Early kinetics of innate and adaptive immune responses during hepatitis B virus infection

Different antiviral effects of IFNα subtypes in a mouse model of HBV infection

Interferon alpha (IFNα) is commonly used for the treatment of chronic hepatitis B (CHB) patients. There are 13 different IFNα subtypes in humans, but only the subtype IFNα2 is used for clinical treatment. The antiviral activities of all other IFNα subtypes against HBV have not been studied. To obtain basic knowledge about the direct antiviral as well as the immunomodulatory effects of IFNα subtypes, we used the HBV hydrodynamic injection (HI) mouse model. Application of most IFNα subtype proteins inhibited HBV replication in vivo, with IFNα4 and IFNα5 being the most effective subtypes. Decreased viral loads after therapeutic application of IFNα4 and IFNα5 correlated with expanded effector cell populations of NK cells and T cells in both liver and spleen. Hydrodynamic injection of plasmids encoding for the effective IFNα subtypes (pIFNα) was even more potent against HBV than injecting IFNα proteins. The combination of pIFNα4 and pIFNα5 showed a synergistic antiviral effect on HBV replication, with a strong increase in NK cell and T cell activity. The results demonstrate distinct anti-HBV effects of different IFNα subtypes against HBV in the mouse model, which may be relevant for new therapeutic approaches.

Predictive value of serum ALT and T-cell receptor beta variable chain for HBeAg seroconversion in chronic hepatitis B patients during tenofovir treatment

Effective antiviral therapy plays a key role in slowing the progression of chronic hepatitis B (CHB). Identification of serum indices, including hepatitis B e antigen (HBeAg) expression and seroconversion, will facilitate evaluation of the efficacy of antiviral therapy in HBeAg-positive CHB patients. The biochemical, serological, virological parameters, and the frequency of circulating CD4CD25 regulatory T cell (Treg) in 32 patients were measured at baseline and every 12 weeks during 96 weeks of tenofovir disoproxil fumarate (TDF) treatment. The relationship between the hepatitis B virus (HBV) deoxyribonucleic acid (DNA) and Treg and alanine aminotransferase (ALT) levels was analyzed, respectively. The molecular profiles of T-cell receptor beta variable chain (TRBV) were determined using gene melting spectral pattern. For the seroconverted 12 patients, ALT declined to normal levels by week 24 and remained at this level in subsequent treatment; moreover, the predictive cutoff value of ALT for HBeAg seroconversion (SC) was 41.5 U/L at week 24. The positive correlation between HBV DNA and Treg and ALT was significant in SC patients, but not in non-SC patients. Six TRBV families (BV3, BV11, BV12, BV14, BV20, and BV24) were predominantly expressed in SC patients at baseline. The decline of ALT could be used to predict HBeAg seroconversion for CHB patients during TDF treatment. In addition, the profile of Tregs and TRBVs may be associated with HBeAg seroconversion and could also be a potential indicator for predicting HBeAg SC and treatment outcome for CHB patients.

KIR : HLA association with clinical manifestations of HBV infection in Madurai, south India

The antiviral action of natural killer (NK) cells is regulated by a wide repertoire of germ-line encoded membrane receptors which recognize the expression of certain self-molecules on target cells. Among the receptors, killer cell immunoglobulinlike receptor (KIR) which recognizes the expression of human leukocyte antigen (HLA) class I has a predominant role in regulating the effector functions of NK cells, particularly in viral infections.We studied a total of 128 hepatitis B virus (HBV) patients (15 acute, 43 asymptomatic, 27 chronic and 43 with other liver diseases) while attending the Department of Medical Gastroenterology, Government Rajaji Hospital, Madurai, India, and 128 ethnic matched control to find the association between the KIR : HLA genes and differential manifestations of HBV. KIR and its ligand HLA polymorphism were identified by DNAPCR methods. The activatory receptor KIR-2DS1 was significantly elevated in various disease categories, namely asymptomatic, chronic and other HBV, except acute HBV infection. Whereas, KIR 2DS3 in acute and chronic patients and KIR 2DS5 and 3DS1 in asymptomatic individuals. Among various KIR-HLA combinations, homozygous 2DS2:C1 and individuals with 3DSI:BW4 (OR = 3.23, CI = 1.55-6.7, Pc = 0.02) are associated with HBV asymptomatism, while most of the two domain inhibitory receptors with their ligands showed significant risk in other liver diseases. Further, KIR3DL1 : HLA Bw4Iso80 (OR = 3.89, 95% CI = 1.58-9.55, Pc = 0.004) is related with higher risk for asymptomatic infection when compared with chronic HBV. Thus, the select KIR : HLA alleles and combinations seem to direct the NK cell activities and immune response in different directions resulting in varied symptoms and manifestations in the subgroups of HBV-infected patients studied.

The role of liver sinusoidal cells in local hepatic immune surveillance

Although the liver's function as unique immune organ regulating immunity has received a lot of attention over the last years, the mechanisms determining hepatic immune surveillance against infected hepatocytes remain less well defined. Liver sinusoidal cells, in particular, liver sinusoidal endothelial cells (LSECs) and Kupffer cells (KCs), serve as physical platform for recruitment and anchoring of blood-borne immune cells in the liver. Liver sinusoidal cells also function as portal of entry for infectious microorganisms targeting the liver such as hepatotropic viruses, bacteria or parasites. At the same time, liver sinusoidal cells actively contribute to achieve immune surveillance against bacterial and viral infections. KCs function as adhesion hubs for CD8 T cells from the circulation, which initiates the interaction of virus-specific CD8 T cells with infected hepatocytes. Through their phagocytic function, KCs contribute to removal of bacteria from the circulation and engage in cross talk with sinusoidal lymphocyte populations to achieve elimination of phagocytosed bacteria. LSECs contribute to local immune surveillance through cross-presentation of viral antigens that causes antigen-specific retention of CD8 T cells from the circulation. Such cross-presentation of viral antigens activates CD8 T cells to release TNF that in turn triggers selective killing of virus-infected hepatocytes. Beyond major histocompatibility complex (MHC)-restricted T-cell immunity, CD1- and MR1-restricted innate-like lymphocytes are found in liver sinusoids whose roles in local immune surveillance against infection need to be defined. Thus, liver sinusoidal cell populations bear key functions for hepatic recruitment and for local activation of immune cells, which are both required for efficient immune surveillance against infection in the liver.

Hepitopes: A live interactive database of HLA class I epitopes in hepatitis B virus

Increased clinical and scientific scrutiny is being applied to hepatitis B virus (HBV), with focus on the development of new therapeutic approaches, ultimately aiming for cure. Defining the optimum natural CD8+ T cell immune responses that arise in HBV, mediated by HLA class I epitope presentation, may help to inform novel immunotherapeutic strategies. Therefore, we have set out to develop a comprehensive database of these epitopes in HBV, coined ‘Hepitopes’. This undertaking has its foundations in a systematic literature review to identify the sites and sequences of all published class I epitopes in HBV. We also collected information regarding the methods used to define each epitope, and any reported associations between an immune response to this epitope and disease outcome. The results of this search have been collated into a new open-access interactive database that is available at http://www.expmedndm.ox.ac.uk/hepitopes. Over time, we will continue to refine and update this resource, as well as inviting contributions from others in the field to support its development. This unique new database is an important foundation for ongoing investigations into the nature and impact of the CD8+ T cell response to HBV.

Cytokine-Mediated Immunopathogenesis of Hepatitis B Virus Infections

Hepatitis B virus (HBV) infection is a worldwide health problem, with approximately one third of populations have been infected, among which 3-5% of adults and more than 90% of children developed to chronic HBV infection. Host immune factors play essential roles in the outcome of HBV infection. Thus, ineffective immune response against HBV may result in persistent virus replications and liver necroinflammations, then lead to chronic HBV infection, liver cirrhosis, and even hepatocellular carcinoma. Cytokine balance was shown to be an important immune characteristic in the development and progression of hepatitis B, as well as in an effective antiviral immunity. Large numbers of cytokines are not only involved in the initiation and regulation of immune responses but also contributing directly or indirectly to the inhibition of virus replication. Besides, cytokines initiate downstream signaling pathway activities by binding to specific receptors expressed on the target cells and play important roles in the responses against viral infections and, therefore, might affect susceptibility to HBV and/or the natural course of the infection. Since cytokines are the primary causes of inflammation and mediates liver injury after HBV infection, we have discussed recent advances on the roles of various cytokines [including T helper type 1 cells (Th1), Th2, Th17, regulatory T cells (Treg)-related cytokines] in different phases of HBV infection and cytokine-related mechanisms for impaired viral control and liver damage during HBV infection. We then focus on experimental therapeutic applications of cytokines to gain a better understanding of this newly emerging aspect of disease pathogenesis.

Evolution in Our Understanding of Hepatitis B Virus Virology and Immunology

Hepatitis B virus (HBV) infection is a major global health challenge. HBV can cause significant morbidity and mortality by establishing acute and chronic hepatitis. Approximately 250 million people worldwide are chronically infected, and more than 2 billion people have been exposed to HBV. Since the discovery of HBV, the advances in our understanding of HBV virology and immunology have translated into effective vaccines and therapies for HBV infection. Although current therapies successfully suppress viral replication but rarely succeed in viral eradication, recent discoveries in HBV virology and immunology provide exciting rationales for novel treatment strategies aiming at HBV cure.

Chronic hepatitis B: immune pathogenesis and emerging immunotherapeutics

Hepatitis B virus (HBV) evades, subverts, activates and regulates host immune components, thereby impacting its natural history and disease pathogenesis. Recent advances in our understanding of immune interactions in chronic viral infection and tumor therapy are applicable to chronic hepatitis B (CHB). With recent successes of tumor immunotherapy, there is a renewed interest in exploring immunotherapeutics in achieving sustained and functional cure of chronic hepatitis B. In this review, we discuss aspects of host innate and adaptive immune regulatory and pathogenic responses relevant for HBV infection. We also highlight several immune modulatory approaches in clinical development to treat CHB.

Hepatitis B: progress in understanding chronicity, the innate immune response, and cccDNA protection

Hepatitis B virus (HBV) infection is a serious health threat around the world. Despite the availability of an effective hepatitis B vaccine, the number of HBV carriers is estimated to be as high as 240 million worldwide. Global mortality due to HBV-related liver diseases such as chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma (HCC) may be as high as 1 million deaths per year. HBV is transmitted via blood and body fluids, and is much more infectious than both human immunodeficiency virus (HIV) and hepatitis C virus. While HBV infection exhibits a variety of clinical presentations, even asymptomatic carriers can develop HCC without liver fibrosis. Current therapeutic options against HBV include pegylated interferon (Peg-IFN) and nucleos(t)ide reverse transcriptase inhibitors (NRTIs), with clinical studies showing a significant association between loss of HBV DNA and a decrease in cancer risk. However, the ultimate goal of HBV therapy is a complete cure of HBV-including the elimination of covalently closed circular DNA (cccDNA)-in order to further decrease the risk of developing HCC. The development of hepatitis B is associated with the host immune response to virus-infected hepatocytes, as HBV is understood to lack direct cytotoxicity. While HBV-specific CD8+ T cells are thus involved in hepatitis development, they also play an important role in eliminating HBV infection. Indeed, the innate immune response during the initial phase of HBV infection is essential to the induction of acquired immunity. However, the innate immune response to HBV infection, including the roles of specific immunocompetent cells and associated molecules, is not well understood. In this review, we focus on the current understanding of the mechanisms underlying hepatitis development by HBV infection. We also address the mechanisms by which HBV protects cccDNA.

Extracellular Vesicles Including Exosomes Regulate Innate Immune Responses to Hepatitis B Virus Infection

The innate immune system is essential for controlling viral infection. Hepatitis B virus (HBV) persistently infects human hepatocytes and causes hepatocellular carcinoma. However, the innate immune response to HBV infection in vivo remains unclear. Using a tree shrew animal model, we showed that HBV infection induced hepatic interferon (IFN)-γ expression during early infection. Our in vitro study demonstrated that hepatic NK cells produced IFN-γ in response to HBV only in the presence of hepatic F4/80⁺ cells. Moreover, extracellular vesicles (EVs) released from HBV-infected hepatocytes contained viral nucleic acids and induced NKG2D ligand expression in macrophages by stimulating MyD88, TICAM-1, and MAVS-dependent pathways. In addition, depletion of exosomes from EVs markedly reduced NKG2D ligand expression, suggesting the importance of exosomes for NK cell activation. In contrast, infection of hepatocytes with HBV increased immunoregulatory microRNA levels in EVs and exosomes, which were transferred to macrophages, thereby suppressing IL-12p35 mRNA expression in macrophages to counteract the host innate immune response. IFN-γ increased the hepatic expression of DDX60 and augmented the DDX60-dependent degradation of cytoplasmic HBV RNA. Our results elucidated the crucial role of exosomes in antiviral innate immune response against HBV.

Humanized mice efficiently engrafted with fetal hepatoblasts and syngeneic immune cells develop human monocytes and NK cells

BACKGROUND & AIMS

Human liver chimeric mice are useful models of human hepatitis virus infection, including hepatitis B and C virus infections. Independently, immunodeficient mice reconstituted with CD34(+) hematopoietic stem cells (HSC) derived from fetal liver reliably develop human T and B lymphocytes. Combining these systems has long been hampered by inefficient liver reconstitution of human fetal hepatoblasts. Our study aimed to enhance hepatoblast engraftment in order to create a mouse model with syngeneic human liver and immune cells.

METHODS

The effects of human oncostatin-M administration on fetal hepatoblast engraftment into immunodeficient fah(-/-) mice was tested. Mice were then transplanted with syngeneic human hepatoblasts and HSC after which human leukocyte chimerism and functionality were analyzed by flow cytometry, and mice were challenged with HBV.

RESULTS

Addition of human oncostatin-M enhanced human hepatoblast engraftment in immunodeficient fah(-/-) mice by 5-100 fold. In contrast to mice singly engrafted with HSC, which predominantly developed human T and B lymphocytes, mice co-transplanted with syngeneic hepatoblasts also contained physiological levels of human monocytes and natural killer cells. Upon infection with HBV, these mice displayed rapid and sustained viremia.

CONCLUSIONS

Our study provides a new mouse model with improved human fetal hepatoblast engraftment and an expanded human immune cell repertoire. With further improvements, this model may become useful for studying human immunity against viral hepatitis.

LAY SUMMARY

Important human pathogens such as hepatitis B virus, hepatitis C virus and human immunodeficiency virus only infect human cells which complicates the development of mouse models for the study of these pathogens. One way to make mice permissive for human pathogens is the transplantation of human cells into immune-compromised mice. For instance, the transplantation of human liver cells will allow the infection of these so-called "liver chimeric mice" with hepatitis B virus and hepatitis C virus. The co-transplantation of human immune cells into liver chimeric mice will further allow the study of human immune responses to hepatitis B virus or hepatitis C virus. However, for immunological studies it will be crucial that the transplanted human liver and immune cells are derived from the same human donor. In our study we describe the efficient engraftment of human fetal liver cells and immune cells derived from the same donor into mice. We show that liver co-engraftment resulted in an expanded human immune cell repertoire, including monocytes and natural killer cells in the liver. We further demonstrate that these mice could be infected with hepatitis B virus, which lead to an expansion of natural killer cells. In conclusion we have developed a new mouse model that could be useful to study human immune responses to human liver pathogens.

New horizon for radical cure of chronic hepatitis B virus infection

About 250 to 350 million people worldwide are chronically infected with hepatitis B virus (HBV), and about 700000 patients per year die of HBV-related cirrhosis or hepatocellular carcinoma (HCC). Several anti-viral agents, such as interferon and nucleos(t)ide analogues (NAs), have been used to treat this disease. NAs especially have been shown to strongly suppress HBV replication, slowing the progression to cirrhosis and the development of HCC. However, reactivation of HBV replication often occurs after cessation of treatment, because NAs alone cannot completely remove covalently-closed circular DNA (cccDNA), the template of HBV replication, from the nuclei of hepatocytes. Anti-HBV immune responses, in conjunction with interferon-γ and tumor necrosis factor-α, were found to eliminate cccDNA, but complete eradication of cccDNA by immune response alone is difficult, as shown in patients who recover from acute HBV infection but often show long-term persistence of small amounts of HBV-DNA in the blood. Several new drugs interfering with the life cycle of HBV in hepatocytes have been developed, with drugs targeting cccDNA theoretically the most effective for radical cure of chronic HBV infection. However, the safety of these drugs should be extensively examined before application to patients, and combinations of several approaches may be necessary for radical cure of chronic HBV infection.

Clonorchis sinensis Co-infection Could Affect the Disease State and Treatment Response of HBV Patients

Background

Clonorchis sinensis (C. sinensis) is considered to be an important parasitic zoonosis because it infects approximately 35 million people, while approximately 15 million were distributed in China. Hepatitis B virus (HBV) infection is a major public health issue. Two types of pathogens have the potential to cause human liver disease and eventually hepatocellular carcinoma. Concurrent infection with HBV and C. sinensis is often observed in some areas where C. sinensis is endemic. However, whether C. sinensis could impact HBV infection or vice versa remains unknown.

Principal Findings

Co-infection with C. sinensis and HBV develops predominantly in males. Co-infected C. sinensis and HBV patients presented weaker liver function and higher HBV DNA titers. Combination treatment with antiviral and anti-C. sinensis drugs in co-infected patients could contribute to a reduction in viral load and help with liver function recovery. Excretory-secretory products (ESPs) may, in some ways, increase HBV viral replication in vitro. A mixture of ESP and HBV positive sera could induce peripheral blood mononuclear cells (PBMCs) to produce higher level of Th2 cytokines including IL-4, IL-6 and IL-10 compared to HBV alone, it seems that due to presence of ESP, the cytokine production shift towards Th2. C. sinensis/HBV co-infected patients showed higher serum IL-6 and IL-10 levels and lower serum IFN-γ levels.

Conclusions/Significance

Patients with concomitant C. sinensis and HBV infection presented weaker liver function and higher HBV DNA copies. In co-infected patients, the efficacy of anti-viral treatment was better in patients who were prescribed with entecavir and praziquantel than entecavir alone. One possible reason for the weaker response to antiviral therapies in co-infected patients was the shift in cytokine production from Th1 to Th2 that may inhibit viral clearance. C. sinensis/HBV co-infection could exacerbate the imbalance of Th1/Th2 cytokine.

Clonorchiasis and hepatitis B infection are infectious diseases that affect millions of people worldwide, especially in China. These two diseases are caused by two different pathogens, C. sinensis and hepatitis B virus, respectively. Concurrent infection between HBV and C. sinensis is often observed in some areas where C. sinensis is endemic. Both diseases share the same target organ, but there is little known on whether concomitant clonorchiasis could have an impact on HBV infection and the efficacy of antiviral treatment. In this study, we showed for the first time that co-infection with C. sinensis and HBV resulted in significantly higher liver transaminases levels as well as HBV DNA copies, indicating that co-infection with C. sinensis and HBV infection may aggravate the disease state. Combination treatment with antiviral and anti-C. sinensis drugs in co-infected patients could contribute to a reduction in viral load and help with liver function recovery. Furthermore, excretory-secretory products (ESPs) of C. sinensis may have a potential role in promoting HBV viral replication. This may explain, at least in part, the higher HBV DNA copies observed in co-infected patients. Additionally, a mixture of ESP and HBV positive sera could induce PBMCs to mainly produce Th2 cytokines such as IL-4, IL-6 and IL-10 compared to HBV alone. A possible reason for higher HBV DNA copies and a weaker response to antiviral therapies in co-infected patients was the shift in cytokine production from Th1 to Th2 that may inhibit viral clearance.

Innate immune targets of hepatitis B virus infection

Approximately 400 million people are chronically infected with hepatitis B virus (HBV) globally despite the widespread immunization of HBV vaccine and the development of antiviral therapies. The immunopathogenesis of HBV infection is initiated and driven by complexed interactions between the host immune system and the virus. Host immune responses to viral particles and proteins are regarded as the main determinants of viral clearance or persistent infection and hepatocyte injury. Innate immune system is the first defending line of host preventing from virus invasion. It is acknowledged that HBV has developed active tactics to escape innate immune recognition or actively interfere with innate immune signaling pathways and induce immunosuppression, which favor their replication. HBV reduces the expression of pattern-recognition receptors in the innate immune cells in humans. Also, HBV may interrupt different parts of antiviral signaling pathways, leading to the reduced production of antiviral cytokines such as interferons that contribute to HBV immunopathogenesis. A full comprehension of the mechanisms as to how HBV inactivates various elements of the innate immune response to initiate and maintain a persistent infection can be helpful in designing new immunotherapeutic methods for preventing and eradicating the virus. In this review, we aimed to summarize different branches the innate immune targeted by HBV infection. The review paper provides evidence that multiple components of immune responses should be activated in combination with antiviral therapy to disrupt the tolerance to HBV for eliminating HBV infection.

IL-10-producing regulatory B-cells suppressed effector T-cells but enhanced regulatory T-cells in chronic HBV infection

Non-specific immune responses to antigens have been demonstrated as being enhanced during chronic hepatitis B virus (HBV) infection. Here, we evaluated the role of interleukin-10 (IL-10)-producing regulatory B-cells (Bregs) in the pathogenesis of HBV-related liver fibrosis (HBV-LF) and assessed their immunoregulatory effects. Sixty-seven patients diagnosed with chronic hepatitis B (CHB) were enrolled in this study. Numbers and frequencies of peripheral B-cells (memory CD19(+)CD24(hi)CD27(+) cells, immature/transitional CD19(+)CD24(hi)CD38(hi) cells, mature CD19(+)CD24(int)CD38(int) cells) were tested and analysed. Flow cytometry-sorted CD4(+)T cells were cultured with autologous Bregs to elucidate the effects of Bregs on CD4(+)T cells, including effector T and regulatory T-cells (Tregs). The potential immunoregulatory mechanism of Bregs was also investigated. The numbers of total B-cells and Bregs were enriched in CHB patients. The frequency of Bregs was negatively correlated with elevated alanine aminotransferase (ALT) and histological inflammation grades (G), but positively correlated with advanced histological fibrosis stages (S) and enhanced HBV replication. The phenotype of Bregs was predominantly characterized as CD19(+)CD24(hi)CD38(hi) In co-culture with Bregs, CD4(+)CD25(-)T cells from CHB patients produced less interferon-γ (IFN-γ) and IL-17 but more IL-4 than CD4(+)CD25(-)T cells alone, whereas their conversions into Tregs and IL-10(+)T cells were enhanced. In addition, Breg depletion in CHB samples dramatically decreased Treg numbers and expression of cytotoxic T-lymphocyte associated antigen-4 (CTLA-4), IL-10 and transforming growth factor-β (TGF-β). Moreover, the observed regulatory effect was partly dependent on IL-10 release and cell-to-cell contact. Elevated Bregs can suppress effector T but enhance Treg functions, which might influence immune tolerance in chronic HBV infection.

Manipulation of Regulatory Cells' Responses to Treatments for Chronic Hepatitis B Virus Infection

BACKGROUND

Identification of effective treatments in hepatitis B virus (HBV) infection remains a controversial topic. Although the currently approved drugs for HBV control the disease's progression and also limit associated outcomes, these drugs may not fully eradicate HBV infection. In addition to better managing patients with chronic hepatitis B (CHB) infection, the induction of seroclearance by these drugs has been a commonly discussed topic in recent years.

OBJECTIVES

In this study, we focused on treating CHB infection via the manipulation of T cells' responses to identify possible approaches to cure CHB.

MATERIALS AND METHODS

All studies relevant to the role of cellular and humoral responses in HBV infection (especially regulatory cells) were investigated via a systematic search of different databases, including PubMed, Scopus, and Google Scholar. Considering extracted data and also our unpublished data regarding the association between regulatory cytokines and CHB, we introduced a novel approach for the induction of seroclearance.

RESULTS

Considering the increased levels of regulatory cytokines and also regulatory T cells (Tregs) during CHB, it seems that these cells are deeply involved in CHB infection. The inhibition of regulatory T cells may reverse the dysfunction of effector T cells in patients with CHB infection. In order to inhibit Tregs' responses, different types of approaches could be employed to restore the impaired function of effector T cells. The blockade of IL-10, IL-35, CTLA-4, PD-1, and TIM-3 were discussed throughout this study. Regardless of the efficacy of these methods, CHB patients may experience serious liver injuries due to the cytotoxic action of CD8+ T cells. Antiviral therapy and a decrease in HBV DNA to undetectable levels could also significantly reduce the risk of the hepatitis B flare.

CONCLUSIONS

The inhibition of Tregs is a novel therapeutic approach to cure chronically HBV infected patients. However, further studies are needed to investigate the safety and efficacy of this approach.

CD3(bright)CD56(+) T cells associate with pegylated interferon-alpha treatment nonresponse in chronic hepatitis B patients

Chronic hepatitis B (CHB) infection is a serious and prevalent health concern worldwide, and the development of effective drugs and strategies to combat this disease is urgently needed. Currently, pegylated interferon-alpha (peg-IFNα) and nucleoside/nucleotide analogues (NA) are the most commonly prescribed treatments. However, sustained response rates in patients remain low, and the reasons are not well understood. Here, we observed that CHB patients preferentially harbored CD3^brightCD56⁺ T cells, a newly identified CD56⁺ T cell population. Patients with this unique T cell population exhibited relatively poor responses to peg-IFNα treatment. CD3^brightCD56⁺ T cells expressed remarkably high levels of the inhibitory molecule NKG2A as well as low levels of CD8. Even if patients were systematically treated with peg-IFNα, CD3^brightCD56⁺ T cells remained in an inhibitory state throughout treatment and exhibited suppressed antiviral function. Furthermore, peg-IFNα treatment rapidly increased inhibitory TIM-3 expression on CD3^brightCD56⁺ T cells, which negatively correlated with IFNγ production and might have led to their dysfunction. This study identified a novel CD3^brightCD56⁺ T cell population preferentially shown in CHB patients, and indicated that the presence of CD3^brightCD56⁺ T cells in CHB patients may be useful as a new indicator associated with poor therapeutic responses to peg-IFNα treatment.

Host-virus interactions in hepatitis B and hepatitis C infection

Hepatitis B virus (HBV) and hepatitis C virus (HCV) are among the most endemic pathogens worldwide, with more than 500 million people globally currently infected with these viruses. These pathogens can cause acute and chronic hepatitis that progress to liver cirrhosis or hepatocellular carcinoma. Both viruses utilize multifaceted strategies to evade the host surveillance system and fall below the immunological radar. HBV has developed specific strategies to evade recognition by the innate immune system and is acknowledged to be a stealth virus. However, extensive research has revealed that HBV is recognized by dendritic cells (DCs) and natural killer (NK) cells. Indoleamine-2, 3-dioxygenase is an enforcer of sequential immune reactions in acute hepatitis B, and this molecule has been shown to be induced by the interaction of HBV-infected hepatocytes, DCs, and NK cells. The interleukin-28B genotype has been reported to influence HCV eradication either therapeutically or spontaneously, but the biological function of its gene product, a type-III interferon (IFN-λ3), remains to be elucidated. Human BDCA3(+)DCs have also been shown to be a potent producer of IFN-λ3 in HCV infection, suggesting the possibility that BDCA3(+)DCs could play a key role in developing therapeutic HCV vaccine. Here we review the current state of research on immune responses against HBV and HCV infection, with a specific focus on innate immunity. A comprehensive study based on clinical samples is urgently needed to improve our understanding of the immune mechanisms associated with viral control and thus to develop novel immune modulatory therapies to cure chronic HBV and HCV infection.

NKT cell subsets as key participants in liver physiology and pathology

Natural killer T (NKT) cells are innate-like lymphocytes that generally recognize lipid antigens and are enriched in microvascular compartments of the liver. NKT cells can be activated by self- or microbial-lipid antigens and by signaling through toll-like receptors. Following activation, NKT cells rapidly secrete pro-inflammatory or anti-inflammatory cytokines and chemokines, and thereby determine the milieu for subsequent immunity or tolerance. It is becoming clear that two different subsets of NKT cells-type I and type II-have different modes of antigen recognition and have opposing roles in inflammatory liver diseases. Here we focus mainly on the roles of both NKT cell subsets in the maintenance of immune tolerance and inflammatory diseases in liver. Furthermore, how the differential activation of type I and type II NKT cells influences other innate cells and adaptive immune cells to result in important consequences for tissue integrity is discussed. It is crucial that better reagents, including CD1d tetramers, be used in clinical studies to define the roles of NKT cells in liver diseases in patients.

NK Cells Help Induce Anti-Hepatitis B Virus CD8+ T Cell Immunity in Mice

Although recent clinical studies demonstrate that NK cell function is impaired in hepatitis B virus (HBV)-persistent patients, whether or how NK cells play a role in anti-HBV adaptive immunity remains to be explored. Using a mouse model mimicking acute HBV infection by hydrodynamic injection of an HBV plasmid, we observed that although serum hepatitis B surface Ag and hepatitis B envelope Ag were eliminated within 3 to 4 wk, HBV might persist for >8 wk in CD8(-/-) mice and that adoptive transfer of anti-HBV CD8(+) T cells restored the ability to clear HBV in HBV-carrier Rag1(-/-) mice. These results indicate that CD8(+) T cells are critical in HBV elimination. Furthermore, NK cells increased IFN-γ production after HBV plasmid injection, and NK cell depletion led to significantly increased HBV persistence along with reduced frequency of hepatitis B core Ag-specific CD8(+) T cells. Adoptive transfer of IFN-γ-sufficient NK cells restored donor CD8(+) T cell function, indicating that NK cells positively regulated CD8(+) T cells via secreting IFN-γ. We also observed that NK cell depletion correlated with decreased effector memory CD8(+) T cell frequencies. Importantly, adoptive transfer experiments showed that NK cells were involved in anti-HBV CD8(+) T cell recall responses. Moreover, DX5(+)CD49a(-) conventional, but not DX5(-)CD49a(+) liver-resident, NK cells were involved in improving CD8(+) T cell responses against HBV. Overall, the current study reveals that NK cells, especially DX5(+)CD49a(-) conventional NK cells, promote the antiviral activity of CD8(+) T cell responses via secreting IFN-γ in a mouse model mimicking acute HBV infection.

CD205-TLR9-IL-12 axis contributes to CpG-induced oversensitive liver injury in HBsAg transgenic mice by promoting the interaction of NKT cells with Kupffer cells

Gut-derived bacterial products contribute to liver inflammation and injury during chronic hepatitis B virus infection; however, the underlying mechanisms remain obscure. In this study, hepatitis B surface antigen transgenic (HBs-Tg) mice and their wild-type (WT) control C57BL/6 mice were injected with CpG-oligodeoxynucleotides (ODNs) to mimic the translocation of gut microbial products into the systemic circulation. We found that, compared with the WT mice, the HBs-Tg mice were oversensitive to CpG-ODN-induced liver injury, which was dependent on natural killer T (NKT) cells. CpG-ODN injection enhanced the expression of Fas ligand (FasL) on NKT cells. In addition, hepatocytes from the HBs-Tg mice expressed higher levels of Fas than did those from the WT mice, which was further augmented by CpG-ODN. Interaction of Fas and FasL was involved in the cytotoxicity of NKT cells against hepatocytes in the HBs-Tg mice. Moreover, Kupffer cells in the HBs-Tg mice expressed higher levels of CD205 and produced greater amounts of interleukin (IL)-12 than did those in the WT mice. Finally, the depletion of Kupffer cells, neutralization of IL-12 or specific silencing of CD205 on Kupffer cells significantly inhibited CpG-ODN-induced liver injury and NKT activation in the HBs-Tg mice. Our data suggest that CD205-expressing Kupffer cells respond to CpG-ODNs and subsequently release IL-12 to promote NKT cell activation. Activated NKT cells induce liver damage through the Fas signaling pathway in HBs-Tg mice.

Global strategies are required to cure and eliminate HBV infection

Chronic HBV infection results in >1 million deaths per year from cirrhosis and liver cancer. No known cure for chronic HBV exists, due in part to the continued presence of transcriptionally active DNA in the nucleus that is not directly targeted by current antiviral therapies. A coordinated approach is urgently needed to advance an HBV cure worldwide, such as those established in the HIV field. We propose the establishment of an International Coalition to Eliminate Hepatitis B Virus (ICE-HBV) to facilitate the formation of international working groups on HBV virology, immunology, innovative tools and clinical trials: to promote awareness and education as well as to drive changes in government policy and ensure funds are channelled to HBV cure research and drug development. With the ICE-HBV in place, it should be possible to enable a HBV cure within the next decade.

The role of innate immunity in the immunopathology and treatment of HBV infection

In this review we give a brief update on sensors recently determined to be capable of detecting HBV, and examine how the virus represses the induction of pro-inflammatory cytokines like type I interferons. We overview cellular components of innate immunity that are present at high frequencies in the liver, and discuss their roles in HBV control and/or pathogenesis. We argue that many innate effectors have adaptive-like features or can exert specific effects on HBV through immunoregulation of T cells. Finally we consider current and possible future strategies to manipulate innate immunity as novel approaches towards a functional cure for HBV.

Host-virus interactions in hepatitis B and hepatitis C infection

Hepatitis B virus (HBV) and hepatitis C virus (HCV) are among the most endemic pathogens worldwide, with more than 500 million people globally currently infected with these viruses. These pathogens can cause acute and chronic hepatitis that progress to liver cirrhosis or hepatocellular carcinoma. Both viruses utilize multifaceted strategies to evade the host surveillance system and fall below the immunological radar. HBV has developed specific strategies to evade recognition by the innate immune system and is acknowledged to be a stealth virus. However, extensive research has revealed that HBV is recognized by dendritic cells (DCs) and natural killer (NK) cells. Indoleamine-2, 3-dioxygenase is an enforcer of sequential immune reactions in acute hepatitis B, and this molecule has been shown to be induced by the interaction of HBV-infected hepatocytes, DCs, and NK cells. The interleukin-28B genotype has been reported to influence HCV eradication either therapeutically or spontaneously, but the biological function of its gene product, a type-III interferon (IFN-λ3), remains to be elucidated. Human BDCA3(+)DCs have also been shown to be a potent producer of IFN-λ3 in HCV infection, suggesting the possibility that BDCA3(+)DCs could play a key role in developing therapeutic HCV vaccine. Here we review the current state of research on immune responses against HBV and HCV infection, with a specific focus on innate immunity. A comprehensive study based on clinical samples is urgently needed to improve our understanding of the immune mechanisms associated with viral control and thus to develop novel immune modulatory therapies to cure chronic HBV and HCV infection.

Hepatitis regulation by the inflammasome signaling pathway

Hepatitis is damage and inflammation of the liver. It is triggered by both environmental and endogenous insults and is a platform for developing liver cirrhosis and cancer. Both innate and adaptive immune activation contribute to hepatic inflammation and disease. Viral hepatitis is the most common form of hepatitis and is typically associated with chronic viral infection. Alcohol-induced and non-alcoholic steatohepatitis are two rising hepatic problems. The innate immune inflammasome signaling cascade mediates the production of essential proinflammatory cytokines interleukin-1β (IL-1β) and IL-18. These cytokines regulate hepatic cell interaction and crosstalk of the various inflammatory pathways and influence disease outcome.

Altered Immune Profiles of Natural Killer Cells in Chronic Hepatitis B Patients: A Systematic Review and Meta-Analysis

BACKGROUND

Natural killer (NK) cells are the main effective component of the innate immune system that responds to chronic hepatitis B (CHB) infection. Although numerous studies have reported the immune profiles of NK cells in CHB patients, they are limited by inconsistent results. Thus, we performed a meta-analysis to characterize reliably the immune profiles of NK cells after CHB infection, specifically frequency, phenotype, and function.

METHODS

A literature search of the computer databases MEDLINE, PUBMED, EMBASE, and Cochrane Center Register of Controlled Trails was performed and 19 studies were selected. The standard mean difference (SMD) and 95% confidence interval (CI) of each continuous variable was estimated with a fixed effects model when I2 < 50% for the test for heterogeneity, or the random effects model otherwise. Publication bias was evaluated using Begg's and Egger's tests.

RESULTS

The meta-analysis of publications that reported frequency of peripheral NK cells showed that NK cell levels in CHB patients were significantly lower compared with that of healthy controls. A higher frequency of CD56bright NK subsets was found in CHB patients, but the CD56dim NK subsets of CHB patients and healthy controls were similar. CHB patients before and after antiviral therapy with nucleotide analogues (NUCs) showed no statistical difference in NK frequency. The activating receptors were upregulated, whereas inhibitory receptors were comparable in the peripheral NK cells of CHB individuals and healthy controls. NK cells of CHB patients displayed higher cytotoxic potency as evidenced by CD107a protein levels and conserved potency to produce interferon-gamma (IFNγ), compared with their healthy counterparts.

CONCLUSION

Our results revealed that CHB patients had a lower frequency of NK cells compared with healthy individuals not treatable with antiviral NUC therapy. With an activating phenotype, NK cells in CHB patients showed better cytotoxic potency and conserved IFNγ production.

Indoleamine-2,3-dioxygenase as an effector and an indicator of protective immune responses in patients with acute hepatitis B

Indoleamine-2, 3-dioxygenase (IDO), an interferon-γ-inducible enzyme catalyzing tryptophan into kynurenine, exerts dual functions in infectious diseases, acting as a suppressor of intracellular pathogens and as an immune regulator. We explored the roles of IDO in hepatitis B virus (HBV) clearance from infected patients. We examined IDO activity, serum chemokines, and cytokines in 53 HBV-positive patients (25 acute hepatitis, 14 chronic hepatitis, and 14 hepatic flare) and 14 healthy volunteers. In order to clarify the mechanisms of IDO induction and its impact on HBV replication, we used a culture model consisting of human natural killer cells, plasmacytoid dendritic cells, and HBV-transfected Huh7 cells in which IDO expression is controlled. A robust activation of IDO with an inverse correlation of alanine aminotransferase at the peak was observed in patients with acute hepatitis B but not in patients with hepatic flare. In acute hepatitis patients who eventually cleared HBV, IDO activity, chemokine (C-X-C motif) ligand 9 (CXCL9), CXCL10, and CXCL11 increased at the peak of alanine aminotransferase. In contrast, in patients with hepatic flare, IDO activity remained at lower levels during the observation period, regardless of the surge of CXCL9, CXCL10, and CXCL11 at the alanine aminotransferase peak. Natural killer cells and plasmacytoid dendritic cells synergistically produced interferon-γ and interferon-α, thereby enhancing IDO activity and HBV suppression in Huh7 cells. Such suppressor capacity of IDO on HBV was abrogated in IDO-knockout cells and recovered by the reinduction of IDO in the cells.

CONCLUSION

IDO is an anti-HBV effector and an indicator of subsequent immune responses operative during the early phase of infection; its activity is boosted by coexisting natural killer cells and plasmacytoid dendritic cells.

Crosstalk between innate and adaptive immunity in hepatitis B virus infection

Hepatitis B virus (HBV) infection is a major public health problem worldwide. HBV is not directly cytotoxic to infected hepatocytes; the clinical outcome of infection results from complicated interactions between the virus and the host immune system. In acute HBV infection, initiation of a broad, vigorous immune response is responsible for viral clearance and self-limited inflammatory liver disease. Effective and coordinated innate and adaptive immune responses are critical for viral clearance and the development of long-lasting immunity. Chronic hepatitis B patients fail to mount efficient innate and adaptive immune responses to the virus. In particular, HBV-specific cytotoxic T cells, which are crucial for HBV clearance, are hyporesponsiveness to HBV infection. Accumulating experimental evidence obtained from the development of animal and cell line models has highlighted the importance of innate immunity in the early control of HBV spread. The virus has evolved immune escape strategies, with higher HBV loads and HBV protein concentrations associated with increasing impairment of immune function. Therefore, treatment of HBV infection requires inhibition of HBV replication and protein expression to restore the suppressed host immunity. Complicated interactions exist not only between innate and adaptive responses, but also among innate immune cells and different components of adaptive responses. Improved insight into these complex interactions are important in designing new therapeutic strategies for the treatment HBV infection. In this review, we summarize the current knowledge regarding the cross-talk between the innate and adaptive immune responses and among different immunocytes in HBV infection.

Viral DNA-Dependent Induction of Innate Immune Response to Hepatitis B Virus in Immortalized Mouse Hepatocytes

Hepatitis B virus (HBV) infects hundreds of millions of people worldwide and causes acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma. HBV is an enveloped virus with a relaxed circular (RC) DNA genome. In the nuclei of infected human hepatocytes, conversion of RC DNA from the incoming virion or cytoplasmic mature nucleocapsid (NC) to the covalently closed circular (CCC) DNA, which serves as the template for producing all viral transcripts, is essential to establish and sustain viral replication. A prerequisite for CCC DNA formation is the uncoating (disassembly) of NCs to expose their RC DNA content for conversion to CCC DNA. We report here that in an immortalized mouse hepatocyte cell line, AML12HBV10, in which RC DNA exposure is enhanced, the exposed viral DNA could trigger an innate immune response that was able to modulate viral gene expression and replication. When viral gene expression and replication were low, the innate response initially stimulated these processes but subsequently acted to shut off viral gene expression and replication after they reached peak levels. Inhibition of viral DNA synthesis or cellular DNA sensing and innate immune signaling diminished the innate response. These results indicate that HBV DNA, when exposed in the host cell cytoplasm, can function to trigger an innate immune response that, in turn, modulates viral gene expression and replication.

IMPORTANCE

Chronic infection by hepatitis B virus (HBV) afflicts hundreds of millions worldwide and is sustained by the episomal covalently closed circular (CCC) DNA in the nuclei of infected hepatocytes. Release of viral genomic DNA from cytoplasmic nucleocapsids (NCs) (NC disassembly or uncoating) is a prerequisite for its conversion to CCC DNA, which can also potentially expose the viral DNA to host DNA sensors and trigger an innate immune response. We have found that in an immortalized mouse hepatocyte cell line in which efficient CCC DNA formation was associated with enhanced exposure of nucleocapsid-associated DNA, the exposed viral DNA indeed triggered host cytoplasmic DNA sensing and an innate immune response that was able to modulate HBV gene expression and replication. Thus, HBV can, under select conditions, be recognized by the host innate immune response through exposed viral DNA, which may be exploited therapeutically to clear viral persistence.

Innate immune recognition of hepatitis B virus

Hepatitis B virus (HBV) is a hepatotropic DNA virus and its infection results in acute or chronic hepatitis. It is reported that the host innate immune system contributes to viral control and liver pathology, while whether and how HBV can trigger the components of innate immunity remains controversial. In recent years, the data accumulated from HBV-infected patients, cellular and animal models have challenged the concept of a stealth virus for HBV infection. This editorial focuses on the current findings about the innate immune recognition to HBV. Such evaluation could help us to understand HBV immunopathogenesis and develop novel immune therapeutic strategies to combat HBV infection.

New paradigms in hepatitis B management: only diamonds are forever

INTRODUCTION

The hepatitis B virus (HBV) causes chronic hepatitis B (CHB) in ∼350 million people worldwide who have an increased risk of end-stage liver disease and/or hepatocellular carcinoma.

SOURCES OF DATA

Several peer-reviewed papers featuring new approaches to anti-HBV management. Additionally, we also reviewed recent abstract presentations at international congresses.

AREAS OF AGREEMENT

There has been great progress in CHB therapy with the development of standard and pegylated interferon (i.e. PEG-IFN) as well as nucleos/tide analogs (NAs). IFN has both antiviral and immunomodulatory effects and through immune-mediated destruction of infected hepatocytes offers the possibility of finite therapy. However, this 'killing for a cure' antiviral strategy may not be tolerated in many, especially in cirrhotic patients. NAs inhibit viral reverse transcriptase, have few side effects and prevent liver disease progression, but cannot offer a cure as they have little effect on the resilient HBV covalently closed circular DNA (cccDNA) intermediate. Moreover, NAs such as tenofovir and entecavir offer a high genetic barrier to resistance, but are expensive and not readily available in many global regions.

GROWING POINTS

Despite significant treatment advances, there is increased recognition of the need for improved anti-HBV treatments, and new virologic tests for monitoring treatment response.

AREAS OF CONTROVERSY

The role of quantitative hepatitis B surface antigen, intrahepatic cccDNA levels and viral genotype in selecting treatment candidates and refining NA stopping rules.

AREAS TIMELY FOR DEVELOPING NEW RESEARCH

Potential new therapies include viral entry inhibitors, RNA interference technologies (i.e. RNAi) and small molecules that modulate cccDNA transcription, as well as novel immunomodulatory therapies to boost HBV-specific T cell responses. The ultimate goal of new tests and anti-HBV therapies is to reduce the burden and expense of life-long CHB treatment, as 'only diamonds are forever'.

Innate detection of hepatitis B and C virus and viral inhibition of the response

Viral hepatitis caused by hepatitis B virus (HBV) and hepatitis C virus (HCV) infections poses a significant burden to the public health system. Although HBV and HCV differ in structure and life cycles, they share unique characteristics, such as tropism to infect hepatocytes and association with hepatic and extrahepatic disorders that are of innate immunity nature. In response to HBV and HCV infection, the liver innate immune cells eradicate pathogens by recognizing specific molecules expressed by pathogens via distinct cellular pattern recognition receptors whose triggering activates intracellular signalling pathways inducing cytokines, interferons and anti-viral response genes that collectively function to clear infections. However, HBV and HCV evolve strategies to inactivate innate signalling factors and as such establish persistent infections without being recognized by the innate immunity. We review recent insights into how HBV and HCV are sensed and how they evade innate immunity to establish chronicity. Understanding the mechanisms of viral hepatitis is mandatory to develop effective and safe therapies for eradication of viral hepatitis.

Gut microbiota modulate the immune effect against hepatitis B virus infection

The immunological mechanisms by which hepatitis B virus (HBV) initiates and maintains acute or chronic infection, even the formation of cirrhosis and hepatocellular carcinoma, are still undefined. An increasing number of studies have shown that intestinal flora regulate immune homeostasis, and, thus, protect the immunologic function against hepatitis virus infection. In this article, we discuss gut microbiota and its potential immune effects against HBV infection. It may provide a novel insight into the pathogenesis of HBV infection, as well as a potential therapeutic target to HBV-related disease.

Towards an HBV cure: state-of-the-art and unresolved questions--report of the ANRS workshop on HBV cure

HBV infection is a major cause of liver cirrhosis and hepatocellular carcinoma. Although HBV infection can be efficiently prevented by vaccination, and treatments are available, to date there is no reliable cure for the >240 million individuals that are chronically infected worldwide. Current treatments can only achieve viral suppression, and lifelong therapy is needed in the majority of infected persons. In the framework of the French National Agency for Research on AIDS and Viral Hepatitis 'HBV Cure' programme, a scientific workshop was held in Paris in June 2014 to define the state-of-the-art and unanswered questions regarding HBV pathobiology, and to develop a concerted strategy towards an HBV cure. This review summarises our current understanding of HBV host-interactions leading to viral persistence, as well as the roadblocks to be overcome to ultimately address unmet medical needs in the treatment of chronic HBV infection.

Treatment of chronic hepatitis B with pattern recognition receptor agonists: Current status and potential for a cure

Hepatitis B virus (HBV) has been considered to be a "stealth virus" that induces negligible innate immune responses during the early phase of infection. However, recent studies with newly developed experimental systems have revealed that virus infection can be recognized by pattern recognition receptors (PRR), eliciting a cytokine response that controls the replication of the virus. The molecular mechanisms by which interferons and other inflammatory cytokines suppress HBV replication and modulate HBV cccDNA metabolism and function are just beginning to be revealed. In agreement with the notion that the developmental and functional status of intrahepatic innate immunity determines the activation and maturation of the HBV-specific adaptive immune response and thus the outcome of HBV infection, pharmacological activation of intrahepatic innate immune responses with TLR7/8/9 or STING agonists efficiently controls HBV infection in preclinical studies and thus holds great promise for the cure of chronic hepatitis B. This article forms part of a symposium in Antiviral Research on "An unfinished story: from the discovery of the Australia antigen to the development of new curative therapies for hepatitis B."

Hepatitis B: future curative strategies

PURPOSE OF REVIEW

Hepatitis B virus (HBV) causes a large proportion of chronic liver disease worldwide. The limited efficiency of current treatments based on the use of nucleotide/nucleoside analogues or interferon-alpha requires the development of new therapeutic tools for the treatment of chronic HBV. We summarize the most recent therapeutic strategies designed to directly target HBV-infected hepatocytes or to restore antiviral immunity during chronic HBV infection.

RECENT FINDINGS

Novel therapies directly target HBV-infected hepatocytes by inducing covalently closed circular DNA degradation or by inhibiting HBV entry or the expression of viral proteins. In addition, immunotherapeutic approaches may boost HBV-specific T-cell responses or stimulate the intrahepatic innate response.

SUMMARY

These new therapeutic approaches have mainly been tested in animal models. In humans, therapeutic strategies could be tailored to different chronic HBV patients in relation to their clinical and virological disease profile.

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.

Induced immunity against hepatitis B virus

Prevention of hepatitis B virus (HBV) infection with its consequent development of HBV chronic liver disease and hepatocellular carcinoma is a global mandatory goal. Fortunately, safe and effective HBV vaccines are currently available. Universal hepatitis B surface antigen HBV vaccination coverage is almost done. Growing knowledge based upon monitoring and surveillance of HBV vaccination programs has accumulated and the policy of booster vaccination has been evaluated. This review article provides an overview of the natural history of HBV infection, immune responses and the future of HBV infection. It also summarizes the updated sources, types and uses of HBV vaccines, whether in the preclinical phase or in the post-field vaccination.

Natural killer cells in hepatitis B virus infection

Natural killer cells are a unique type of lymphocytes with cytotoxic capacity, and play important roles against tumors and infections. Recently, natural killer cells have been increasingly valued in their effects in hepatitis B virus infection. Since hepatitis B virus is not cytopathic, the subsequent antiviral immune responses of the host are responsible for sustaining the liver injury, which may result in cirrhosis and even hepatocellular carcinoma. Many studies have confirmed that natural killer cells participate in anti-hepatitis B virus responses both in the early phase after infection and in the chronic phase via cytolysis, degranulation, and cytokine secretion. However, natural killer cells play dichotomic roles: they exert antiviral and immunoregulatory functions whilst contribute to the pathogenesis of liver injury. Here, we review the roles of natural killer cells in hepatitis B virus infection, introducing novel therapeutic strategies for controlling hepatitis B virus infection via the modulation of natural killer cells.

Type II NKT Cells in Inflammation, Autoimmunity, Microbial Immunity, and Cancer

Natural killer T cells (NKT) recognize self and microbial lipid antigens presented by non-polymorphic CD1d molecules. Two major NKT cell subsets, type I and II, express different types of antigen receptors (TCR) with distinct mode of CD1d/lipid recognition. Though type II NKT cells are less frequent in mice and difficult to study, they are predominant in human. One of the major subsets of type II NKT cells reactive to the self-glycolipid sulfatide is the best characterized and has been shown to induce a dominant immune regulatory mechanism that controls inflammation in autoimmunity and in anti-cancer immunity. Recently, type II NKT cells reactive to other self-glycolipids and phospholipids have been identified suggesting both promiscuous and specific TCR recognition in microbial immunity as well. Since the CD1d pathway is highly conserved, a detailed understanding of the biology and function of type II NKT cells as well as their interplay with type I NKT cells or other innate and adaptive T cells will have major implications for potential novel interventions in inflammatory and autoimmune diseases, microbial immunity, and cancer.

T-cell exhaustion in chronic hepatitis B infection: current knowledge and clinical significance

Hepatitis B virus (HBV) infection is the major cause of inflammatory liver disease, of which the clinical recovery and effective anti-viral therapy is associated with the sustained viral control of effector T cells. In humans, chronic HBV infection often shows weak or absent virus-specific T-cell reactivity, which is described as the ‘exhaustion' state characterized by poor effector cytotoxic activity, impaired cytokine production and sustained expression of multiple inhibitory receptors, such as programmed cell death-1 (PD-1), lymphocyte activation gene-3, cytotoxic T lymphocyte-associated antigen-4 and CD244. As both CD4⁺ and CD8⁺ T cells participate in the immune responses against chronic hepatitis virus through distinct manners, compelling evidences have been proposed, which restore the anti-viral function of these exhausted T cells by blocking those inhibitory receptors with its ligand and will pave the way for the development of more effective immunotherapeutic and prophylactic strategies for the treatment of chronic infectious diseases. A large number of studies have stated the essentiality of T-cell exhaustion in virus-infected diseases, such as LCMV, hepatitis C virus (HCV), human immunodeficiency virus infections and cancers. Besides, the functional restoration of HCV- and HIV-specific CD8⁺ T cells by PD-1 blockade has already been repeatedly verified, and also for the immunological control of tumors in humans, blocking the PD-1 pathway could be a major immunotherapeutic strategy. Although the specific molecular pathways of T-cell exhaustion remain ambiguous, several transcriptional pathways have been implicated in T-cell exhaustion recently; among them Blimp-1, T-bet and NFAT2 were able to regulate exhausted T cells during chronic viral infection, suggesting a distinct lineage fate for this sub-population of T cells. This paper summarizes the current literature relevant to T-cell exhaustion in patients with HBV-related chronic hepatitis, the options for identifying new potential therapeutic targets to treat HBV infection and highlights priorities for further study.

Interleukin 6 inhibits HBV entry through NTCP down regulation

Hepatitis B virus (HBV) infection is a major public health problem. Recently, the human liver bile acid transporter Na(+)/taurocholate cotransporting polypeptide (NTCP) has been identified as an HBV specific receptor. NTCP expression is known to be strongly regulated by IL-6. This study was aimed at characterizing the effect of IL-6 on HBV entry. HBV entry was inhibited by up to 90% when cells were pretreated with IL-6 as shown by a strong inhibition of long term HBsAg secretion. This effect was confirmed by showing a severe reduction of intracellular HBV cccDNA. In parallel, we observed a 98% decrease in NTCP mRNA steady state level and an 80% reduction in NTCP-mediated taurocholate uptake. IL-6-mediated inhibition of NTCP-mediated taurocholate uptake and viral entry exhibited similar dose-dependence and kinetics while restoration of NTCP expression suppressed the inhibitory effect of IL-6. NTCP-mediated HBV entry is therefore markedly inhibited by IL-6.

Circulating CD56dim natural killer cells and CD56+ T cells that produce interferon-γ or interleukin-10 are expanded in asymptomatic, E antigen-negative patients with persistent hepatitis B virus infection

Infection with hepatitis B virus (HBV) can result in spontaneous resolution or chronic infection, which can remain asymptomatic or can progress to cirrhosis and/or hepatocellular carcinoma. The host immune response is thought to be a major determinant of the outcome of HBV infection and virus-specific cytotoxic T lymphocytes (CTL) can mediate immunity against the virus and cause liver pathology. Antigen-nonspecific innate lymphocytes may also contribute to HBV infection and liver disease, therefore, we examined the frequencies, phenotypes, cytolytic activities and cytokine profiles of circulating natural killer (NK) cells, CD1d-restricted invariant natural killer T (iNKT) cells and CD56(+) T cells in 102 asymptomatic HBV-infected patients and compared them with those in 66 uninfected control subjects. NK cells expressing low levels of CD56 (CD56(dim)) and CD56(+) T cells were significantly expanded in the circulation of HBV-infected patients compared with control subjects. CD1d expression and iNKT cell frequencies were similar in both groups. Despite these expansions, we did not detect augmented natural or cytokine-induced cytotoxicity in the HBV-infected subjects. All lymphocyte populations studied produced interferon-γ (IFN-γ) significantly more frequently when taken from HBV-infected patients compared with when taken from healthy controls. Additionally, NK cells from the patients more frequently produced interleukin-10. As our HBV-infected cohort consisted of asymptomatic patients with low viral loads, we propose that CD56(dim) NK cells and CD56(+) T cells control HBV infection by noncytolytic mechanisms.

Association between TNFAIP3 nonsynonymous single-nucleotide polymorphism rs2230926 and chronic hepatitis B virus infection in a Chinese Han population

BACKGROUND

Single-nucleotide polymorphisms (SNPs) in tumor necrosis factor alpha-inducible protein 3 (TNFAIP3) gene have been linked to inflammatory, immunological and malignant diseases. Hepatitis B virus (HBV) infection is characterized by immunopathogenesis. This study investigated the association of rs2230926, a nonsynonymous SNP in TNFAIP3 gene, with chronic HBV infection.

METHODS

Four hundred and fifty-five patients with chronic HBV infection with clinical diseases of chronic hepatitis (n = 183), liver cirrhosis (n = 167) and hepatocellular carcinoma (n = 105), 92 HBV infection resolvers and 171 healthy controls were included. All subjects were of Chinese Han ethnicity. Genotyping of rs2230926 was carried out by polymerase chain reaction-restriction fragment length polymorphism method.

RESULTS

The gender and age between HBV patients, HBV infection resolvers and healthy controls had no statistical difference. The genotypes of rs2230926 in HBV patients, HBV infection resolvers and healthy controls are in Hardy-Weinberg equilibrium. The genotype and allele frequencies of TNFAIP3 rs2230926 polymorphism between HBV patients, HBV infection resolvers and healthy controls had no significant difference. The genotype and allele frequencies of TNFAIP3 rs2230926 polymorphism between HBV patients with chronic hepatitis, liver cirrhosis and hepatocellular carcinoma also showed no significant difference.

CONCLUSIONS

The TNFAIP3 rs2230926 polymorphism is not suggested to be associated with the susceptibility of chronic HBV infection or the progression of HBV-related diseases in this study. Replicative studies and studies in large control and HBV patient populations of different ethnicity by genotyping more polymorphisms in TNFAIP3 gene are needed.

Immunobiology of hepatitis B virus infection

The adaptive immune response, particularly the virus-specific CD8(+) T-cell response, is largely responsible for viral clearance and disease pathogenesis during hepatitis B virus (HBV) infection. The HBV-specific CD8(+) T-cell response is vigorous, polyclonal and multispecific in acutely infected patients who successfully clear the virus and relatively weak and narrowly focused in chronically infected patients. The immunological basis for this dichotomy is unclear. A recent study using HBV transgenic mice and HBV-specific T-cell receptor transgenic mice suggests that intrahepatic antigen presentation by HBV positive hepatocytes suppresses HBV-specific CD8(+) T-cell responses through a co-inhibitory molecule, programmed cell death 1 (PD-1). In contrast, antigen presentation by activated professional antigen-presenting cells induces functional differentiation of HBV-specific CD8(+) T cells. These findings suggest that the outcome of T-cell priming is largely dependent on the nature of antigen-presenting cells. Another study suggests that the timing of HBV-specific CD4(+) T-cell priming regulates the magnitude of the HBV-specific CD8(+) T-cell response. Other factors that could regulate HBV-specific cellular immune responses are high viral loads, mutational epitope inactivation, T-cell receptor antagonism and infection of immunologically privileged tissues. However, these pathways become apparent only in the setting of an ineffective cellular immune response, which is therefore the fundamental underlying cause. Understanding the cellular and molecular mechanisms by which HBV evades host immune responses will eventually help develop new immunotherapeutic strategies designed to terminate chronic HBV infection.

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.

Role of natural kill cells in hepatitis B virus infection

Natural killer (NK) cells are a unique group of lymphocytes with cytotoxicity, playing an important role in anti-tumor and anti-infection activities. Recently, NK cells are increasingly recognized to play a role during hepatitis B virus (HBV) infection. Studies have confirmed NK cells participate in anti-HBV responses by secreting cytokines, mediating apoptosis and killing target cells, indicating a potential strategy for controlling HBV infection via regulation of NK cell functions. This review discusses the contribution of NK cells to HBV elimination, liver injury, and other parts of immune system and the formulation of new therapeutic strategies.