Not interferon, but interleukin-6 controls early gene expression in hepatitis B virus infection

Alternative splicing-regulated protein of hepatitis B virus hacks the TNF-α-stimulated signaling pathways and limits the extent of liver inflammation

Hepatitis B splicing-regulated protein (HBSP) of the hepatitis B virus (HBV) was uncovered a few years ago but its function remains unknown. HBSP expression occurs from a spliced viral transcript that increases during the course of liver disease. This study aimed at characterizing the impact of HBSP on cellular signaling pathways in vitro and on liver pathogenesis in transgenic (Tg) mice. By RT-qPCR array, NF-κB-inducible genes appeared modulated in HepG2 cells transduced with a HBSP-encoding lentivirus. Using luciferase and Western blot assays, we observed a decreased activation of the NF-κB pathway in HBSP-expressing cells following TNF-α treatment, as illustrated by lower levels of phosphorylated IκB-α. Meanwhile, the level of phosphorylated JNK increased together with the sensitivity to apoptosis. The contrasting effects on JNK and IκB-α activation upon TNF-α stimulation matched with a modulated maturation of TGF-β-activated kinase 1 (TAK1) kinase, assessed by 2-dimensional SDS-PAGE. Inhibition of the NF-κB pathway by HBSP was confirmed in the liver of HBSP Tg mice and associated with a significant decrease of chemically induced chronic liver inflammation, as assessed by immunohistochemistry. In conclusion, HBSP contributes to limit hepatic inflammation during chronic liver disease and may favor HBV persistence by evading immune response.

HBV and the immune response

Hepatitis B virus (HBV) infection acquired in adult life is generally self-limited while chronic persistence of the virus is the prevalent outcome when infection is acquired perinatally. Both control of infection and liver cell injury are strictly dependent upon protective immune responses, because hepatocyte damage is the price that the host must pay to get rid of intracellular virus. Resolution of acute hepatitis B is associated with functionally efficient, multispecific antiviral T-cell responses which are preceded by a poor induction of intracellular innate responses at the early stages of infection. Persistent control of infection is provided by long-lasting protective memory, which is probably sustained by continuous stimulation of the immune system by trace amounts of virus which are never totally eliminated, persisting in an occult episomic form in the nucleus of liver cells even after recovery from acute infection. Chronic virus persistence is instead characterized by a lack of protective T-cell memory maturation and by an exhaustion of HBV-specific T-cell responses. Persistent exposure of T cells to high antigen loads is a key determinant of functional T-cell impairment but also other mechanisms can contribute to T-cell inhibition, including the tolerogenic effect of the liver environment. The degree of T-cell impairment is variable and its severity is related to the level of virus replication and antigen load. The antiviral T-cell function is more efficient in patients who can control infection either partially, such as inactive HBsAg carriers with low levels of virus replication, or completely, such as patients who achieve HBsAg loss either spontaneously or after antiviral therapy. Thus, understanding the features of the immune responses associated with control of infection is needed for the successful design of novel immune modulatory therapies based on the reconstitution of efficient antiviral responses in chronic HBV patients.

Toll-like receptor (TLR)-mediated innate immune responses in the control of hepatitis B virus (HBV) infection

The role of adaptive immune responses in the control of hepatitis B virus (HBV) infection is well accepted. The contribution of innate immune responses to the viral control is recognized but yet not fully understood. Toll-like receptors (TLRs) sense pathogen-associated molecule patterns and activate antiviral mechanisms including the intracellular antiviral pathways and the production of antiviral effectors like interferons (IFNs) and pro-inflammatory cytokines. Activation of the TLR3 pathway and the production of IFN-β represent one of the major mechanisms leading to the suppression of HBV replication in the liver, as shown in different in vitro and in vivo models. TLR4 signaling and TLR2 signaling result in the activation of intracellular pathways including MAPK and PI-3 K/Akt in hepatocytes and reduce HBV replication in an IFN-independent manner. HBV is able to counteract the actions of TLR3 and TLR2/4 through downregulation of TLR expression and attenuation of the cellular signaling pathways. Thus, TLR ligands are promising candidates as immunomodulators and therapeutics for the treatment of chronic HBV infection. Specific antiviral treatment against HBV could recover the TLR functions in chronic HBV infection and increase the effectiveness of therapeutic approaches based on TLR activation.

Hepatitis B virus polymerase disrupts K63-linked ubiquitination of STING to block innate cytosolic DNA-sensing pathways

The cellular innate immune system recognizing pathogen infection is essential for host defense against viruses. In parallel, viruses have developed a variety of strategies to evade the innate immunity. The hepatitis B virus (HBV), a DNA virus that causes chronic hepatitis, has been shown to inhibit RNA helicase RIG-I-mediated interferon (IFN) induction. However, it is still unknown whether HBV could affect the host DNA-sensing pathways. Here we report that in transiently HBV-transfected Huh7 cells, the stably HBV-producing cell line HepAD38, and HBV-infected HepaRG cells and primary human hepatocytes, HBV markedly interfered with IFN-β induction and antiviral immunity mediated by the stimulator of interferon genes (STING), which has been identified as a central factor in foreign DNA recognition and antiviral innate immunity. Screening analysis demonstrated that the viral polymerase (Pol), but not other HBV-encoded proteins, was able to inhibit STING-stimulated interferon regulatory factor 3 (IRF3) activation and IFN-β induction. Moreover, the reverse transcriptase (RT) and the RNase H (RH) domains of Pol were identified to be responsible for the inhibitory effects. Furthermore, Pol was shown to physically associate with STING and dramatically decrease the K63-linked polyubiquitination of STING via its RT domain without altering the expression level of STING. Taken together, these observations suggest that besides its inherent catalytic function, Pol has a role in suppression of IFN-β production by direct interaction with STING and subsequent disruption of its K63-linked ubiquitination, providing a new mechanism for HBV to counteract the innate DNA-sensing pathways.

IMPORTANCE

Although whether and how HBV infection induces the innate immune responses are still controversial, it has become increasingly clear that HBV has developed strategies to counteract the pattern recognition receptor-mediated signaling pathways. Previous studies have shown that type I IFN induction activated by the host RNA sensors could be inhibited by HBV. However, it remains unknown whether HBV as a DNA virus utilizes evasion mechanisms against foreign DNA-elicited antiviral signaling. In recent years, the cytosolic DNA sensor and key adaptor STING has been demonstrated to be essential in multiple foreign DNA-elicited innate immune signalings. Here, for the first time, we report STING as a new target of HBV to antagonize IFN induction and identify the viral polymerase responsible for the inhibitory effect, thus providing an additional molecular mechanism by which HBV evades the innate immunity; this implies that in addition to its inherent catalytic function, HBV polymerase is a multifunctional immunomodulatory protein.

Contribution of Toll-like receptors to the control of hepatitis B virus infection by initiating antiviral innate responses and promoting specific adaptive immune responses

It is well accepted that adaptive immunity plays a key role in the control of hepatitis B virus (HBV) infection. In contrast, the contribution of innate immunity has only received attention in recent years. Toll-like receptors (TLRs) sense pathogen-associated molecule patterns and activate antiviral mechanisms, including intracellular antiviral pathways and the production of antiviral effector interferons (IFNs) and pro-inflammatory cytokines. Experimental results from in vitro and in vivo models have demonstrated that TLRs mediate the activation of cellular signaling pathways and the production of antiviral cytokines, resulting in a suppression of HBV replication. However, HBV infection is associated with downregulation of TLR expression on host cells and blockade of the activation of downstream signaling pathways. In primary HBV infection, TLRs may slow down HBV infection, but contribute only indirectly to viral clearance. Importantly, TLRs may modulate HBV-specific T- and B-cell responses in vivo, which are essential for the termination of HBV infection. Thus, TLR agonists are promising candidates to act as immunomodulators for the treatment of chronic HBV infection. Antiviral treatment may recover TLR expression and function in chronic HBV infection and may increase the efficacy of therapeutic approaches based on TLR activation. A combined therapeutic strategy with antiviral treatment and TLR activation could facilitate the restoration of HBV-specific immune responses and thereby, achieve viral clearance in chronically infected HBV patients.

Kupffer cells interact with hepatitis B surface antigen in vivo and in vitro, leading to proinflammatory cytokine production and natural killer cell function

BACKGROUND

Based on their localization, Kupffer cells (KCs) likely interact with hepatitis B virus (HBV). However, the role of KCs in inducing immunity toward HBV is poorly understood. Therefore, the interaction of hepatitis B surface antigen (HBsAg) and KCs, and possible functional consequences, were assessed.

METHODS

KCs in liver tissue from patients with chronic HBV were analyzed for presence of HBsAg and their phenotype, and compared with KCs in control liver tissue. Liver graft perfusate-derived KCs and in vitro-generated monocyte-derived macrophages were investigated for functional interaction with patient-derived HBsAg.

RESULTS

Intrahepatic KCs were HBsAg positive and more activated than those from control livers. KCs internalized HBsAg in vitro, which did not change their phenotype, but strongly induced proinflammatory cytokine production. Additionally, monocyte-derived macrophages also interacted with HBsAg, leading to activation and cytokine production. Furthermore, HBsAg-exposed macrophages and KC activated natural killer (NK) cells, resulting in increased CD69 expression and interferon-γ production.

CONCLUSIONS

KCs directly interact with HBsAg in vivo and in vitro. HBsAg-induced cytokine production by KCs and monocyte-derived macrophages and subsequent NK cell activation may be an early event in viral containment and may support induction of HBV-specific immunity upon HBV infection, but may also contribute to liver pathology.

HBx inhibits CYP2E1 gene expression via downregulating HNF4α in human hepatoma cells

CYP2E1, one of the cytochrome P450 mixed-function oxidases located predominantly in liver, plays a key role in metabolism of xenobiotics including ethanol and procarcinogens. Recently, down-expression of CYP2E1 was found in hepatocellular carcinoma (HCC) with the majority to be chronic hepatitis B virus (HBV) carriers. In this study, we tested a hypothesis that HBx may inhibit CYP2E1 gene expression via hepatocyte nuclear factor 4α (HNF4α). By enforced HBx gene expression in cultured HepG2 cells, we determined the effect of HBx on CYP2E1 mRNA and protein expression. With a bioinformatics analysis, we found a consensus HNF-4α binding sequence located on −318 to −294 bp upstream of human CYP2E1 promoter. Using reporter gene assay and site-directed mutagenesis, we have shown that mutation of this site dramatically decreased CYP2E1 promoter activity. By silencing endogenous HNF-4α, we have further validated knockdown of HNF-4α significantly decreased CYP2E1expression. Ectopic overexpression of HBx in HepG2 cells inhibits HNF-4α expression, and HNF-4α levels were inversely correlated with viral proteins both in HBV-infected HepG2215 cells and as well as HBV positive HCC liver tissues. Moreover, the HBx-induced CYP2E1 reduction could be rescued by ectopic supplement of HNF4α protein expression. Furthermore, human hepatoma cells C34, which do not express CYP2E1, shows enhanced cell growth rate compared to E47, which constitutively expresses CYP2E1. In addition, the significantly altered liver proteins in CYP2E1 knockout mice were detected with proteomics analysis. Together, HBx inhibits human CYP2E1 gene expression via downregulating HNF4α which contributes to promotion of human hepatoma cell growth. The elucidation of a HBx-HNF4α-CYP2E1 pathway provides novel insight into the molecular mechanism underlining chronic HBV infection associated hepatocarcinogenesis.

The hepatitis B virus-associated tumor microenvironment in hepatocellular carcinoma

In contrast to a majority of cancer types, the initiation of hepatocellular carcinoma (HCC) is intimately associated with a chronically diseased liver tissue, with one of the most prevalent etiological factors being hepatitis B virus (HBV). Transformation of the liver in HBV-associated HCC often follows from or accompanies long-term symptoms of chronic hepatitis, inflammation and cirrhosis, and viral load is a strong predictor for both incidence and progression of HCC. Besides aiding in transformation, HBV plays a crucial role in modulating the accumulation and activation of both cellular components of the microenvironment, such as immune cells and fibroblasts, and non-cellular components of the microenvironment, such as cytokines and growth factors, markedly influencing disease progression and prognosis. This review will explore some of these components and mechanisms to demonstrate both underlying themes and the inherent complexity of these interacting systems in the initiation, progression, and metastasis of HBV-positive HCC.

Genetic deletion of AEG-1 prevents hepatocarcinogenesis

Activation of the oncogene AEG-1 (MTDH, LYRIC) has been implicated recently in the development of hepatocellular carcinoma (HCC). In mice, HCC can be initiated by exposure to the carcinogen DEN, which has been shown to rely upon activation of NF-κB in liver macrophages. Because AEG-1 is an essential component of NF-κB activation, we interrogated the susceptibility of mice lacking the AEG-1 gene to DEN-induced hepatocarcinogenesis. AEG-1-deficient mice displayed resistance to DEN-induced HCC and lung metastasis. No difference was observed in the response to growth factor signaling or activation of AKT, ERK, and β-catenin, compared with wild-type control animals. However, AEG-1-deficient hepatocytes and macrophages exhibited a relative defect in NF-κB activation. Mechanistic investigations showed that IL6 production and STAT3 activation, two key mediators of HCC development, were also deficient along with other biologic and epigenetics findings in the tumor microenvironment, confirming that AEG-1 supports an NF-κB-mediated inflammatory state that drives HCC development. Overall, our findings offer in vivo proofs that AEG-1 is essential for NF-κB activation and hepatocarcinogenesis, and they reveal new roles for AEG-1 in shaping the tumor microenvironment for HCC development.

The role of Kupffer cells in hepatitis B and hepatitis C virus infections

Globally, over 500 million people are chronically infected with the hepatitis B virus (HBV) or hepatitis C virus (HCV). These chronic infections cause liver inflammation, and may result in fibrosis/cirrhosis or hepatocellular carcinoma. Albeit that HBV and HCV differ in various aspects, clearance, persistence, and immunopathology of either infection depends on the interplay between the innate and adaptive responses in the liver. Kupffer cells, the liver-resident macrophages, are abundantly present in the sinusoids of the liver. These cells have been shown to be crucial players to maintain homeostasis, but also contribute to pathology. However, it is important to note that especially during pathology, Kupffer cells are difficult to distinguish from infiltrating monocytes/macrophages and other myeloid cells. In this review we discuss our current understanding of Kupffer cells, and assess their role in the regulation of anti-viral immunity and disease pathogenesis during HBV and HCV infection.

Contradictory immune response in post liver transplantation hepatitis B and C

Hepatitis B and C often progress to decompensated liver cirrhosis requiring orthotopic liver transplantation (OLT). After OLT, hepatitis B recurrence is clinically controlled with a combination of hepatitis B immunoglobulin (HBIG) and nucleos(t)ide analogues. Another approach is to induce self-producing anti-hepatitis B virus (HBV) antibodies using a HBV envelope antigen vaccine. Patients who had not been HBV carriers such as acutely infected liver failure or who received liver from HBV self-limited donor are good candidate. For chronic HBV carrier patients, a successful response can only be achieved in selected patients such as those treated with experimentally reduced immunosuppression protocols or received an anti-HBV adaptive memory carrying donor liver. Hepatitis C virus (HCV) reinfects transplanted livers at a rate of >90%. HCV reinfected patients show different severities of hepatitis, from mild and slowly progressing to severe and rapidly progressing, possibly resulting from different adaptive immune responses. More than half the patients require interferon treatment, although the success rate is low and carries risks for leukocytopenia and rejection. Managing the immune response has an important role in controlling recurrent hepatitis C. This study aimed to review the adaptive immune response in post-OLT hepatitis B and C.

Interleukin-6 upregulates Th17 response via mTOR/STAT3 pathway in acute-on-chronic hepatitis B liver failure

BACKGROUND

Interleukin (IL)-17-producing CD4(+) T cells (Th17) have been shown to play crucial roles in the pathogenesis of hepatitis B virus (HBV)-associated acute-on-chronic liver failure (ACLF). However, the mechanism underlying the enhanced Th17 responses in these patients remains elusive. In this study, the relevance of the IL-6/signal transducer and activator of transcription 3 (STAT3)/mammalian target of rapamycin (mTOR)/Th17 loop in HBV-associated ACLF was investigated.

METHODS

Eight patients with HBV-associated ACLF, eight asymptomatic chronic HBV carriers and eight healthy controls were enrolled in our study. The frequency of peripheral Th17 cells was determined by flow cytometry. IL-17 and IL-6 mRNA levels in peripheral blood mononuclear cells were quantified using quantitative real-time reverse polymerase chain reaction. The activation of STAT3 was seen upon stimulation with IL-6. Rapamycin, an mTOR inhibitor, was used for analysis of the suppressive effect on the Th17 response in vitro.

RESULTS

The percentage of peripheral Th17 cells significantly increased in ACLF patients. CD4(+) T cells from ACLF patients produced higher levels of IL-17 and IL-6 upon stimulation in vitro. Activation of STAT3 in response to IL-6 was elevated in ACLF patients. The IL-6-induced upregulation of IL-17 production by CD4(+) T cells could be reversed by an mTOR inhibitor through decreasing STAT3 activation.

CONCLUSIONS

STAT3 activation upon IL-6 stimulation contributed to the enhanced Th17 response in HBV-associated ACLF patients and mTOR regulated STAT3 phosphorylation. mTOR can be a novel target to suppress Th17-mediated liver injury in HBV-associated ACLF patients.

Tumor necrosis factor-alpha induced by hepatitis B virus core mediating the immune response for hepatitis B viral clearance in mice model

Persistent hepatitis B viral (HBV) infection results in chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma (HCC). An efficient control of virus infections requires the coordinated actions of both innate and adaptive immune responses. In order to define the role of innate immunity effectors against HBV, viral clearance was studied in a panel of immunodeficient mouse strains by the hydrodynamic injection approach. Our results demonstrate that HBV viral clearance is not changed in IFN-α/β receptor (IFNAR), RIG-I, MDA5, MYD88, NLRP3, ASC, and IL-1R knock-out mice, indicating that these innate immunity effectors are not required for HBV clearance. In contrast, HBV persists in the absence of tumor necrosis factor-alpha (TNF-α) or in mice treated with the soluble TNF receptor blocker, Etanercept. In these mice, there was an increase in PD-1-expressing CD8⁺ T-cells and an increase of serum HBV DNA, HBV core, and surface antigen expression as well as viral replication within the liver. Furthermore, the induction of TNF-α in clearing HBV is dependent on the HBV core, and TNF blockage eliminated HBV core-induced viral clearance effects. Finally, the intra-hepatic leukocytes (IHLs), but not the hepatocytes, are the cell source responsible for TNF-α production induced by HBcAg. These results provide evidences for TNF-α mediated innate immune mechanisms in HBV clearance and explain the mechanism of HBV reactivation during therapy with TNF blockage agents.

Virus-related liver cirrhosis: molecular basis and therapeutic options

Chronic infections with hepatitis B virus (HBV) and/or hepatitis C virus (HCV) are the major causes of cirrhosis globally. It takes 10-20 years to progress from viral hepatitis to cirrhosis. Intermediately active hepatic inflammation caused by the infections contributes to the inflammation-necrosis-regeneration process, ultimately cirrhosis. CD8(+) T cells and NK cells cause liver damage via targeting the infected hepatocytes directly and releasing pro-inflammatory cytokine/chemokines. Hepatic stellate cells play an active role in fibrogenesis via secreting fibrosis-related factors. Under the inflammatory microenvironment, the viruses experience mutation-selection-adaptation to evade immune clearance. However, immune selection of some HBV mutations in the evolution towards cirrhosis seems different from that towards hepatocellular carcinoma. As viral replication is an important driving force of cirrhosis pathogenesis, antiviral treatment with nucleos(t)ide analogs is generally effective in halting the progression of cirrhosis, improving liver function and reducing the morbidity of decompensated cirrhosis caused by chronic HBV infection. Interferon-α plus ribavirin and/or the direct acting antivirals such as Vaniprevir are effective for compensated cirrhosis caused by chronic HCV infection. The standard of care for the treatment of HCV-related cirrhosis with interferon-α plus ribavirin should consider the genotypes of IL-28B. Understanding the mechanism of fibrogenesis and hepatocyte regeneration will facilitate the development of novel therapies for decompensated cirrhosis.

Hepatocystin contributes to interferon-mediated antiviral response to hepatitis B virus by regulating hepatocyte nuclear factor 4α

Hepatocystin/80K-H is known as a causative gene for autosomal dominant polycystic liver disease. However, the role of hepatocystin in hepatitis B virus-related liver disease remains unknown. Here, we investigated the role of hepatocystin on the cytokine-mediated antiviral response against hepatitis B virus infection. We investigated the antiviral effect and mechanism of hepatocystin by ectopic expression and RNAi knockdown in cell culture and mouse livers. Hepatocystin suppressed the replication of hepatitis B virus both in vitro and in vivo. This inhibitory effect was HBx-independent and mediated by the transcriptional regulation of viral genome via the activation of exogenous signal-regulated kinase 1/2 and the reduced expression of hepatocyte nuclear factor 4α, a transcription factor essential for hepatitis B virus replication. The amino-terminal region of hepatocystin was essential for regulation of this antiviral signaling pathway. We also found that hepatocystin acts as a critical component in interferon-mediated mitogen-activated protein kinase signaling pathway, and the interferon-induced antiviral activity against hepatitis B virus is associated with the expression levels of hepatocystin. We demonstrated that hepatocystin plays a critical role in modulating the susceptibility of hepatitis B virus to interferon, suggesting that the modulation of hepatocystin expression is important for cytokine-mediated viral clearance during hepatitis B virus infection.

Potential roles played by IL-6 in hepatitis B infection

ABSTRACT: 

Hepatitis B is a main disorder of the liver, which is induced by HBV. Hepatitis B can induce liver diseases, such as inflammation, cirrhosis and hepatocellular carcinoma (HCC). Recent studies demonstrated that several patients are unable to eradicate the virus from hepatocytes and develop chronic hepatitis B infections. The main mechanisms responsible for development of chronic hepatitis B and its related cirrhosis as well as HCC are yet to be identified. IL-6 is a proinflammatory cytokine that participates in stimulation of immune responses against viral infections. In addition, it has been documented that IL-6 can play key roles in induction of fibrosis and cancers. Therefore, the aim of this article is to clarify the main roles of IL-6 in stimulation of appropriate immune responses against hepatitis B virus and induction of hepatitis B-dependent cirrhosis as well as HCC.

Hepatitis B virus polymerase suppresses NF-κB signaling by inhibiting the activity of IKKs via interaction with Hsp90β

Nuclear factor-κB (NF-κB) plays a central role in the regulation of diverse biological processes, including immune responses, development, cell growth, and cell survival. To establish persistent infection, many viruses have evolved strategies to evade the host’s antiviral immune defenses. In the case of hepatitis B virus (HBV), which can cause chronic infection in the liver, immune evasion strategies used by the virus are not fully understood. It has recently been reported that the polymerase of HBV (Pol) inhibits interferon-β (IFN-β) activity by disrupting the interaction between IKKε and the DDX3. In the current study, we found that HBV Pol suppressed NF-κB signaling, which can also contribute to IFN-β production. HBV Pol did not alter the level of NF-κB expression, but it prevented NF-κB subunits involved in both the canonical and non-canonical NF-κB pathways from entering the nucleus. Further experiments demonstrated that HBV Pol preferentially suppressed the activity of the IκB kinase (IKK) complex by disrupting the association of IKK/NEMO with Cdc37/Hsp90, which is critical for the assembly of the IKK complex and recruitment of the IKK complex to the tumor necrosis factor type 1 receptor (TNF-R1). Furthermore, we found that HBV Pol inhibited the NF-κB-mediated transcription of target genes. Taken together, it is suggested that HBV Pol could counteract host innate immune responses by interfering with two distinct signaling pathways required for IFN-β activation. Our studies therefore shed light on a potential therapeutic target for persistent infection with HBV.

Innate immune responses in hepatitis B virus (HBV) infection

Hepatitis B virus (HBV) infection has a low rate of chronicity compared to HCV infection, but chronic liver inflammation can evolve to life threatening complications. Experimental data from HBV infected chimpanzees and HBV transgenic mice have indicated that cytotoxic T cells are the main cell type responsible for inhibition of viral replication, but also for hepatocyte lysis during chronic HBV infection. Their lower activation and impaired function in later stages of infection was suggested as a possible mechanism that allowed for low levels of viral replication. The lack of an interferon response in these models also indicated the importance of adaptive immunity in clearing the infection. Increased knowledge of the signalling pathways and pathogen associated molecular patterns that govern activation of innate immunity in the early stages of viral infections in general has led to a re-evaluation of the innate immune system in HBV infection. Numerous studies have shown that HBV employs active strategies to evade innate immune responses and induce immunosuppression. Some of the immune components targeted by HBV include dendritic cells, natural killer cells, T regulatory cells and signalling pathways of the interferon response. This review will present the current understanding of innate immunity in HBV infection and of the challenges associated with clearing of the HBV infection.

Interplay between hepatitis B virus and the innate immune responses: implications for new therapeutic strategies

Hepatitis B virus (HBV) infection is still a worldwide health problem; however, the current antiviral therapies for chronic hepatitis B are limited in efficacy. The outcome of HBV infection is thought to be the result of complex interactions between the HBV and the host immune system. While the role of the adaptive immune responses in the resolution of HBV infection has been well characterized, the contribution of innate immune mechanisms remains elusive until recent evidence implicates that HBV appears to activate the innate immune response and this response is important for controlling HBV infection. Here, we review our current understanding of innate immune responses to HBV infection and the multifaceted evasion by the virus and discuss the potential strategies to combat chronic HBV infection via induction and restoration of host innate antiviral responses.

Kupffer Cells in Health and Disease

Kupffer cells (KC), the resident macrophages of the liver, represent the largest population of mononuclear phagocytes in the body. Phenotypic, developmental, and functional aspects of these cells in steady state and in different diseases are the focus of this review. Recently it has become evident that KC precursors seed the liver already early in fetal development, and the population can be maintained independently from circulating monocytes. However, inflammatory conditions allow rapid differentiation of monocytes into mature cells that are indistinguishable from genuine KC. KC are located in the lumen of sinusoids that receive blood both from the portal vein, carrying nutrients and microbial products from the gut, and from the hepatic artery. This positions KC ideally for their prime function, namely surveillance and clearance of the circulation. As such, they are important in iron recycling by phagocytosing effete erythrocytes, for instance. The immunophenotype of KC, characterized by a wide variety of endocytic receptors, is indicative of this scavenger function. In maintaining homeostasis, KC have an ambivalent response to exogenous triggers. On the one hand, their surveillance function requires alert responses to potentially hazardous substances. On the other hand, continuous exposure of the cells to the trigger-rich content of blood originating from the gut dampens their responsiveness to further stimuli. This ambivalence is also reflected in their diverse roles in disease pathogenesis. For the latter, we sketch the contribution of KC by giving examples of their role in metabolic disease, infections, and liver injury.

Relationship between interleukin-6 polymorphism and susceptibility to chronic hepatitis B virus infection

AIM: To identify the relationship between tag single nucleotide polymorphisms (tag SNPs) of interleukin-6 (IL-6) gene and susceptibility to chronic hepatitis B virus (HBV) infection in a Han Chinese population.

METHODS: We performed a case-control study of 501 Chinese patients with chronic HBV infection and 301 self-limiting HBV-infected individuals as controls. Genomic DNA was isolated from the whole blood of all subjects using phenol/chloroform with MaXtract high-density tubes. Tag SNPs were identified using genotype data from the panel (Han Chinese in Beijing) of the phase II HapMap Project. Four tag SNPs in IL-6 (rs17147230A/T, rs2066992G/T, rs2069837A/G and rs2069852A/G) were genotyped by the Multiplex Snapshot technique. The genotype and allele frequencies were calculated and analyzed.

RESULTS: Five haplotypes were involved in the analysis, with frequencies higher than 0.03. One of the haplotypes, TTAA, was significantly different between the two groups. Overall haplotype P values were: ATAA, P = 0.605, OR (95%CI) = 1.056 (0.860-1.297); TGAG, P = 0.385, OR (95%CI) = 1.179 (0.813-1.709); TGGG, P = 0.549, OR (95%CI) = 1.087 (0.827-1.429); TTAA, P = 0.004, OR (95%CI) = 0.655 (0.491-0.873); TTAG, P = 0.266, OR (95%CI) = 1.272 (0.832-1.944). However, the four SNPs showed no significant genotype/allele associations with susceptibility to chronic HBV infection. Overall allele P values were: rs17147230, P = 0.696, OR (95%CI) = 1.041 (0.850-1.276); rs2066992, P = 0.460, OR (95%CI) = 1.090 (0.868-1.369); rs2069837, P = 0.898, OR (95%CI) = 0.983 (0.759-1.274); rs2069852, P = 0.165, OR (95%CI) = 0.859 (0.693-1.064). Overall genotype P values were: rs17147230, P = 0.625; rs2066992, P = 0.500; rs2069837, P = 0.853; and rs2069852, P = 0.380.

CONCLUSION: The four tag SNPs of IL-6 gene may be associated with susceptibility to chronic HBV infection in the Han Chinese population.

Alpha-interferon suppresses hepadnavirus transcription by altering epigenetic modification of cccDNA minichromosomes

Covalently closed circular DNA (cccDNA) of hepadnaviruses exists as an episomal minichromosome in the nucleus of infected hepatocyte and serves as the transcriptional template for viral mRNA synthesis. Elimination of cccDNA is the prerequisite for either a therapeutic cure or immunological resolution of HBV infection. Although accumulating evidence suggests that inflammatory cytokines-mediated cure of virally infected hepatocytes does occur and plays an essential role in the resolution of an acute HBV infection, the molecular mechanism by which the cytokines eliminate cccDNA and/or suppress its transcription remains elusive. This is largely due to the lack of convenient cell culture systems supporting efficient HBV infection and cccDNA formation to allow detailed molecular analyses. In this study, we took the advantage of a chicken hepatoma cell line that supports tetracycline-inducible duck hepatitis B virus (DHBV) replication and established an experimental condition mimicking the virally infected hepatocytes in which DHBV pregenomic (pg) RNA transcription and DNA replication are solely dependent on cccDNA. This cell culture system allowed us to demonstrate that cccDNA transcription required histone deacetylase activity and IFN-α induced a profound and long-lasting suppression of cccDNA transcription, which required protein synthesis and was associated with the reduction of acetylated histone H3 lysine 9 (H3K9) and 27 (H3K27) in cccDNA minichromosomes. Moreover, IFN-α treatment also induced a delayed response that appeared to accelerate the decay of cccDNA. Our studies have thus shed light on the molecular mechanism by which IFN-α noncytolytically controls hepadnavirus infection.

Hepatitis B virus (HBV) infection affects approximately one-third of the world population and more than 350 million people are chronically infected by the virus, for which the currently available antiviral therapies fail to provide a cure. This is because the HBV DNA polymerase inhibitors have no direct effect on the nuclear form of HBV genome, the covalently closed circular (ccc) DNA. Elimination or transcriptional silencing of cccDNA is the prerequisite for either a therapeutic cure or immunological resolution of HBV infection. However, due to the lack of proper experimental systems, the molecular mechanism of cccDNA biosynthesis, maintenance and transcription regulation remains to be elucidated. We report herein the establishment of a cell-based assay where the replication of duck hepatitis B virus (DHBV), a close relative of HBV, is supported by cccDNA. This experimental system not only allows us to demonstrate the unique property of alpha-interferon suppression of cccDNA transcription, but also shows for the first time that DHBV cccDNA transcription requires histone deacetylase activity. It is conceivable that the principles revealed by studying DHBV cccDNA metabolism and transcription regulation should provide valuable insight in HBV cccDNA biology and clues for the development of therapeutics to control chronic hepatitis B.

Interleukin-1 and tumor necrosis factor-α trigger restriction of hepatitis B virus infection via a cytidine deaminase activation-induced cytidine deaminase (AID)

Virus infection is restricted by intracellular immune responses in host cells, and this is typically modulated by stimulation of cytokines. The cytokines and host factors that determine the host cell restriction against hepatitis B virus (HBV) infection are not well understood. We screened 36 cytokines and chemokines to determine which were able to reduce the susceptibility of HepaRG cells to HBV infection. Here, we found that pretreatment with IL-1β and TNFα remarkably reduced the host cell susceptibility to HBV infection. This effect was mediated by activation of the NF-κB signaling pathway. A cytidine deaminase, activation-induced cytidine deaminase (AID), was up-regulated by both IL-1β and TNFα in a variety of hepatocyte cell lines and primary human hepatocytes. Another deaminase APOBEC3G was not induced by these proinflammatory cytokines. Knockdown of AID expression impaired the anti-HBV effect of IL-1β, and overexpression of AID antagonized HBV infection, suggesting that AID was one of the responsible factors for the anti-HBV activity of IL-1/TNFα. Although AID induced hypermutation of HBV DNA, this activity was dispensable for the anti-HBV activity. The antiviral effect of IL-1/TNFα was also observed on different HBV genotypes but not on hepatitis C virus. These results demonstrate that proinflammatory cytokines IL-1/TNFα trigger a novel antiviral mechanism involving AID to regulate host cell permissiveness to HBV infection.

Interleukin-1 and tumor necrosis factor-α trigger restriction of hepatitis B virus infection via a cytidine deaminase activation-induced cytidine deaminase (AID)

Virus infection is restricted by intracellular immune responses in host cells, and this is typically modulated by stimulation of cytokines. The cytokines and host factors that determine the host cell restriction against hepatitis B virus (HBV) infection are not well understood. We screened 36 cytokines and chemokines to determine which were able to reduce the susceptibility of HepaRG cells to HBV infection. Here, we found that pretreatment with IL-1β and TNFα remarkably reduced the host cell susceptibility to HBV infection. This effect was mediated by activation of the NF-κB signaling pathway. A cytidine deaminase, activation-induced cytidine deaminase (AID), was up-regulated by both IL-1β and TNFα in a variety of hepatocyte cell lines and primary human hepatocytes. Another deaminase APOBEC3G was not induced by these proinflammatory cytokines. Knockdown of AID expression impaired the anti-HBV effect of IL-1β, and overexpression of AID antagonized HBV infection, suggesting that AID was one of the responsible factors for the anti-HBV activity of IL-1/TNFα. Although AID induced hypermutation of HBV DNA, this activity was dispensable for the anti-HBV activity. The antiviral effect of IL-1/TNFα was also observed on different HBV genotypes but not on hepatitis C virus. These results demonstrate that proinflammatory cytokines IL-1/TNFα trigger a novel antiviral mechanism involving AID to regulate host cell permissiveness to HBV infection.

Expression pattern of serum cytokines in hepatitis B virus infected patients with persistently normal alanine aminotransferase levels

Purpose

About 60–80 % of chronic hepatitis B virus (HBV) carriers are characterized with persistently normal alanine transaminase (ALT). Differences of cytokine expression are associated with the prognosis of HBV infection. We investigated the expression pattern of 30 cytokines associated with anti-HBV immunity in patients with normal ALT.

Methods

Four patient groups (immune tolerance, inactive hepatitis B surface antigen carriers, resolved hepatitis B, and control; 10 subjects per group) were assigned. Thirty cytokines, including IFN-γ, IL-1β, IL-2, IL-4, IL-6, IL-7, IL-9, IL-10, IL-12p40, IL-12p70, IL-15, IL-17A, IL-17C, IL-21, IL-22, IL-23p19, IL-28A, IL-29, CCL5, CCL16, CCL20, CCL22, CXCL9, CXCL10, CXCL11, TNFRSF8, TNFRSF18, IL-6R, gp130, and TGF-β1, were measured using a human cytokine antibody array. Signal intensities were obtained by laser scanner. Protein-protein interactions were analyzed by STRING (Search Tool for the Retrieval of Interacting Genes/Proteins).

Results

Significant differences of signal intensities were observed for IL-2, IL-4, IL-6, IL-7, IL-9, IL-10, IL-12p40, IL-12p70, IL-15, IL-21, IL-23p19, IL-28A, and IL-29. The lowest intensity was in controls. Among three HBV infection groups, significant differences were observed in IL-2, IL-4, IL-12p70, IL-15, IL-21, IL-23p19, and IL-29. The highest intensity was in the inactive group. All cytokines with significant differences were involved JAK-STAT signaling that up-regulate FOXP3, SOCS3 and MX1.

Conclusion

Differential expression of cytokines in JAK-STAT signaling is an important factor associated with prognosis of HBV infection. The elevation of γC cytokines, IL-12p70, IL-23p19, and IL-29 may promote spontaneous HBeAg seroconversion and HBV clearance.

Electronic supplementary material

The online version of this article (doi:10.1007/s10875-013-9931-0) contains supplementary material, which is available to authorized users.

Soluble interleukin-6 receptor-mediated innate immune response to DNA and RNA viruses

The interleukin-6 (IL-6) receptor, which exists as membrane-bound and soluble forms, plays critical roles in the immune response. The soluble IL-6 receptor (sIL6R) has been identified as a potential therapeutic target for preventing coronary heart disease. However, little is known about the role of this receptor during viral infection. In this study, we show that sIL6R, but not IL-6, is induced by viral infection via the cyclooxygenase-2 pathway. Interestingly, sIL6R, but not IL-6, exhibited extensive antiviral activity against DNA and RNA viruses, including hepatitis B virus, influenza virus, human enterovirus 71, and vesicular stomatitis virus. No synergistic effects on antiviral action were observed by combining sIL6R and IL-6. Furthermore, sIL6R mediated antiviral action via the p28 pathway and induced alpha interferon (IFN-α) by promoting the nuclear translocation of IFN regulatory factor 3 (IRF3) and NF-κB, which led to the activation of downstream IFN effectors, including 2',5'-oligoadenylate synthetase (OAS), double-stranded RNA-dependent protein kinase (PKR), and myxovirus resistance protein (Mx). Thus, our results demonstrate that sIL6R, but not IL-6, plays an important role in the host antiviral response.

Immunocompetent nontransgenic mouse models for studying hepatitis B virus immune responses

Although the chronicity of hepatitis B virus (HBV) infection is the result of impaired HBV-specific immune responses that cannot eliminate or clear the infected hepatocytes efficiently, many issues remained unsettled. It is thus crucial to have a suitable laboratory animal to study the immunopathogenesis of HBV infection and the mechanisms of HBV persistence. To meet the requirement of a mouse model resembling natural chronic HBV infection in human, there are several approaches in the development of mouse animal model by using hydrodynamic-based transfection of HBV DNA, delivery of adenovirus or adeno-associated viral vectors containing HBV DNA for studying HBV immune responses. These immunocompetent nontransgenic mouse animal models will provide new approaches to investigate the mechanisms of immune pathogenesis in HBV infection.

Interferon-induced proteins with tetratricopeptide repeats 1 and 2 are cellular factors that limit hepatitis B virus replication

Interferon (IFN)-α is able to stimulate many cellular genes and inhibit the replication of various viruses. However, it is unknown whether some IFN-stimulated genes (ISGs) specifically inhibit hepatitis B virus (HBV) replication. Therefore, we attempted to identify ISGs with antiviral activities against HBV. Knockdown of IFN-induced proteins with tetratricopeptide repeats 1 and 2 (IFIT1 and IFIT2) in HepG2.2.15 led to markedly increased HBV replication. Consistently, this effect was verified by transient transfection with a replication-competent HBV clone in HepG2 and Huh7. However, IFN-α stimulation could override the knockdown by siRNAs and enhance the expression of IFIT1 and IFIT2, leading to reduced HBV replication. Silencing of IFIT1 or IFIT2 decreased the expression of the corresponding genes while other ISGs like MxA were not affected. Northern blot analysis showed that IFIT1 and IFIT2 knockdown slightly increased the levels of HBV 3.5, 2.4 and 2.1 kb transcripts, while IFIT1 and IFIT2 overexpression did not change their levels. Consistently, the reporter assays with HBV promoters demonstrated that IFIT1 and IFIT2 differentially but only modestly regulated HBV promoter activity. Thus, IFIT1 and IFIT2 contribute significantly to the regulation of HBV replication, likely at both transcriptional and posttranscriptional steps.

Inhibition of hepatitis B virus replication by the host zinc finger antiviral protein

The zinc finger antiviral protein (ZAP) is a mammalian host restriction factor that inhibits the replication of a variety of RNA viruses, including retroviruses, alphaviruses and filoviruses, through interaction with the ZAP-responsive elements (ZRE) in viral RNA, and recruiting the exosome to degrade RNA substrate. Hepatitis B virus (HBV) is a pararetrovirus that replicates its genomic DNA via reverse transcription of a viral pregenomic (pg) RNA precursor. Here, we demonstrate that the two isoforms of human ZAP (hZAP-L and -S) inhibit HBV replication in human hepatocyte-derived cells through posttranscriptional down-regulation of viral pgRNA. Mechanistically, the zinc finger motif-containing N-terminus of hZAP is responsible for the reduction of HBV RNA, and the integrity of the four zinc finger motifs is essential for ZAP to bind to HBV RNA and fulfill its antiviral function. The ZRE sequences conferring the susceptibility of viral RNA to ZAP-mediated RNA decay were mapped to the terminal redundant region (nt 1820–1918) of HBV pgRNA. In agreement with its role as a host restriction factor and as an innate immune mediator for HBV infection, ZAP was upregulated in cultured primary human hepatocytes and hepatocyte-derived cells upon IFN-α treatment or IPS-1 activation, and in the livers of hepatitis B patients during immune active phase. Knock down of ZAP expression increased the level of HBV RNA and partially attenuated the antiviral effect elicited by IPS-1 in cell cultures. In summary, we demonstrated that ZAP is an intrinsic host antiviral factor with activity against HBV through down-regulation of viral RNA, and that ZAP plays a role in the innate control of HBV replication. Our findings thus shed light on virus-host interaction, viral pathogenesis, and antiviral approaches.

The dynamics of virus and host interaction greatly influence viral pathogenesis, and host cells have evolved multiple mechanisms to inhibit viral replication. Since it was first discovered as a cellular restriction factor for retroviruses, the host-encoded zinc finger antiviral protein (ZAP) has been shown to antagonize a variety of viral species, possibly through a common mechanism by which ZAP targets viral RNA for degradation. Here we report that hepatitis B virus (HBV) is also vulnerable to ZAP-mediated viral RNA reduction. ZAP is able to interact with HBV RNA through its zinc finger motifs, and the ZAP-responsive element which determines ZAP's antiviral specificity and activity is located within the 100-nucleotide-long terminal redundant region in the viral RNA genome. While the replication of HBV is constitutively restricted under the basal expression of intrahepatic ZAP, activation of host innate defenses, and potentially the acquired immune responses as well, could further elevate ZAP expression to suppress HBV replication. Therefore, our study not only expands the antiviral spectrum of ZAP, but also provides cumulative and novel information for a better understanding of ZAP biology and antiviral mechanisms. We also envision that the endogenous or engineered ZAP could be utilized in the future for development of therapeutic means to treat chronic hepatitis B, which currently affects more than 5% of the world's population.

Increased expression of Gp96 by HBx-induced NF-κB activation feedback enhances hepatitis B virus production

Elevated expression of heat shock protein gp96 in hepatitis B virus (HBV)-infected patients is positively correlated with the progress of HBV-induced diseases, but little is known regarding the molecular mechanism of virus-induced gp96 expression and its impact on HBV infection. In this study, up-regulation of gp96 by HBV replication was confirmed both in vitro and in vivo. Among HBV components, HBV x protein (HBx) was found to increase gp96 promoter activity and enhance gp96 expression by using a luciferase reporter system, and western blot analysis. Further, we found that HBx-mediated regulation of gp96 expression requires a NF-κB cis-regulatory element on the gp96 promoter, and chromatin immunoprecipitation results demonstrated that HBx promotes the binding of NF-κB to the gp96 promoter. Significantly, both gain- and loss-of-function studies showed that gp96 enhances HBV production in HBV-transfected cells and a mouse model based on hydrodynamic transfection. Moreover, up-regulated gp96 expression was observed in HBV-infected patients, and gp96 levels were correlated with serum viral loads. Thus, our work demonstrates a positive feedback regulatory pathway involving gp96 and HBV, which may contribute to persistent HBV infection. Our data also indicate that modulation of gp96 function may represent a novel strategy for the intervention of HBV infection.

New insights into how HBV manipulates the innate immune response to establish acute and persistent infection

The mechanisms by which HBV establishes and maintains chronic infection are poorly understood. Although adult acquired HBV is generally cleared by a robust immune response, most individuals infected at childbirth or in very early childhood develop lifelong chronic infection. In addition, acute infections are unresolved in approximately 5% of individuals infected in adulthood. The host cell mechanisms that ensure establishment and resolution of acute infection and persistent infection remain unclear. Currently, two schools of thought suggest that either HBV is a 'stealth' virus, which initially establishes infection by avoiding host innate immune responses, or that HBV facilitates initial infection and progression to persistence by actively manipulating the host innate immune response to its advantage. There is increasing evidence that activation of innate host cell signalling pathways plays a major role in limiting adult acquired HBV infection and that, in turn, HBV has evolved numerous strategies to counteract these defence mechanisms. In this review, we summarize current knowledge regarding innate immune responses to HBV infection and discuss how HBV regulates cell signalling pathways to its advantage, particularly in the setting of chronic HBV infection. In turn, we show how an intimate knowledge of innate immune responses is driving development of novel therapeutic agents to treat chronic HBV infection.

Identification of an intrahepatic transcriptional signature associated with self-limiting infection in the woodchuck model of hepatitis B

The woodchuck model of hepatitis B virus (HBV) infection displays many characteristics of human infection and has particular value for characterizing the host immune responses during the development of chronic infection. Using the newly developed custom woodchuck microarray platform, we compared the intrahepatic transcriptional profiles of neonatal woodchucks with self-limiting woodchuck hepatitis virus (WHV) infection to those woodchucks progressing to persistent WHV infection. This revealed that WHV does not induce significant intrahepatic gene expression changes during the early-acute stage of infection (8 weeks), suggesting it is a stealth virus. At the mid-acute phase of infection (14 weeks), resolution was associated with induction of a prominent cytotoxic T-cell signature. Strikingly, this was accompanied by high-level expression of PD-1 and various other inhibitory T-cell receptors, which likely act to minimize liver damage by cytotoxic T cells during viral clearance. In contrast to the expression of perforin and other cytotoxic effector genes, the interferon-γ (IFN-γ) signaling response in the mid-acute phase was comparable to that in chronically infected adult animals. The absence of a strong IFN-α/β transcriptional response indicated that type I IFN is not a critical mediator of self-limiting infection. Nevertheless, a number of antiviral genes, including viperin, were differentially expressed during resolving infection, suggesting that a subset of IFN-stimulated genes (ISG) may play a role in the control of WHV replication.

CONCLUSION

We identified new immune pathways associated with the clearance of hepadnavirus infection revealing novel molecular targets with potential for the therapeutic treatment of chronic hepatitis B.

Hepatitis B virus: from immunobiology to immunotherapy

Owing to the major limitations of current antiviral therapies in HBV (hepatitis B virus) infection, there is a strong need for novel therapeutic approaches to this major health burden. Stimulation of the host's innate and adaptive immune responses in a way that results in the resolution of viral infection is a promising approach. A better understanding of the virus-host interaction in acute and chronic HBV infection revealed several possible novel targets for antiviral immunotherapy. In the present review, we will discuss the current state of the art in HBV immunology and illustrate how control of infection could be achieved by immunotherapeutic interventions.

Serum cytokine levels in chronic hepatitis B patients receiving peginterferon alpha-2a therapy

BACKGROUND

The relationship between cytokines and responses to peginterferon alpha-2a treatment in chronic hepatitis B patients has not yet been fully elucidated. We analyzed the serum levels of interleukin (IL)-1alpha, IL-1beta, IL-2, IL-4, IL-6, IL-8, IL-10, vascular endothelial growth factor, interferon-gamma, tumor necrosis factor-alpha, monocyte chemotactic protein-1 (MCP1) and epidermal growth factor during the treatment with peginterferon alpha-2a.

METHODS

Ninety-three serum samples from 20 chronic hepatitis B patients were collected before, during and after 48 weeks of peginterferon therapy and were assayed for 12 cytokines. The patients were categorized as either virologic responders (VRs) or non-responders (NRs) according to their HBV DNA levels taken at 6th month during treatment. The Evidence Investigator (Randox, Antrim, UK), a protein chip analyzer, was used to quantify cytokines.

RESULTS

Among the 12 cytokines, the levels of MCP1 were increased and the levels of IL-4 were decreased during the treatment in VRs. However these cytokines were not significantly changed in NRs in the treatment phases. Area under the receiver operating characteristic curve (AUROC) value of HBV DNA measured before the treatment was 0.81 in predicting VRs, and that of the baseline MCP1 was 0.76. IL-6 levels at 3rd and 6th months during the treatment also showed AUROC values 0.85 and 0.78 respectively in predicting sustained VRs.

CONCLUSION

Serum cytokine levels reflect the pathological differences of individual treatment phases and could also be useful in monitoring responses to peginterferon treatment in chronic hepatitis B patients.

Role of Toll-like receptor 2 in the immune response against hepadnaviral infection

BACKGROUND & AIMS

The Toll-like receptor 2 (TLR2) has recently been recognized to play an important role in the pathogenesis of chronic hepatitis B virus (HBV) infection. In the present study, we examined the role of TLR2 in hepadnaviral infection in hepatoma cell lines and the woodchuck model.

METHODS

The expression of TLR2 and pro-inflammatory cytokines was quantified by real time RT-PCR. TLR2-associated signaling pathways in hepatocytes were examined by Western blot. HBV replication and gene expression were assessed by Southern blot, Northern blot and specific ELISA, respectively.

RESULTS

TLR2 ligands activated NF-κB, PI3K/Akt, and different arms of MAPK signaling pathways and induced the production of pro-inflammatory cytokines in hepatocytes. TLR2-mediated innate immune responses led to reduction of HBV/woodchuck hepatitis virus (WHV) replication and gene expression in HepG2.2.15 cells and primary woodchuck hepatocytes. Furthermore, the antiviral activity of TLR2 ligands was abolished by pretreatment with U0126 and rapamycin, inhibitors of the MAPK/ERK and PI3K/Akt pathways, respectively. In the woodchuck model, relatively low levels of TLR2 expression were found in peripheral blood mononuclear cells (PBMCs) and in liver tissues from chronic WHV carriers. TLR2 expression in PBMCs was inversely correlated with WHV DNA titers in acute WHV infection and in entecavir-treated chronic WHV carriers.

CONCLUSIONS

These data suggest that hepatocytes play an active role in TLR2-mediated antiviral responses during hepadnaviral infection. The mutual inhibition of HBV replication and TLR2 signaling represents an important aspect of HBV infection and should be considered in the new therapeutic concept against chronic HBV infection.

Transcriptomic analysis of the woodchuck model of chronic hepatitis B

The Eastern woodchuck (Marmota monax) is naturally infected with woodchuck hepatitis virus (WHV), a hepadnavirus closely related to the human hepatitis B virus (HBV). The woodchuck is used as an animal model for studying chronic hepatitis B (CHB) and HBV-associated hepatocellular carcinoma (HCC) in humans, but the lack of sequence information has hitherto precluded functional genomics analysis. To address this major limitation of the model, we report here the sequencing, assembly, and annotation of the woodchuck transcriptome, together with the generation of custom woodchuck microarrays. Using this new platform, we characterized the transcriptional response to persistent WHV infection and WHV-induced HCC. This revealed that chronic WHV infection, like HBV, is associated with (1) a limited intrahepatic type I interferon response; (2) intrahepatic induction of markers associated with T cell exhaustion; (3) elevated levels of suppressor of cytokine signaling 3 (SOCS3) in the liver; and (4) intrahepatic accumulation of neutrophils. Underscoring the translational value of the woodchuck model, this study also determined that WHV-induced HCC shares molecular characteristics with a subtype of human HCC with poor prognosis.

CONCLUSION

Our data establish the translational value of the woodchuck model and provide new insight into immune pathways which may play a role either in the persistence of HBV infection or the sequelae of CHB.

Mucroporin-M1 inhibits hepatitis B virus replication by activating the mitogen-activated protein kinase (MAPK) pathway and down-regulating HNF4α in vitro and in vivo

Hepatitis B virus (HBV) is a noncytopathic human hepadnavirus that causes acute, chronic hepatitis and hepatocellular carcinoma (HCC). As the clinical utility of current therapies is limited, new anti-HBV agents and sources for such agents are still highly sought after. Here, we report that Mucroporin-M1, a scorpion venom-derived peptide, reduces the amount of extracellular HBsAg, HBeAg, and HBV DNA productions of HepG2.2.15 cells in a dose-dependent manner and inhibits HBV capsid DNA, HBV intracellular RNA replication intermediates and the HBV Core protein in the cytoplasm of HepG2.2.15 cells. Using a mouse model of HBV infection, we found that HBV replication was significantly inhibited by intravenous injection of the Mucroporin-M1 peptide. This inhibitory activity was due to a reduction in HBV promoter activity caused by a decrease in the binding of HNF4α to the precore/core promoter region. Furthermore, we confirmed that Mucroporin-M1 could selectively activate mitogen-activated protein kinases (MAPKs) and lead to the down-regulation of HNF4α expression, which explains the decreased binding of HNF4α to the HBV promoter. Moreover, when the protein phosphorylation activity of the MAPK pathway was inhibited, both HNF4α expression and HBV replication recovered. Finally, we proved that treatment with the Mucroporin-M1 peptide increased phosphorylation of the MAPK proteins in HBV-harboring mice. These results implicate Mucroporin-M1 peptide can activate the MAPK pathway and then reduce the expression of HNF4α, resulting in the inhibition of HBV replication in vitro and in vivo. Our work also opens new doors to discovering novel anti-HBV agents or sources.

Cytokine profiles in high risk injection drug users suggests innate as opposed to adaptive immunity in apparent resistance to hepatitis C virus infection

A cohort of injection drug users (IDU) have been identified who despite a long history of IDU and sharing of injecting equipment remain seronegative and aviraemic for hepatitis C virus (HCV). They have been termed HCV exposed uninfected (EU). The study of potential innate or adaptive immune mechanisms of resistance to HCV infection in this group is of interest. The aim of this study was to determine the levels of a broad range of cytokines in serum of exposed, uninfected individuals to ascertain whether there is a specific cytokine profile associated with apparent resistance to HCV. Sera from 22 EU individuals were analysed for a range of cytokines and chemokines, and compared to 16 treatment-naive chronic HCV cases (HCV Ab+ RNA+), 16 individuals with spontaneous resolution of HCV (HCV-Ab+ and HCV-RNA-) and 10 healthy unexposed controls. EU subjects had strikingly higher levels of both IL-6 (on average more than 100-fold, P = 0.001) and IL-8 (on average more than 10-fold, P < 0.001) than the comparison groups. Additionally higher levels of tumour necrosis factor-alpha (TNF-α; on average up to threefold, P = 0.02) were seen in EU individuals. The levels of interferon-alpha (IFN-α) were upregulated in all HCV exposed groups in comparison to healthy controls (P = 0.013). Adaptive immune cytokine levels were no different between the groups. Cytokine profiling demonstrated raised levels of pro-inflammatory innate immune cytokines and chemokines in EU IDU, in particular interleukin-6 and interleukin-8. These findings suggest innate immune activation may be the key to prevention of infection in this cohort.

Hepatitis B virus nucleocapsid but not free core antigen controls viral clearance in mice

We have recently shown that hepatitis B virus (HBV) core antigen (HBcAg) is the major viral factor for HBV clearance using a hydrodynamics-based mouse model. Knockout of HBcAg hampers the development of antiviral immune responses and thus promotes HBV persistence. Here, we further demonstrated that only in the capsid form, but not the free or dimer form, can HBcAg exert its contributory role in HBV clearance. HBcAg is the main structural protein of HBV icosahedral nucleocapsid. A mutant HBV DNA which expresses an assembly-defective HBcAg, HBcAgY132A, surprisingly prolonged HBV surface antigenemia in both C57BL/6 and BALB/c mice without affecting viral transcription and translation. This result was not due to a loss of the possible immune epitope caused by the single-amino-acid substitution of HBcAg. Moreover, the particular HBV mutant failed to induce robust humoral and cellular immunity against HBV. These data revealed the requirement of capsid structure for inducing adequate immunity that leads to HBV clearance in mice.

Transfer of HBV genomes using low doses of adenovirus vectors leads to persistent infection in immune competent mice

Studies of mechanisms responsible for the persistence of hepatitis B virus (HBV) infection have been hindered by a lack of appropriate animal models. HBV genomes can be delivered to livers of mice using hydrodynamic injection or high doses of an adenoviral vector; these lead to clearance of HBV. We found that infection of immunocompetent mice with low doses of an adenoviral vector resulted in persistent HBV infection; the mice neither underwent seroconversion to production of antibodies against HBV nor developed a strong HBV-specific effector T-cell response. As in patients with chronic HBV infection, DNA vaccination failed to generate T cells that cleared infection. This model of persistent HBV infection could be used to study the pathogenesis of chronic HBV infection and develop new therapeutic strategies.

Preclinical development of TLR ligands as drugs for the treatment of chronic viral infections

INTRODUCTION

Toll-like receptors (TLRs) have been identified as key regulators of innate and adaptive immune responses in viral infection. Recent progress in this field revealed that there are significant interactions between the TLR system and pathogens in chronic viral infections. Therefore, TLR ligands have great potential for the treatment of chronic viral infections.

AREAS COVERED

This review provides an overview of the methodology for preclinical testing of TLR ligands for three major viral infections: hepatitis B virus (HBV), hepatitis C virus (HCV) and human immunodeficiency virus (HIV). TLR ligands have shown potent antiviral activity in different cell culture systems as well as animal models for these infections and induce the production of antiviral cytokines, modulated cellular immunological functions and antiviral effects in vivo.

EXPERT OPINION

The recent progress in this field demonstrated that activation of a large number of TLR ligands is effective against viral infections in cell culture systems and animal models. Exploring these models, further in-depth elucidation of the molecular and immunological mechanisms of the antiviral activity of TLR ligands will be necessary to develop them into clinical useful drugs.

Serum cytokine levels in patients with chronic hepatitis B according to lamivudine therapy

BACKGROUND

Cytokines are known to play critical roles in the pathogenesis of chronic hepatitis B (CHB). However, the relationship between cytokines and treatment responses to drugs for CHB is not clearly defined yet. We measured the serum cytokine levels of interleukin (IL)-1α, IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, vascular endothelial growth factor, interferon-γ, tumor necrosis factor- (TNF-α), macrophage/monocyte chemotactic protein 1, and epidermal growth factor to elucidate the cytokine expression pattern according to the patients' responses to lamivudine.

METHODS

Fifty-eight specimens from 27 CHB patients and 98 specimens from healthy individuals were tested for 12 kinds of cytokines. The patients were grouped as: before treatment, ongoing treatment, duringmaintaining remission, and patients with viral breakthrough owing to resistance against lamivudine. The Evidence Investigator (Randox, Antrim, UK), a protein chip analyzer, was used to quantify serum cytokines.

RESULTS

Among 12 cytokines, IL-6, IL-8, IL-10, and TNF-α were significantly elevated in patients with resistance against lamivudine compared with patients maintaining response. IL-8, IL-10, and TNF-α levels also weak to moderate correlated with ALT and HBV-DNA concentrations.

CONCLUSIONS

Serum cytokine levels would reflect the pathological differences of the individual treatment phases and may become useful indices in monitoring the treatment response of CHB.

A new class of synthetic peptide inhibitors blocks attachment and entry of human pathogenic viruses

Many enveloped viruses, including herpes viruses, hepatitis B virus (HBV), and hepatitis C virus (HCV), and human immunodeficiency virus (HIV), are among the most important human pathogens and are often responsible for coinfections involving ≥2 types of viruses. However, therapies that are effective against multiple virus classes are rare. Here we present a new class of synthetic anti-lipopolysaccharide peptides (SALPs) that bind to heparan sulfate moieties on the cell surface and inhibit infection with a variety of enveloped viruses. We demonstrate that SALPs inhibit entry of human immunodeficiency virus type 1 (HIV-1), herpes simplex virus (HSV) 1 and 2, HBV, and HCV to their respective host cells. Despite their high antiviral efficiency, SALPs were well tolerated, and neither toxicity nor measurable inhibitor-induced adverse effects were observed. Since these broad-spectrum antiviral peptides target a host cell rather than a viral component, they may also be useful for suppression of viruses that are resistant to antiviral drugs.

Relevance of interleukin-10RB to chronic hepatitis B virus infection and biological activities of interferon-λ and interleukin-22

Purpose

The association of a single nucleotide polymorphism of interleukin (IL)-10RB codon 47 with the chronic hepatitis B virus (HBV) infection has been reported in two ethnic populations with different results, but not in a Korean population. IL-10RB is a subunit of receptor complexes for interferon-lambda (IFN-λ) and IL-22, which have antiviral and hepatocyte-protective activity, respectively. This study examined the association of IL-10RB K47E with the outcomes of HBV infection in Korean subjects and the cellular response to these cytokines.

Methods

Genotypes of IL-10RB and the outcomes of HBV infection were analyzed in 1,000 Korean patients. The effect of IFN-λ or IL-22 on HBV replication and cell viability was assessed in hepatoma cells expressing IL-10RB K47 or E47. The transcript level of IL-10RB was examined in Epstein Barr virus-transformed B cells and hepatoma cells.

Results

IL-10RB K47E was associated with chronic HBV infection but not with hepatoma in the Korean population. IL-10RB K47E was associated with the transcript level of IL-10RB in transformed B cells but not with the responses in hepatoma cells to IFN-λ or IL-22. HBV replication or 5-fluorouracil-induced cell death was suppressed by treatment of IFN-λ or IL-22 in an IL-10RB K47E-independent manner.

Conclusions

IL-10RB K47E is related to chronic HBV infection in a Korean population, but not to cellular responsiveness to IFN-λ and IL-22.

Electronic supplementary material

The online version of this article (doi:10.1007/s12072-012-9361-8) contains supplementary material, which is available to authorized users.

Living in the liver: hepatic infections

The liver has vital metabolic and clearance functions that involve the uptake of nutrients, waste products and pathogens from the blood. In addition, its unique immunoregulatory functions mediated by local expression of co-inhibitory receptors and immunosuppressive mediators help to prevent inadvertent organ damage. However, these tolerogenic properties render the liver an attractive target site for pathogens. Although most pathogens that reach the liver via the blood are eliminated or controlled by local innate and adaptive immune responses, some pathogens (such as hepatitis viruses) can escape immune control and persist in hepatocytes, causing substantial morbidity and mortality worldwide. Here, we review our current knowledge of the mechanisms of liver targeting by pathogens and describe the interplay between pathogens and host factors that promote pathogen elimination and maintain organ integrity or that allow pathogen persistence.

Transforming growth factor-β1 suppresses hepatitis B virus replication by the reduction of hepatocyte nuclear factor-4α expression

Several studies have demonstrated that cytokine-mediated noncytopathic suppression of hepatitis B virus (HBV) replication may provide an alternative therapeutic strategy for the treatment of chronic hepatitis B infection. In our previous study, we showed that transforming growth factor-beta1 (TGF-β1) could effectively suppress HBV replication at physiological concentrations. Here, we provide more evidence that TGF-β1 specifically diminishes HBV core promoter activity, which subsequently results in a reduction in the level of viral pregenomic RNA (pgRNA), core protein (HBc), nucleocapsid, and consequently suppresses HBV replication. The hepatocyte nuclear factor 4alpha (HNF-4α) binding element(s) within the HBV core promoter region was characterized to be responsive for the inhibitory effect of TGF-β1 on HBV regulation. Furthermore, we found that TGF-β1 treatment significantly repressed HNF-4α expression at both mRNA and protein levels. We demonstrated that RNAi-mediated depletion of HNF-4α was sufficient to reduce HBc synthesis as TGF-β1 did. Prevention of HNF-4α degradation by treating with proteasome inhibitor MG132 also prevented the inhibitory effect of TGF-β1. Finally, we confirmed that HBV replication could be rescued by ectopic expression of HNF-4α in TGF-β1-treated cells. Our data clarify the mechanism by which TGF-β1 suppresses HBV replication, primarily through modulating the expression of HNF-4α gene.