting intricate molecular mechanisms behind their transmission. Notably, the purity of our exosome preparations was monitored using markers such as TSG101 and CD81. Importantly, these exosomes were found to carry both HDV RNA and proteins, highlighting their role in HDV dissemination. This novel study underscores the role of exosomes in mediating the transmission of HDV components between hepatocytes independent of HBV. These revelations about the exosomal pathway of HDV transmission provide a foundation for the development of innovative therapeutic strategies against HDV infections.

Pangenomic antiviral effect of REP 2139 in CRISPR/Cas9 engineered cell lines expressing hepatitis B virus surface antigen

Chronic hepatitis B remains a global health problem with 296 million people living with chronic HBV infection and being at risk of developing cirrhosis and hepatocellular carcinoma. Non-infectious subviral particles (SVP) are produced in large excess over infectious Dane particles in patients and are the major source of Hepatitis B surface antigen (HBsAg). They are thought to exhaust the immune system, and it is generally considered that functional cure requires the clearance of HBsAg from blood of patient. Nucleic acid polymers (NAPs) antiviral activity lead to the inhibition of HBsAg release, resulting in rapid clearance of HBsAg from circulation in vivo. However, their efficacy has only been demonstrated in limited genotypes in small scale clinical trials. HBV exists as nine main genotypes (A to I). In this study, the HBsAg ORFs from the most prevalent genotypes (A, B, C, D, E, G), which account for over 96% of human cases, were inserted into the AAVS1 safe-harbor of HepG2 cells using CRISPR/Cas9 knock-in. A cell line producing the D144A vaccine escape mutant was also engineered. The secretion of HBsAg was confirmed into these new genotype cell lines (GCLs) and the antiviral activity of the NAP REP 2139 was then assessed. The results demonstrate that REP 2139 exerts an antiviral effect in all genotypes and serotypes tested in this study, including the vaccine escape mutant, suggesting a pangenomic effect of the NAPs.

Characterization of the antiviral effects of REP 2139 on the HBV lifecycle in vitro

During hepatitis B virus (HBV) infection, HBV subviral particles (SVP) are produced in large excess in comparison to infectious virions and account for the major source of HBV surface antigen (HBsAg) in the blood. This abundant circulating HBsAg has been postulated to promote HBV chronicity by inducing immune exhaustion against HBsAg. Nucleic acid polymers (NAPs) such as REP 2139 display promising antiviral activity against both HBV and hepatitis Delta virus (HDV) in clinical trials. REP 2139 is accompanied by clearance of HBsAg from blood with concomitant reappearance of anti-HBsAg antibodies. To decipher the mechanism-of-action of NAPs, a recently developed cell-based assay in human HepG2.2.15 cells was used (Blanchet et al., 2019). This assay recapitulates the HBsAg secretion inhibition observed in treated patients. In the present study, we analysed the antiviral effect of REP 2139 on the HBV lifecycle. Importantly, we confirm here the potent inhibitory activity of the compound on HBsAg secretion, and report minor or no effect on other viral markers such as intracellular DNA and RNA, and HBeAg or Dane particle secretion. Notably, intracellular HBsAg accumulation is prevented by proteasomal and lysosomal degradation.

Update Treatment for HBV Infection and Persistent Risk for Hepatocellular Carcinoma: Prospect for an HBV Cure

Since the discovery of the hepatitis B virus (HBV) by Blumberg et al. in 1965, its genome, sequence, epidemiology, and hepatocarcinogenesis have been elucidated. Globally, hepatitis B virus (HBV) is still responsible for the majority of hepatocellular carcinoma (HCC). HCC is the sixth-most common cancer in the world and the second-most common cancer death. The ultimate goal of treating HBV infection is the prevention of HCC. Fortunately, anti-HBV treatment with nucleos(t)ide analogues (NAs), which began with lamivudine in 1998, has resulted in remarkable improvements in the survival of patients with chronic hepatitis B and a reduced incidence of HCC. These results were documented with lamivudine, entecavir, and tenofovir. Nonetheless, as the duration of antiviral treatment increases, the risk for HCC still remains despite undetectable HBV DNA in serum, as reported by different investigators with observation up to 4⁻5 years. In our own experience, we are witnessing the development of HCC in patients who have received antiviral treatment. Some have enjoyed negative serum HBV DNA for over 12 years before developing HCC. Current treatment with NAs can effectively suppress the replication of the virus but cannot eradicate the covalently closed circular DNA (cccDNA) that is within the nucleus of hepatocytes. There still remains a great need for a cure for HBV. Fortunately, several compounds have been identified that have the potential to eradicate HBV, and there are ongoing clinical trials in progress in their early stages.

Hepatitis B virus: virology, molecular biology, life cycle and intrahepatic spread

Hepatitis B virus is a member of the Hepadnaviridae family and responsible for causing acute and chronic hepatitis in humans. The current estimates of people chronically infected with the virus are put at 250 million worldwide. Immune-mediated liver damage in these individuals may lead to the development of cirrhosis and hepatocellular carcinoma later in life. This review deals with our current understanding of the virology, molecular biology, life cycle and cell-to-cell spread of this very important pathogen, all of which are considered essential for current and future approaches to antiviral treatment.

The Efficacy and Safety of Entecavir and Interferon Combination Therapy for Chronic Hepatitis B Virus Infection: A Meta-Analysis

The objective of this study was to evaluate the effectiveness and safety of entecavir (ETV) and interferon (IFN) combination therapy in the treatment of chronic hepatitis B (CHB) mono-infection via a meta-analysis of randomized controlled trials (RCTs). All eligible RCTs evaluating combination therapy for treating CHB were identified from nine electronic databases. A meta-analysis was performed in accordance with the Cochrane Systemic Review handbook. Eleven trials encompassing 1010 participants were included in this meta-analysis. It showed that at 12 and ≥ 96 weeks of therapy, the combination of ETV and IFN was not better than ETV in improving the undetectable HBV DNA (12 weeks: RR=1.12, 95% CI=0.88-1.42; ≥ 96 weeks: RR = 0.64, 95% CI=0.21-1.98, respectively) and HBeAg seroconversion rates (12 weeks: RR=1.35, 95% CI=0.60-3.04; ≥ 96 weeks: RR=1.36, 95% CI=0.75-2.64, respectively). But at 48 weeks of therapy and approximately 2 years of follow up, combination therapy was superior to ETV in improving the undetectable HBV DNA (48 weeks: RR=1.46, 95% CI=1.13-1.90; follow up: RR=2.20, 95% CI=1.26-3.81, respectively) and HBeAg seroconversion rates (48 weeks: RR=1.82, 95% CI=1.44-2.30; follow up: RR=1.92, 95% CI=1.19-3.11, respectively). When compared to IFN group, at 24 and 48 weeks of therapy, combination group showed a greater undetectable HBV DNA (24 weeks: RR=2.14, 95% CI=1.59-2.89; 48 weeks: RR=2.28, 95% CI=1.54-3.37, respectively) and ALT normalization rate (24 weeks: RR=1.56, 95% CI= 1.24-1.96; 48 weeks: RR=1.55, 95% CI = 1.16-2.07, respectively). At 48 weeks of therapy, combination group achieved a greater HBeAg seroconversion rate than IFN (48 weeks: RR=1.58, 95% CI=1.24-2.00). No significant differences were observed in the side effects of the three therapies. So we can conclude that ETV and IFN combination therapy is more effective than ETV or IFN mono-therapy in CHB treatment. ETV, IFN, and the combination of the two are safe in CHB treatment.

Chronic hepatitis B: Virology, natural history, current management and a glimpse at future opportunities

The host immune system plays an important role in chronic hepatitis B (CHB), both in viral clearance and hepatocellular damage. Advances in our understanding of the natural history of the disease have led to redefining the major phases of infection, with the "high replicative, low inflammatory" phase now replacing what was formerly termed the "immune tolerant" phase, and the "nonreplicative phase" replacing what was formerly termed the "inactive carrier" phase. As opposed to the earlier view that HBV establishes chronic infection by exploiting the immaturity of the neonate's immune system, new findings on trained immunity show that the host is already somewhat "matured" following birth, and is actually very capable of responding immunologically, potentially altering future hepatitis B treatment strategies. While existing therapies are effective in reducing viral load and necroinflammation, often restoring the patient to near-normal health, they do not lead to a cure except in very rare cases and, in many patients, viremia rebounds after cessation of treatment. Researchers are now challenged to devise therapies that will eliminate infection, with a particular focus on eliminating the persistence of viral cccDNA in the nuclei of hepatocytes. In the context of chronic hepatitis B, new definitions of 'cure' are emerging, such as 'functional' and 'virological' cure, defined by stable off-therapy suppression of viremia and antigenemia, and the normalization of serum ALT and other liver-related laboratory tests. Continued advances in the understanding of the complex biology of chronic hepatitis B have resulted in the development of new, experimental therapies targeting viral and host factors and pathways previously not accessible to therapy, approaches which may lead to virological cures in the near term and functional cures upon long term follow-up. This article forms part of a symposium in Antiviral Research on "An unfinished story: from the discovery of the Australia antigen to the development of new curative therapies for hepatitis B."

Management of chronic hepatitis B infection: current treatment guidelines, challenges, and new developments

Chronic hepatitis B (CHB) virus infection is a global public health problem, affecting more than 400 million people worldwide. The clinical spectrum is wide, ranging from a subclinical inactive carrier state, to progressive chronic hepatitis, cirrhosis, decompensation, and hepatocellular carcinoma. However, complications of hepatitis B virus (HBV)-related chronic liver disease may be reduced by viral suppression. Current international guidelines recommend first-line treatment of CHB infection with pegylated interferon, entecavir, or tenofovir, but the optimal treatment for an individual patient is controversial. The indications for treatment are contentious, and increasing evidence suggests that HBV genotyping, as well as serial on-treatment measurements of hepatitis B surface antigen and HBV DNA kinetics should be used to predict antiviral treatment response. The likelihood of achieving a sustained virological response is also increased by extending treatment duration, and using combination therapy. Hence the paradigm for treatment of CHB is constantly evolving. This article summarizes the different indications for treatment, and systematically reviews the evidence for the efficacy of various antiviral agents. It further discusses the shortcomings of current guidelines, use of rescue therapy in drug-resistant strains of HBV, and highlights the promising clinical trials for emerging therapies in the pipeline. This concise overview presents an updated practical approach to guide the clinical management of CHB.

HBx Gene Mutations in Hepatitis B Virus and Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most prevalent cancers which are found in many Asian and African countries. There are several risk factors that may develop to HCC. Along with several other factors contributing to HCC, hepatitis B virus (HBV) infection also accounts for a major cause. HBV infection represents a major health problem worldwide. Among all of HBV genes, HBx is believed to play a prominent role in carcinogenesis, although the actual mechanism is not yet fully understood. The HBx gene of HBV is the most common open reading frame that may undergo mutations and may develop into HCC. This review summarizes the current knowledge about the most important roles of HBx gene that may lead to the development of HCC.

Virus-like particles as a highly efficient vaccine platform: diversity of targets and production systems and advances in clinical development

Virus-like particles (VLPs) are a class of subunit vaccines that differentiate themselves from soluble recombinant antigens by stronger protective immunogenicity associated with the VLP structure. Like parental viruses, VLPs can be either non-enveloped or enveloped, and they can form following expression of one or several viral structural proteins in a recombinant heterologous system. Depending on the complexity of the VLP, it can be produced in either a prokaryotic or eukaryotic expression system using target-encoding recombinant vectors, or in some cases can be assembled in cell-free conditions. To date, a wide variety of VLP-based candidate vaccines targeting various viral, bacterial, parasitic and fungal pathogens, as well as non-infectious diseases, have been produced in different expression systems. Some VLPs have entered clinical development and a few have been licensed and commercialized. This article reviews VLP-based vaccines produced in different systems, their immunogenicity in animal models and their status in clinical development.

The structure of HBsAg particles is not modified upon their adsorption on aluminium hydroxide gel

Current Hepatitis B vaccines are based on recombinant Hepatitis B surface antigen (HBsAg) virus-like particles adsorbed on aluminium (Al) gel. These particles exhibit a lipoprotein-like structure with about 70 protein S molecules in association with various types of lipids. To determine whether the adsorption on Al gel affects HBsAg structure, we investigated the effect of adsorption and mild desorption processes on the protein and lipid parts of the particles, using various techniques. Electron microscopy showed that the size and morphology of native and desorbed HBsAg particles were comparable. Moreover, infrared and Raman spectroscopy revealed that the secondary structure of the S proteins was not affected by the adsorption/desorption process. Affinity measurements with Surface Plasmon Resonance showed no difference between native and desorbed HBsAg for HBsAg-specific RF-1 monoclonal antibody. Steady-state and time-resolved fluorescence data of the intrinsic fluorescence of the S proteins further indicated that the adsorption/desorption of HBsAg particles on Al gel did not modify the environment of the most emitting Trp residues, confirming that the conformation of the S proteins remains intact. Moreover, using environment-sensitive 3-hydroxyflavone probes, no significant changes of the lipid core and lipid membrane surface of the HBsAg particles were observed during the adsorption/desorption process. Finally, the ratio between lipids and proteins in the particles was found to be similar before and after the adsorption/desorption process. Taken together, our data show that adsorption on Al gel does not affect the structure of the HBsAg particles.

HIV/HBV Co-Infections: Epidemiology, Natural History, and Treatment: A Review Article

Hepatitis B virus (HBV) infection, one of the major health priorities, accounts approximately for 350 million chronic cases and a global total of 33 million people were living with human immunodeficiency virus (HIV) in the world.Co-infection with HIV and the HBV presents a significant challenge to health care providers, with different prevalence rates in different parts of the world. It is important to screen all HIV infected individuals for HBV infection and reverse. Infection with HBV becomes more violent in patients co-infected with human immunodeficiency syndrome. HIV/HBV co-infected individuals are at increased risk of chronic hepatitis, cirrhosis, and hepatocellular carcinoma, and of experiencing HAART toxicity. In this review, the latest statistics on epidemiology of HIV, HBV and their co-infection has been presented along with prominent characteristics of HBV. Transmission routes which are the common between HBV and HIV are described and the most important ones are described according to the regional and age features. Also, there is a series of actions being performed once HBV infections occur to prevent HIV or to diagnose if the HBV-infected individuals are also infected with HIV. As in treatment case, some of the frequent treatment methods including applying interferon and using nucleoside and nucleotide analogues have been discussed. Finally, we would explain the new recommendations for treating patients who were co-infected with HBV and HIV, including staging HBV and HIV treatment, based on the stage of each disease. It also outlines the optimal treatment options, whether the patient is treated for HBV first, HIV first, or HIV and HBV together.

Cholesterol depletion of hepatoma cells impairs hepatitis B virus envelopment by altering the topology of the large envelope protein

Previous reports have shown that cholesterol depletion of the membrane envelope of the hepatitis B virus (HBV) impairs viral infection of target cells. A potential function of this lipid in later steps of the viral life cycle remained controversial, with secretion of virions and subviral particles (SVP) being either inhibited or not affected, depending on the experimental approach employed to decrease the intracellular cholesterol level. This work addressed the role of host cell cholesterol on HBV replication, assembly, and secretion, using an alternative method to inhibition of the enzymes involved in the biosynthesis pathway. Growing HBV-producing cells with lipoprotein-depleted serum (LPDS) resulted in an important reduction of the amount of cholesterol within 24 h of treatment (about 40%). Cell exposure to chlorpromazine, an inhibitor of the clathrin-mediated pathway used by the low-density lipoprotein receptor for endocytosis, also impacted the cholesterol level; however, this level of inhibition was not achievable when the synthesis inhibitor lovastatin was used. HBV secretion was significantly inhibited in cholesterol-depleted cells (by ∼80%), while SVP release remained unaffected. The viral DNA genome accumulated in LPDS-treated cells in a time-dependent manner. Specific immunoprecipitation of nucleocapsids and mature virions revealed an increased amount of naked nucleocapsids, while synthesis of the envelope proteins occurred as normally. Following analysis of the large envelope protein conformation in purified microsomes, we concluded that cholesterol is important in maintaining the dual topology of this polypeptide, which is critical for viral envelopment.

Antiviral treatment of chronic hepatitis B virus (HBV) infections

While 25 compounds have been formally licensed for the treatment of HIV infection (AIDS), only seven licensed products are currently available for the treatment of chronic hepatitis B virus (HBV) infection: interferon-α, pegylated interferon-α, lamivudine, adefovir (dipivoxil), entecavir, telbivudine and tenofovir (disoproxil fumarate). In contrast to the treatment of HIV infections where the individual drugs are routinely used in combination, for the treatment of chronic HBV infection the individual drugs are generally used in monotherapy. In principle, combination drug therapy should allow reducing the likelihood of drug-resistant development.

Biological and clinical implications of HBV infection in peripheral blood mononuclear cells

The liver is the main site of HBV replication, however extrahepatic organs, such as the lymphoid system, are an important reservoir of the virus. Viral DNA into different mononuclear cell subsets has been mainly detected in monocytes and B lymphocytes. The attachment site of the virus has been identified in the preS1 encoded protein of the virus envelope, the same involved in hepatocyte infection. The risk of HBV transmission by infected lymphocytes has been clearly documented in the setting of liver transplantation where de novo HBV infection has been found in up to about 80% of liver grafts from HBsAg negative but anti-HBc positive donors. In the hemodialysis setting the percentage of HBV DNA detection in mononuclear cells of HBsAg negative patients has been described in up to 54% of the cases. Vertical transmission studies indicate that HBV-infected mononuclear cells of the mother may result in viral infection of mononuclear cells of the newborns and possible HBV vaccine response failure. HBV can also infect bone marrow cells and in vitro studies demonstrate a block of hematopoiesis by HBV, supporting clinical observations of isolate cases of aplastic anemia associated to the infection.

Effect of basal core promoter and pre-core mutations on hepatitis B virus replication

There are two hypotheses explaining a fulminant outcome after hepatitis B virus (HBV) infection, both of which may be applicable at the same time: (i) basal core promoter (BCP) mutations increase viral replication, allowing rapid spread of the virus through the liver, and (ii) pre-core (pre-C) mutations abrogating hepatitis B e antigen (HBeAg) synthesis remove its tolerogenic effect, leading to a vigorous immune response. This study investigated the effect of these mutations on virus replication efficiency and HBeAg production. Substitutions A1762T/G1764A and T1753C, C1766T and T1768A in the BCP region, and G1896A and G1899A in the pre-C region, were examined either alone or in combination, using a common genetic background. Huh7 cells were transfected with these constructs and real-time PCR was used to quantify released virion-associated and intracellular HBV DNA, pregenomic RNA and pre-C mRNA. In addition, culture supernatants were tested for hepatitis B surface antigen (HBsAg) and HBeAg. The double BCP mutation (A1762T/G1764A) and the pre-C mutations (G1896A, G1899A), either alone or in combination, had no appreciable effect on the replication capacity of the virus. In contrast, clones with mutations at positions 1766/1768, 1762/1764/1766 and 1753/1762/1764 exhibited increased-replication phenotypes. HBeAg was undetectable in all cultures transfected with constructs bearing the G1896A stop-codon mutation, as expected. In contrast, constructs with additional mutations in the BCP region had appreciably lower levels of HBeAg expression than the wild type. Thus, core promoter mutations other than those at 1762/1764 appear to upregulate viral DNA replication and, at the same time, greatly reduce HBeAg production.

Antiviral treatment of chronic hepatitis B virus infections: the past, the present and the future

A decade ago, standard therapy against chronic hepatitis B virus infections only consisted of lamivudine or IFN-alpha. Treatment with lamivudine and IFN has been compounded by, respectively, the emergence of drug-resistant virus strains and the appearance of serious side effects. In the last 10 years, hepatitis B treatment has made much progress. Several treatments are now licensed for the treatment of patients with chronic hepatitis B and others are under development. Here, we provide an overview of the potential and mode of action of anti-HBV agents that are currently available, and/or may become available in the near future. Foremost among these newer compounds are adefovir dipivoxil, entecavir and telbivudine.

The ultrastructural morphology of native hepatitis B virus

Cell lines (2.2.15 cells) capable of supporting the replication of hepatitis B virus (HBV) DNA and intact viral particles have been established by HBV DNA transfection into HepG2 cells. The purpose of this study was to determine the ultrastructural morphology of native HBV particles without purification in the culture supernatants and in sera from patients. Electron microscopy (EM) and immunogold EM of the samples were carried out using polyclonal and monoclonal anti-hepatitis B surface antigen antibodies. HBV particles in the purified samples from the culture supernatants by density-gradient centrifugation were examined to compare the morphology with that of unpurified samples. EM and immunogold EM studies demonstrated the presence of Dane particles (41.8 nm in diameter), cobra-shaped (head diameter, 42.4 nm), and horn-shaped (head diameter, 43.5 nm) particles in the culture supernatants and in the sera from two patients. The tail of the cobra-like particles had a diameter of 21.0 nm and a length of 214 nm. The hornlike particles had a long branch 20.1 nm in diameter with a length of 189 nm, and a short branch 21.4 nm in diameter with a length of 112 nm. The ratio of Dane particles and cobra- and horn-shaped particles in the supernatants was 5 : 4 : 1. After ultracentrifugation, the cobra- and horn-shaped particles completely disappeared; there were only Dane particles together with spheres of 22 nm and filaments. In conclusion, this study showed for the first time that the native replicative form of HBV is cobra- and horn-shaped.

Morphology of hepatitis C and hepatitis B virus particles as detected by immunogold electron microscopy

We performed indirect immunogold electron microscopy (EM) for immunological identification and characterization of hepatitis C virus (HCV). To clarify the morphology of HCV, an indirect immunogold EM of two plasma samples from patients with high HCV RNA titers was carried out using antibodies specific for the putative HCV envelope protein (E) 1. Spherical virus particles 55-65 nm in diameter with delicate spike projections were detected in the 1.14-1.16 g/ml fractions after sucrose density gradient centrifugation. Polyclonal and monoclonal antibodies to the putative HCV E1 specifically recognized these particles. In addition, immunogold EM of the samples was also performed to uncover the morphology of HCV core particles. Spherical particles 33-40 nm in diameter (average, 37 nm) were detected in the 1.22- to 1.25-g/ml fractions by conventional EM after sucrose density gradient centrifugation. Immunogold EM using rabbit polyclonal antibody (RR8) specific for the putative HCV core protein and colloidal gold-labeled goat antirabbit IgG showed binding of the gold particles with RR8. Some of the HCV core particles showed icosahedric morphology. Optical rotation technique showed that the HCV core particles exhibit sixfold symmetry and that the length of the regular hexagon side is approximately 20 nm, suggesting that they have an icosahedric structure. Further, the detection limit of the indirect immunogold EM was evaluated in 11 plasma samples from chronic hepatitis B patients with different degrees of hepatitis B virus (HBV) DNA titers using antihepatitis B surface antigen antibody. The study showed that the detection limit of virus using this method is 10(7) virions/ml.

Hepatitis B virus nucleocapsid particles do not cross the hepatocyte nuclear membrane in transgenic mice

Transgenic mice that express the hepatitis B virus core protein were used to examine factors that influence the intracellular localization of nucleocapsid particles in the primary hepatocyte in vivo. In this model, viral nucleocapsid particles are strictly localized to the nucleus of the hepatocyte except when the nuclear membrane dissolves during cell division, at which time they enter the cytoplasm. The cytoplasmic nucleocapsid particles do not reenter the nucleus, however, when the nuclear membrane re-forms after cell division. The data support the notion that nucleocapsid particles can form de novo within the nucleus, and they suggest that performed nucleocapsid particles cannot be transported across the intact nuclear membrane in either direction. The results imply that nucleocapsid disassembly is probably required for entry of the hepadnaviral genome into the nucleus, and they question the role of the intranuclear viral nucleocapsid particle during the viral life cycle.

Hepatitis B surface antigen assembles in a post-ER, pre-Golgi compartment

Expression of hepatitis B surface antigen (HBsAg), the major envelope protein of the virus, in the absence of other viral proteins leads to its secretion as oligomers in the form of disk-like or tubular lipoprotein particles. The observation that these lipoprotein particles are heavily disulphide crosslinked is paradoxical since HBsAg assembly is classically believed to occur in the ER, and hence in the presence of high levels of protein disulphide isomerase (PDI) which should resolve these higher intermolecular crosslinks. Indeed, incubation of mature, highly disulphide crosslinked HBsAg with recombinant PDI causes the disassembly of HBsAg to dimers. We have used antibodies against resident ER proteins in double immunofluorescence studies to study the stages of the conversion of the HBsAg from individual protein subunits to the secreted, crosslinked, oligomer. We show that HBsAg is rapidly sorted to a post-ER, pre-Golgi compartment which excludes PDI and other major soluble resident ER proteins although it overlaps with the distribution of rab2, an established marker of an intermediate compartment. Kinetic studies showed that disulphide-linked HBsAg dimers began to form during a short (2 min) pulse, increased in concentration to peak at 60 min, and then decreased as the dimers were crosslinked to form higher oligomers. These higher oligomers are the latest identifiable intracellular form of HBsAg before its secretion (t 1/2 = 2 h). Brefeldin A treatment does not alter the localization of HBsAg in this PDI excluding compartment, however, it blocks the formation of new oligomers causing the accumulation of dimeric HBsAg. Hence this oligomerization must occur in a pre-Golgi compartment. These data support a model in which rapid dimer formation, catalyzed by PDI, occurs in the ER, and is followed by transport of dimers to a pre-Golgi compartment where the absence of PDI and a different lumenal environment allow the assembly process to be completed.

Epitope mapping of the PreS1 domain of the hepatitis B virus large surface protein

The large (L) surface glycoprotein of hepatitis B virus is an important component of the virion envelope derived from translation initiation at the 5' end of the PreS1 domain of the surface antigen open reading frame. Since key roles in virion assembly and infectivity have been postulated for this protein, further understanding of its structure and topology is important. To this end we have mapped the epitopes recognized by a panel of monoclonal antibodies specific for this polypeptide by examining their reactivity with a series of deletion mutants of the PreS1 region expressed in cultured cells. On the basis of this and other techniques, the antibodies fall into two groups mapping to two distinct epitopes spanning residues 27-35 and 72-78, respectively. Immunoprecipitation studies indicate that both regions are exposed on the surface of HBV-encoded particles.

The essential region for assembly and particle formation in hepatitis B virus surface antigen produced in yeast cells

The hepatitis B virus (HBV) genome carries a HBV surface antigen (HBsAg) gene that can encode a polypeptide of 226 amino acids (aa). This gene can be expressed in the yeast, Saccharomyces cerevisiae, and the products can be assembled into 22-nm particles indistinguishable from those recovered from a patient's serum. We constructed a set of deletion derivatives of the HBsAg gene, and examined the particle-forming ability of the resulting polypeptides by expressing the gene in yeast. Elimination of 9 aa from the N terminus had no effect, whereas the elimination of 21-80 aa decreased the ability to form particles, and the particles formed were correspondingly smaller. Elimination of 100 aa that delete the major hydrophobic domain of the molecule abolished the ability to form particles completely. Deletion of 53 aa from the C terminus showed little effect. However, deletions proceeding further toward the center of the molecule rendered the polypeptides unstable.

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.

Replication of duck hepatitis B virus in primary duck hepatocytes and its dependence on the state of differentiation of the host cell

Primary duck hepatocytes obtained from Pekin ducks congenitally infected with duck hepatitis B virus were used to monitor expression of viral proteins and replication of viral DNA in cell culture. Duck hepatitis B virus core antigen, duck hepatitis B virus pre-surface antigen and duck hepatitis B virus DNA were detectable for at least 12 days after cell plating. Whereas expression of duck hepatitis B pre-surface antigen was constant during this time, expression of duck hepatitis B core antigen and of viral DNA rapidly declined. This diminished production of viral components in vitro was paralleled by a change of the hepatocytes toward a fibroblast-like morphology. Supplementation of cell culture medium with 2% dimethyl sulfoxide, a solvent known to maintain the differentiated state of cultured cells, retained competence of the cultured hepatocytes to express duck hepatitis B core antigen and duck hepatitis B virus DNA at high levels. In a second set of experiments, duck hepatitis B virus negative hepatocytes were infected with duck hepatitis B virus from serum of congenitally infected ducks. Dimethyl sulfoxide remarkably improved the competence of cultured duck hepatocytes to become productively infected. This function was maintained for at least 12 days postplating.

Hepatitis B virus markers and persistent antigenemia in adolescents

Adolescents attending a municipal outpatient adolescent clinic in New York City were evaluated for the prevalence of hepatitis B virus (HBV) markers and persistent antigenemia. Among 313 teenagers tested in 1 year, 11.8% were HBV marker positive, and 4.8% had persistent antigenemia. Hispanic teens had a marker rate of 6.4% and an antigenemia rate of 1.4%. Dominican Republic teens had a significantly higher marker rate than Puerto Rican teens. Among Hispanics, sexual activity status and foreign- vs. U.S.-born status were not significantly related to the presence of HBV markers. Asian teenagers had a 50% marker rate and a 27.2% rate for persistent antigenemia. Marker and antigenemia rates were highest in the most recent immigrants. Unexplained persistent hematuria occurred more frequently in patients with HBV markers than in patients without markers. We recommend routine hepatitis B surface antigen screening in Hispanic and Asian adolescents. The greatest at-risk groups are Asians, especially recent immigrants, immigrants from the Dominican Republic, and probably patients with unexplained persistent hematuria.

Infectious hepatitis in dialysis patients

Infectious hepatitis is a major problem for patients with end-stage renal disease and for staff caring for these patients. Initially hepatitis B was the major cause of hepatitis in dialysis patients and staff. Patients had a tendency to develop chronic hepatitis or become chronic carriers of the virus while staff either developed typical acute hepatitis or a primary antibody response. The discovery of the hepatitis B surface antigen (HBsAg), the screening of transfused blood for HBsAg, and the institution of infection control measures including isolation techniques have resulted in a remarkable decrease in the incidence of this disease. Nonetheless, the problem of infectious hepatitis continues as non-A, non-B hepatitis has become more commonplace among dialysis patients. Unfortunately, no viral markers have been discovered, and blood products remain the major vehicle of transmission. The institution of infection control measures similar to those used to control hepatitis B has probably been effective in controlling the spread of this disease. It is hoped that the discovery of the etiologic agent(s), with the eventual goal of screening blood products and the development of a vaccine, will lead to full control of this disorder.

Chronic hepatitis B. Impact of hepatitis D virus superinfection and the hepatitis B e-system on histological outcome, and correlation of the hepatitis B e-system to HBV-DNA in serum

Chronic evolution after acute hepatitis B virus infection. During a 13 months period 1977-1978 a total of 129 cases of acute viral hepatitis type B occurred among patients who were admitted with hepatitis to Roslagstull, Hospital, Stockholm, Sweden. Less than 1% progressed to chronicity. Prevalence of Delta superinfection was studied among 60 patients with chronic hepatitis B. Nineteen (32%) were anti-delta positive. The majority of the positive patients were either non-European immigrants or addicts, both 9/19 (47%). Infections with the delta agent was found to have occurred in Stockholm already in the early 1970s. Rate of HBeAg clearance during chronic HBV was studied among 36 HBeAg positive patients. Seroconversion to anti-HBe was noted in 17 patients (47%), whereas HBeAg persisted in 19 during a mean follow-up period of 53 months. The spontaneous annual HBeAg seroconversion rate was 11%. HBeAg clearance occurred as frequently among homosexual men as among patients in other categories. However, 12/14 homosexual men were HBeAg positive after 2 years follow-up, compared with 1/13 drug addicts. Thus, homosexual men seemed to require a longer time for HBeAg seroconversion than i.v. drug addicts. HBV-DNA in serum, a strong indicator of viral particles and infectivity was analysed among patients with HBeAg seroconversion, initial HBeAg negativity and/or delta superinfection. HBV-DNA was found in 75-80% of our HBeAg positive patients. A correlation between chronic liver disease and presence of HBV-DNA in serum was also found. Thus, HBV DNA was found in 63% of patients with CAH or CAH/CI as compared with only 39% of patients with CPH. Delta infected patients had HBV-DNA more often than those without hepatitis D infection. Seven delta infected, anti-HBe positive, patients were still HBV-DNA positive five to eight years later. Therefore delta infected anti-HBe positive patients can be infectious for prolonged periods. Histological outcome. 63% (12/19) anti-delta positive patients were classified as CAH with or without cirrhosis as against 39% (16/41) of the anti-delta negative patients. Eleven of 15 homosexual men (73%) had histological findings classified as CAH or CAH/CI. None of them were superinfected with HDV. Thus homosexual men developed severe hepatic lesions without being delta infected. In contrast 78% (7/9) i.v. drug addicts with CAH were delta infected. A numerical scoring system was applied and compared with conventional morphological classification of liver histology to assess the histological outcome of 42 patients with repetitive liver biopsies.

Antibodies to pre-S and X determinants arise during natural infection with ground squirrel hepatitis virus

The DNA sequence of the ground squirrel hepatitis virus (GSHV) genome predicts the existence of several proteins in addition to the major surface (S) and core antigens. These include the pre-S1 and pre-S2 proteins, initiated at sites within the open reading frame preceding and continuous with the coding region for the S gene product, and the X protein, the putative product of an independent reading frame. Using an antibody directed against a peptide predicted by codons 130 to 143 of the pre-S1 reading frame, we identified a 43-kilodalton product of the pre-S1 coding region in preparations of GSHV surface antigen purified from the sera of infected animals. In addition, by immunoprecipitation of S- and pre-S-specific in vitro translation products with ground squirrel sera obtained after GSHV infection, we determined that antibodies arise to both S and pre-S determinants. The antibody response to pre-S includes, in some cases, reactivity to pre-S1-specific domains and is not always associated with an anti-S response. Similarly, by production of the viral X gene product in vitro followed by immunoprecipitation with ground squirrel sera, we showed that antibodies to this viral gene product also arise during infection, indicating that X antigenic determinants are synthesized during viral infection and are recognized by the host immune system.

Hepatitis B e-antigen titres for evaluating infectivity during hepatitis B virus infection

By means of an ELISA the level of hepatitis B e-antigen (HBeAg) titre was determined in 51 patients with acute and 123 patients with persistent hepatitis B virus (HBV) infection. We also investigated 120 sera of these patients for infectivity by detecting HBV-specific DNA polymerase (DNA-P). Additional determination of the HBeAg titre revealed that the detection of HBeAg at a dilution of at least 1:50 correlates with the detection of DNA-P in 95% of cases, while in sera with an HBeAg titre of 1:25 or less DNA-P is only detectable in up to 5% of cases. Since the detection of DNA-P indicates high infectivity, certain titres of HBeAg can be employed to differentiate three different degrees of infectivity: (1) Sera without HBeAg show no or only little infectivity; (2) sera containing HBeAg greater than or equal to 1:50 are highly infectious; (3) HBeAg titres up to 1:25 indicate a medium degree of infectivity. These three markers for different degrees of infectivity were applied to study the course of infectivity during acute and persistent forms of HBV infection. In acute hepatitis B the period for the elimination of HBeAg is independent of the HBeAg titre in the first serum sample. In all cases the elimination of HBeAg in acute hepatitis B did not exceed 4 months. Patients with persistent HBV infection and an initial HBeAg titre greater than or equal to 1:50 remained at this high degree of infectivity for at least 18-30 months in 70% of cases. Only 30% of this collective showed a decrease in infectivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological characterization of acute infection with ground squirrel hepatitis virus

Ground squirrel hepatitis virus (GSHV) is a small DNA virus, structurally and antigenically related to the human hepatitis B virus, which occurs naturally among certain wild populations of ground squirrels (P. L. Marion et al., Proc. Natl. Acad. Sci. U.S.A. 77:2941-2945, 1980). Serum from naturally infected animals was used to transmit GSHV in the laboratory by parenteral inoculation of susceptible squirrels. Sixty percent of recipient animals developed viral surface antigenemia after a latent period of 2 to 3 months; three of these animals have remained viremic for over 9 months. Like hepatitis B virus, GSHV demonstrates marked hepatotropism, with viral DNA detected in significant quantities only in the liver, where an average of 6 X 10(2) to 6 X 10(3) viral DNA molecules per cell were found by molecular hybridization. However, histological signs of liver injury after acute infection are minimal. In contrast to infection of its natural host, parenteral administration of GSHV to rats, mice, guinea pigs, and hamsters did not result in demonstrable antigenemia, suggesting that the host range of GSHV, like that of hepatitis B virus, is narrow.

Specificity of hepatitis B virus affinity for human hepatic tissue

Using radiolabeled purified hepatitis B surface antigen and human liver slices, the affinity of hepatitis B virus to its host organ was evaluated. Saturable adsorption of the 125I-HBs Ag complex to liver was demonstrated over both time and complex concentration which could be blocked by excess unlabeled antigen. The specific binding was not found using human pancreas, lung, or kidney tissue. Correspondingly, no specific binding could be found for murine liver but it could be demonstrated with woodchuck liver. The woodchuck is a natural host for one of the newly described hepatitis B-like viruses which is antigenically cross-reactive with the B virus.

Removal of hepatitis B virus from a concentrate of coagulation factors II, VII, IX and X by hydrophobic interaction chromatography

Deliberately added hepatitis B surface antigen (HBsAg) and hepatitis B virus (HBV) could be removed by hydrophobic interaction chromatography from a concentrate of coagulation factors II, VII, IX and X. Chromatography in high concentrations of salt, preferably on octanoic acid hydrazide-Sepharose 4B, resulted in 104 -105 -fold reduction of HBsAg. The binding properties of HBsAg and HBV to the hydrophobic gels were similar and the chromatographic method seems particularly useful in removing low concentrations of virus-related material from protein solutions. The yield of protein from the coagulation factor concentrate was about 85% and the material showed the same stability and biological activities as before the chromatography.

Detection of HBsAg containing cells in liver biopsies by different stains and classification of positively reacting ground-glass hepatocytes

The diagnostic significance of orcein, aldehydthionine, and chromotrope anilinblue stains for the demonstration of HBsAg containing hepatocytes was investigated in 602 unselected liver biopsies. Five types of specifically stained ground-glass hepatocytes (GGH) were distinguished: Type I showed a positive staining reaction of the cytoplasmic periphery (marginal GGH), type II a diffuse staining of the total cytoplasm (diffuse GGH). Type III contained round or oval globular positive cytoplasmic masses (globular GGH). Type IV showed only very small round, drop-like or sickle-shaped positive structures (spotty GGH). The GGH with fatty changes were designated as type V. In all carriers and patients with minimal hepatitis GGH, mostly type I and II, appeared in extensive clusters within the lobules. In chronic persistent hepatitis, there were moderately numerous, partly grouped, partly disseminated ground-glass hepatocytes of type II and III. In chronic active hepatitis there were only a few GGH of type IV. In acute viral hepatitis, there were no typical GGH, however, positively stained phagocytes were seen. The intracellular antigen localization and the intralobular distribution of GGH are considered to be the result of an immune reaction. Single so-called 'metabolic' GGH sometimes showed similar pictures. However, they could usually be distinguished from virus containing GGH because of their granular cytoplasmic structure and a lower staining intensity in the applied stains. Among the three stains the orcein stain yielded the best results. In some cases with HBsAg-positive chronic active hepatitis virus infection could not be proved by means of staining.

An ultrastructural and immunohistochemical study on the delta antigen associated with the hepatitis B virus

Thirteen liver biopsies in which the delta antigen was detected by immunofluorescence were studied by electron microscopy and immune electron microscopy with peroxidase labelled IgG and F(ab1)2 fraction obtained from a human antiserum containing high-titre anti-delta antibodies. The findings were compared with those obtained in 11 HBcAg positive and in two HBsAg negative controls. Neither unique particulate morphology nor any HB virus ultrastructural component were visualised in the delta positive specimens; 20-23 nm naked core particles were observed in 10 of 11 biopsies displaying the HBcAg in immunofluorescence. Delta positive nuclei frequently contained dense round structures of diameter varying between 20 and 30 nm with a soft indistinct edge. These granules did not exhibit characteristic ultrastructural features which enabled them to be distinguished from other granular material observed occasionally in nuclei of normal and diseased livers. However, their association with the delta antigen has been proved by the deposition on identical structures of peroxidase labelled anti-delta antibody. These results suggest that the delta antigen is unrelated to the Dane particle, the putative HB virus. The granules observed in the delta positive nuclei are composed of an amorphous matrix, possibly insoluble aggregates of the delta antigen.

Lyme arthritis: correlation of serum and cryoglobulin IgM with activity, and serum IgG with remission

Forty-eight patients with erythema chronicum migrans (ECM) were studied prospectively for 6 to 18 months. Twenty-six patients had no later symptoms, but 22 subsequently developed Lyme arthritis and 9 of them also experienced neurologic abnormalities. Eighty-seven percent of patients with active ECM followed by subsequent involvement had cryoglobulins containing IgM compared to only 13% of those with active ECM and no later symptoms. The former group also had significantly lower IgG, C3 and C4 levels. Sixty-seven percent of patients still had serum cryoglobulins when neurologic disease was most active, and 45% had them when joint symptoms were most severe, but only 11% continued to have small amounts in remission. The number of patients who continued to have serum cryoglobulins with recurrent attacks of arthritis decreased with time. In contrast, patients always had cryoglobulins in joint fluid, a finding Lyme arthritis shares with rheumatoid arthritis. The cryoprecipitates from 2 of 10 patients contained particles with internal structure, but their viral nature is problematic. All components of antisera obtained from goats and rabbits immunized with cryoglobulins were absorbed by normal human sera. The amount of IgM in cryoglobulins correlated directly with serum IgM, which generally rose during exacerbations and fell during remissions; serum IgG and IgA moved conversely. Thus, IgM was an important correlate of clinical disease activity and IgG or remission.