Extrahepatic replication of duck hepatitis B virus: more than expected

New insights into hepatitis B virus lymphotropism: Implications for HBV-related lymphomagenesis

HBV is one of the most widespread hepatitis viruses worldwide, and a correlation between chronic infection and liver cancer has been clearly reported. The carcinogenic capacity of HBV has been reported for other solid tumors, but the largest number of studies focus on its possible lymphomagenic role. To update the correlation between HBV infection and the occurrence of lymphatic or hematologic malignancies, the most recent evidence from epidemiological and in vitro studies has been reported. In the context of hematological malignancies, the strongest epidemiological correlations are with the emergence of lymphomas, in particular non-Hodgkin’s lymphoma (NHL) (HR 2.10 [95% CI 1.34-3.31], p=0.001) and, more specifically, all NHL B subtypes (HR 2.14 [95% CI 1.61-2.07], p<0.001). Questionable and unconfirmed associations are reported between HBV and NHL T subtypes (HR 1.11 [95% CI 0.88-1.40], p=0.40) and leukemia. The presence of HBV DNA in peripheral blood mononuclear cells has been reported by numerous studies, and its integration in the exonic regions of some genes is considered a possible source of carcinogenesis. Some in vitro studies have shown the ability of HBV to infect, albeit not productively, both lymphomonocytes and bone marrow stem cells, whose differentiation is halted by the virus. As demonstrated in animal models, HBV infection of blood cells and the persistence of HBV DNA in peripheral lymphomonocytes and bone marrow stem cells suggests that these cellular compartments may act as HBV reservoirs, allowing replication to resume later in the immunocompromised patients (such as liver transplant recipients) or in subjects discontinuing effective antiviral therapy. The pathogenetic mechanisms at the basis of HBV carcinogenic potential are not known, and more in-depth studies are needed, considering that a clear correlation between chronic HBV infection and hematological malignancies could benefit both antiviral drugs and vaccines.

Detection and Quantification of Hepatitis B Virus Genomes in Peripheral Blood Mononuclear Cells of Chronic Hepatitis B Virus Infection, Cirrhosis, and Hepatocellular Carcinoma Patients

Background: Several studies have revealed that the hepatitis B virus (HBV) exists in peripheral blood mononuclear cells (PBMCs). It remains poorly understood whether HBV DNA and covalently closed circular DNA (cccDNA) can emerge in PBMCs of patients with different stages of HBV infection. Objectives: This study aimed to compare the detection of HBV DNA and quantification and presence of cccDNA within PBMC from patients with chronic hepatitis B (CHB), cirrhosis, and hepatocellular carcinoma (HCC). Methods: The present study was conducted on 120 participants (30 CHB patients, 30 cirrhosis patients, 30 HCC patients, and 30 healthy controls) from Tehran, Iran. HBV serological markers were tested by enzyme-linked immunosorbent assay (ELISA). PBMCs of all individuals were assayed for HBV DNA detection, quantification, and the presence of cccDNA. Results: Of 90 HBV patients, 58 (64.4%) were positive for HBV DNA in PBMCs. HBV DNA was detected in PBMCs isolated from 13/30 CHB, 20/30 cirrhosis, and 25/30 HCC patients. In addition, 6 (20%) CHB, 13 (43.3%) cirrhosis, and 16 (15.3%) HCC patients were cccDNA positive. The HBV viral loads in serums were statistically higher than the HBV viral loads of PBMCs (P < 0.001). A positive correlation was found between HBV DNA loads in serums and PBMCs of patients. Moreover, HBV DNA quantity of serums and PBMCs showed a significant association in terms of hepatitis B e antigen (HBeAg) status. Conclusions: HBV quantity in PBMCs correlated with serum HBV viral loads. HBV genomes in PBMCs may be a risk factor for HBV disease progression.

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.

Therapeutic strategies for a functional cure of chronic hepatitis B virus infection

Treatment of chronic hepatitis B virus (HBV) infection with the viral DNA polymerase inhibitors or pegylated alpha-interferon has led to a significant retardation in HBV-related disease progression and reduction in mortality related to chronic hepatitis B associated liver decompensation and hepatocellular carcinoma. However, chronic HBV infection remains not cured. The reasons for the failure to eradicate HBV infection by long-term antiviral therapy are not completely understood. However, clinical studies suggest that the intrinsic stability of the nuclear form of viral genome, the covalently closed circular (ccc) DNA, sustained low level viral replication under antiviral therapy and homeostatic proliferation of hepatocytes are the critical virological and pathophysiological factors that affect the persistence and therapeutic outcomes of HBV infection. More importantly, despite potent suppression of HBV replication in livers of the treated patients, the dysfunction of HBV-specific antiviral immunity persists. The inability of the immune system to recognize cells harboring HBV infection and to cure or eliminate cells actively producing virus is the biggest challenge to finding a cure. Unraveling the complex virus–host interactions that lead to persistent infection should facilitate the rational design of antivirals and immunotherapeutics to cure chronic HBV infection.

Hepatocyte-like cells transdifferentiated from a pancreatic origin can support replication of hepatitis B virus

Recently, a rat pancreatic cell line (AR42J-B13) was shown to transdifferentiate to hepatocyte-like cells upon induction with dexamethasone (Dex). The aim of this study is to determine whether transdifferentiated hepatocytes can indeed function like bona fide liver cells and support replication of hepatotropic hepatitis B virus (HBV). We stably transfected AR42J-B13 cells with HBV DNA and examined the expression of hepatocyte markers and viral activities in control and transdifferentiated cells. A full spectrum of HBV replicative intermediates, including covalently closed circular DNA (cccDNA) and Dane particles, were detected only after induction with Dex and oncostatin M. Strikingly, the small envelope protein and RNA of HBV were increased by 40- to 100-fold upon induction. When HBV RNAs were examined by primer extension analysis, novel core- and precore-specific transcripts were induced by Dex which initiated at nucleotide (nt) 1820 and nt 1789, respectively. Most surprisingly, another species of core-specific RNA, which initiates at nt 1825, is always present at almost equal intensity before and after Dex treatment, a result consistent with Northern blot analysis. The fact that HBV core protein is dramatically produced only after transdifferentiation suggests the possibility of both transcriptional and translational regulation of HBV core antigen in HBV-transfected AR42J-B13 cells. Upon withdrawal of Dex, HBV replication and gene expression decreased rapidly-less than 50% of the cccDNA remained detectable in 1.5 days. Our studies demonstrate that the transdifferentiated AR42J-B13 cells can function like bona fide hepatocytes. This system offers a new opportunity for basic research of virus-host interactions and pancreatic transdifferentiation.

Detection of HBsAg, HBcAg, and HBV DNA in ovarian tissues from patients with HBV infection

AIM: To investigate the presence of HBsAg, HBcAg, and HBV DNA in ovarian tissues from patients with HBV infection.

METHODS: HBsAg and HBcAg were examined in ovarian biopsy tissues from 26 patients with HBV infection by immunocytochemistry, and HBV DNA was detected in ovarian tissues by PCR.

RESULTS: HBsAg and HBcAg were present with the same positive rate of 34.6% (9/26). The total positive rate was 46.2% (12/26). HBsAg and HBcAg were positive in 6 (23.1%) of the 26 patients. Brown positive particles were diffusely distributed in ovarian cells. The positive rate of HBV DNA was 58.3% (7/12).

CONCLUSION: HBsAg, HBcAg, and HBV DNA can be detected in ovarian tissues from patients with HBV infection. The presence of HBsAg and HBcAg in ovarian tissues does not correlate with the HBV markers in serum.

Hepatitis B virus DNA in liver, serum, and peripheral blood mononuclear cells after the clearance of serum hepatitis B virus surface antigen

The integration of hepatitis B virus (HBV) DNA in the liver of chronic HBV carriers has been documented extensively. However, the status of the viral genome during acute infection has not been assessed conclusively. While HBV DNA sequences are detected often in serum, liver, and peripheral blood mononuclear cells (PBMCs) after the clearance of serum the hepatitis B virus surface antigen (HBsAg), the precise status of the viral genome, and in particular the possible persistence of integrated genomes in PBMCs, has not been established. A highly sensitive PCR-derived assay (Alu-PCR) was employed to re-examine liver and PBMC specimens obtained from patients with acute (n = 19) and chronic (n = 22) hepatitis in whom serum HBsAg was present (n = 12) (HBV-related chronic active hepatitis) or absent with anti-HCV (n = 10) (HCV-related chronic active hepatitis). Viral integration was demonstrated in 3 out of 19 liver specimens from patients with acute hepatitis and 12 out of 12 specimens from patients with chronic hepatitis. Viral integration was also observed in 4 out of 7 PBMC samples from HBV-related chronic active hepatitis patients and 2 out of 10 liver and PBMC samples from HCV-related chronic active hepatitis patients. In one liver specimen from an acute hepatitis patient, HBV DNA was found integrated in the intronic sequence of the tumour necrosis factor (TNF)-induced protein gene; viral integration into cellular sequences was also found in the PBMCs of four HBV-related chronic active hepatitis and two HCV-related chronic active hepatitis. The results demonstrate the early integration of HBV genome during acute viral infections and the persistence of the viral genome in an integrated form in PBMCs.

Occult hepatitis B

Worldwide, chronic hepatitis B virus (HBV) infection is the primary cause of cirrhosis and hepatocellular carcinoma and is one of the ten leading causes of death. Traditionally, people with chronic HBV infection have been identified with blood tests for HBV antigens and antibodies. Recently, another group of patients with chronic HBV infection has been identified by sensitive, molecular testing for HBV DNA. Members of this group are often referred to as having occult hepatitis B because they are HBV-DNA positive, but hepatitis B surface antigen negative. Occult hepatitis B occurs in a number of clinical settings. In this review, we examine occult hepatitis B in people co-infected with hepatitis C, in whom occult hepatitis B has been associated with advanced fibrosis and diminished response to interferon alpha. Although much more research is needed, existing reports justify a heightened awareness of the medical importance and means of testing for occult hepatitis B.

Persistence of extrahepatic hepatitis B virus DNA in the absence of detectable hepatic replication in patients with baboon liver transplants

The presence of hepatitis B virus (HBV) DNA in extrahepatic tissues has been well documented. Whether HBV DNA can persist in extrahepatic tissues for long periods of time in the absence of replication in the liver has not been determined previously. Recently, two patients with end-stage liver disease secondary to chronic active HBV were treated with baboon liver xenotransplants as these animals are felt to be resistant to HBV infection. Multiple tissues from these two patients were examined for HBV DNA using polymerase chain reaction (PCR). HBV DNA was not detectable in four of five samples of the liver xenografts. A positive signal was observed in a single assay for one sample, but this sample was not positive in subsequent assays. HBV DNA was detected in peripheral blood lymphocytes, spleen, kidney, bone marrow, pancreas, lymph node, heart and small intestine. The level of HBV DNA in these tissues was too low for the detection of HBV DNA replicative intermediates by Southern hybridization; thus, it could not be determined whether the HBV DNA in these tissues represented actively replicating HBV in extrahepatic sites, integrated HBV sequences, HBV in infiltrating lymphocytes, or deposition of HBV immune complexes originating from the plasma. However, it is clear from this study that HBV DNA persisted in multiple tissues for 70 days after replication in the liver had ceased or at least was below the level of detection by PCR.

HBcAg and HBsAg expression in ductular cells in chronic hepatitis B

The possible involvement of bile duct epithelium (BDE) in chronic hepatitis B was examined by immunohistochemical investigation of HBcAg and HBsAg expression in biliary cells in 47 liver biopsies with both viral antigens detectable in hepatocytes. HBcAg- and HBsAg-positive cells were identified in nine and five cases, respectively, in atypical and occasionally in typical ductules in cases of acute exacerbation, chronic active hepatitis and active cirrhosis. Atypical ductules were usually located in areas of periportal fibrosis and in cirrhotic septa. Liver cell plates expressing viral markers and undergoing ductular transformation (positive reaction of hepatocytes to BDE-specific, wide-spectrum keratin) were also observed in acinar zone 1, at the periphery and within parenchymal nodules in a number of cases. The presence of both viral antigens in atypical ductules in cases of advanced chronic liver disease most probably expresses the persistence of the virus in cells deriving from biliary metaplasia of infected hepatocytes. However, the detection of the virus in a few typical ductules is indicative of a direct viral infection. According to these findings, ductular cells seem to serve as a suitable host for HBV, their genotype permitting viral replication and antigen production.

Coinfection study of precore mutant and wild-type hepatitis B-like virus in ducklings

The precore mutant hepatitis B virus often emerges from a mixed infection with combined wild-type and precore mutant viruses. Nevertheless, the precore mutant does not seem to be an evolutionarily favored strain. To investigate the interaction between wild-type and precore mutant hepadnaviruses in an animal model of perinatal transmission, we used an e antigen-defective mutant duck hepatitis B virus with mutations inside the stem-loop structure of precore messenger RNA for this coinfection study. Thirty 1-day-old ducklings were infected with wild-type duck hepatitis B virus, precore mutant virus or both viruses. The amounts of viremia and the distribution of viruses were analyzed by spot hybridization, polymerase chain reaction, restriction fragment length polymorphism, cloning and sequencing. We found that all the ducklings became chronic carriers of duck hepatitis B virus. The precore mutant replicate was less active than wild-type duck hepatitis B virus, and it could be overgrown by wild-type virus during the course of coinfection. These results demonstrated that wild-type duck hepatitis B virus might become the predominant species in a situation similar to the perinatal cotransmission in human beings. This might at least in part explain why the prototype virus could prevail for years.

Oral famciclovir against duck hepatitis B virus replication in hepatic and nonhepatic tissues of ducklings infected in ovo

Detection of hepadnaviral DNA in extrahepatic tissues of human and animal models of hepatitis B virus (HBV) has raised the question of whether virus replication in organs other than the liver could be targeted for the treatment of chronic hepatitis B. Since duck hepatitis B virus (DHBV) replication is dynamic in the liver, kidney, pancreas, and spleen of newly hatched ducklings infected in ovo, we used the duck model and the new antiherpesvirus agent, famciclovir (FCV), to determine whether antiviral effect of nucleoside analogues on DHBV replication is pluripotential. Day-old ducklings hatched from eggs laid by a DHBV-carrier duck were bled and administered FCV (25 mg/kg/bd) orally for periods of 1, 2, 3, 6, 9, and 12 days. Seventeen (17) hours after the last dose of each regimen the duckling(s) was bled and postmortem samples of liver, kidney, pancreas, and spleen were snap-frozen and stored at -70 degrees C. Analysis of plasma samples of ducklings treated for 2 days and longer by dot-blot hybridisation showed that levels of DHBV DNA were reduced significantly compared to levels in samples collected before treatment begun. Southern blot hybridisation of tissue DNA corroborated these results and showed that DHBV DNA replicative intermediates in all the tissues examined were reduced to levels that reflected the amount of virus released into the blood of each treated duckling. It is concluded from these results that if antiviral agents could be transformed to active metabolites in any infected tissues including the liver, replication of hepadnaviruses would be inhibited.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the antiviral effects of 2' carbodeoxyguanosine in ducks chronically infected with duck hepatitis B virus

This study was carried out to evaluate benefits and limitations of long-term therapy of hepatitis B virus infections with a nucleoside analog inhibitor of virus replication. The model we used was the domestic duck chronically infected with duck hepatitis B virus by in ovo infection. 2' Carbodeoxyguanosine was used as an inhibitor of viral DNA synthesis. In all animals examined there was a reduction in virus production during therapy. A dose of 2' carbodeoxyguanosine of 10 micrograms/kg every other day reduced the number of infected hepatocytes from greater than 95% to 25% to 50% in less than 3 mo, whereas a 10-fold higher dose produced a decline to less than 10%. Histological evaluation revealed mild to moderate liver injury in ducks receiving the higher dose of 2' carbodeoxyguanosine, suggesting that disappearance of infected hepatocytes may have been accelerated by a toxic effect of the drug. Drug treatment did not completely eliminate duck hepatitis B virus from any duck, and replication was restored in all hepatocytes within a few weeks to several months after antiviral therapy was terminated. Our results suggest that elimination of a chronic infection with a single inhibitor of replication may be difficult in a host that lacks an antiviral immune response capable of eliminating at least a portion of the infected hepatocytes and of ultimately producing antibodies capable of neutralizing residual virus.

Transgenome transcription and replication in the liver and extrahepatic tissues of a human hepatitis B virus transgenic mouse

We have produced a transgenic mouse (B32-1) carrying the complete genome of the human hepatitis B virus (HBV). High titers of the viral surface (HBsAg) and the e antigen (HBeAg) were detected in the serum of the mouse. In the liver and 12 of 16 extrahepatic tissues analyzed, Northern blot hybridization indicated the presence of the 2.1-kilobase (kb) and the 3.5-kb major HBV transcripts. A liver cDNA library was constructed from which the liver RNAs from four cDNA clones with splicing were found. Sequencing analysis showed that the splicing occurred between nucleotides 2451 and 487 of the viral genome, resulting in a truncated viral polymerase gene, as in human hepatocytes. Southern blot analysis of total DNA preparations of the tissues revealed the presence of episomal HBV genome, indicating replication of the viral transgenome in these tissues. However, replication was detected only in some but not all of the tissues that transcribed the 3.5-kb RNA. Partial double-stranded as well as full-length and subgenomic-length single-stranded HBV DNA species of discrete sizes were detected which may represent replication intermediates of preferred replication termination sites of the HBV transgenome. Since many molecular characteristics of mouse B32-1 were similar to those found in HBV-infected humans, HBV transgenic mice similar to B32-1 would be useful in further elucidation of other aspects of the replication and transcription mechanisms of HBV in the liver and extrahepatic tissues.

Duck hepatitis B virus infection of non-hepatocytes

One hundred and seventeen ducklings, 42 inoculated with duck hepatitis B virus (DHBV) 2 days after hatching and 55 connatally infected, were studied over a 6-month period in parallel with 20 ducklings without DHBV infection. Using immunohistochemical, in situ and blot hybridization analyses, the natural course of hepatic and extrahepatic infection was examined. DHBV infection started in the liver 2-4 days post-inoculation. There, DHBV was found not only in hepatocytes, but also in bile duct epithelial cells. Further, DHBV infection occurred in exocrine and endocrine pancreas (beginning 6-10 days and 20 days post-inoculation, respectively) and in germinal centers of the spleen (beginning 8 weeks post-inoculation). Occasionally viral DNA was also found in kidney glomeruli. Using strand-specific RNA probes, viral DNA in pancreas and spleen was clearly demonstrated to be replicating intermediates. Hepatic and extrahepatic infection with DHBV was not associated with histologic inflammation or pathologic changes in these tissues or the liver. These data indicate that DHBV can infect cells other than hepatocytes. The biological significance of non-hepatocyte infection for the life-cycle of the virus and its potential significance for viral persistence remain to be determined.