Cell-type-specific expression analysis of liver transcriptomics with clinical parameters to decipher the cause of intrahepatic inflammation in chronic hepatitis B

Functional cure for chronic hepatitis B (CHB) remains challenging due to the lack of direct intervention methods for hepatic inflammation. Multi-omics research offers a promising approach to understand hepatic inflammation mechanisms in CHB. A Bayesian linear model linked gene expression with clinical parameters, and population-specific expression analysis (PSEA) refined bulk gene expression into specific cell types across different clinical phases. These models were integrated into our analysis of key factors like inflammatory cells, immune activation, T cell exhaustion, chemokines, receptors, and interferon-stimulated genes (ISGs). Validation through multi-immune staining in liver specimens from CHB patients bolstered our findings. In CHB patients, increased gene expression related to immune cell activation and migration was noted. Marker genes of macrophages, T cells, immune-negative regulators, chemokines, and ISGs showed a positive correlation with serum alanine aminotransferase (ALT) levels but not hepatitis B virus DNA levels. The PSEA model confirmed T cells as the source of exhausted regulators, while macrophages primarily contributed to chemokine expression. Upregulated ISGs (ISG20, IFI16, TAP2, GBP1, PSMB9) in the hepatitis phase were associated with T cell and macrophage infiltration and positively correlated with ALT levels. Conversely, another set of ISGs (IFI44, ISG15, IFI44L, IFI6, MX1) mainly expressed by hepatocytes and B cells showed no correlation with ALT levels. Our study presents a multi-omics analysis integrating bulk transcriptomic, single-cell sequencing data, and clinical data from CHB patients to decipher the cause of intrahepatic inflammation in CHB. The findings confirm that macrophages secrete chemokines like CCL20, recruiting exhausted T cells into liver tissue; concurrently, hepatocyte innate immunity is suppressed, hindering the antiviral effects of ISGs.

Replication and Expression of the Consensus Genome of Hepatitis B Virus Genotype C from the Chinese Population

Hepatitis B virus (HBV) genotype C is a prevalent HBV genotype in the Chinese population. Although genotype C shows higher sequence heterogeneity and more severe liver disease than other genotypes, its pathogenesis and immunological traits are not yet fully elucidated. In this study, we first established and chemically synthesized the consensus sequence based on representative 138 full-length HBV genotype C genomes from the Chinese population. The pHBV1.3C plasmid system, containing a 1.3-fold full-length HBV genotype C consensus sequence, was constructed for subsequent validation. Next, we performed functional assays to investigate the replicative competence of pHBV1.3C in vitro through the transient transfection of HepG2 and Huh7 cells and validated the in vivo function via a hydrodynamic injection to BALB/c recipient mice. The in vitro investigation revealed that the extracellular HBV DNA and intracellular replicative intermediate (i.e., pregenomic RNA, pgRNA) were apparently measurable at 48 h, and the HBsAg and HBcAg were still positive in hepatoma cells at 96 h. We also found that HBsAg and HBeAg accumulated at the extracellular and intracellular levels in a time-dependent manner. The in vivo validation demonstrated that pHBV1.3C plasmids induced HBV viremia, triggered morphological changes and HBsAg- or HBcAg- positivity of hepatocytes, and ultimately caused inflammatory infiltration and focal or piecemeal necrosis in the livers of the murine recipients. HBV protein (HBsAg) colocalized with CD8+ T cells or CD4+ T cells in the liver. F4/80+ Kupffer cells were abundantly recruited around the altered murine hepatocytes. Taken together, our results indicate that the synthetic consensus sequence of HBV genotype C is replication-competent in vitro and in vivo. This genotype C consensus genome supports the full HBV life cycle, which is conducive to studying its pathogenesis and immune response, screening novel antiviral agents, and further optimizing testing and therapeutics.

Single-cell RNA sequencing of liver fine-needle aspirates captures immune diversity in the blood and liver in chronic hepatitis B patients

BACKGROUND AND AIMS

HBV infection is restricted to the liver, where it drives exhaustion of virus-specific T and B cells and pathogenesis through dysregulation of intrahepatic immunity. Our understanding of liver-specific events related to viral control and liver damage has relied almost solely on animal models, and we lack useable peripheral biomarkers to quantify intrahepatic immune activation beyond cytokine measurement. Our objective was to overcome the practical obstacles of liver sampling using fine-needle aspiration and develop an optimized workflow to comprehensively compare the blood and liver compartments within patients with chronic hepatitis B using single-cell RNA sequencing.

APPROACH AND RESULTS

We developed a workflow that enabled multi-site international studies and centralized single-cell RNA sequencing. Blood and liver fine-needle aspirations were collected, and cellular and molecular captures were compared between the Seq-Well S 3 picowell-based and the 10× Chromium reverse-emulsion droplet-based single-cell RNA sequencing technologies. Both technologies captured the cellular diversity of the liver, but Seq-Well S 3 effectively captured neutrophils, which were absent in the 10× dataset. CD8 T cells and neutrophils displayed distinct transcriptional profiles between blood and liver. In addition, liver fine-needle aspirations captured a heterogeneous liver macrophage population. Comparison between untreated patients with chronic hepatitis B and patients treated with nucleoside analogs showed that myeloid cells were highly sensitive to environmental changes while lymphocytes displayed minimal differences.

CONCLUSIONS

The ability to electively sample and intensively profile the immune landscape of the liver, and generate high-resolution data, will enable multi-site clinical studies to identify biomarkers for intrahepatic immune activity in HBV and beyond.

Role of Matrix Metalloproteinases in Musculoskeletal Diseases

Musculoskeletal disorders include rheumatoid arthritis, osteoarthritis, sarcopenia, injury, stiffness, and bone loss. The prevalence of these conditions is frequent among elderly populations with significant mobility and mortality rates. This may lead to extreme discomfort and detrimental effect on the patient’s health and socioeconomic situation. Muscles, ligaments, tendons, and soft tissue are vital for body function and movement. Matrix metalloproteinases (MMPs) are regulatory proteases involved in synthesizing, degrading, and remodeling extracellular matrix (ECM) components. By modulating ECM reconstruction, cellular migration, and differentiation, MMPs preserve myofiber integrity and homeostasis. In this review, the role of MMPs in skeletal muscle function, muscle injury and repair, skeletal muscle inflammation, and muscular dystrophy and future approaches for MMP-based therapies in musculoskeletal disorders are discussed at the cellular and molecule level.

Adipose-derived stem cells alleviate liver injury induced by type 1 diabetes mellitus by inhibiting mitochondrial stress and attenuating inflammation

Background

Type 1 diabetes mellitus (T1D) is a worldwide health priority due to autoimmune destruction and is associated with an increased risk of multiorgan complications. Among these complications, effective interventions for liver injury, which can progress to liver fibrosis and hepatocellular carcinoma, are lacking. Although stem cell injection has a therapeutic effect on T1D, whether it can cure liver injury and the underlying mechanisms need further investigation.

Methods

Sprague–Dawley rats with streptozotocin (STZ)-induced T1D were treated with adipose-derived stem cell (ADSC) or PBS via the tail vein formed the ADSC group or STZ group. Body weights and blood glucose levels were examined weekly for 6 weeks. RNA-seq and PCR array were used to detect the difference in gene expression of the livers between groups.

Results

In this study, we found that ADSCs injection alleviated hepatic oxidative stress and injury and improved liver function in rats with T1D; potential mechanisms included cytokine activity, energy metabolism and immune regulation were potentially involved, as determined by RNA-seq. Moreover, ADSC treatment altered the fibroblast growth factor 21 (FGF21) and transforming growth factor β (TGF-β) levels in T1D rat livers, implying its repair capacity. Disordered intracellular energy metabolism, which is closely related to mitochondrial stress and dysfunction, was inhibited by ADSC treatment. PCR array and ingenuity pathway analyses suggested that the ADSC-induced suppression of mitochondrial stress is related to decreased necroptosis and apoptosis. Moreover, mitochondria-related alterations caused liver inflammation, resulting in liver injury involving the T lymphocyte-mediated immune response.

Conclusions

Overall, these results improve our understanding of the curative effect of ADSCs on T1D complications: ADSCs attenuate liver injury by inhibiting mitochondrial stress (apoptosis and dysfunctional energy metabolism) and alleviating inflammation (inflammasome expression and immune disorder). These results are important for early intervention in liver injury and for delaying the development of liver lesions in patients with T1D.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02760-z.

Immunobiology and pathogenesis of hepatitis B virus infection

Hepatitis B virus (HBV) is a non-cytopathic, hepatotropic virus with the potential to cause a persistent infection, ultimately leading to cirrhosis and hepatocellular carcinoma. Over the past four decades, the basic principles of HBV gene expression and replication as well as the viral and host determinants governing infection outcome have been largely uncovered. Whereas HBV appears to induce little or no innate immune activation, the adaptive immune response mediates both viral clearance as well as liver disease. Here, we review our current knowledge on the immunobiology and pathogenesis of HBV infection, focusing in particular on the role of CD8⁺ T cells and on several recent breakthroughs that challenge current dogmas. For example, we now trust that HBV integration into the host genome often serves as a relevant source of hepatitis B surface antigen (HBsAg) expression during chronic infection, possibly triggering dysfunctional T cell responses and favouring detrimental immunopathology. Further, the unique haemodynamics and anatomy of the liver - and the changes they frequently endure during disease progression to liver fibrosis and cirrhosis - profoundly influence T cell priming, differentiation and function. We also discuss why therapeutic approaches that limit the intrahepatic inflammatory processes triggered by HBV-specific T cells might be surprisingly beneficial for patients with chronic infection.

Animal Models for the Study of Hepatitis B Virus Pathobiology and Immunity: Past, Present, and Future

Hepatitis B virus (HBV) infection is a global public health problem that plagues approximately 240 million people. Chronic hepatitis B (CHB) often leads to liver inflammation and aberrant repair which results in diseases ranging from liver fibrosis, cirrhosis, to hepatocellular carcinoma. Despite its narrow species tropism, researchers have established various in vivo models for HBV or its related viruses which have provided a wealth of knowledge on viral lifecycle, pathogenesis, and immunity. Here we briefly revisit over five decades of endeavor in animal model development for HBV and summarize their advantages and limitations. We also suggest directions for further improvements that are crucial for elucidation of the viral immune-evasion strategies and for development of novel therapeutics for a functional cure.

HBV X protein-based therapeutic vaccine accelerates viral antigen clearance by mobilizing monocyte infiltration into the liver in HBV carrier mice

Background

Hepatitis B virus (HBV) persistently infected about 250 million people worldwide, and a curative treatment remains an unmet medical need. Among many approaches to treat chronic hepatitis B (CHB), therapeutic vaccines have been developed for two decades, but none have yielded promising results in clinical trials. Therefore, dissection of HBV clearance mechanisms during therapeutic vaccination in appropriate models, which could give rise to new curative therapies, is urgently needed. Growing evidence indicates that prolonged and intensive exposure of antigen-specific T cells to viral antigens is a major cause of T cell exhaustion, and decreases anti-HBV immunity efficacy of therapeutic vaccination. HBV X protein (HBx) is expressed at low levels, and the understanding of its immunogenicity and potential in therapeutic CHB vaccines is limited.

Methods

HBV genome sequences from CHB patients were cloned into a pAAV plasmid backbone and transfected into immunocompetent mouse hepatocytes through hydrodynamic injection. Mice carrying > 500 IU/mL serum HBV surface antigen (HBs) for more than 4 weeks were considered HBV carriers mimicking human CHB and received 3 doses of weekly HBx vaccine by subcutaneous immunization. Serum HBV clearance was evaluated by monitoring serum HBs and HBV-DNA titers. Residual HBV in the liver was evaluated by western blotting for HBV core antigen. The splenic antigen-specific T cell response was quantified by a 15-mer overlapping peptide-stimulated interferon-γ enzyme-linked immunospot assay. Blood and hepatic immune cells were quantified by flow cytometric analysis.

Results

Our HBx-based vaccine induced systemic HBx-specific CD4⁺ and CD8⁺ T cell responses in HBV carrier mice and demonstrated significant HBs and HBV-DNA elimination. The protective effect persisted for at least 30 days without additional booster immunization. Different infiltrating myeloid cell subsets, each with distinctive roles during immune-mediated HBV clearance, were found in the liver of vaccinated mice. During vaccine therapy, inflammatory monocyte depletion resulted in sustained HBV clearance inhibition, whereas phagocytic monocyte-derived macrophage and Kupffer cell elimination resulted in only transient inhibition of vaccine-induced HBV clearance.

Conclusions

We report the potential role of HBx as a major immunogen in an HBV therapeutic vaccine and the significance of a liver-infiltrating monocyte subset during hepatic viral clearance.

MMP2/MMP9-mediated CD100 shedding is crucial for inducing intrahepatic anti-HBV CD8 T cell responses and HBV clearance

BACKGROUND & AIMS

CD100 is constitutively expressed on T cells and can be cleaved from the cell surface by matrix metalloproteases (MMPs) to become soluble CD100 (sCD100). Both membrane-bound CD100 (mCD100) and sCD100 have important immune regulatory functions that promote immune cell activation and responses. This study investigated the expression and role of mCD100 and sCD100 in regulating antiviral immune responses during HBV infection.

METHODS

mCD100 expression on T cells, sCD100 levels in the serum, and MMP expression in the liver and serum were analysed in patients with chronic HBV (CHB) and in HBV-replicating mice. The ability of sCD100 to mediate antigen-presenting cell maturation, HBV-specific T cell activation, and HBV clearance were analysed in HBV-replicating mice and patients with CHB.

RESULTS

Patients with CHB had higher mCD100 expression on T cells and lower serum sCD100 levels compared with healthy controls. Therapeutic sCD100 treatment resulted in the activation of DCs and liver sinusoidal endothelial cells, enhanced HBV-specific CD8 T cell responses, and accelerated HBV clearance, whereas blockade of its receptor CD72 attenuated the intrahepatic anti-HBV CD8 T cell response. Together with MMP9, MMP2 mediated mCD100 shedding from the T cell surface. Patients with CHB had significantly lower serum MMP2 levels, which positively correlated with serum sCD100 levels, compared with healthy controls. Inhibition of MMP2/9 activity resulted in an attenuated anti-HBV T cell response and delayed HBV clearance in mice.

CONCLUSIONS

MMP2/9-mediated sCD100 release has an important role in regulating intrahepatic anti-HBV CD8 T cell responses, thus mediating subsequent viral clearance during HBV infection.

LAY SUMMARY

Chronic hepatitis B virus (HBV) infection is a major public health problem worldwide. The clearance of HBV relies largely on an effective T cell immune response, which usually becomes dysregulated in chronic HBV infection. Our study provides a new mechanism to elucidate HBV persistence and a new target for developing immunotherapy strategies in patients chronically infected with HBV.

In Vivo Model Systems for Hepatitis B Virus Research

Hepatitis B virus (HBV) affects more than 257 million people globally, resulting in progressively worsening liver disease, manifesting as fibrosis, cirrhosis, and hepatocellular carcinoma. The exceptionally narrow species tropism of HBV restricts its natural hosts to humans and non-human primates, including chimpanzees, gorillas, gibbons, and orangutans. The unavailability of completely immunocompetent small-animal models has contributed to the lack of curative therapeutic interventions. Even though surrogates allow the study of closely related viruses, their host genetic backgrounds, immune responses, and molecular virology differ from those of HBV. Various different models, based on either pure murine or xenotransplantation systems, have been introduced over the past years, often making the choice of the optimal model for any given question challenging. Here, we offer a concise review of in vivo model systems employed to study HBV infection and steps in the HBV life cycle or pathogenesis.

Immunotherapy for Chronic Hepatitis B Virus Infection

While new therapies for chronic hepatitis C virus infection have delivered remarkable cure rates, curative therapies for chronic hepatitis B virus (HBV) infection remain a distant goal. Although current direct antiviral therapies are very efficient in controlling viral replication and limiting the progression to cirrhosis, these treatments require lifelong administration due to the frequent viral rebound upon treatment cessation, and immune modulation with interferon is only effective in a subgroup of patients. Specific immunotherapies can offer the possibility of eliminating or at least stably maintaining low levels of HBV replication under the control of a functional host antiviral response. Here, we review the development of immune cell therapy for HBV, highlighting the potential antiviral efficiency and potential toxicities in different groups of chronically infected HBV patients. We also discuss the chronic hepatitis B patient populations that best benefit from therapeutic immune interventions.

Innate-like Cytotoxic Function of Bystander-Activated CD8+ T Cells Is Associated with Liver Injury in Acute Hepatitis A

Acute hepatitis A (AHA) involves severe CD8⁺ T cell-mediated liver injury. Here we showed during AHA, CD8⁺ T cells specific to unrelated viruses became activated. Hepatitis A virus (HAV)-infected cells produced IL-15 that induced T cell receptor (TCR)-independent activation of memory CD8⁺ T cells. TCR-independent activation of non-HAV-specific CD8⁺ T cells were detected in patients, as indicated by NKG2D upregulation, a marker of TCR-independent T cell activation by IL-15. CD8⁺ T cells derived from AHA patients exerted innate-like cytotoxicity triggered by activating receptors NKG2D and NKp30 without TCR engagement. We demonstrated that the severity of liver injury in AHA patients correlated with the activation of HAV-unrelated virus-specific CD8⁺ T cells and the innate-like cytolytic activity of CD8⁺ T cells, but not the activation of HAV-specific T cells. Thus, host injury in AHA is associated with innate-like cytotoxicity of bystander-activated CD8⁺ T cells, a result with implications for acute viral diseases.

How Does Interleukin-22 Mediate Liver Regeneration and Prevent Injury and Fibrosis?

Interleukin-22 (IL-22) is a pluripotent T cell-derived cytokine which is a member of IL-10 cytokine family. It is the only interleukin produced by immune cells but does not target immune system components. IL-22 is mainly produced by dendritic cells (DCs) and TH17, TH22, NK, and NKT cells and targets a number of body tissues including liver, pancreas, and other epithelial tissues. It provokes a series of downstream signaling pathways upon binding with IL-22R complex which protects liver damage through STAT3 activation. IL-22BP is an inhibitor of IL-22 which has 20-1000x more affinity to bind with IL-22 compared to IL-22R1 that inhibits IL-22 activity. Its level was found to be positively correlated with the severity of liver damage and fibrosis. So, the present review is an effort to reveal the exact mechanism lying in the hepatoprotective activity of IL-22 and some of its future therapeutic implications.

Experimental in vitro and in vivo models for the study of human hepatitis B virus infection

Chronic infection with the hepatitis B virus (HBV) affects an estimate of 240 million people worldwide despite the availability of a preventive vaccine. Medication to repress viral replication is available but a cure is rarely achieved. The narrow species and tissue tropism of the virus and the lack of reliable in vitro models and laboratory animals susceptible to HBV infection, have limited research progress in the past. As a result, several aspects of the HBV life cycle as well as the network of virus host interactions occurring during the infection are not yet understood. Only recently, the identification of the functional cellular receptor enabling HBV entry has opened new possibilities to establish innovative infection systems. Regarding the in vivo models of HBV infection, the classical reference was the chimpanzee. However, because of the strongly restricted use of great apes for HBV research, major efforts have focused on the development of mouse models of HBV replication and infection such as the generation of humanized mice. This review summarizes the animal and cell culture based models currently available for the study of HBV biology. We will discuss the benefits and caveats of each model and present a selection of the most important findings that have been retrieved from the respective systems.

Immune-mediated Liver Injury in Hepatitis B Virus Infection

Hepatitis B virus (HBV) is responsible for approximately 350 million chronic infections worldwide and is a leading cause of broad-spectrum liver diseases such as hepatitis, cirrhosis and liver cancer. Although it has been well established that adaptive immunity plays a critical role in viral clearance, the pathogenetic mechanisms that cause liver damage during acute and chronic HBV infection remain largely known. This review describes our current knowledge of the immune-mediated pathogenesis of HBV infection and the role of immune cells in the liver injury during hepatitis B.

Sorafenib Action in Hepatitis B Virus X-Activated Oncogenic Androgen Pathway in Liver through SHP-1

BACKGROUND

Hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) shows a higher incidence in men, mainly because of hepatitis B X (HBx)-mediated enhancement of androgen receptor (AR) activity. We aimed to examine this pathway in hepatocarcinogenesis and to identify drug(s) specifically blocking this carcinogenic event in the liver.

METHODS

HBx transgenic mice that spontaneously develop HCC (n = 28-34 per group) were used, either by knockout of hepatic AR or by castration. Efficacy of several HCC-targeted drugs in suppressing HBx-induced AR activity was evaluated, and cellular factors mediating suppression were investigated in cultured cells. Tissue specificity of the candidate drug was validated using mouse tissues. Data were analyzed with Chi-square and Student's t tests. All statistical tests were two-sided.

RESULTS

The androgen pathway was shown to be important in early stage hepatocarcinogenesis of HBx transgenic mice. The tumor incidence was decreased from 80% to 32% by AR knockout (P < .001) and from 90% to 25% by early castration (P < .001). Sorafenib markedly inhibited the HBx-enhanced AR activity through activating the SHP-1 phosphatase, which antagonized the activation of Akt/GSK3β and c-Src by HBx. Moreover, SHP-1 protein level was much higher in the liver than in testis, which enabled sorafenib to inhibit aberrant AR activity in the HBx-expressing liver, while not affecting the physiological AR function in normal liver or testis.

CONCLUSIONS

The androgen pathway may be a druggable target for the chemoprevention of HBV-related HCC, and sorafenib might be used as a tissue- and disease-specific regimen for the chemoprevention of HBV-related HCC.

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.

Activation and Exhaustion of Adaptive Immune Cells in Hepatitis B Infection

In hepatitis B virus (HBV) infection, the immune reaction is responsible for viral clearance and preventing their spread within the host. However, the immune system is dysfunctional in patients with chronic HBV infection, leading to an inadequate immune response against the virus. A major factor contributing to inefficient immune function is the phenomenon of immune exhaustion. Hence, understanding immune activation and exhaustion during HBV infection is important, as it would provide insight in developing immunotherapy to control chronic HBV infection. The aim of this review is to highlight the existing information on immune effector functions and immune exhaustion in response to HBV infection.

Metabolic regulation of hepatitis B immunopathology by myeloid-derived suppressor cells

Infection with hepatitis B virus (HBV) results in disparate degrees of tissue injury: the virus can either replicate without pathological consequences or trigger immune-mediated necroinflammatory liver damage. We investigated the potential for myeloid-derived suppressor cells (MDSCs) to suppress T cell-mediated immunopathology in this setting. Granulocytic MDSCs (gMDSCs) expanded transiently in acute resolving HBV, decreasing in frequency prior to peak hepatic injury. In persistent infection, arginase-expressing gMDSCs (and circulating arginase) increased most in disease phases characterized by HBV replication without immunopathology, whilst L-arginine decreased. gMDSCs expressed liver-homing chemokine receptors and accumulated in the liver, their expansion supported by hepatic stellate cells. We provide in vitro and ex vivo evidence that gMDSCs potently inhibited T cells in a partially arginase-dependent manner. L-arginine-deprived T cells upregulated system L amino acid transporters to increase uptake of essential nutrients and attempt metabolic reprogramming. These data demonstrate the capacity of expanded arginase-expressing gMDSCs to regulate liver immunopathology in 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.

Anti-inflammatory and anti-fibrotic profile of fish oil emulsions used in parenteral nutrition-associated liver disease

Home parenteral nutrition (PN) is associated with many complications including severe hepatobiliary dysfunction. Commercial ω-6 fatty acid-soybean based-lipid emulsions in PN may mediate long term PN associate liver disease (PNALD) whereas ω-3-fish oil parenteral emulsions have shown to reverse PNALD in children. However, its clinical effectiveness in adults has been scarcely reported. In this work, we study the role of soybean and fish oil lipid commercial emulsions on inflammatory and profibrotic liver markers in adults with long term PNALD and in in vitro cellular models. Inflammatory and profibrotic markers were measured in serum of ten adults with long term PNALD and in culture supernatants of monocytes. Liver epithelial to mesenchymal transition (EMT) was induced by transforming growth factor beta 1 (TGFβ1) to evaluate in vitro liver fibrosis. Omegaven®, a 100% fish oil commercial emulsion, was infused during four months in two patients with severe long term PNALD reversing, at the first month, the inflammatory, profibrotic and clinical parameters of PNALD. The effect was maintained during the treatment course but impaired when conventional lipid emulsions were reintroduced. The other patients under chronic soybean oil-based PN showed elevated inflammatory and profibrotic parameters. In vitro human monocytes stimulated with lipopolysaccharide induced a strong inflammatory response that was suppressed by Omegaven®, but increased by soybean emulsions. In other experiments, TGFβ1 induced EMT that was suppressed by Omegaven® and enhanced by soybean oil lipid emulsions. Omegaven® improves clinical, anti-inflammatory and anti-fibrotic parameters in adults with long-term home PNALD.

The immune tolerant phase of chronic HBV infection: new perspectives on an old concept

Chronic hepatitis B virus (HBV) infection progresses through distinct disease phases that are strongly associated with patient age. The so-called immune tolerant (IT) phase represents the classical early phase of infection; it is associated with high levels of HBV replication and lack of clinical signs of liver Inflammation. Whether this phase of HBV infection is also associated with immunological features of "tolerance' has recently been challenged. Here, we review the data that dispute this concept of immune tolerance and then propose an alternative interpretation of the immunopathological events that take place during this early phase of CHB infection.

Hepatic immune regulation and its involvement in viral hepatitis infection

The liver has unique immune regulatory functions that promote the induction of tolerance rather than responses to antigens encountered locally. These functions are mediated by local expression of coinhibitory receptors and immunosuppressive mediators that help prevent overwhelming tissue damage. Over the years, we have gained more insight into the local regulatory cues that determine the functional complexity of immune responses regulated locally in the liver. Both the unique hepatic microenvironment and the particular liver sinusoidal cell populations, in addition to hepatocytes, actively modulate immune responses locally in the liver and thereby determine the outcome of hepatic immune responses. This is of high biological and clinical relevance in hepatitis B virus and hepatitis C virus infections, which can cause acute and persistent infections associated with chronic inflammation in humans that eventually progress to cirrhosis and hepatocellular carcinoma. Here, we review current knowledge about the balance between immunity and tolerance in the liver and how this may affect our understanding of the determinants of hepatitis B virus and hepatitis C virus clearance, persistence, and virus-induced liver disease.

Mouse models of hepatitis B virus infection comprising host-virus immunologic interactions

Hepatitis B virus (HBV) infection is one of the most prevalent infectious diseases associated with various human liver diseases, including acute, fulminant and chronic hepatitis; liver cirrhosis; and hepatocellular carcinoma. Despite the availability of an HBV vaccine and the development of antiviral therapies, there are still more than 350 million chronically infected people worldwide, approximately 5% of the world population. To understand the virus biology and pathogenesis in HBV-infected patients, several animal models have been developed to mimic hepatic HBV infection and the immune response against HBV, but the narrow host range of HBV infection and lack of a full immune response spectrum in animal models remain significant limitations. Accumulating evidence obtained from studies using a variety of mouse models that recapitulate hepatic HBV infection provides several clues for understanding host-virus immunologic interactions during HBV infection, whereas the determinants of the immune response required for HBV clearance are poorly defined. Therefore, adequate mouse models are urgently needed to elucidate the mechanism of HBV elimination and identify novel targets for antiviral therapies.

Increased metabolites of 5-lipoxygenase from hypoxic ovarian cancer cells promote tumor-associated macrophage infiltration

5-lipoxygenase (5-LOX), a member of the lipoxygenase gene family, is a key enzyme assisting in the conversion of arachidonic acid to 5-HETE and leukotrienes. Tumor-associated macrophages (TAMs) have a critical role in the progression and metastasis of many tumors, including ovarian tumors. Moreover, TAMs are often found in a high density in the hypoxic areas of tumors. However, the relevant mechanisms have not been studied explicitly until now. In this study, we found that the expression of 5-LOX strongly correlated with the density of TAMs in hypoxic areas of human ovarian tumor tissues. In cultured ovarian cancer cells, 5-LOX metabolites were increased under hypoxic conditons. Increased 5-LOX metabolites from hypoxic ovarian cancer cells promoted migration and invasion of macrophages, which was further demonstrated to be mediated by the upregulation of matrix metalloproteinase (MMP)-7 expression through the p38 pathway. Besides, we also showed that 5-LOX metabolites enhanced the release of tumor necrosis factor (TNF-α) and heparin-binding epidermal growth factor-like growth factor through upregulation of MMP-7. Furthermore, in animal models, Zileuton (a selective and specific 5-LOX inhibitor) reduced the MMP-7 expression and the number of macrophages infiltrating in the xenograft. Our findings suggest for the first time that increased metabolites of 5-LOX from hypoxic ovarian cancer cells promote TAM infiltration. These results of this study have immediate translational implications for the therapeutic exploitation of TAMs.

Mouse models of hepatitis B and delta virus infection

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. Therapeutic regimens currently available can efficiently suppress HBV replication; however, the unique replication strategies employed by HBV permit the virus to persist within the infected hepatocytes. As a consequence, relapse of viral activity is commonly observed after cessation of treatment with polymerase inhibitors. Among the HBV chronically infected patients, more than 15million patients are estimated to be co-infected with the hepatitis delta virus (HDV), a defective satellite virus that needs the HBV envelope for propagation. No specific drugs are currently available against HDV, while nucleos(t)ide analogs are not effective against HDV replication. Since chronic HBV/HDV co-infection leads to the most severe form of chronic viral hepatitis in men, a better understanding of the molecular mechanisms of HDV-mediated pathogenesis and the development of improved therapeutic approaches is urgently needed. The obvious limitations imposed by the use of great apes and the paucity of robust experimental models of HBV infection have hindered progresses in understanding the complex network of virus-host interactions that are established in the course of HBV and HDV infections. This review focuses on summarizing recent advances obtained with well-established and more innovative experimental mouse models, giving emphasis on the strength of infection systems based on the reconstitution of the murine liver with human hepatocytes, as tools for elucidating the whole life cycle of HBV and HDV, as well as for studies on interactions with the infected human hepatocytes and for preclinical drug evaluation.

Pathogenesis of chronic viral hepatitis: differential roles of T cells and NK cells

Chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infections account for 57% of cases of liver cirrhosis and 78% of cases of primary liver cancer worldwide and cause a million deaths per year. Although HBV and HCV differ in their genome structures, replication strategies and life cycles, they have common features, including their noncytopathic nature and their capacity to induce chronic liver disease, which is thought to be immune mediated. However, the rate of disease progression from chronic hepatitis to cirrhosis varies greatly among infected individuals, and the factors that regulate it are largely unknown. This review summarizes our current understanding of the roles of antigen-specific and nonspecific immune cells in the pathogenesis of chronic hepatitis B and C and discusses recent findings that identify natural killer cells as regulators of T cell function and liver inflammation.

Liver immune-pathogenesis and therapy of human liver tropic virus infection in humanized mouse models

Hepatitis B virus (HBV) and hepatitis C virus (HCV) infect and replicate primarily in human hepatocytes. Few reliable and easy accessible animal models are available for studying the immune system's contribution to the liver disease progression during hepatitis virus infection. Humanized mouse models reconstituted with human hematopoietic stem cells (HSCs) have been developed to study human immunology, human immunodeficiency virus 1 infection, and immunopathogenesis. However, a humanized mouse model engrafted with both human immune and human liver cells is needed to study infection and immunopathogenesis of HBV/HCV infection in vivo. We have recently developed the humanized mouse model with both human immune and human liver cells (AFC8-hu HSC/Hep) to study immunopathogenesis and therapy of HCV infection in vivo. In this review, we summarize the current models of HBV/HCV infection and their limitations in immunopathogenesis. We will then present our recent findings of HCV infection and immunopathogenesis in the AFC8-hu HSC/Hep mouse, which supports HCV infection, human T-cell response and associated liver pathogenesis. Inoculation of humanized mice with primary HCV isolates resulted in long-term HCV infection. HCV infection induced elevated infiltration of human immune cells in the livers of HCV-infected humanized mice. HCV infection also induced HCV-specific T-cell immune response in lymphoid tissues of humanized mice. Additionally, HCV infection induced liver fibrosis in humanized mice. Anti-human alpha smooth muscle actin (αSMA) staining showed elevated human hepatic stellate cell activation in HCV-infected humanized mice. We discuss the limitation and future improvements of the AFC8-hu HSC/Hep mouse model and its application in evaluating novel therapeutics, as well as studying both HCV and HBV infection, human immune responses, and associated human liver fibrosis and cancer.

Hepatitis B virus (HBV) induces the expression of interleukin-8 that in turn reduces HBV sensitivity to interferon-alpha

High levels of serum interleukin-8 (IL-8) have been detected in chronic hepatitis B (CHB) patients during episodes of hepatitis flares. We investigated whether hepatitis B virus (HBV) may directly induce IL-8 production and whether IL-8 may antagonize interferon-alpha (IFN-α) antiviral activity against HBV. We showed that CHB patients had significantly higher IL-8 levels both in serum and in liver tissue than controls. In HBV-replicating HepG2 cells, IL-8 transcription was significantly activated. AP-1, C/EBP and NF-kB transcription factors were concurrently necessary for maximum IL-8 induction. Moreover, HBx viral protein was recruited onto the IL-8 promoter and this was paralleled by IL8-bound histone hyperacetylation and by active recruitment of transcriptional coactivators. Inhibition of IL-8 increases the antiviral activity of IFN-α against HBV. Our results indicate that HBV activates IL-8 gene expression by targeting the epigenetic regulation of the IL-8 promoter and that IL-8 may contribute to reduce HBV sensitivity to IFN-α.

The L60V variation in hepatitis B virus core protein elicits new epitope-specific cytotoxic T lymphocytes and enhances viral replication

Mutations in the core protein (HBc) of hepatitis B virus (HBV) are associated with aggressive hepatitis and advanced liver diseases in chronic hepatitis B (CHB). In this study, we identified the L60V variation in HBc that generates a new HLA-A2-restricted CD8(+) T cell epitope by screening an overlapping 9-mer peptide pool covering HBc and its variants. The nonameric epitope V60 was determined by structural and immunogenic analysis. The HBc L60V variation is correlated with hepatic necroinflammation and higher viral levels, and it may be associated with a poor prognosis in CHB patients. Immunization with the defined HBV epitope V60 peptide elicited specific cytotoxic T lymphocyte (CTL)-induced liver injury in HLA-A2(+) HBV transgenic mice. In addition, in vitro and in vivo experiments both demonstrated that the HBc L60V variation facilitates viral capsid assembly and increases HBV replication. These data suggest that the HBc L60V variation can impact both HBV replication and HBV-specific T cell responses. Therefore, our work provides further dissection of the impact of the HBc L60V variation, which orchestrates HBV replication, viral persistence, and immunopathogenesis during chronic viral infection.

Protective and pathological properties of IL-22 in liver disease: implications for viral hepatitis

Chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infection affect >500 million people worldwide and are significant causes of liver cirrhosis and hepatocellular carcinoma. The pathogenesis of HBV and HCV infection can vary widely with respect to the outcome of initial infection to self-resolving acute or chronic disease, the extent of viremia and liver inflammation during chronic infection, and the eventual development of liver cirrhosis and hepatocellular carcinoma. The host immune response is an important factor in the variable consequences of these infections, because the innate and adaptive intrahepatic antiviral responses are an intricate balance of immune effector cells and cytokines that control virus replication but can also cause liver damage. IL-22 is an important cytokine that plays a pleiotropic protective, but sometimes also pathological, role in several tissues/organs, including the liver. Therefore, IL-22 is likely to be an important factor in the pathogenesis and clinical outcome of HBV and HCV infection. However, the precise beneficial, and possible detrimental, effects of this cytokine may vary among different disease states that are associated with distinct inflammatory microenvironments. This review summarizes our understanding of the protective and pathological activities of IL-22, with an emphasis on the liver, and discusses the implications of these effects as they relate to viral hepatitis.

Inducible nitric oxide synthase inhibition increases MMP-2 activity leading to imbalance between extracellular matrix deposition and degradation after polypropylene mesh implant

Prosthetic mesh implants are commonly used to correct abdominal wall defects. However, success of the procedure is conditioned by an adequate inflammatory response to the device. We hypothesized that nitric oxide produced by nitric oxide synthase 2 (NOS2) and MMP-2 and -9 participate in response induced by mesh implants in the abdominal wall and, consequently, affect the outcome of the surgical procedure. In the first step, temporal inflammatory markers profile was evaluated. Polypropylene meshes were implanted in the peritoneal side of the abdominal wall of C57Black mice. After 2, 4, 7, 15, and 30 days, tissues around the mesh implant were collected and inflammatory markers were analyzed. In the second step, NOS2 activity was inhibited with nitro-L-arginine methyl ester (L-NAME). Samples were collected after 15 days (when inflammation was reduced), and the inflammatory and tissue remodeling markers were investigated. Polypropylene mesh implant induced a pro-inflammatory environment mediated by intense MMP-2 and -9 activities, NO release, and interleukin-1β production peaking in 7 days and gradually decreasing after 15 days. NOS2 inhibition increased MMP-2 activity and resulted in a higher visceral adhesion incidence at the mesh implantation site when compared with non-treated animals that underwent the same procedure. We conclude that NOS2-derived NO is crucial for adequate response to polypropylene mesh implant integration in the peritoneum. NO deficiency results in an imbalance between extracellular matrix deposition/degradation contributing to visceral adhesions incidence.

Transcriptomic analysis of the woodchuck model of chronic hepatitis B

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

CONCLUSION

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

Experimental models and therapeutic approaches for HBV

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. In spite of the existence of an effective vaccine, approximately 360 million people are chronically infected worldwide, who are at high risk of developing liver cirrhosis and hepatocellular carcinoma. Although current therapeutic regimens can efficiently suppress viral replication, the unique replication strategies employed by HBV permit the virus to persist within the infected hepatocytes. As a consequence, relapse of viral activity is commonly observed after cessation of treatment with polymerase inhibitors. The narrow host range of HBV has hindered progresses in understanding specific steps of HBV replication and the development of more effective therapeutic strategies aiming at achieving sustained viral control and, eventually, virus eradication. This review will focus on summarizing recent advances obtained with well-established and more innovative experimental models, giving emphasis on the strength of the different systems as tools for elucidating distinct aspects of HBV persistence and for the development of new therapeutic approaches.

Antiplatelet therapy prevents hepatocellular carcinoma and improves survival in a mouse model of chronic hepatitis B

Chronic infection with hepatitis B virus (HBV) is a major risk factor for the development of hepatocellular carcinoma (HCC). The pathogenesis of HBV-associated HCC involves both viral and host factors. The latter include a functionally inefficient CD8(+) T-cell response that fails to clear the infection from the liver but sustains a chronic necroinflammatory process that contributes to the development of HCC. According to this scenario, amelioration of immune-mediated chronic liver injury may prevent HCC. Because platelets facilitate immune-mediated liver injury by promoting the hepatic accumulation of virus-specific CD8(+) T cells, we evaluated the long-term consequences of antiplatelet therapy in an HBV transgenic mouse model of chronic immune-mediated necroinflammatory liver disease that progresses to HCC. Treatment with aspirin and clopidogrel during the chronic phase of the disease diminished the number of intrahepatic HBV-specific CD8(+) T cells and HBV-nonspecific inflammatory cells, the severity of liver fibrosis, and the development of HCC. Antiplatelet therapy improved overall survival without causing significant side effects. In contrast, the same antiplatelet regimen had no antitumor effect when HCC was induced nonimmunologically by chronic exposure to a hepatotoxic chemical. The unprecedented observation that antiplatelet therapy inhibits or delays immune-mediated hepatocarcinogenesis suggests that platelets may be key players in the pathogenesis of HBV-associated liver cancer and supports the notion that immune-mediated necroinflammatory reactions are an important cause of hepatocellular transformation during chronic hepatitis.

Immunopathogenesis and prognostic immune markers of chronic hepatitis B virus infection

Host immune responses induced by hepatitis B virus (HBV) infection not only substantially drive disease progression, but also significantly influence efficacy of antiviral treatments in HBV-infected individuals. Therefore, it is important to fully understand the course of immune pathogenesis and to find efficient immunological markers that can predict the disease progression of chronic HBV infection. This review introduces the current progress in clinical immunology and analyzes the mechanisms of antiviral effects and liver injury, which are induced by both innate and adaptive immune responses. The recently identified immunological markers indicated to be closely correlated with disease progression and antiviral efficacy during HBV infection are also summarized. Careful monitoring of these immune markers may help physicians to make decisions on when to begin or withdraw antiviral drugs, or to formulate the prognosis of acute-on-chronic liver failure (ACLF) patients in the clinic. Finally, this review highlights some novel therapeutic strategies to modulate host immunity that have been proposed to sustain antiviral control of chronic HBV infection, as well as the challenges that we are presently facing in the field.

Nitric oxide modulates metalloproteinase-2, collagen deposition and adhesion rate after polypropylene mesh implantation in the intra-abdominal wall

Prosthetic meshes are commonly used to correct abdominal wall defects. However, the inflammatory reaction induced by these devices in the peritoneum is not completely understood. We hypothesized that nitric oxide (NO), produced by nitric oxide synthase 2 (NOS2) may modulate the response induced by mesh implants in the abdominal wall and, consequently, affect the outcome of the surgical procedure. Polypropylene meshes were implanted in the peritoneal side of the abdominal wall in wild-type and NOS2-deficient (NOS2(-/-)) mice. After 15 days tissues around the mesh implant were collected, and inflammatory markers (the cytokine interleukin 1β (IL-1β) and NO) and tissue remodeling (collagen and metalloproteinases (MMP) 2 and 9) were analyzed. The lack of NOS2-derived NO induced a higher incidence of visceral adhesions at the mesh implantation site compared with wild-type mice that underwent the same procedure (P<0.05). Additionally, higher levels of IL-1β were present in the mesh-implanted NOS2(-/-) animals compared with control and wild-type mice. Mesh implantation induced collagen I and III deposition, but in smaller amounts in NOS2(-/-) mice. MMP-9 activity after the surgical procedure was similarly increased in both groups. Conversely, MMP-2 activity was unchanged in mesh-implanted wild-type mice, but was significantly increased in NOS2(-/-) mice (P<0.01), due to decreased S-nitrosylation of the enzyme in these animals. We conclude that NOS2-derived NO is crucial for an adequate response to and integration of polypropylene mesh implants in the peritoneum. NO deficiency results in a prolonged inflammatory reaction to the mesh implant, and reduced collagen deposition may contribute to an increased incidence of visceral adhesions.

A proinflammatory role for interleukin-22 in the immune response to hepatitis B virus

BACKGROUND & AIMS

T-helper (Th)17 cells that secrete interleukin (IL)-22 have immunomodulatory and protective properties in the liver and other tissues. IL-22 induces expression of proinflammatory genes but is also mitogenic and antiapoptotic in hepatocytes. Therefore, it could have multiple functions in the immune response to hepatitis B virus (HBV).

METHODS

We examined the role of IL-22 in regulating liver inflammation in HBV transgenic mice and measured levels of IL-22 in HBV-infected patients.

RESULTS

In HBV transgenic mice, injection of a single dose of IL-22 increased hepatic expression of proinflammatory genes but did not directly inhibit virus replication. When splenocytes from HBV-immunized mice were transferred into HBV transgenic mice, the severity of the subsequent liver damage was ameliorated by neutralization of IL-22. In this model, IL-22 depletion did not affect interferon gamma-mediated noncytopathic inhibition of virus replication initiated by HBV-specific cytotoxic T cells, but it significantly inhibited recruitment of antigen-nonspecific inflammatory cells into the liver. In patients with acute HBV infections, the percentage of Th17 cells in peripheral blood and concentration of IL-22 in serum were significantly increased.

CONCLUSIONS

IL-22 appears to be an important mediator of the inflammatory response following recognition of HBV by T cells in the liver. These findings might be relevant to the development of cytokine-based therapies for patients with HBV infection.

Delayed induction, not impaired recruitment, of specific CD8⁺ T cells causes the late onset of acute hepatitis C

BACKGROUND & AIMS

Hepatitis C virus (HCV) infection is characterized by lack of immune-mediated liver injury despite a high level of HCV replication during the incubation phase, which lasts about 8 weeks. We investigated whether this results from delayed recruitment of HCV-specific T cells and whether it facilitates HCV persistence.

METHODS

Six chimpanzees were infected with HCV; blood and liver samples were collected for 28 weeks and analyzed for immune cells and chemokines.

RESULTS

Two chimpanzees developed self-limited infections, whereas the remaining 4 developed chronic infections. Levels of the chemokines CXCL10, CXCL11, CCL4, and CCL5 increased in blood and liver samples from all chimpanzees within 1 month of HCV infection. Chemokine induction correlated with intrahepatic type I interferon (IFN) responses in vivo and was blocked by neutralizing antibodies against IFN-β in vitro. Despite the early-stage induction of chemokines, the intrahepatic lymphocytic infiltrate started to increase no earlier than 8 weeks after HCV infection, when HCV-specific, tetramer-positive CD8(+) T cells appeared in the circulation. The HCV-specific CD8(+) T cells expressed chemokine receptors when they were initially detected in blood samples, so they could be recruited to the liver as soon as they entered the circulation.

CONCLUSIONS

Chemokines are induced during early stages of HCV infection, which requires a type I IFN-mediated response. The delayed onset of acute hepatitis does not result from delayed recruitment of HCV-specific T cells, but could instead be related to a primary delay in the induction of HCV-specific T cells. Divergent outcomes occur without evident differences in chemokine induction and T-cell recruitment.

Kupffer cells hasten resolution of liver immunopathology in mouse models of viral hepatitis

Kupffer cells (KCs) are widely considered important contributors to liver injury during viral hepatitis due to their pro-inflammatory activity. Herein we utilized hepatitis B virus (HBV)-replication competent transgenic mice and wild-type mice infected with a hepatotropic adenovirus to demonstrate that KCs do not directly induce hepatocellular injury nor do they affect the pathogenic potential of virus-specific CD8 T cells. Instead, KCs limit the severity of liver immunopathology. Mechanistically, our results are most compatible with the hypothesis that KCs contain liver immunopathology by removing apoptotic hepatocytes in a manner largely dependent on scavenger receptors. Apoptotic hepatocytes not readily removed by KCs become secondarily necrotic and release high-mobility group box 1 (HMGB-1) protein, promoting organ infiltration by inflammatory cells, particularly neutrophils. Overall, these results indicate that KCs resolve rather than worsen liver immunopathology.

Kupffer cells (KCs), the resident macrophages of the liver, are considered important contributors to liver injury during viral hepatitis due to their pro-inflammatory activity. Herein we utilized two different mouse models of viral hepatitis (where liver damage is triggered, as during viral hepatitis in humans, by virus-specific CD8 T cells) to show that KCs do not directly induce liver injury nor do they affect the pathogenic potential of virus-specific CD8 T cells. Instead, KCs limit the severity of liver immunopathology. Mechanistically, our results are most compatible with the hypothesis that KCs contain liver immunopathology by removing dying hepatocytes. Dying hepatocytes not readily removed by KCs release high-mobility group box 1 (HMGB-1) protein, promoting organ infiltration by inflammatory cells, particularly neutrophils. These results indicate that KCs resolve rather than worsen liver disease.

Hyper-activated pro-inflammatory CD16 monocytes correlate with the severity of liver injury and fibrosis in patients with chronic hepatitis B

BACKGROUND

Extensive mononuclear cell infiltration is strongly correlated with liver damage in patients with chronic hepatitis B virus (CHB) infection. Macrophages and infiltrating monocytes also participate in the development of liver damage and fibrosis in animal models. However, little is known regarding the immunopathogenic role of peripheral blood monocytes and intrahepatic macrophages.

METHODOLOGY/PRINCIPAL FINDINGS

The frequencies, phenotypes, and functions of peripheral blood and intrahepatic monocyte/macrophage subsets were analyzed in 110 HBeAg positive CHB patients, including 32 immune tolerant (IT) carriers and 78 immune activated (IA) patients. Liver biopsies from 20 IA patients undergoing diagnosis were collected for immunohistochemical analysis. IA patients displayed significant increases in peripheral blood monocytes and intrahepatic macrophages as well as CD16(+) subsets, which were closely associated with serum alanine aminotransferase (ALT) levels and the liver histological activity index (HAI) scores. In addition, the increased CD16(+) monocytes/macrophages expressed higher levels of the activation marker HLA-DR compared with CD16(-) monocytes/macrophages. Furthermore, peripheral blood CD16(+) monocytes preferentially released inflammatory cytokines and hold higher potency in inducing the expansion of Th17 cells. Of note, hepatic neutrophils also positively correlated with HAI scores.

CONCLUSIONS

These distinct properties of monocyte/macrophage subpopulations participate in fostering the inflammatory microenvironment and liver damage in CHB patients and further represent a collaborative scenario among different cell types contributing to the pathogenesis of HBV-induced liver disease.

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.

Hapten application to the skin induces an inflammatory program directing hapten-primed effector CD8 T cell interaction with hapten-presenting endothelial cells

Contact hypersensitivity is a CD8 T cell-mediated response to hapten sensitization and challenge of the skin. Effector CD8 T cell recruitment into the skin parenchyma to elicit the response to hapten challenge requires prior CXCL1/KC-directed neutrophil infiltration within 3-6 h after challenge and is dependent on IFN-γ and IL-17 produced by the hapten-primed CD8 T cells. Mechanisms directing hapten-primed CD8 T cell localization and activation in the Ag challenge site to induce this early CXCL1 production in response to 2,4-dinitrofluorobenzene were investigated. Both TNF-α and IL-17, but not IFN-γ, mRNA was detectable within 1 h of hapten challenge of sensitized mice and increased thereafter. Expression of ICAM-1 was observed by 1 h after challenge of sensitized and nonsensitized mice and was dependent on TNF-α. The induction of IL-17, IFN-γ, and CXCL1 in the challenge site was not observed when ICAM-1 was absent or neutralized by specific Ab. During the elicitation of the contact hypersensitivity response, endothelial cells expressed ICAM-1 and produced CXCL1 suggesting this as the site of CD8 T cell localization and activation. Endothelial cells isolated from challenged skin of naive and sensitized mice had acquired the hapten and the ability to activate hapten-primed CD8 T cell cytokine production. These results indicate that hapten application to the skin of sensitized animals initiates an inflammatory response promoting hapten-primed CD8 T cell localization to the challenge site through TNF-α-induced ICAM-1 expression and CD8 T cell activation to produce IFN-γ and IL-17 through endothelial cell presentation of hapten.

Hypercytolytic activity of hepatic natural killer cells correlates with liver injury in chronic hepatitis B patients

Natural killer (NK) cells are abundant in the liver and serve as a major innate immune component against microbial infection. Although NK cells have been implicated in inducing hepatocellular damage in patients with chronic hepatitis virus infections, the roles that hepatic NK cells play in chronic hepatitis B virus (HBV) infections remain obscure. In this study, we comprehensively characterized intrahepatic and peripheral NK cells and investigated their impact on liver pathology in a cohort of HBV-infected individuals; this cohort included 51 immune-activated (IA) patients, 27 immune-tolerant (IT) carriers, and 26 healthy subjects. We found that NK cells expressing NK receptors (activation receptors) preferentially accumulated in the livers of IA patients, in which they were activated and skewed toward cytolytic activity but without a concomitant increase in interferon-γ production, in comparison with those of IT carriers and healthy subjects. Further analysis showed that the livers of IA patients, in comparison with those of IT and healthy subjects, expressed higher levels of interleukin-12 (IL-12), IL-15, and IL-18 in situ and lower levels of IL-10, which in vitro can induce the activation and degranulation of NK cells from healthy individuals. Finally, hepatic NK cells displayed more cytolytic activity than peripheral NK cells, and this was found to be positively correlated with the liver histological activity index and serum alanine aminotransferase levels in these IA patients.

CONCLUSION

In IA patients, hepatic NK cells are activated and preferentially skew toward cytolytic activity, which depends on an imbalanced cytokine milieu and correlates with liver injury during chronic HBV infection.

Evidence for an antagonist form of the chemokine CXCL10 in patients chronically infected with HCV

Chronic infection with hepatitis C virus (HCV) is a major public health problem, with nearly 170 million infected individuals worldwide. Current treatment for chronic infection is a combination of pegylated IFN-α2 and ribavirin (RBV); however, this treatment is effective in fewer than 50% of patients infected with HCV genotype 1 or 4. Recent studies identified the chemokine CXCL10 (also known as IP-10) as an important negative prognostic biomarker. Given that CXCL10 mediates chemoattraction of activated lymphocytes, it is counterintuitive that this chemokine correlates with therapeutic nonresponsiveness. Herein, we offer new insight into this paradox and provide evidence that CXCL10 in the plasma of patients chronically infected with HCV exists in an antagonist form, due to in situ amino-terminal truncation of the protein. We further demonstrated that dipeptidyl peptidase IV (DPP4; also known as CD26), possibly in combination with other proteases, mediates the generation of the antagonist form(s) of CXCL10. These data offer what we believe to be the first evidence for CXCL10 antagonism in human disease and identify a possible factor contributing to the inability of patients to clear HCV.