Innate response to hepatitis B virus infection: observations challenging the concept of a stealth virus

Cell Culture Models for Hepatitis B and D Viruses Infection: Old Challenges, New Developments and Future Strategies

Chronic Hepatitis B and D Virus (HBV and HDV) co-infection is responsible for the most severe form of viral Hepatitis, the Hepatitis Delta. Despite an efficient vaccine against HBV, the HBV/HDV infection remains a global health burden. Notably, no efficient curative treatment exists against any of these viruses. While physiologically distinct, HBV and HDV life cycles are closely linked. HDV is a deficient virus that relies on HBV to fulfil is viral cycle. As a result, the cellular response to HDV also influences HBV replication. In vitro studying of HBV and HDV infection and co-infection rely on various cell culture models that differ greatly in terms of biological relevance and amenability to classical virology experiments. Here, we review the various cell culture models available to scientists to decipher HBV and HDV virology and host-pathogen interactions. We discuss their relevance and how they may help address the remaining questions, with one objective in mind: the development of new therapeutic approaches allowing viral clearance in patients.

Interferon and Hepatitis B: Current and Future Perspectives

Chronic hepatitis B virus (HBV) infection remains a major health burden worldwide for which there is still no effective curative treatment. Interferon (IFN) consists of a group of cytokines with antiviral activity and immunoregulatory and antitumor effects, that play crucial roles in both innate and adaptive immune responses. IFN-α and its pegylated form have been used for over thirty years to treat chronic hepatitis B (CHB) with advantages of finite treatment duration and sustained virologic response, however, the efficacy is limited and side effects are common. Here, we summarize the status and unique advantages of IFN therapy against CHB, review the mechanisms of IFN-α action and factors affecting IFN response, and discuss the possible improvement of IFN-based therapy and the rationale of combinations with other antiviral agents in seeking an HBV cure.

Acute-on-Chronic Liver Failure From Chronic-Hepatitis-B, Who Is the Behind Scenes

Acute-on-chronic liver failure (ACLF) is an acute syndrome accompanied with decompensation of cirrhosis, organ failure with high 28-day mortality rate. Systemic inflammation is the main feature of ACLF, and poor outcome is closely related with exacerbated systemic inflammatory responses. It is well known that severe systemic inflammation is an important event in chronic hepatitis B (CHB)-ACLF, which eventually leads to liver injury. However, the initial CHB-ACLF events are unclear; moreover, the effect of these events on host immunity as well as that of immune imbalance on CHB-ACLF progression are unknown. Here, we investigate the initial events of ACLF progression, discuss possible mechanisms underlying ACLF progression, and provide a new model for ACLF prediction and treatment. We review the characteristics of ACLF, and consider its plausible immune predictors and alternative treatment strategies.

Interaction analysis of IL-12A and IL-12B gene variants with chronic hepatitis B infection in Tunisian patients

Given the key role of interleukin-12 (IL-12) in the control of HBV, we investigated the possible correlation between IL-12A rs568408 and IL-12B rs3212227 polymorphisms and the risk of chronic HBV infection in Tunisian population. Two hundred patients with chronic HBV infection and two hundred healthy controls were genotyped using PCR-RFLP. A allele, AA and AG genotypes of IL-12A rs568408 were more represented in the chronic HBV infection group compared to the control group, and they were associated with 1.65-, 2.58- and 3.13-fold risks of developing this infection, respectively. Gene-gene interaction analysis showed that subjects carrying the IL-12A rs568408AA/AG and IL-12B rs3212227AA genotypes had a 3.16-fold increased risk of chronic HBV infection. This study suggested that IL-12A rs568408 and gene-gene interactions of IL-12A rs568408 and IL-12B rs3212227 contributed to the outcome of chronic HBV infection, meanwhile indicating their usefulness as a predictive and diagnostic biomarker of chronic HBV infection.

A Telomerase-Derived Peptide Exerts an Anti-Hepatitis B Virus Effect via Mitochondrial DNA Stress-Dependent Type I Interferon Production

Previously, a telomerase-derived 16-mer peptide, GV1001, developed as an anticancer vaccine, was reported to exert antiviral effects on human immunodeficiency virus or hepatitis C virus in a heat shock protein-dependent manner. Here we investigated whether GV1001 exerts antiviral effects on hepatitis B virus (HBV) and elucidated its underlying mechanisms. GV1001 inhibited HBV replication and hepatitis B surface antigen (HBsAg) secretion in a dose-dependent manner, showing synergistic antiviral effects with nucleos(t)ide analogs (NAs) including entecavir and lamivudine. This peptide also inhibited viral cccDNA and pgRNA. The intravenous GV1001 treatment of transgenic mice had anti-HBV effects. Our mechanistic studies revealed that GV1001 suppresses HBV replication by inhibiting capsid formation via type I interferon-mediated induction of heme oxygenase-1 (HO-1). GV1001 promoted the mitochondrial DNA stress-mediated release of oxidized DNA into the cytosol, resulting in IFN-I-dependent anti-HBV effects via the STING-IRF3 axis. We found that the anti-HBV effect of GV1001 was due to its ability to penetrate into the cytosol via extracellular heat shock protein, leading to phagosomal escape-mediated mtDNA stress. We demonstrated that the cell-penetrating and cytosolic localization capacity of GV1001 results in antiviral effects on HBV infections via mtDNA stress-mediated IFN-I production. Thus, GV1001, a peptide proven to be safe for human use, may be an anti-HBV drug that can be synergistically used with nucleot(s)ide analog.

Immune network for viral hepatitis B: Topological representation

The liver is a well-known immunotolerogenic environment, which provides the adequate setting for liver infectious pathogens persistence such as the hepatitis B virus (HBV). Consequently, HBV infection can derive in the development of chronic disease in a proportion of the patients. If this situation persists in time, chronic hepatitis B (CHB) would end in cirrhosis, hepatocellular carcinoma and eventually, the death of the patient. It is thought that this immunotolerogenic environment is the result of complex interactions between different elements of the immune system and the viral biology. Therefore, the purpose of this work is to unravel the mechanisms implied in the development of CHB and to design a tool able to help in the study of adequate therapies. Firstly, a conceptual framework with the main components of the immune system and viral dynamics was constructed providing an overall insight on the pathways and interactions implied in this disease. Secondly, a review of the literature was performed in a modular fashion: (i) viral dynamics, (ii) innate immune response, (iii) humoral and (iv) cellular adaptive immune responses and (v) tolerogenic aspects. Finally, the information collected was integrated into a single topological representation that could serve as the plan for the systems pharmacology model architecture. This representation can be considered as the previous unavoidable step to the construction of a quantitative model that could assist in biomarker and target identification, drug design and development, dosing optimization and disease progression analysis.

Toward Curative Immunomodulation Strategies for Chronic Hepatitis B Virus Infection

Chronic hepatitis B virus (HBV) infection remains a major cause of morbidity and mortality worldwide. HBV surface antigen loss is considered a functional cure and is an ideal goal for antiviral therapy. However, current treatment regimens, including nucleos(t)ide analogues or interferons monotherapy and combination therapy, rarely achieve this goal in chronic hepatitis B patients. Nucleos(t)ide analogues (NAs), as well as many direct antiviral drugs in ongoing development, are able to inhibit HBV replication and gene expression, but it is hard to achieve immune control and prevent recurrence after therapy cessation. Host immunity, especially HBV-specific T cell response, is proven to play a critical role in control or clearance of HBV infection. Considering HBV chronically infected patients display varying degrees of dysfunction regarding their immune system, novel approaches to enhancing antiviral immune responses are necessary in order to combine with current antiviral agents. In this Review, we focus on the role of innate and adaptive immune responses in HBV immunopathogenesis and discuss attractive strategies or drugs that aim to activate or rebuild antiviral immunity to achieve the goal of an HBV functional cure.

Hepatitis B e Antigen Inhibits NF-κB Activity by Interrupting K63-Linked Ubiquitination of NEMO

Viruses have adopted diverse strategies to suppress antiviral responses. Hepatitis B virus (HBV), a virus that is prevalent worldwide, manipulates the host's innate immune system to evade scavenging. It is reported that the hepatitis B e antigen (HBeAg) can interfere with NF-κB activity, which then leads to high viral loads, while HBV with the G1896A mutation remains infectious without the production of HBeAg but can induce more severe proinflammatory response and liver damage. The aim of current work was to study the molecular mechanism by which HBeAg suppresses interleukin-1β (IL-1β)-stimulated NF-κB activity, which leads to the suppression of the innate immune responses to HBV infection. Our study revealed that HBeAg could interact with NEMO, a regulatory subunit associated with IκB kinase, which regulates the activation of NF-κB. HBeAg suppressed the IL-1β-induced tumor necrosis factor (TNF)-associated factor 6 (TRAF6)-dependent K63-linked ubiquitination of NEMO, thereby downregulating NF-κB activity and promoting virus replication. We further demonstrated the inhibitory effect of HBeAg on the NF-κB signaling pathway using primary human hepatocytes, HBV-infected HepG2-NTCP cells, and clinical liver samples. Our study reveals a molecular mechanism whereby HBeAg suppresses IL-1β-induced NF-κB activation by decreasing the TRAF6-dependent K63-linked ubiquitination of NEMO, which may thereby enhance HBV replication and promote a persistent infection.IMPORTANCE The role of HBeAg in inflammatory responses during the infection of hepatitis B virus (HBV) is not fully understood, and several previous reports with regard to the NF-κB pathway are controversial. In this study, we showed that HBeAg could suppress both Toll-like receptor 2 (TLR2)- and IL-1β-induced activation of NF-κB in cells and clinical samples, and we further revealed novel molecular mechanisms. We found that HBeAg can associate with NEMO, the regulatory subunit for IκB kinase (IKK) that controls the NF-κB signaling pathway, and thereby inhibits TRAF6-mediated K63-linked ubiquitination of NEMO, resulting in downregulation of NF-κB activity and promotion of virus replication. In contrast, the HBeAg-negative HBV mutant can induce higher levels of NF-κB activity. These results are important for understanding the HBV-induced pathogenesis of chronic hepatitis and indicate that different clinical measures should be considered to treat HBeAg-positive and HBeAg-negative infections. Our findings represent a conceptual advance in HBV-related suppression of NF-κB signaling.

Natural killer cell activation contributes to hepatitis B viral control in a mouse model

The roles of CD4 + T cells and CD8 + T cells in hepatitis B virus (HBV) infection have been well documented. However, the role of innate immunity in HBV infection remains obscure. Here we examined the effect of activation of innate immunity by polyinosinic: polycytidylic acid (PolyI:C) on HBV infection. A chronic HBV replication mouse model was established by hydrodynamical injection of pAAV/HBV1.2 plasmid into C57BL/6 mice. We found that HBV did not seem to induce an active NK-cell response in the mouse model. Early PolyI:C treatment markedly decreased serum HBV levels and led to HBV clearance. Following PolyI:C injection, NK cells were activated and accumulated in the liver. Depletion of NK cells markedly attenuated the anti-HBV activity of PolyI:C. Moreover, we found that IFN-γ production from NK cells was essential for the antiviral effect of PolyI:C in the model. Importantly, activation of NK cells by PolyI:C could also lead to HBV suppression in HBV-tolerant mice and HBV-transgenic mice. These results suggest that activated NK cells might suppress HBV and contribute to HBV clearance during natural HBV infection. In addition, therapeutic activation of NK cells may represent a new strategy for the treatment of chronic HBV infection.

The Smc5/6 Complex Restricts HBV when Localized to ND10 without Inducing an Innate Immune Response and Is Counteracted by the HBV X Protein Shortly after Infection

The structural maintenance of chromosome 5/6 complex (Smc5/6) is a restriction factor that represses hepatitis B virus (HBV) transcription. HBV counters this restriction by expressing HBV X protein (HBx), which targets Smc5/6 for degradation. However, the mechanism by which Smc5/6 suppresses HBV transcription and how HBx is initially expressed is not known. In this study we characterized viral kinetics and the host response during HBV infection of primary human hepatocytes (PHH) to address these unresolved questions. We determined that Smc5/6 localizes with Nuclear Domain 10 (ND10) in PHH. Co-localization has functional implications since depletion of ND10 structural components alters the nuclear distribution of Smc6 and induces HBV gene expression in the absence of HBx. We also found that HBV infection and replication does not induce a prominent global host transcriptional response in PHH, either shortly after infection when Smc5/6 is present, or at later times post-infection when Smc5/6 has been degraded. Notably, HBV and an HBx-negative virus establish high level infection in PHH without inducing expression of interferon-stimulated genes or production of interferons or other cytokines. Our study also revealed that Smc5/6 is degraded in the majority of infected PHH by the time cccDNA transcription could be detected and that HBx RNA is present in cell culture-derived virus preparations as well as HBV patient plasma. Collectively, these data indicate that Smc5/6 is an intrinsic antiviral restriction factor that suppresses HBV transcription when localized to ND10 without inducing a detectable innate immune response. Our data also suggest that HBx protein may be initially expressed by delivery of extracellular HBx RNA into HBV-infected cells.

Advances and Challenges in Studying Hepatitis B Virus In Vitro

Hepatitis B virus (HBV) is a small DNA virus that infects the liver. Current anti-HBV drugs efficiently suppress viral replication but do not eradicate the virus due to the persistence of its episomal DNA. Efforts to develop reliable in vitro systems to model HBV infection, an imperative tool for studying HBV biology and its interactions with the host, have been hampered by major limitations at the level of the virus, the host and infection readouts. This review summarizes major milestones in the development of in vitro systems to study HBV. Recent advances in our understanding of HBV biology, such as the discovery of the bile-acid pump sodium-taurocholate cotransporting polypeptide (NTCP) as a receptor for HBV, enabled the establishment of NTCP expressing hepatoma cell lines permissive for HBV infection. Furthermore, advanced tissue engineering techniques facilitate now the establishment of HBV infection systems based on primary human hepatocytes that maintain their phenotype and permissiveness for infection over time. The ability to differentiate inducible pluripotent stem cells into hepatocyte-like cells opens the door for studying HBV in a more isogenic background, as well. Thus, the recent advances in in vitro models for HBV infection holds promise for a better understanding of virus-host interactions and for future development of more definitive anti-viral drugs.

Re-evaluation of hepatitis B virus clinical phases by systems biology identifies unappreciated roles for the innate immune response and B cells

To identify immunological mechanisms that govern distinct clinical phases of a chronic hepatitis B virus (HBV) infection-immune tolerant (IT), immune active (IA), inactive carrier (IC), and hepatitis B e antigen (HBeAg)-negative (ENEG) hepatitis phases-we performed a systems biology study. Serum samples from untreated chronic HBV patients (n = 71) were used for multiplex cytokine measurements, quantitative hepatitis B surface antigen (HBsAg), HBeAg levels, HBV genotype, and mutant analysis. Leukocytes were phenotyped using multicolor flow cytometry, and whole-blood transcriptome profiles were generated. The latter were compared with liver biopsy transcriptomes from IA (n = 16) and IT (n = 3) patients. HBV viral load as well as HBeAg and HBsAg levels (P < 0.001), but not leukocyte composition, differed significantly between distinct phases. Serum macrophage chemotactic protein 1, interleukin-12p40, interferon (IFN)-gamma-inducible protein 10, and macrophage inflammatory protein 1 beta levels were different between two or more clinical phases (P < 0.05). Comparison of blood transcriptomes identified 64 differentially expressed genes. The gene signature distinguishing IA from IT and IC patients was predominantly composed of highly up-regulated immunoglobulin-encoding genes. Modular repertoire analysis using gene sets clustered according to similar expression patterns corroborated the abundant expression of B-cell function-related genes in IA patients and pointed toward increased (ISG) transcript levels in IT patients, compared to subsequent phases. Natural killer cell activities were clustered in clinical phases with biochemical liver damage (IA and ENEG phases), whereas T-cell activities were higher in all phases, compared to IT patients. B-cell-related transcripts proved to be higher in biopsies from IA versus IT patients.

CONCLUSION

HBV clinical phases are characterized by distinct blood gene signatures. Innate IFN and B-cell responses are highly active during the IT and IA phases, respectively. This suggests that the presumed immune tolerance in chronic HBV infections needs to be redefined.

Immune Response in Hepatitis B Virus Infection

Hepatitis B virus (HBV) can replicate within hepatocytes without causing direct cell damage. The host immune response is, therefore, not only essential to control the spread of virus infection, but it is also responsible for the inflammatory events causing liver pathologies. In this review, we discuss how HBV deals with host immunity and how we can harness it to achieve virus control and suppress liver damage.

Tumor necrosis factor-alpha blockage therapy impairs hepatitis B viral clearance and enhances T-cell exhaustion in a mouse model

Hepatitis B virus (HBV) reactivation and recurrence are common in patients undergoing immunosuppression therapy. Tumor necrosis factor (TNF) blockage therapy is effective for the treatment of many autoimmune inflammatory diseases. However, the role of TNF-α blockage therapy in the innate and adaptive immune responses against HBV is still not clear. A detailed analysis of HBV infection under TNF-α blockage therapy is essential for the prophylaxis and therapy for HBV reactivation and recurrence. In this study, HBV clearance and T-cell responses were analyzed in a HBV-transfected mouse model under anti-TNF blockage therapy. Our results demonstrated that under TNF-α blockage therapy, HBV viral clearance was impaired with persistent elevated HBV viral load in a dose- and temporal-dependent manner. The impairment of HBV clearance under anti-TNF-α blockage therapy occurred at early time points after HBV infection. In addition, TNF-α blockade maintained a higher serum HBV viral load and increased the number of intrahepatic programmed cell death (PD)-1(high)CD127(low) exhausted T cells. Furthermore, TNF-α blockade abolished Toll-like receptor 9 (TLR9) ligand-induced facilitation of HBV viral clearance. Taken together, TNF-α blockade impairs HBV clearance and enhances viral load, and these effects depend on early administration after HBV infection. Our results here demonstrate that early TNF-α blockade reduces viral clearance and persistently maintains elevated HBV viral load in a mouse model, suggesting that HBV may reactivate during therapy with TNF-α-blocking agents.

Modeling host interactions with hepatitis B virus using primary and induced pluripotent stem cell-derived hepatocellular systems

Hepatitis B virus (HBV) chronically infects 400 million people worldwide and is a leading driver of end-stage liver disease and liver cancer. Research into the biology and treatment of HBV requires an in vitro cell-culture system that supports the infection of human hepatocytes, and accurately recapitulates virus-host interactions. Here, we report that micropatterned cocultures of primary human hepatocytes with stromal cells (MPCCs) reliably support productive HBV infection, and infection can be enhanced by blocking elements of the hepatocyte innate immune response associated with the induction of IFN-stimulated genes. MPCCs maintain prolonged, productive infection and represent a facile platform for studying virus-host interactions and for developing antiviral interventions. Hepatocytes obtained from different human donors vary dramatically in their permissiveness to HBV infection, suggesting that factors--such as divergence in genetic susceptibility to infection--may influence infection in vitro. To establish a complementary, renewable system on an isogenic background in which candidate genetics can be interrogated, we show that inducible pluripotent stem cells differentiated into hepatocyte-like cells (iHeps) support HBV infection that can also be enhanced by blocking interferon-stimulated gene induction. Notably, the emergence of the capacity to support HBV transcriptional activity and initial permissiveness for infection are marked by distinct stages of iHep differentiation, suggesting that infection of iHeps can be used both to study HBV, and conversely to assess the degree of iHep differentiation. Our work demonstrates the utility of these infectious systems for studying HBV biology and the virus' interactions with host hepatocyte genetics and physiology.

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.

Are novel combination therapies needed for chronic hepatitis B?

The treatment of chronic hepatitis B remains limited to monotherapy with pegInterferon-alpha or one of 5 different nucleoside analogues (NUC). While viral suppression can be achieved in approximately 95% of patients with new-generation NUCs, the rate of HBeAg seroconversion ranges from only 20% with NUCs to 30% with pegInterferon-alpha. HBsAg loss is achieved in only 10% of patients with both classes of drugs after a follow-up of 5years. Attempts to improve the response by administering two different NUCs or a combination of NUC and pegInterferon-alpha have been unsuccessful. This situation has led researchers to investigate a number of steps in the HBV replication cycle as potential targets for new antiviral drugs. Novel targets and compounds could readily be evaluated in in vitro and in vivo models of HBV infection. The addition of one or more new drugs to the current regimen should offer the prospect of markedly improving the response to therapy, reducing the future burden of drug resistance, cirrhosis and hepatocellular carcinoma.

RANTES gene polymorphisms (-403G>A and -28C>G) associated with hepatitis B virus infection in a Saudi population

Besides the host immune response, genetic and environmental factors play crucial roles in the manifestation of hepatitis B virus (HBV) infection. "Regulated on activation normal T-cell expressed and secreted" factor (RANTES) plays a vital role in CD4(+), CD8(+) T-lymphocyte and dendritic cell activation and proliferation in inflammation. Single nucleotide polymorphisms (SNPs) in the RANTES gene are associated with several viral and non-viral diseases. Association studies have invariably indicated a lack of association between RANTES gene SNPs and HBV infection in ethnic populations, even though RANTES gene SNPs exhibit distinct ethnic distributions. Despite the high prevalence of HBV infections in Saudi Arabia, no studies have been made concerning a possible relationship between RANTES gene polymorphisms and susceptibility to and progression of HBV infection. We examined -403G>A and -28C>G RANTES gene variants in 473 healthy controls and 484 HBV patients in ethnic Saudi populations. Significant differences were found in the genotype and allele distributions of the SNPs between the controls and the HBV patients. Both SNPs were significantly linked to viral clearance in these subjects. Our data demonstrate for the first time in a Saudi population, a relationship between the RANTES gene polymorphisms and the clinical course of HBV infection and underscore the importance of evaluating the genetic background of the affected individual to determine how it may affect disease progression.

The hepatitis B e antigen (HBeAg) targets and suppresses activation of the toll-like receptor signaling pathway

BACKGROUND & AIMS

Viruses target innate immune pathways to evade host antiviral responses. Recent studies demonstrate a relationship between hepatitis B disease states and the host's innate immune response, although the mechanism of immunomodulation is unknown. In humans, the innate immune system recognizes pathogens via pattern recognition receptors such as the Toll-like receptors (TLR), initiating anti-inflammatory responses. TLR expression and pro-inflammatory cytokine production is reduced in hepatitis B e antigen (HBeAg)-positive patients following TLR stimulation. The aim of this study was to investigate interactions between TLR signaling pathways and the mature HBeAg protein localized in the cytosol.

METHODS

The ability of HBeAg to inhibit TLR signaling and association with TLR adapters was evaluated by immunoprecipitation, immunostaining, and reporter studies.

RESULTS

Our findings show that HBeAg co-localizes with Toll/IL-1 receptor (TIR)-containing proteins TRAM, Mal, and TLR2 at the sub-cellular level, which was not observed for Hepatitis B core antigen. Co-immunoprecipitation analysis demonstrated HBeAg interacted with TIR proteins Mal and TRAM, while a mutated HBeAg ablated interaction between Mal and MyD88. Importantly, HBeAg also disrupted homotypic TIR:TIR interaction critical for TLR-mediated signaling. Finally, HBeAg suppressed TIR-mediated activation of the inflammatory transcription factors, NF-κB and Interferon-β promoter activity.

CONCLUSIONS

Our study provides the first molecular mechanism describing HBeAg immunomodulation of innate immune signal transduction pathways via interaction and targeting of TLR-mediated signaling pathways. These finding suggest the mechanism as to how HBeAg evades innate immune responses contributing to the pathogenesis of chronic hepatitis B infection and the establishment of viral persistence.

Evidence for reduced selection pressure on the hepatitis B virus core gene in hepatitis B e antigen-negative chronic hepatitis B

The mechanisms underlying the high levels of hepatitis B virus (HBV) replication that cause hepatitis B e antigen (HBeAg)-negative chronic hepatitis B (e−CHB) are unknown. Impaired anti-HBV immunity, which may be measurable as a relaxation of selection pressure on the virus, is possible. A group of Tongans (n = 345) with a chronic HBV infection, including seven with e−CHB, were genotyped at HLA class I. The repertoire of HBV core-gene codons under positive selection pressure was defined by phylogenetic analysis (by using the paml program) of 708 cloned sequences extracted from the 67 of these 345 subjects with the same repertoire of HLA class I alleles as the seven e−CHB individuals and matched controls (see below). The frequency of non-synonymous mutations at these codons was measured in longitudinal data from 15 subjects. Finally, the number of non-synonymous mutations at these codons was compared in seven groups comprised of one subject with e−CHB and 1–3 HLA class I-matched controls with an inactive, HBeAg-negative chronic HBV infection (e−InD). Nineteen codons in the core gene were under positive selection pressure. There was a high frequency of new non-synonymous mutations at these codons (P<0.0001) in longitudinal data. The mean number of these 19 codons with non-synonymous mutations was lower (P = 0.02) in HBV from subjects with e−CHB (4.4±0.5 codons per subject) versus those with e−InD (6.4±0.4 codons per subject). There is a subtle relaxation in selection pressure on the HBV core gene in e−CHB. This may be due to impaired antiviral immunity, and could contribute to the high levels of viral replication that cause liver inflammation in this disease.

Role of the propeptide in controlling conformation and assembly state of hepatitis B virus e-antigen

Hepatitis B virus "e-antigen" (HBeAg) is thought to be a soluble dimeric protein that is associated with chronic infection. It shares 149 residues with the viral capsid protein "core-antigen" (HBcAg), but has an additional 10-residue, hydrophobic, cysteine-containing amino-terminal propeptide whose presence correlates with physical, serological, and immunological differences between the two proteins. In HBcAg dimers, the subunits pair by forming a four-helix bundle stabilized by an intermolecular disulfide bond. The structure of HBeAg is probably similar but, instead, has two intramolecular disulfide bonds involving the propeptide. To compare the proteins directly and thereby clarify the role of the propeptide, we identified mutations and solution conditions that render both proteins as either soluble dimers or assembled capsids. Thermally induced unfolding monitored by circular dichroism, and electrophoresis of oxidized and reduced dimers, showed that the propeptide has a destabilizing effect and that the intramolecular disulfide bond forms preferentially and blocks the formation of the intermolecular disulfide bond that otherwise stabilizes the dimer. The HBeAg capsids are less regular than the HBcAg capsids; nevertheless, cryo-electron microscopy reconstructions confirm that they are constructed of dimers resembling those of HBcAg capsids. In them, a portion of the propeptide is visible near the dimer interface, suggesting that it intercalates there, consistent with the known formation of a disulfide bond between C(-7) in the propeptide and C61 in the dimer interface. However, this intercalation distorts the dimer into an assembly-reluctant conformation.

The host-pathogen interaction during HBV infection: immunological controversies

HBV is a hepatotropic and non-cytopathic virus that causes more than one million deaths annually from liver cirrhosis and hepatocellular carcinoma. As the virus itself is non-cytopathic, it is widely accepted that both viral control and liver pathology are mediated by the host immune system. Until recently, the focus has been on the crucial role of adaptive immune responses in controlling HBV infection, but the potential contribution of the innate system is now an important area of controversy. Unanswered questions include whether and when HBV can trigger components of innate immunity, and whether HBV can actively suppress the induction of innate immunity. We discuss the data available from animal models and human HBV infection addressing the role of innate immunity in the first part of this review. In the second part, we address the immunopathogenesis of the inflammatory events that characterize chronic hepatitis B. The mechanisms thought to be responsible for liver inflammation, namely the intrahepatic recruitment of inflammatory cells, which is orchestrated by chemokines, have been described; however, the underlying immunological triggers are much less clear. The prevailing idea is that liver inflammation results from a recovery of HBV-specific T-cells directly causing liver injury, but this scenario is supported by scanty experimental data. By contrast, recent findings raise the possibility of a contribution from innate components, such as natural killer cells.

Hepatitis B immunology for clinicians

Hepatitis B virus (HBV) is a hepatotrophic DNA virus that causes acute and chronic hepatitis. Despite an effective vaccine, more than 350 million people are chronically infected with HBV worldwide and are at risk for progressive liver disease. There are marked geographic variations in HBV prevalence (ranging from 0.1% to 2% in low prevalence areas and 10% to 20% in high prevalence areas) related to the timing and mode of HBV exposure. In many developed countries, HBV exposure typically occurs in adults via sexual transmission with a low chronicity rate (5%). In regions with high HBV prevalence (eg, Asia, sub-Saharan Africa), HBV exposure tends to occur in the perinatal period (eg, vertical transmission from mother to infant) with a high rate of persistence in the absence of timely vaccination. The course of viral infection is defined by the interplay between the virus and host immune defense. This article introduces the innate and adaptive immune defense mechanisms in general and as related to HBV. In particular, the current concepts regarding the innate and adaptive immune components contributing to the clinical, virologic and therapeutic outcome in acute and chronic hepatitis B are examined.