Detection of receptors for hepatitis B virus on cells of extrahepatic origin

Hepatitis B or C viral infection and the risk of cervical cancer

BACKGROUND

The present study aimed to evaluate the effects of hepatitis B virus (HBV) or hepatitis C virus (HCV) infection on the risk of cervical cancer.

METHODS

We conducted a case-control study including 838 cervical cancer cases and 838 benign disease controls matched for age, ethnicity, and place of birth. Venous blood was tested for HBV and HCV serological markers. Multiple odds ratios (OR) and corresponding 95% confidence intervals (CI) for cervical cancer were estimated using logistic regression. HBV antigens were examined using immunohistochemical staining.

RESULTS

Anti-HCV was positive in 10 cases (1.2%) and 0 controls (0%). Cases had higher percentage of chronic HBV infection (HBsAg-positive/anti-HBc-positive) and prior HBV infection (HBsAg-negative/anti-HBc-positive) than controls (6.3% vs 4.4%; 11.6% vs 7.3%). Both chronic HBV infection (OR 1.6; 95% CI 1.0-2.4) and prior HBV infection (OR 1.7; 95% CI 1.2-2.4) were associated with cervical cancer in univariate logistic regression analyses. In subgroup analysis among HPV-positive patients, the association between chronic HBV infection and cervical cancer disappeared (OR 1.2; 95% CI 0.4-3.4); while in subgroup among patients younger than 50 years, the association remained significant with adjustment for HPV infection and parity (adjusted OR 2.1; 95% CI 1.0-4.4). HBsAg and HBcAg were detected in 8% and 12% of cervical cancer cases who had seropositive HBsAg, respectively. Compared with the benign controls, individuals with both HBsAg and HPV positive had an increased risk of cervical cancer (adjusted OR 67.1; 95% CI 23.4-192.7).

CONCLUSIONS

HBV infection was associated with cervical cancer in patients with age younger than 50 years. Further prospective studies are needed to confirm this relationship.

Hepadnaviral Lymphotropism and Its Relevance to HBV Persistence and Pathogenesis

Since the discovery of hepatitis B virus (HBV) over five decades ago, there have been many independent studies showing presence of HBV genomes in cells of the immune system. However, the nature of HBV lymphotropism and its significance with respect to HBV biology, persistence and the pathogenesis of liver and extrahepatic disorders remains underappreciated. This is in contrast to studies of other viral pathogens in which the capability to infect immune cells is an area of active investigation. Indeed, in some viral infections, lymphotropism may be essential, and even a primary mechanism of viral persistence, and a major contributor to disease pathogenesis. Nevertheless, there are advances in understanding of HBV lymphotropism in recent years due to cumulative evidence showing that: (i) lymphoid cells are a reservoir of replicating HBV, (ii) are a site of HBV-host DNA integration and (iii) virus genomic diversification leading to pathogenic variants, and (iv) they play a role in HBV resistance to antiviral therapy and (v) likely contribute to reactivation of hepatitis B. Further support for HBV lymphotropic nature is provided by studies in a model infection with the closely related woodchuck hepatitis virus (WHV) naturally infecting susceptible marmots. This animal model faithfully reproduces many aspects of HBV biology, including its replication scheme, tissue tropism, and induction of both symptomatic and silent infections, immunological processes accompanying infection, and progressing liver disease culminating in hepatocellular carcinoma. The most robust evidence came from the ability of WHV to establish persistent infection of the immune system that may not engage the liver when small quantities of virus are experimentally administered or naturally transmitted into virus-naïve animals. Although the concept of HBV lymphotropism is not new, it remains controversial and not accepted by conventional HBV researchers. This review summarizes research advances on HBV and hepadnaviral lymphotropism including the role of immune cells infection in viral persistence and the pathogenesis of HBV-induced liver and extrahepatic diseases. Finally, we discuss the role of immune cells in HBV diagnosis and assessment of antiviral therapy efficacy.

Hypothesis: Could Hepatitis B vaccine act as an immune adjuvant in glioblastoma? Clues to conduct further epidemiological analyses

A failure of neurodevelopmental differentiation at the level of oligodendroglial-astrocytic biprogenitors (O2A) is shown to be involved in the pathogenesis of both multiple sclerosis (MS) and glioblastoma multiforme (GBM). In this review article, we suggest that certain antigens of Hepatitis B Virus (HBV) and HBV-Vaccine (HBV-V) could act as immune stimulants in GBM treatment based on several lines of evidence. HBV-Vs may cause rare but prominent neuroimmune side effects including demyelination and multiple sclerosis, which may be associated with HBV-proteins creating antigenic mimicry of oligodendroglial progenitors. The combined prevalance of HBV and Hepatitis C Virus-carrier state is less in patients with brain tumors compared to healthy subjects. Furthermore, within the population of patients with brain tumors, the prevalence is even about two times lesser in GBM in comparison to those with a diagnosis of meningioma. Although indirectly, this epidemiological data may indicate that the immune response triggered against hepadnavirus antigens would eliminate aberrantly differentiating O2A progenitor cells giving rise to GBMs. Moreover, Hepatitis B surface antigen-antibody variable domain is among the top 100 differentially expressed transcripts in fresh frozen and formalin-fixed paraffin-embeded specimens obtained from pediatric GBM tissues in comparison to the control brain tissues. However, the provided evidence is still premature and we think that HBV-V warrants investigation first by epidemiological studies and then by animal experiments to determine whether it reduces the risk of GBM and whether it could slow GBM growth via immune stimulation.

Hepatitis B Virus Infection Predicts Better Survival In Patients With Colorectal Liver-only Metastases Undergoing Liver Resection

Objective: Hepatitis B virus (HBV) infection has been shown to decrease the risk of liver metastasis in patients with non-metastatic colorectal cancer (CRC). However, the prognostic value of HBV infection in long-term survival of patients with colorectal liver-only metastases (CRLM) after liver resection has not yet been evaluated. This study aims to explore the association between HBV infection and survival in CRLM patients.

Methods: A total of 289 CRLM patients undergoing liver resection were recruited at our center from September 1999 to August 2015. Patients were divided into an HBV infection group and a non-HBV infection group. Progression-free survival (PFS) and overall survival (OS) related to HBV infection were analyzed using both Kaplan-Meier and multivariate Cox regression methods.

Results: HBV infection was found in 12.1 %(35/289) of patients. Of these patients, 31.4 %(11/35) had chronic hepatitis B (CHB), 42.9 % (15/35) were inactive hepatitis B surface antigen (HBsAg) carriers (IC) and 25.7 % (9/35) did not undergo HBV DNA detection. HBV infection was associated with more liver metastases (P = 0.025) and larger-sized liver metastases (P = 0.049). The 3-year OS and PFS rates in the HBV infection group were higher than those in the HBV non-infected group (OS: 75.0 % vs 64.8 %, P = 0.031; PFS: 55.9 % vs 39.6 %, P = 0.034). In multivariate Cox analysis, HBV infection was identified as an independent factor for better 3-year OS (hazard ratio (HR), 0.446; 95 %confidence interval (CI), 0.206-0.966; P = 0.041) but not an independent factor for 3-year PFS.

Conclusions: HBV-infected CRLM patients survived longer than non-infected patients. In clinical work, therapeutic regimens and follow-up for HBsAg-positive patients may be different from that for HBsAg-negative patients, even though objective prospective studies are still needed.

Selection of HBV preS1-binding penta-peptides by phage display

Chronic hepatitis B virus (HBV) infection can lead to liver cirrhosis and hepatocellular carcinoma. Current therapies have a very limited efficacy in virus clearance. New antiviral targets and agents are urgently needed. The envelope of HBV virion contains three surface glycoproteins, namely the large (LHBs), middle (MHBs), and small (SHBs) proteins. LHBs has an amino terminal preS which is composed of the preS1 and preS2 domains. The amino half of preS1 which is myristoylated plays a pivotal role in HBV entry, which can be exploited as an antiviral target. A common motif of five amino acids had been previously discovered to bind preS11–65 and HBV particles. In this study, we used preS11–65 to screen a phage display library of random penta-peptides to select the penta-peptides possessing a high preS1-binding affinity. After nine rounds of panning, we obtained one peptide designated as A5 which could bind preS1 with a high affinity. By systematically substituting each residue of A5 with the other 19 amino acids, we identified a novel peptide with an increased preS1-binding affinity. Both peptides could inhibit HBV attachment to HepG2 cells, making them be potential candidates for HBV entry inhibitors.

New insights into hepatitis B and hepatitis delta virus entry

Notwithstanding the medical importance of the HBV infection, our understanding of how this pathogen enters hepatocytes is incomplete. This reflects a long-lasting dependence of in vitro infection studies solely on primary human hepatocytes, which are difficult to obtain and maintain in a susceptible state. The establishment of a polarizable HBV-susceptible human hepatoma cell line (HepaRG) and the utilization of Tupaia belangeri hepatocytes (PTHs) resolved this issue. Since then, important insight into viral and cellular determinants participating in HBV binding and infection have been achieved. We now know that the large viral surface protein (L) plays a pivotal role in HBV entry. It mediates diverse functions, commencing binding of virions to heparan sulfate proteoglycans at the hepatocytes surface as a prerequisite for entry. Subsequently, (a) highly specific event(s) involving the myristoylated N-terminal preS1 subdomain of L, as well as the cytosolic and antigenic loops of the S-domain, initiates a series of less well understood steps, resulting in a pH independent, reduction-sensitive fusion of the viral membrane with a cellular membrane. One of these steps is highly sensitive to synthetic N-acylated preS1 lipopeptides and can be blocked in vitro and in vivo at picomolar concentrations. This opens novel therapeutic options addressing virus entry. Future approaches aiming at the elucidation of HBV hepatotropism, the identification of (a) specific receptor(s), the clarification of the endocytic entry pathway and imaging of fluorescently-labeled virions will allow us to decipher more precisely the HBV entry pathway in the near future. Furthermore, clinical efficacy studies with HBV–preS-derived lipopeptides will tell us whether entry inhibition is a passable way to defend acute and chronic HBV and hepatitis delta virus infections.

Viral and cellular determinants involved in hepadnaviral entry

Hepadnaviridae is a family of hepatotropic DNA viruses that is divided into the genera orthohepadnavirus of mammals and avihepadnavirus of birds. All members of this family can cause acute and chronic hepatic infection, which in the case of human hepatitis B virus (HBV) constitutes a major global health problem. Although our knowledge about the molecular biology of these highly liver-specific viruses has profoundly increased in the last two decades, the mechanisms of attachment and productive entrance into the differentiated host hepatocytes are still enigmatic. The difficulties in studying hepadnaviral entry were primarily caused by the lack of easily accessible in vitro infection systems. Thus, for more than twenty years, differentiated primary hepatocytes from the respective species were the only in vitro models for both orthohepadnaviruses (e.g. HBV) and avihepadnaviruses (e.g. duck hepatitis B virus [DHBV]). Two important discoveries have been made recently regarding HBV: (1) primary hepatocytes from tree-shrews; i.e., Tupaia belangeri, can be substituted for primary human hepatocytes, and (2) a human hepatoma cell line (HepaRG) was established that gains susceptibility for HBV infection upon induction of differentiation in vitro. A number of potential HBV receptor candidates have been described in the past, but none of them have been confirmed to function as a receptor. For DHBV and probably all other avian hepadnaviruses, carboxypeptidase D (CPD) has been shown to be indispensable for infection, although the exact role of this molecule is still under debate. While still restricted to the use of primary duck hepatocytes (PDH), investigations performed with DHBV provided important general concepts on the first steps of hepadnaviral infection. However, with emerging data obtained from the new HBV infection systems, the hope that DHBV utilizes the same mechanism as HBV only partially held true. Nevertheless, both HBV and DHBV in vitro infection systems will help to: (1) functionally dissect the hepadnaviral entry pathways, (2) perform reverse genetics (e.g. test the fitness of escape mutants), (3) titrate and map neutralizing antibodies, (4) improve current vaccines to combat acute and chronic infections of hepatitis B, and (5) develop entry inhibitors for future clinical applications.

Overexpression of hepatitis B virus-binding protein, squamous cell carcinoma antigen 1, extends retention of hepatitis B virus in mouse liver

How receptors mediate the entry of hepatitis B virus (HBV) into the target liver cells is poorly understood. Recently, human squamous cell carcinoma antigen 1 (SCCA1) has been found to mediate binding and internalization of HBV to liver-derived cell lines in vitro. In this report, we investigate if SCCA1 is able to function as an HBV receptor and mediate HBV entry into mouse liver. SCCA1 transgene under the control of Rous sarcoma virus promoter was constructed in a minicircle DNA vector that was delivered to NOD/SCID mouse liver using the hydrodynamic technique. Subsequently, HBV-positive human serum was injected intravenously. We demonstrated that approximately 30% of the mouse liver cells expressed a high level of recombined SCCA1 protein for at least 37 d. The HBV surface antigen was found to persist in mouse liver for up to 17 d. Furthermore, HBV genome also persisted in mouse liver, as determined by polymerase chain reaction, for up to 17 d, and in mouse circulation for 7 d. These results suggest that SCAA1 might serve as an HBV receptor or co-receptor and play an important role in mediating HBV entry into hepatocytes, although its role in human HBV infection remains to be determined.

Detection of surface asialoglycoprotein receptor expression in hepatic and extra-hepatic cells using a novel monoclonal antibody

The asialoglycoprotein receptor (ASGPR) is a heterodimeric membrane protein which is involved in the internalization of desialylated glycoproteins and also in the binding and uptake of various pathogenic viruses. To facilitate the analysis of ASGPR expression, we generated a monoclonal antibody, termed ASSA-1, that is specific to the ASGPR H1 subunit based on ELISA and Western blots analysis. ASSA-1 also reacted to surface-displayed ASGPR in live cells thus enabling analysis of ASGPR expression by immunofluorescence flow cytometry, which we used to analyze established human liver cell lines previously confirmed to be positive for ASGPR mRNA expression. In agreement with previous reports, surface ASGPR was also detected in extra-hepatic cells and, surprisingly, even in human T cell lines, which was then further confirmed in activated, but not in resting, primary human peripheral blood lymphocytes. These observations suggest that ASGPR has a broad pattern of expression that even extends into cells from the immune system, which biological meanings still have to be analyzed. We expect that monoclonal antibody ASSA-1 will serve as a new powerful tool in analyzing the biological role of ASGPR in hepatic and extra-hepatic cells.

Expression of beta-2-glycoprotein Ⅰ receptor on membranes of hepatoma cell line SMMC-7721

AIM: To further study the interaction between beta-2-glycoprotein Ⅰ(β₂GPⅠ) and the membrane of hepatoma SMMC-7721 cells, and to explore the mechanism of hepatitis B virus (HBV) infection.

METHODS: Fluorescence microscopy and fluorescence activated cell sorter (FACS) was used to observe the interaction of β₂GPⅠ with the hepatoma cell line SMMC-7721, gastric carcinoma cell line SGC-7901 and lymphoma cell line HL-60.

RESULTS: Fluorescence microscopy revealed specific binding of FITC-β₂GPⅠ to SMMC-7721 cells, but neither to HL-60 nor SGC-7901 cells. FACS analysis demonstrated that the binding rate of FITC-β₂GPⅠ (20 μL) to SMMC-7721 cells was significantly higher than that in HL-60 or SGC-7901 cells (19% vs 1.7%, 1.9%, both P < 0.01). When 50 μL FITC-β₂GPⅠ was used, the binding rate of FITC-β₂GPⅠ to SMMC-7721 cells was 20.8%, which was not significantly higher than 19%. The binding rate to SMMC-7721 cells did not increase with the increasing amounts of FITC-β₂GPⅠ.

CONCLUSION: There exists the specific β₂GPⅠbinding protein in the membrane of SMMC-7721 cells.

Expression and immunoactivity of chimeric particulate antigens of receptor binding site-core antigen of hepatitis B virus

AIM: To improve the immunogenicity of receptor binding site of hepatitis B virus (HBV) on preS1 antigen using HBV core antigen as an immuno-carrier.

METHODS: One to 6 tandem copies of HBV preS1 (21-47) fragment were inserted into HBcAg at the sites of aa 78 and 82, and expressed in E.coli. ELISA, Western blot and animal immunization were used to analyze the antigenicity and immmunogenicity of purified particulate antigens. The ability to capture HBV by antibodies elicited by chimeric particles was detected with immuno-capture PCR.

RESULTS: Recombinant antigens CI, CII, CIII carrying 1-3 copies of HBV preS1 (21-47) individually could form virus-like particles (VLPs), similar to HBcAg in morphology. But recombinant antigens carrying 4-6 copies of HBV preS1 (21-47) were poorly expressed in E.coli. Chimeric antigens were lacking of immunoreactivity with anti-HBc monoclonal antibodies (McAbs), but still reserved good immunoreactivity with anti-HBe McAbs. CI, CII, CIII could strongly react with anti-preS1 McAb, suggesting that preS1 (21-47) fragment was well exposed on the surface of chimeric VLPs. Three chimeric VLP antigens (CI, CII and CIII) could stimulate mice to produce high-level antibody responses, and their immunogenicity was stronger than non-particulate antigen 21-47*6, containing 6 copies of preS1 (21-47). Mouse antibodies to CI, CII and CIII were able to capture HBV virions in immuno-capture PCR assay in vitro.

CONCLUSION: Chimeric particulate antigens of receptor binding site-core antigen of HBV can elicit strong antibody responses to preS1. They have a potential to be developed into prophylactic or therapeutic vaccines against HBV infection.

Correlation of HBV DNA levels in serum and liver of chronic hepatitis B patients with cirrhosis

AIM

We sought to evaluate whether serum HBV DNA levels correlates with the liver free HBV DNA levels in chronic hepatitis B.

METHODS

Thirty-three consecutive chronic hepatitis B patients with cirrhosis were included in this study. Twenty cases had detectable serum HBV DNA (> 1.8 pg/ml). All had detectable free liver HBV DNA.

RESULTS

There was a strong correlation between the serum and liver HBV DNA levels (P = 0.0018, r = 0.717). Thirteen cases had undetectable serum HBV DNA. Among them, six cases still had detectable liver free HBV DNA. Eight cases were HBeAg-positive. Among them, seven cases were positive for both serum and liver HBV DNA, and one case was negative for both serum and liver HBV DNA. Twenty-five cases were HBeAg-negative and anti-HBe-positive. Among them, 13 cases were positive for serum HBV DNA, and 19 cases were positive for liver HBV DNA. No significant difference was noted for positivity of serum HBV DNA or liver free HBV DNA between HBeAg-positive and HBeAg-negative groups. The level of serum HBV DNA(491 +/- 772 pg/ml versus 203 +/- 447 pg/ml, p = 0.07) and liver free HBV DNA (33 +/- 81 pg/microg versus 6 +/- 15 pg/microg, p = 0.13) was also not statistically different.

CONCLUSION

In conclusion, serum HBV DNA levels is strongly correlated with liver HBV DNA levels in chronic hepatitis B with cirrhosis. Liver free HBV DNA can still be detected in about half of the cirrhotic patients with undetectable serum HBV DNA. Serum HBeAg is not a good predictor of serum or liver HBV DNA levels in cirrhotic patients.

Rare occurrence of metastatic colorectal cancers in livers with replicative hepatitis B infection

BACKGROUND

It has been demonstrated that colorectal carcinomas rarely metastasize to diseased livers. However, this phenomenon has not been thoroughly evaluated in patients with various forms of chronic hepatitis B virus (HBV) infection. Therefore, the present study examined the relationship between the incidence of hepatic metastasis of colorectal carcinomas and chronic HBV infection, with emphasis on the influence of HBV viral replication and chronic liver damage.

METHODS

We analyzed the clinicopathological data of 512 patients undergoing surgical treatment of colorectal carcinomas at our department from 1992 to 1998. Among these cases, 74 had chronic HBV infection, including 28 cases with HBV replication and 21 with chronic liver damage.

RESULTS

The incidence of liver metastasis in the HBV infection group (13.5%) was significantly lower than that of the noninfection group (27.1%, P <0.05). In addition, patients with HBV infection survived longer than those without infection (P = 0.018). Furthermore, liver metastatic rate in patients with HBV replication (3.6%) was lower than those without virus replication (19.6%, P <0.05). In contrast, there was no significant difference in liver metastasis between HBV infected patients with or without chronic liver damage (P >0.05).

CONCLUSIONS

Chronic HBV infection with viral replication reduces hepatic metastasis of colorectal cancer, and thus prolongs the survival of patients.

Detection of cellular receptors specific for the hepatitis B virus preS surface protein on cell lines of extrahepatic origin

Hepatitis B virus infection is primarily mediated by the interaction of the preS region of the viral envelope protein with its still unknown cellular receptor. Using recombinantly expressed preS proteins, the distribution of preS-binding receptors on cell lines from extrahepatic origins was determined by immunofluorescence and flow cytometry. In contrast to human liver cell lines, most cell lines from extrahepatic origins did not bind preS proteins. Nevertheless, exceptions were found in the bone marrow-derived cell line, KG-1, and the osteogenic sarcoma cell line SaOS-2, as well as in the previously reported EBV-transformed B-cell line, Wa. To determine the biochemical nature of these receptors, Wa-cells were cell surface biotinylated and the preS-binding receptors were isolated by immunoprecipitation. A specific band with a molecular weight of approximately 30 kDa was identified in a SDS-polyacrylamide gel, which further characterization is expected to provide clues regarding the infection mechanism of HBV in hepatic- and extra-hepatic cells.

Activation of the envelope proteins by a metalloproteinase enables attachment and entry of the hepatitis B virus into T-lymphocyte

Previously, we identified an HBV binding factor (HBV-BF), a 50-kDa serum glycoprotein which interacts with HBV envelope proteins and which is also located in the membrane of normal human hepatocyte (A. Budkowska et al. (1993) J. Virol. 67, 4316). Here we show that HBV-BF is a neutral metalloproteinase which shares substrate specificity and properties with a newly described family of membrane type matrix metalloproteinases. HBV-BF treatment of the HBV resulted in the cleavage of the N-terminal part of the middle HBV envelope protein at the pre-S2(136-141) amino acid sequence VRGLYF/L (containing a single arginine cleavage site). HBV-BF affected the reactivity of the large HBV protein with pre-S1-specific MAbs, probably inducing the conformational change of the pre-S1 domain. The HBV-BF-digested virus remained morphologically intact with unchanged S antigenic determinants. The structural modifications of the viral envelope proteins induced by HBV-BF enabled cell membrane attachment and viral entry into the T-lymphocyte. Both processes were blocked by the metalloproteinase inhibitor 1,10 phenanthroline. Thus, the host-dependent proteolytic activation of the envelope proteins seems to be essential for the HBV entry into the cell. HBV-BF under a membrane bound or a secreted form could be (one of) the molecule(s) responsible for the HBV proteolytic activation.

Transcription of hepatitis B virus in peripheral blood mononuclear cells from persistently infected patients

Hepatitis B virus (HBV) has been reported to exist in peripheral blood mononuclear cells (PBMC), but it is not clear whether it replicates there. A precondition for replication should be the formation of covalently closed viral DNA and transcription of all essential viral mRNAs. The mRNAs of HBV form a nested box with common 3' ends. In order to detect even low levels of potential replication, we developed a quantitative reverse transcription-PCR method for detection of a smaller HBV mRNA species in the presence of the larger ones. All three highly viremic patients tested so far had mRNAs for the large and the small surface proteins and the X protein of the virus within PBMC but not in the virus from their sera. Furthermore, we detected by PCR covalently closed viral DNA in their PBMC. These data suggest that HBV may be not only taken up but also replicated by mononuclear blood cells and that these cells may be an extrahepatic site of viral persistence. X mRNA was detected in the largest amount. Possibly, X protein interferes with functions of the mononuclear cells during the immune response against the virus.

Effect of hepatitis B virus on tumour necrosis factor (TNF alpha) gene expression in human THP-1 monocytic and Namalwa B-cell lines

In response to viruses, monocytes and B cells produce TNF alpha. Therefore, we investigated TNF alpha gene expression and protein secretion in a human monocytic cell line, THP-1, and a Burkitt's lymphoma B-cell line, Namalwa, in response to hepatitis B virus (HBV). Stimulation by phorbol myristate acetate (PMA) (100 ng/ml for 48 h) induced TNF alpha secretion in THP-1 and Namalwa cells (100 to 300 pg/ml). In THP cells, the optimum response (> 2000 pg/ml) was obtained in the presence of a second mitogenic signal such as lipopolysaccharide (LPS) (10 microg/ml for 24 h). In our activation conditions, Northern blot analysis revealed a marked accumulation of TNF alpha mRNA species at 1.7 kb in both cell lines. When PMA- or PMA+LPS-stimulated THP-1 cells were exposed to HBV, TNF alpha protein and mRNA significantly decreased (> 50%). In contrast, HBV exposure of PMA-activated Namalwa cells resulted in strongly increased TNF alpha protein secretion (1 ng/ml). In this case, HBV induced TNF alpha mRNA accumulation that consisted of two types: a regular 1.7 kb and two novel high molecular weight (HMW) species at 3.7 and 4.3 kb. Exposure of stimulated THP-1 and Namalwa cells to HBV resulted in HBs and pre-S1 antigen production in the supernatants. In addition, HMW HBV DNA forms were detected in both cell lines, but with distinct HindIII restriction patterns. These findings indicate that TNF alpha gene expression may be differently regulated by HBV in activated human macrophages and B cells, and thus TNF alpha may be involved in the pathogenesis of HBV.

Recent advances in the molecular biology of hepatitis B virus

Hepatitis B virus (HBV) is an enveloped hepatotropic DNA virus. Acute and chronic HBV infection causes significant liver diseases such as acute hepatis, fulminant hepatitis and chronic active hepatitis that may lead to liver cirrhosis and the development of hepatocellular carcinoma. The use of molecular biological techniques has substantially improved our understanding of the HBV life cycle. In this review, we discuss recent advances that have contributed to a better understanding of HBV biology. Recent studies in the understanding of the life cycle of HBV such as viral entry, replication, transcriptional regulation, viral regulatory proteins, viral assembly and secretion, and nucleic acid based approaches to antiviral therapy will be emphasized. These advances in molecular biology and relationship to clinical disease will be instrumental in developing effective therapeutic approaches for the estimated 300 million individuals worldwide chronically infected with HBV.

Susceptibility to duck hepatitis B virus infection is associated with the presence of cell surface receptor sites that efficiently bind viral particles

To test the hypothesis that susceptibility of hepatocytes to duck hepatitis B virus (DHBV) infection requires cell surface receptors that bind the virus in a specific manner, we developed an assay for the binding of DHBV particles to monolayers of intact cells, using radiolabeled immunoglobulin G specific for DHBV envelope protein. Both noninfectious DHBV surface antigen particles and infectious virions bound to a susceptible fraction (approximately 60%) of Pekin duck hepatocytes. In contrast, binding did not occur to cells that were not susceptible to DHBV infection, including Pekin duck fibroblasts and chicken hepatocytes, and binding to Muscovy duck hepatocytes, which are only weakly susceptible (approximately 1% of cells) to DHBV infection, was virtually undetectable. Within a monolayer, individual Pekin duck hepatocytes appeared to differ markedly in the capacity to bind DHBV, which may explain difficulties that have been encountered in infecting 100% of cells in culture. We have also found that the loss of susceptibility to infection with DHBV that occurs when Pekin duck hepatocytes are maintained for more than a few days in culture correlates with a decline in the number of cells that bind virus particles efficiently. All of these results support the interpretation that the binding event detected by our assay is associated with the interaction between DHBV and specific cell surface receptors that are required for initiation of infection. Our assay may facilitate isolation and identification of hepatocyte receptors for this virus.

Lymphotropism of hepatitis B and C viruses: an update and a newcomer

The mechanisms of viral persistence are complex and include infection of the lymphoid cells. In the case of hepatitis B virus, early observations have suggested that HBV may infect peripheral blood mononuclear cells (PBMC). In animal models studies in chronic hepatitis B patients have further confirmed that viral DNA replicative intermediates, as well as viral transcripts and proteins, can be detected in PBMC under certain conditions. The consequences of this lymphotropism are not fully understood, but it seems likely that PBMC represent an extrahepatic reservoir of virus. The ability of hepatitis C virus to infect PBMC has been demonstrated in vivo and in vitro. The link between HCV lymphotropism and both the natural history of the viral infection and the immunological disorders frequently observed in HCV infections still needs to be established. In both cases, the infection of PBMC by HBV or HCV may represent the source of infection of the liver graft in patients transplanted for end-stage liver disease associated with HBV or HCV.

Expression and characterization of the multiplied, recombinant preS1 antigen of hepatitis B virus

The amino acid sequence encoded by the preS1 region of hepatitis B virus genome is expressed on the surface of virions and subviral particles. The preS1 region is involved in the recognition of specific receptors responsible for the attachment of HBV to the host cell. The cell receptor binding site was assigned to the preS1 (20-47 aa) fragment. In order to obtain a large quantity of preS1 binding domains of HBV the expression vector pWX4 was constructed. It contains four tandemly joined DNA sequences, each coding for preS1 (20-49 aa), fused with the 3' end of a DNA fragment coding for 450 aa of beta-galactosidase. E. coli cells transformed with this vector produce fusion protein beta-gal-preSlx4 in the form of inclusion bodies. Owing to the specific trypsin digestion, the preSlx4 domain was cleaved from the fusion protein. The resulting product, a 16 kDa protein, was isolated and purified by anion exchange chromatography. The presence of four Asp-Pro bonds in this sequence and the primary structure of the first 28 N-terminal amino acids were determined. Following the confirmation of the antigenic properties, the recombinant preS1 protein was used for detection of the anti-preS1 response in sera from HBV infected patients.

Hepatitis B virus surface antigen binds to apolipoprotein H

We have previously demonstrated that a plasma membrane-enriched fraction isolated from human liver is capable of binding recombinant hepatitis B surface antigen (rHBsAg) (P. Pontisso, M. A. Petit, M. Bankowski, and M. E. Peeples, J. Virol. 63:1981-1988, 1989). In this study we have separated the plasma membrane proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and used a ligand-blotting technique to identify a 46-kDa rHBsAg-binding protein. This protein could be removed from the membranes with a weakly acidic buffer, implying that it is peripherally bound. Examination of human serum revealed that the 46-kDa binding protein is a serum protein. Isolation of plasma lipoproteins revealed that the binding protein is in part associated with chylomicrons and high-density lipoproteins, both of which are targeted to the hepatocyte during the normal course of lipid metabolism. The binding protein was identified as apolipoprotein H (apo H), also known as beta 2-glycoprotein I, on the basis of copurification of the rHBsAg-binding activity with the apo H protein and the ability of cDNA-expressed apo H to bind rHBsAg. Serum-derived HBsAg also binds to apo H, indicating that binding is not unique to rHBsAg. Binding is saturable, requires only the small S protein of rHBsAg, and is inhibited by excess rHBsAg, antibodies to HBsAg, and antibodies to apo H. The binding activity of apo H is destroyed upon reduction, indicating that 1 or more of its 22 disulfide bonds are required for interaction with rHBsAg. The possibility that an interaction between hepatitis B virus particles and lipoprotein particles may facilitate entry of the virus into hepatocytes is discussed.

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

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

Hepatitis B virus (HBV) binding factor in human serum: candidate for a soluble form of hepatocyte HBV receptor

A hepatitis B virus (HBV) binding factor (HBV-BF) was identified in normal human serum interacting with the pre-S1 and pre-S2 epitopes of the viral envelope located within the protein domains involved in recognition of hepatocyte receptor(s). This molecule was characterized as a 50-kDa glycoprotein showing an isoelectric point of 7.13 with a biological activity depending on its native molecular conformation and on intact sulfhydryl bonds. Monoclonal antibodies to HBV-BF recognized a membrane component of the normal human liver whereas they were unreactive with hepatocyte membranes of other species and with those of the HepG2 cell line. These results suggest that the HBV-BF represents a soluble fragment of the membrane component and can be related to the HBV receptor mediating attachment of HBV to human liver cells.

Hepatitis B virus differentially suppresses myelopoiesis and displays tropism for immature hematopoietic cells

The hematopoietic cell lines HL-60 and THP-1 were challenged with hepatitis B virus (HBV) in vitro to study interactions between the virus and host cell. Exposure to HBV suppressed the ability of HL-60 cells to differentiate into granulocytes after treatment with retinoic acid (RA) or dimethyl sulfoxide (DMSO), and RA-induced activation of the monocytic cell line THP-1 was also suppressed. Terminal differentiation of both cell lines by phorbol 12-myristate 13-acetate (PMA) was not affected by HBV. The suppressive effect on RA- or DMSO-induced differentiation was unique to HBV, since cell exposure to human cytomegalovirus, another virus that inhibits hematopoiesis, failed to block cellular differentiation. At 5 days postinfection, extracellular viral DNA was detected in immature but not in differentiated cultures and higher levels of core antigen (HBcAg) and surface antigen (HBsAg) were seen in undifferentiated cells than in RA- or PMA-treated cells. In addition, release of HBsAg into the medium was 2 to 12 times greater in untreated cultures than for RA- or PMA-treated cells. Thus, HBV suppresses hematopoiesis by blocking the maturational development of progenitors and selectively infects immature myeloid cells compared with mature end-stage cells.

Studies on the attachment and penetration of hepatitis B virus

There are two identified liver-specific attachment sites in the preS2 domain and one in the preS1 domain. Which mechanism leads to attachment in vivo is not known. The subsequent penetration seems to require proteolysis which does not occur spontaneously in HepG2 cells, but presumably in vivo. The role of the small HBs protein for attachment remains enigmatic so far, but it must have a function because an escape mutant exists against a monoclonal antibody which binds to an epitope of the small protein. The occurrence of this escape mutant in vaccinated persons proves that the standard hepatitis B vaccine does induce neutralizing antibodies, but it also suggests very strongly that the neutralizing preS epitopes be included in future hepatitis B vaccines.

Cells transfected with human interleukin 6 cDNA acquire binding sites for the hepatitis B virus envelope protein

Earlier studies revealed that human interleukin 6 (IL-6) contains recognition sites for the hepatitis B virus (HBV) envelope (env) protein, and that IL-6 and anti-IL-6 antibodies, respectively, inhibited the interaction of cells expressing a receptor for HBV with the preS(21-47) segment of the HBV env protein, encompassing the complementary attachment site for IL-6. This suggested that IL-6 mediates HBV-cell interactions. We report that: (a) Chinese hamster ovary cells transfected with human IL-6 cDNA and Spodoptera frugiperda ovarian insect cells infected with recombinant baculovirus carrying human IL-6 cDNA expressed receptors for the preS(21-47) region of the HBV env protein, indicating that expression of IL-6 on the surface of cells is sufficient to endow them with receptors for HBV. (b) Among peptides covering the entire sequence of human IL-6 and the corresponding antipeptide antibodies, the peptide IL-6[35-66] and anti-IL-6[35-66] most effectively inhibited the interaction between human hepatoma HepG2 cells and the preS(21-47) ligand, suggesting that this region of the human IL-6 sequence encompasses a binding site for the HBV env protein. (c) Studies with replacement set peptides from the preS(21-47) sequence indicated that residues 21-25, 28, 31, 33-35, 39, and 43-45 can be replaced by alanine (serine) residues, while all the other residues are essential for maintaining the cell receptor/IL-6 binding activity. Further delineation of complementary sites on IL-6 and on the HBV env protein may contribute to the design of compounds inhibiting HBV replication.

Phytohemagglutinin and concanavalin A activate hepatitis B virus in peripheral blood mononuclear cells of patients with chronic hepatitis B virus infection

Peripheral blood mononuclear cells (PBMC) from 25 patients with chronic hepatitis B were tested for the presence of free monomeric hepatitis B virus (HBV) DNA migrating as a single 3.2 Kb band by Southern blot analysis. The PBMC were cultured for 7 days in the presence of phytohemagglutinin (PHA) or concanavalin A (ConA) both of which yielded a proliferative response. By contrast, both bacterial lipopolysaccharide (LPS) and interleukin 2 (IL2) failed to do so. Dot blot assays were used to monitor HBV DNA level increase within PBMC. Following mitogen exposure HBV DNA levels increased above pre-stimulation levels in 19/25 PHA cultures, 6/15 ConA cultures, 1/15 LPS cultures, and 1/15 IL2 cultures. In 15 patients, Southern blot analysis was carried out before and after PHA exposure. In 13/15 cases, a single 3.2 Kb band was observed in unstimulated cultures as well as in PHA cultures even though PHA induced a HBV DNA increase. One case exhibited bands migrating faster than the 3.2 Kb signal, compatible with replicating intermediates and one case provided evidence of viral concatemers within PBMC after PHA stimulation. No HBV DNA was detected in the culture supernatants. The increase of HBV DNA level in PBMC induced by mitogen was strongly associated with an increase in HBV DNA expression (HBV RNA and HBs antigen). These studies indicate that HBV DNA present in human PBMC does represent a potential reservoir for infection with endogenous reactivation following PBMC activation.

Receptor for pre-S1(21-47) component of hepatitis B virus on the liver cell: role in virus cell interaction

Attachment of hepatitis B virus to a hepatoblastoma cell line (HepG2) was examined using a synthetic peptide corresponding to the pre-S1 (21-47) region of the envelope protein. Scatchard analysis revealed a single class binding site of Kd 104 +/- 27 nM/l and 5.4 +/- 1.2 x 10(5) sites per cell. Competition of HBV with pre-S1 peptides was dose dependent, and demonstrated it as the dominant binding site. In view of the suggested sequence homology between the peptide and IgA, cross-competition studies were carried out. The results indicate no direct role of IgA receptor in HBV binding. The receptor for the pre-S1 peptide was identified as a single major peptide of molecular weight 31 kD using in-situ ligand receptor crosslinking.

PreS1-specific binding proteins as potential receptors for hepatitis B virus in human hepatocytes

Cellular receptors play an important role in viral pathogenesis. Until now, there has been no reliable information on the receptor(s) for hepatitis B virus (HBV). Therefore, we attempted to identify specific receptors in human hepatocytes using an immunological approach. Anti-idiotypic (Ab2) antibodies were raised in rabbits against our monoclonal antibody (MAb1) F35.25. MAb1 F35.25 (i) recognized the hepatocyte receptor binding site on HBV (located between amino acid residues 21 and 47 of the preS1 sequence) and (ii) blocked the attachment of preS1-positive HBV particles to human hepatocytes. The presence of Ab2 antibodies in rabbit sera was determined by the ability of antisera to inhibit Id (Ab1)/antigen (HBV) recognition. Affinity-purified Ab2 IgGs to F35.25 represented an internal image for the preS1 domain 12-53. Our present studies indicate that Ab2 IgGs to F35.25 (i) recognized the membrane-associated structure of the preS1-specific HBV receptor in a HepG2 cell binding assay, as visualized by immunoenzymatic staining; (ii) strongly bound to a major 35-kDa component and to three other related proteins of 50, 43, and 40 kDa in extracts of HepG2 cells; and (iii) reacted with several soluble and membrane-associated proteins in normal human liver cells. The binding was insensitive to reduction. All preS1 binding proteins were V8 protease sensitive and endoglycosidase H resistant. The 35-kDa species was trypsin resistant and generated a band of 32 kDa by endoglycosidase F treatment. Together, our results suggest that the identified preS1-specific binding proteins may be involved in the putative complex structure of the hepatocyte receptor for HBV.

Search for hepatitis B virus cell receptors reveals binding sites for interleukin 6 on the virus envelope protein

The major target organ for hepatitis B virus (HBV) is the liver. However, cells other than hepatocytes, including peripheral blood lymphocytes and monocytes, may become infected with HBV. The cell receptor binding site was assigned to the preS(21-47) segment of the HBV envelope protein. HBV receptors were detected on human liver and hepatoma cells, on B lymphocytes, and, as shown here, on monocytes, and T cell lines, activated by Escherichia coli lipopolysaccharide and concanavalin A, respectively. The cell receptors for HBV have not been characterized until now. The detection of HBV receptors and their "activation antigen" characteristic on distinct cells suggested paths for identification of the receptors with already defined cell surface proteins. This search revealed that interleukin 6 contains recognition sites for the preS(21-47) sequence and mediates HBV-cell interactions. Thus, HBV belongs to a group of viruses utilizing cytokines or cytokine receptors for replication and interference with the host immune system.

Hepatitis B virus. New and evolving issues

Recent developments in molecular biology have advanced our understanding of the pathogenesis of HBV-induced disease. New data derived from the molecular analysis of clinical material have begun to bridge the gap between bench research and the clinical arena. In this review, we consider topics that have relevance to clinical management and that have not been summarized in the recent literature. The recent advances that have been made in the areas of HBV variants, in vitro cell culture systems, and extrahepatic infection are discussed in greater detail.

Inhibition of duck hepatitis B virus infection by lysosomotropic agents

The early phases of hepadnaviral infection were studied in primary duck hepatocyte cultures. Incubation of duck hepatocytes in vitro with duck hepatitis B virus (DHBV) resulted in infection with high levels of viral replication. The lysosomotropic agents ammonium chloride and chloroquine effectively inhibited viral infection, indicating that DHBV infection, similar to infection with other enveloped viruses, depends on receptor-mediated endocytosis and involves membrane fusion triggered by low pH.

Antigenic mimicry of an immunoglobulin A epitope by a hepatitis B virus cell attachment site

The preS(21-47) sequence of the hepatitis B virus (HBV) envelope protein is involved in binding of the virus to cell receptors. A protein similarity search revealed a partial homology between this sequence and a segment of the human immunoglobulin A (IgA) heavy chain constant region, suggesting that the cell attachment site for HBV might be located on secretory component representing a receptor for polymeric IgA. Data presented herein do not support this hypothesis but provide evidence for immunological cross-reactivity between IgA and the preS(21-47) region of the HBV env protein.