Genomic analysis of the host response to hepatitis B virus infection

Virus-induced type I IFN stimulates generation of immunoproteasomes at the site of infection

IFN-gamma is known as the initial and primary inducer of immunoproteasomes during viral infections. We now report that type I IFN induced the transcription and translation of immunoproteasome subunits, their incorporation into the proteasome complex, and the generation of an immunoproteasome-dependent CD8 T cell epitope in vitro and provide in vivo evidence that this mechanism occurs prior to IFN-gamma responses at the site of viral infection. Type I IFN-mediated generation of immunoproteasomes was initiated by either poly(I:C) or HCV RNA in human hepatoma cells and was inhibited by neutralization of type I IFN. In serial liver biopsies of chimpanzees with acute HCV infection, increases in immunoproteasome subunit mRNA preceded intrahepatic IFN-gamma responses by several weeks, instead coinciding with intrahepatic type I IFN responses. Thus, viral RNA-induced innate immune responses regulate the antigen-processing machinery, which occurs prior to the detection of IFN-gamma at the site of infection. This mechanism may contribute to the high effectiveness (95%) of type I IFN-based therapies if administered early during HCV infection.

Hepatocellular carcinoma pathogenesis: from genes to environment

Hepatocellular carcinoma is among the most lethal and prevalent cancers in the human population. Despite its significance, there is only an elemental understanding of the molecular, cellular and environmental mechanisms that drive disease pathogenesis, and there are only limited therapeutic options, many with negligible clinical benefit. This Review summarizes the current state of knowledge of this, the most common and dreaded liver neoplasm, and highlights the principal challenges and scientific opportunities that are relevant to controlling this accelerating global health crisis.

Gene expression analysis of primary normal human hepatocytes infected with human hepatitis B virus

AIM

To find the relationship between hepatitis B virus (HBV) and hepatocytes during the initial state of infection by cDNA microarray.

METHODS

Primary normal human hepatocytes (PNHHs) were isolated and infected with HBV. From the PNHHs, RNA was isolated and inverted into complement DNA (cDNA) with Cy3- or Cy5- labeled dUTP for microarray analysis. The labeled cDNA was hybridized with microarray chip, including 4224 cDNAs. From the image of the microarray, expression profiles were produced and some of them were confirmed by RT-PCR, immunoblot analysis, and NF-kappaB luciferase reporter assay.

RESULTS

From the cDNA microarray, we obtained 98 differentially regulated genes. Of the 98 genes, 53 were up regulated and 45 down regulated. Interestingly, in the up regulated genes, we found the TNF signaling pathway-related genes: LT-alpha, TRAF2, and NIK. By using RT-PCR, we confirmed the up-regulation of these genes in HepG2, Huh7, and Chang liver cells, which were transfected with pHBV1.2x, a plasmid encoding all HBV messages. Moreover, these three genes participated in HBV-mediated NF-kappaB activation.

CONCLUSION

During the initial state of HBV infection, hepatocytes facilitate the activation of NF-kappaB through up regulation of LT-alpha, TRAF2, and NIK.

The immune response during hepatitis B virus infection

Hepatitis B virus (HBV) is a major cause of chronic liver inflammation worldwide. Recent knowledge of the virological and immunological events secondary to HBV infection has increased our understanding of the mechanisms involved in viral clearance and persistence. In this review, how the early virological and immunological events might influence the development of a coordinate activation of adaptive immunity necessary to control HBV infection is analysed. The mechanism(s) by which high levels of viral antigens, liver immunological features, regulatory cells and dendritic cell defects might maintain the HBV-specific immunological collapse, typical of chronic hepatitis B patients, is also examined.

Genomics of Hepatitis B and C Infections: Diagnostic and Therapeutic Applications of Microarray Profiling

Microarray profiling offers many potential advances in diagnostic and therapeutic intervention in human disease because of its unparalleled ability to conduct high-throughput analysis of gene expression. However, limitations of this technique relate in part to issues regarding the various methodologies and experimental designs as well as difficulties in the interpretation of results. Despite this, microarray profiling has led to a better understanding of the molecular pathogenesis of hepatitis B virus (HBV) and hepatitis C virus (HCV) infection. Key events in clearance and the development of chronicity of HCV have been identified that may prove to have a role in the development of future treatments. In addition, pharmacogenomic studies of interferon-based treatment for chronic HCV and HBV have provided mechanistic insights into the therapeutic action of interferons. These advances have implications with respect to the development of improved therapeutic agents. New biomarkers for cancer screening and gene profiles with prognostic value for survival have also been developed for hepatocellular carcinoma, which frequently complicates chronic viral hepatitis. Thus, microarray profiling offers enormous potential for improvements in antiviral therapy and our understanding of blood-borne viral hepatitis.

Interferon-inducible expression of APOBEC3 editing enzymes in human hepatocytes and inhibition of hepatitis B virus replication

Hypermutations in hepatitis B virus (HBV) DNA by APOBEC3 cytidine deaminases have been detected in vitro and in vivo, and APOBEC3G (A3G) and APOBEC3F (A3F) have been shown to inhibit the replication of HBV in vitro, but the presumably low or even absent hepatic expression of these enzymes has raised the question as to their physiological impact on HBV replication. We show that normal human liver expresses the mRNAs of APOBEC3B (A3B), APOBEC3C (A3C), A3F, and A3G. In primary human hepatocytes, interferon alpha (IFN-alpha) stimulated the expression of these cytidine deaminases up to 14-fold, and the mRNAs of A3G, A3F, and A3B reached expression levels of 10%, 3%, and 3%, respectively, relative to GAPDH mRNA abundance. On transfection, the full-length protein A3B(L) inhibited HBV replication in vitro as efficiently as A3G or A3F, whereas the truncated splice variant A3B(S) and A3C had no effect. A3B(L) and A3B(S) were detected predominantly in the nucleus of uninfected cells; however, in HBV-expressing cells both proteins were found also in the cytoplasm and were associated with HBV viral particles, similarly to A3G and A3F. Moreover, A3G, A3F, and A3B(L), but not A3B(S), induced extensive G-to-A hypermutations in a fraction of the replicated HBV genomes. In conclusion, the editing enzymes A3B(L), A3F, and most markedly A3G, which are expressed in liver and up-regulated by IFN-alpha in hepatocytes, are candidates to contribute to the noncytolytic clearance of HBV.

Hepatocytes as cytotoxic effector cells can induce cell death by CD95 ligand-mediated pathway

The liver plays an increasingly recognized role in the host's immune responses. The direct contribution of hepatocytes as effector cells to local immunity, pathogen containment, and liver disease is not determined. This in vitro study examined whether hepatocytes can eliminate other cells via a CD95 ligand (CD95L or FasL)/CD95 (Fas)-mediated mechanism and whether this cytotoxic activity can be modulated by cytokines such as interferon gamma (IFN-gamma) or tumor necrosis factor alpha (TNF-alpha). We have found that normal woodchuck and human hepatocytes, both cultured and primary freshly isolated, as well as human HepG2 cells, intrinsically transcribe not only CD95 but also CD95L when examined by reverse transcription-polymerase chain reaction (RT-PCR) assays. The functional competence of CD95L, which was detectable in hepatocytes and HepG2 cells by Western blotting, was confirmed in bioassays by induction of apoptosis of CD95-bearing P815 and LS102.9 cell targets and validated by inhibition of the cell killing with CD95 antagonistic antibody or with a general caspase inhibitor. Furthermore, exposure of cultured hepatocytes to IFN-gamma or their stable transfection with IFN-gamma cDNA or TNF-alpha cDNA increased hepatocyte CD95L/CD95-mediated cell killing. In conclusion, hepatocytes express both CD95L and CD95 and they can induce death of other cells by a CD95L-dependent mechanism. IFN-gamma and, to a lesser extent, TNF-alpha can enhance hepatocyte CD95L-mediated cytotoxicity. This suggests that the local cytokine environment may modulate the hepatocyte contribution to liver immunity.

Hepatitis B virus drug resistance: mechanism and clinical implications for the prevention of treatment failure

Hepatitis B virus (HBV) infection remains a major public health problem worldwide. Recently, the research efforts to identify new inhibitors enabled the development of antiviral agents to treat patients chronically infected by HBV. In clinical practice, the use of nucleoside analogs, which inhibit viral polymerase activity, induces suppression of viral replication accompanied by an improvement in biochemical and histological conditions in most patients. However, many clinical studies revealed the emergence of drug-resistant mutants during extended treatment. This review focuses on the mechanism of HBV drug-resistant mutant selection and on the clinical implications of HBV drug resistance for the prevention of treatment failure.

Expression of the interleukin-7 receptor alpha chain (CD127) on virus-specific CD8+ T cells identifies functionally and phenotypically defined memory T cells during acute resolving hepatitis B virus infection

Virus-specific CD8+ T cells play a central role in the outcome of several viral infections, including hepatitis B virus (HBV) infection. A key feature of virus-specific CD8+ T cells is the development of memory. The mechanisms resulting in the establishment of T-cell memory are still only poorly understood. It has been suggested that T-cell memory may depend on the survival of virus-specific CD8+ T cells in the contraction phase. Indeed, a population of effector cells that express high levels of the interleukin-7 receptor alpha chain (CD127) as the precursors of memory CD8+ T cells has recently been identified in mice. However, very little information is currently available about the kinetics of CD127 expression in an acute resolving viral infection in humans and its association with disease pathogenesis, viral load, and functional and phenotypical T-cell characteristics. To address these important issues, we analyzed the HBV-specific CD8+ T-cell response longitudinally in a cohort of six patients with acute HBV infection who spontaneously cleared the virus. We observed the emergence of CD127 expression on antigen-specific CD8+ memory T cells during the course of infection. Importantly, the up-regulation of CD127 correlated phenotypically with a loss of CD38 and PD-1 expression and acquisition of CCR7 expression: functionally with an enhanced proliferative capacity and clinically with the decline in serum alanine aminotransferase levels and viral clearance. These results suggest that the expression of CD127 is a marker for the development of functionally and phenotypically defined antigen-specific CD8+ memory T cells in cleared human viral infections.

Pathogenetic and antiviral immune responses against hepatitis B virus

Hepatitis B virus (HBV) is a noncytopathic virus that causes liver disease of variable duration and severity. It is widely assumed that during HBV infection the host immune response is responsible for both hepatocellular damage and viral clearance. Whereas there is considerable evidence that the innate immune response does not play a significant role in these processes, the adaptive immune response, particularly virus-specific cytotoxic T lymphocytes (CTLs), seems to contribute to nearly all of the liver injury associated with HBV infection. By killing infected cells and producing antiviral cytokines capable of purging HBV from viable hepatocytes, CTLs are also thought to eliminate the virus. Although liver damage is initiated and mediated by the CTLs, antigen-nonspecific inflammatory cells can worsen CTL-induced immunopathology and platelets may facilitate the accumulation of CTLs in the liver. The mechanisms responsible for disease pathogenesis and viral clearance during HBV infection are the subject of this review.

Salient molecular features of hepatitis C virus revealed

Hepatitis C virus (HCV) is a positive strand RNA virus with a narrow host and tissue tropism. It ranks among the most significant of human pathogens, causing inflammation, scarring and cancer of the liver. Recent investigations have shed light on some of the salient molecular features of this virus. These include a requirement for CD81 (a tetraspanin transmembrane protein for viral entry), a novel mechanism for the initiation of RNA synthesis, phosphorylation of a viral protein in the regulation of RNA amplification and virus assembly and, finally, a viral protease suppressing activation of the innate immune response in infected cells.

Interferon prevents formation of replication-competent hepatitis B virus RNA-containing nucleocapsids

We have previously shown that IFN-beta inhibits hepatitis B virus (HBV) replication by noncytolytic mechanisms that either destabilize pregenomic (pg)RNA-containing capsids or prevent their assembly. Using immortalized murine hepatocyte cell lines stably transfected with a doxycycline (dox)-inducible HBV replication system, we now show that replication-competent pgRNA-containing capsids are not produced when the cells are pretreated with IFN-beta before HBV expression is induced with dox. Furthermore, the turnover rate of preformed HBV RNA-containing capsids is not changed in the presence of IFN-beta or IFN-gamma under conditions in which further pgRNA synthesis is inhibited by dox removal. In summary, these results demonstrate that types 1 and 2 IFN activate hepatocellular mechanism(s) that prevent the formation of replication-competent HBV capsids and, thereby, inhibit HBV replication.

Toll-like receptor signaling inhibits hepatitis B virus replication in vivo

Toll-like receptors (TLR) play a key role in innate immunity. To examine the ability of diverse TLRs to modulate hepatitis B virus (HBV) replication, HBV transgenic mice received a single intravenous injection of ligands specific for TLR2, TLR3, TLR4, TLR5, TLR7, and TLR9. All of the ligands except for TLR2 inhibited HBV replication in the liver noncytopathically within 24 h in a alpha/beta interferon-dependent manner. The ability of these TLR ligands to induce antiviral cytokines at the site of HBV replication suggests that TLR activation could represent a powerful and novel therapeutic strategy for the treatment of chronic HBV infection.

Extensive editing of both hepatitis B virus DNA strands by APOBEC3 cytidine deaminases in vitro and in vivo

Because the replication of hepatitis B virus (HBV) proceeds via an obligatory reverse transcription step in the viral capsid, cDNA is potentially vulnerable to editing by cytidine deaminases of the APOBEC3 family. To date only two edited HBV genomes, referred to as G --> A hypermutants, have been described in vivo. Recent work suggested that HBV replication was indeed restricted by APOBEC3G but by a mechanism other than editing. The issue of restriction has been explored by using a sensitive PCR method allowing differential amplification of AT-rich DNA. G --> A hypermutated HBV genomes were recovered from transfection experiments involving APOBEC3B, -3C, -3F, and -3G indicating that all four enzymes were able to extensively deaminate cytidine residues in minus-strand DNA. Unexpectedly, three of the four enzymes (APOBEC3B, -3F, and -3G) deaminated HBV plus-strand DNA as well. From the serum of two of four patients with high viremia, G --> A hypermutated genomes were recovered at a frequency of approximately 10(-4), indicating that they are, albeit relatively rare, part of the natural cycle of HBV infection. These findings suggest that human APOBEC3 enzymes can impact HBV replication via cytidine deamination.

Immunology of hepatitis B virus and hepatitis C virus infection

More than 500 million people worldwide are persistently infected with the hepatitis B virus (HBV) and/or hepatitis C virus (HCV) and are at risk of developing chronic liver disease, cirrhosis and hepatocellular carcinoma. Despite many common features in the pathogenesis of HBV- and HCV-related liver disease, these viruses markedly differ in their virological properties and in their immune escape and survival strategies. This review assesses recent advances in our understanding of viral hepatitis, contrasts mechanisms of virus-host interaction in acute hepatitis B and hepatitis C, and outlines areas for future studies.

Entecavir for the treatment of chronic hepatitis B

Chronic infection with the hepatitis B virus remains a serious and life-threatening disease for approximately 5% of the world's population, despite the availability of effective vaccines. Although prognoses can be improved by chemotherapy, treatment options are limited and none has been consistently successful. Interferon-alpha, the longest established therapy, has limited efficacy, is slow-acting and frequently causes adverse effects. Newer drugs comprise of mainly nucleoside and nucleotide analogs. The two that are currently approved, lamivudine and adefovir dipivoxil, are well tolerated; both produce rapid and dramatic responses, but their effects may not be sustainable in the long-term due to the emergence of resistant virus. Development of resistance to lamivudine is approximately ten-times more frequent than development of resistance to adefovir dipivoxil (approximately 60 and 6%, respectively) during the first 3 years of therapy. Entecavir, a carbocyclic deoxyguanosine analog that is active against both lamivudine- and adefovir dipivoxil-resistant HBV, is in the vanguard of new antihepatitis B virus drugs that have progressed to Phase III clinical trials. It is the most potent antihepatitis B virus agent discovered to date.

Synoviocyte-packaged Chlamydia trachomatis induces a chronic aseptic arthritis

The basic mechanisms underlying reactive arthritis and specifically the joint injury that follows intra-articular Chlamydia trachomatis infection have not been defined. The present study addresses this question through the development of an experimental model. Stable cell lines were generated from synoviocytes harvested from the knee joints of Lewis rats. The synoviocytes were cocultivated with C. trachomatis to allow invasion by the microbe and were then transferred by intra-articular injection into the knee joints of Lewis rats. The ensuing arthritis could be subdivided into an early phase (</= 14 d) and a late phase. The early phase was characterized by intense, primarily neutrophilic, synovitis; accelerated cartilage injury; dissemination of Chlamydia to liver and spleen; and viable Chlamydia in the joints. The late phase was marked by mixed mononuclear lymphocyte infiltration in the joint; dysplastic cartilage injury and repair; absence of viable organisms; and development of a distinctive humoral response. Western blot analysis comparing reactive arthritis patients to the experimental model indicates that candidate arthritogenic chlamydial antigens are comparable between the two. This model demonstrates that an intense synovitis can be induced by this intracellular pathogen, and that chronic inflammation can persist well beyond the culture-positive phase. Furthermore, these data show that the synoviocyte is a suitable host cell for C. trachomatis and can function as a reservoir of microbial antigens sufficient to perpetuate joint injury.