Impairment of liver regeneration correlates with activated hepatic NKT cells in HBV transgenic mice

The role of natural killer T cells in liver transplantation

Natural killer T cells (NKTs) are innate-like lymphocytes that are abundant in the liver and participate in liver immunity. NKT cells express both NK cell and T cell markers, modulate innate and adaptive immune responses. Type I and Type II NKT cells are classified according to the TCR usage, while they recognize lipid antigen in a non-classical major histocompatibility (MHC) molecule CD1d-restricted manner. Once activated, NKT cells can quickly produce cytokines and chemokines to negatively or positively regulate the immune responses, depending on the different NKT subsets. In liver transplantation (LTx), the immune reactions in a series of processes determine the recipients' long-term survival, including ischemia-reperfusion injury, alloresponse, and post-transplant infection. This review provides insight into the research on NKT cells subpopulations in LTx immunity during different processes, and discusses the shortcomings of the current research on NKT cells. Additionally, the CD56-expressing T cells are recognized as a NK-like T cell population, they were also discussed during these processes.

The hepatic GABAergic system promotes liver macrophage M2 polarization and mediates HBV replication in mice

Macrophages display functional phenotypic plasticity. Hepatitis B virus (HBV) infection induces polarizations of liver macrophages either to M1-like pro-inflammatory phenotype or to M2-like anti-inflammatory phenotype. Gamma-aminobutyric acid (GABA) signaling exists in various non-neuronal cells including hepatocytes and some immune cells. Here we report that macrophages express functional GABAergic signaling components and activation of type A GABA receptors (GABAARs) promotes M2-polarization thus advancing HBV replication. Notably, intraperitoneal injection of GABA or the GABAAR agonist muscimol increased HBV replication in HBV-carrier mice that were generated by hydrodynamical injection of adeno-associated virus/HBV1.2 plasmids (pAAV/HBV1.2). The GABA-augmented HBV replication in HBV-carrier mice was significantly reduced by the GABAAR inhibitor picrotoxin although picrotoxin had no significant effect on serum HBsAg levels in control HBV-carrier mice. Depletion of liver macrophages by liposomal clodronate treatment also significantly reduced the GABA-augmented HBV replication. Yet adoptive transfer of liver macrophages isolated from GABA-treated donor HBV-carrier mice into the liposomal clodronate-pretreated recipient HBV-carrier mice restored HBV replication. Moreover, GABA or muscimol treatment increased the expression of "M2" cytokines in macrophages, but had no direct effect on HBV replication in the HepG2.2.15 cells, HBV1.3-transfected Huh7, HepG2, or HepaRG cells, or HBV-infected Huh7-NTCP cells. Taken together, these results suggest that increasing GABA signaling in the liver promotes HBV replication in HBV-carrier mice by suppressing the immunity of liver macrophages, but not by increasing the susceptibility of hepatocytes to HBV infection. Our study shows that a previously unknown GABAergic system in liver macrophage has an essential role in HBV replication.

Case Report: The application of associating liver partition and portal vein ligation for staged hepatectomy in patients with hepatitis b virus-related hepatocellular carcinoma after undergoing treatment with an immune checkpoint inhibitor: a report of two cases

Hepatocellular carcinoma (HCC) is often diagnosed at an unresectable stage without opportunities for curative therapy. Future liver remnant (FLR) insufficiency limits the range of patients who can undergo radical resection. Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) can ultimately achieve short-term hypertrophy of the FLR in patients with viral hepatitis-related fibrosis/cirrhosis and R0 resection. However, the influence of immune checkpoint inhibitors (ICIs) on liver regeneration remains unknown. We report two patients diagnosed with Barcelona Clinic Liver Cancer (BCLC)-B stage hepatitis B virus (HBV)-related HCC who underwent pioneering ALPPS after immunotherapy without posthepatectomy liver failure (PHLF). ALPPS has been shown to be safe and feasible in patients with HCC who underwent immunotherapy previously for the first time and might provide an alternative salvage option for future conversion therapy of HCC.

New insights into iNKT cells and their roles in liver diseases

Natural killer T cells (NKTs) are an important part of the immune system. Since their discovery in the 1990s, researchers have gained deeper insights into the physiology and functions of these cells in many liver diseases. NKT cells are divided into two subsets, type I and type II. Type I NKT cells are also named iNKT cells as they express a semi-invariant T cell-receptor (TCR) α chain. As part of the innate immune system, hepatic iNKT cells interact with hepatocytes, macrophages (Kupffer cells), T cells, and dendritic cells through direct cell-to-cell contact and cytokine secretion, bridging the innate and adaptive immune systems. A better understanding of hepatic iNKT cells is necessary for finding new methods of treating liver disease including autoimmune liver diseases, alcoholic liver diseases (ALDs), non-alcoholic fatty liver diseases (NAFLDs), and liver tumors. Here we summarize how iNKT cells are activated, how they interact with other cells, and how they function in the presence of liver disease.

Dysregulation of Liver Regeneration by Hepatitis B Virus Infection: Impact on Development of Hepatocellular Carcinoma

The liver is unique in its ability to regenerate in response to damage. The complex process of liver regeneration consists of multiple interactive pathways. About 2 billion people worldwide have been infected with hepatitis B virus (HBV), and HBV causes 686,000 deaths each year due to its complications. Long-term infection with HBV, which causes chronic inflammation, leads to serious liver-related diseases, including cirrhosis and hepatocellular carcinoma. HBV infection has been reported to interfere with the critical mechanisms required for liver regeneration. In this review, the studies on liver tissue characteristics and liver regeneration mechanisms are summarized. Moreover, the inhibitory mechanisms of HBV infection in liver regeneration are investigated. Finally, the association between interrupted liver regeneration and hepatocarcinogenesis, which are both triggered by HBV infection, is outlined. Understanding the fundamental and complex liver regeneration process is expected to provide significant therapeutic advantages for HBV-associated hepatocellular carcinoma.

Liver Regeneration in Chronic Liver Injuries: Basic and Clinical Applications Focusing on Macrophages and Natural Killer Cells

BACKGROUND & AIMS

Liver regeneration is a necessary but complex process involving multiple cell types besides hepatocytes. Mechanisms underlying liver regeneration after partial hepatectomy and acute liver injury have been well-described. However, in patients with chronic and severe liver injury, the remnant liver cannot completely restore the liver mass and function, thereby involving liver progenitor-like cells (LPLCs) and various immune cells.

RESULTS

Macrophages are beneficial to LPLCs proliferation and the differentiation of LPLCs to hepatocytes. Also, cells expressing natural killer (NK) cell markers have been studied in promoting both liver injury and liver regeneration. NK cells can promote LPLC-induced liver regeneration, but the excessive activation of hepatic NK cells may lead to high serum levels of interferon-γ, thus inhibiting liver regeneration.

CONCLUSIONS

This review summarizes the recent research on 2 important innate immune cells, macrophages and NK cells, in LPLC-induced liver regeneration and the mechanisms of liver regeneration during chronic liver injury, as well as the latest macrophage- and NK cell-based therapies for chronic liver injury. These novel findings can further help identify new treatments for chronic liver injury, saving patients from the pain of liver transplantations.

Phototherapy Facilitates Tumor Recruitment and Activation of Natural Killer T cells for Potent Cancer Immunotherapy

Adoptively transferred natural killer T (NKT) cells confer distinct cancer surveillance without causing obvious side effects, making them a promising candidate for cancer immunotherapy. However, their therapeutic efficacy is limited by inefficient tumor infiltration and inadequate activation in an immunosuppressive tumor microenvironment. To overcome these obstacles, we develop a strategy of using photothermal therapy (PTT) to promote the antitumor ability of adoptively transferred NKT cells. The transferred NKT cells are efficiently recruited to PTT-treated tumors in response to PTT-created inflammation. Moreover, PTT treatment promotes the activation of NKT cells and enhances the NKT cell-initiated immune cascade. As a consequence, the combined therapy of PTT plus NKT cell transfer exhibits excellent growth inhibition of local tumors. Moreover, it efficiently rejects distant tumors and elicits long-term immunological memory to prevent tumor recurrence. Overall, the current study opens new paths to the clinical translation of NKT cells for cancer immunotherapy.

Susceptibility-Related Cytokine Panel for Prediction of Polygonum multiflorum-Induced Hepatotoxicity in Humans

BACKGROUND

Drug-induced liver injury is a common adverse effect in clinical practice, with severe cases resulting in liver failure and even death. Identification and prediction of individuals susceptible to idiosyncratic DILI continues to remain a challenge.

METHODS

In this study, we report that cytokines in human serum can be used to identify and predict individuals susceptible to Polygonum multiflorum-induced DILI (PM-DILI) in retrospective and prospective cohort studies.

FINDINGS

In the retrospective pilot study, we compared serum cytokine expression profiles of the PM-DILI group (n=10) and the PM-Tolerant group (n=12) and found 10 cytokines with significant differences. In the replication cohort study, differences in the 10 cytokines between PM-DILI (n =11) and PM-Tolerant (n=13) groups were verified. Among them, 6 cytokines showed no significant differences at two time points, including liver injury and recovery stage of PM-DILI, suggesting that these 6 cytokines have no correlation with PM-DILI, however, they may be related to susceptibility. Furthermore, all the retrospective cohorts were combined, and a PM-DILI susceptibility prediction model was built by screening the 6 cytokines. The combination of (TNF-α and CCL-2) or VEGF showed the highest sensitivity and specificity. Finally, the efficacy of the above 3 cytokine combination models in predicting PM-DILI-susceptible individuals was verified before PM exposure in another independent prospective cohort (n=24), with sensitivity and specificity of 66.7% and 83.3%, respectively.

CONCLUSION

This proof-of-concept study demonstrates that the serum cytokine combination reflecting dysimmunity could be used as a new method to predict PM-DILI, thus providing a new perspective for improving the clinical management of IDILI.

Natural Killer T Cells in Various Mouse Models of Hepatitis

Natural killer T (NKT) cells are a key component of innate immunity. Importantly, a growing body of evidence indicates that NKT cells play an integral role in various acute and chronic liver injuries. NKT cells participate in the progression of an injury through the secretion of cytokines, which promote neutrophil infiltration and enhance Fas ligand (FasL) and granzyme-mediated NKT cytotoxic activity. Therefore, examining the role of NKT cells in hepatic disease is critical for a comprehensive understanding of disease pathogenesis and may provide insight into novel approaches for treatment. For more than a century, mouse models that imitate the physiopathological conditions of human disease have served as a critical tool in biological and medical basic research, including studies of liver disease. Here, we review the role of NKT cells in various mouse models of hepatitis.

Endogenous Interleukin 18 Suppresses Liver Regeneration After Hepatectomy in Mice

The comprehensive role of interleukin (IL) 18 during liver regeneration is barely studied. Our aim is to evaluate the role of IL18 in liver regeneration after partial hepatectomy (PH) in mice. The expression profile of IL18 in the liver and the gut after 70% PH was measured. Liver samples after 70% and 85% PH from IL18 knockout (IL18^-/- ) mice and wild type (WT) mice were collected for comparison of liver regeneration. The effect of recombinant IL18 on liver regeneration was tested in IL18^-/- mice, and the utility of IL18 binding protein (BP) was also evaluated following 70% PH in WT mice. Expression levels of IL18 in the liver and the gut elevated after 70% PH. The liver weight/body weight ratios (LBWRs) after PH were significantly higher in IL18^-/- mice than those in WT mice. Recombinant IL18 injection significantly decreased LBWR at 7 days after 70% PH in IL18^-/- mice. The expression of cyclin D1, EdU labeling index, and Ki-67 proliferation index were much higher in IL18^-/- mice than those in WT mice after 70% PH. The expression level of glypican 3 (GPC3) in WT mice significantly elevated during liver regeneration. In contrast, the expression level of GPC3 in IL18^-/- mice remained roughly unchanged during liver regeneration. IL18BP injection significantly increased the LBWR at 7 days after 70% PH in WT mice. In conclusion, endogenous IL18 inhibited liver regeneration after PH in mice, possibly through up-regulating GPC3. IL18BP may be an effective agent to promote liver regeneration after PH.

Tissue-specific functions of invariant natural killer T cells

Invariant natural killer T cells (iNKT cells) are an innate-like T cell subset that expresses an invariant T cell receptor (TCR) α-chain and recognizes lipids presented on CD1d. They secrete diverse cytokines and can influence many types of immune responses. Despite having highly similar TCR specificities, iNKT cells differentiate in the thymus into distinct subsets that are analogous to T helper 1 (T_H1), T_H2 and T_H17 cell subsets. Additional iNKT cell subsets that may require peripheral activation have also been described, including one that produces IL-10. In general, iNKT cells are non-circulating, tissue-resident lymphocytes, but the prevalence of different iNKT cell subsets differs markedly between tissues. Here, we summarize the functions of iNKT cells in four tissues in which they are prevalent, namely, the liver, the lungs, adipose tissue and the intestine. Importantly, we explain how local iNKT cell responses at each site contribute to tissue homeostasis and protection from infection but can also contribute to tissue inflammation and damage.

Liver regeneration microenvironment of hepatocellular carcinoma for prevention and therapy

Research on liver cancer prevention and treatment has mainly focused on the liver cancer cells themselves. Currently, liver cancers are no longer viewed as only collections of genetically altered cells but as aberrant organs with a plastic stroma, matrix, and vasculature. Improving the microenvironment of the liver to promote liver regeneration and repair by affecting immune function, inflammation and vasculature can regulate the dynamic imbalance between normal liver regeneration and repair and abnormal liver regeneration, thus improving the microenvironment of liver regeneration for the prevention and treatment of liver cancer. This review addresses the basic theory of the liver regeneration microenvironment, including the latest findings on immunity, inflammation and vasculature. Attention is given to the potential design of molecular targets in the microenvironment of hepatocellular carcinoma (HCC). In an effort to improve the liver regeneration microenvironment of HCC, researchers have extensively utilized the enhancement of immunity, anti-inflammation and the vasculature niche, which are discussed in detail in this review. In addition, the authors summarize the latest pro-fibrotic transition characteristics of the vascular niche and review potential cell therapies for liver disease.

Hepatitis B virus X protein-elevated MSL2 modulates hepatitis B virus covalently closed circular DNA by inducing degradation of APOBEC3B to enhance hepatocarcinogenesis

Chronic hepatitis B virus (HBV) infection is a leading cause in the occurrence of hepatitis B, liver cirrhosis, and liver cancer, in which nuclear HBV covalently closed circular DNA (cccDNA), the genomic form that templates viral transcription and sustains viral persistence, plays crucial roles. In the present study, we explored the hypothesis that HBV X protein (HBx)-elevated male-specific lethal 2 (MSL2) activated HBV replication by modulating cccDNA in hepatoma cells, leading to hepatocarcinogenesis. Immunohistochemical analysis revealed that the expression of MSL2 was positively associated with that of HBV and was increased in the liver tissues of HBV-transgenic mice and clinical HCC patients. Interestingly, microarray profiling identified that MSL2 was associated with those genes responding to the virus. Mechanistically, MSL2 could maintain HBV cccDNA stability through degradation of APOBEC3B by ubiquitylation in hepatoma cells. Above all, HBx accounted for the up-regulation of MSL2 in stably HBx-transfected hepatoma cell lines and liver tissues of HBx-transgenic mice. Luciferase reporter gene assays revealed that the promoter region of MSL2 regulated by HBx was located at nucleotide -1317/-1167 containing FoxA1 binding element. Chromatin immunoprecipitation assay validated that HBx could enhance the binding property of FoxA1 to MSL2 promoter region. HBx up-regulated MSL2 by activating YAP/FoxA1 signaling. Functionally, silencing MSL2 was able to block the growth of hepatoma cells in vitro and in vivo.

CONCLUSION

HBx-elevated MSL2 modulates HBV cccDNA in hepatoma cells to promote hepatocarcinogenesis, forming a positive feedback loop of HBx/MSL2/cccDNA/HBV. Our finding uncovers insights into the mechanism by which MSL2 as a promotion factor in host cells selectively activates extrachromosomal DNA. (Hepatology 2017;66:1413-1429).

Impaired liver regeneration is associated with reduced cyclin B1 in natural killer T cell-deficient mice

Background

It has been shown that the proportion of natural killer T cells is markedly elevated during liver regeneration and their activation under different conditions can modulate this process. As natural killer T cells and liver injury are central in liver regeneration, elucidating their role is important.

Methods

The aim of the current study is to explore the role of natural killer T cells in impaired liver regeneration. Concanvalin A was injected 4 days before partial hepatectomy to natural killer T cells- deficient mice or to anti CD1d1-treated mice. Ki-67 and proliferating cell nuclear antigen were used to measure hepatocytes proliferation. Expression of hepatic cyclin B1 and proliferating cell nuclear antigen were evaluated by Western Blot and liver injury was assessed by ALT and histology.

Results

Natural killer T cells- deficient or mice injected with anti CD1d antibodies exhibited reduced liver regeneration. These mice were considerably resistant to ConA-induced liver injury. In the absence of NKT cells hepatic proliferating cell nuclear antigen and cyclin B1 decreased in mice injected with Concanvalin A before partial hepatectomy. This was accompanied with reduced serum interleukin-6 levels.

Conclusions

Natural killer T cells play an important role in liver regeneration, which is associated with cyclin B1 and interleukin-6.

Natural killer T cells contribute to the control of acute retroviral infection

Background

Natural killer T cells (NKT cells) play an important role in the immunity against viral infections. They produce cytokines or have direct cytolytic effects that can restrict virus replication. However, the exact function of NKT cells in retroviral immunity is not fully elucidated. Therefore, we analyzed the antiretroviral functions of NKT cells in mice infected with the Friend retrovirus (FV).

Results

After FV infection numbers of NKT cells remained unchanged but activation as well as improved effector functions of NKT cells were found. While the release of pro-inflammatory cytokines was not changed after infection, activated NKT cells revealed an elevated cytotoxic potential. Stimulation with α-Galactosylceramide significantly increased not only total NKT cell numbers and activation but also the anti-retroviral capacity of NKT cells.

Conclusion

We demonstrate a strong activation and a potent cytolytic function of NKT cells during acute retroviral infection. Therapeutic treatment with α-Galactosylceramide could further improve the reduction of early retroviral replication by NKT cells, which could be utilized for future treatment against viral infections.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-017-0327-8) contains supplementary material, which is available to authorized users.

Idiosyncratic Drug-Induced Liver Injury: Is Drug-Cytokine Interaction the Linchpin?

Idiosyncratic drug-induced liver injury continues to be a human health problem in part because drugs that cause these reactions are not identified in current preclinical testing and because progress in prevention is hampered by incomplete knowledge of mechanisms that underlie these adverse responses. Several hypotheses involving adaptive immune responses, inflammatory stress, inability to adapt to stress, and multiple, concurrent factors have been proposed. Yet much remains unknown about how drugs interact with the liver to effect death of hepatocytes. Evidence supporting hypotheses implicating adaptive or innate immune responses in afflicted patients has begun to emerge and is bolstered by results obtained in experimental animal models and in vitro systems. A commonality in adaptive and innate immunity is the production of cytokines, including interferon-γ (IFNγ). IFNγ initiates cell signaling pathways that culminate in cell death or inhibition of proliferative repair. Tumor necrosis factor-α, another cytokine prominent in immune responses, can also promote cell death. Furthermore, tumor necrosis factor-α interacts with IFNγ, leading to enhanced cellular responses to each cytokine. In this short review, we propose that the interaction of drugs with these cytokines contributes to idiosyncratic drug-induced liver injury, and mechanisms by which this could occur are discussed.

Hepatitis B virus inhibits insulin receptor signaling and impairs liver regeneration via intracellular retention of the insulin receptor

Hepatitis B virus (HBV) causes severe liver disease but the underlying mechanisms are incompletely understood. During chronic HBV infection, the liver is recurrently injured by immune cells in the quest for viral elimination. To compensate tissue injury, liver regeneration represents a vital process which requires proliferative insulin receptor signaling. This study aims to investigate the impact of HBV on liver regeneration and hepatic insulin receptor signaling. After carbon tetrachloride-induced liver injury, liver regeneration is delayed in HBV transgenic mice. These mice show diminished hepatocyte proliferation and increased expression of fibrosis markers. This is in accordance with a reduced activation of the insulin receptor although HBV induces expression of the insulin receptor via activation of NF-E2-related factor 2. This leads to increased intracellular amounts of insulin receptor in HBV expressing hepatocytes. However, intracellular retention of the receptor simultaneously reduces the amount of functional insulin receptors on the cell surface and thereby attenuates insulin binding in vitro and in vivo. Intracellular retention of the insulin receptor is caused by elevated amounts of α-taxilin, a free syntaxin binding protein, in HBV expressing hepatocytes preventing proper targeting of the insulin receptor to the cell surface. Consequently, functional analyses of insulin responsiveness revealed that HBV expressing hepatocytes are less sensitive to insulin stimulation leading to delayed liver regeneration. This study describes a novel pathomechanism that uncouples HBV expressing hepatocytes from proliferative signals and thereby impedes compensatory liver regeneration after liver injury.

Autologous NeoHep Derived from Chronic Hepatitis B Virus Patients' Blood Monocytes by Upregulation of c-MET Signaling

In view of the escalating need for autologous cell‐based therapy for treatment of liver diseases, a novel candidate has been explored in the present study. The monocytes isolated from hepatitis B surface antigen (HBsAg) nucleic acid test (NAT)‐positive (HNP) blood were differentiated to hepatocyte‐like cells (NeoHep) in vitro by a two‐step culture procedure. The excess neutrophils present in HNP blood were removed before setting up the culture. In the first step of culture, apoptotic cells were depleted and genes involved in hypoxia were induced, which was followed by the upregulation of genes involved in the c‐MET signaling pathway in the second step. The NeoHep were void of hepatitis B virus and showed expression of albumin, connexin 32, hepatocyte nuclear factor 4‐α, and functions such as albumin secretion and cytochrome P450 enzyme‐mediated detoxification of xenobiotics. The engraftment of NeoHep derived from HBsAg‐NAT‐positive blood monocytes in partially hepatectomized NOD.CB17‐Prkdc^scid/J mice liver and the subsequent secretion of human albumin and clotting factor VII activity in serum make NeoHep a promising candidate for cell‐based therapy. Stem Cells Translational Medicine2017;6:174–186

Liver immunology and its role in inflammation and homeostasis

The human liver is usually perceived as a non-immunological organ engaged primarily in metabolic, nutrient storage and detoxification activities. However, we now know that the healthy liver is also a site of complex immunological activity mediated by a diverse immune cell repertoire as well as non-hematopoietic cell populations. In the non-diseased liver, metabolic and tissue remodeling functions require elements of inflammation. This inflammation, in combination with regular exposure to dietary and microbial products, creates the potential for excessive immune activation. In this complex microenvironment, the hepatic immune system tolerates harmless molecules while at the same time remaining alert to possible infectious agents, malignant cells or tissue damage. Upon appropriate immune activation to challenge by pathogens or tissue damage, mechanisms to resolve inflammation are essential to maintain liver homeostasis. Failure to clear 'dangerous' stimuli or regulate appropriately activated immune mechanisms leads to pathological inflammation and disrupted tissue homeostasis characterized by the progressive development of fibrosis, cirrhosis and eventual liver failure. Hepatic inflammatory mechanisms therefore have a spectrum of roles in the healthy adult liver; they are essential to maintain tissue and organ homeostasis and, when dysregulated, are key drivers of the liver pathology associated with chronic infection, autoimmunity and malignancy. In this review, we explore the changing perception of inflammation and inflammatory mediators in normal liver homeostasis and propose targeting of liver-specific immune regulation pathways as a therapeutic approach to treat liver disease.

Natural killer T cells in liver injury, inflammation and cancer

The liver is an organ that has the largest amount of natural killer T(NKT) cells, which play critical roles in the pathogenesis of liver diseases. In this article, the authors summarize recent findings about the roles of NKT cells in liver injury, inflammation, fibrosis, regeneration and cancer. In brief, NKT cells accelerate liver injury by producing pro-inflammatory cytokines and directly killing hepatocytes. NKT cells are involved in complex roles in liver fibrogenesis. For instance, NKT cells inhibit liver fibrosis via suppressing hepatic stellate cell activation and can also promote liver fibrosis via enhancing liver inflammation and injury. Inactivated or weakly activated NKT cells play a minimal role in controlling liver regeneration, whilst activated NKT cells have an inhibitory effect on liver regeneration. In liver cancer, NKT cells play both pro-tumor and anti-tumor roles in controlling tumor progress.

Oral ampicillin inhibits liver regeneration by breaking hepatic innate immune tolerance normally maintained by gut commensal bacteria

Commensal bacteria have been proposed to play a role in liver repair after partial (67%) hepatectomy. However, the underlying immune mechanisms remain elusive. Here, we show that liver regeneration was impaired in antibiotic (Atb) water-treated mice and this impairment strongly correlated with commensal bacterial load. Among the various Atbs used in our cocktail, ampicillin-sensitive commensal bacterial was associated with normal liver regeneration. The number of CD1d-dependent natural killer T (NKT) cells in Atb-treated hepatectomized mice was markedly increased, and these NKT cells were functionally overactivated to produce higher interferon-γ. Deficiency of NKT cells or antibody blockade of the CD1d-NKT interaction increased hepatocyte proliferation, which improved liver regeneration. Importantly, an increased number of Kupffer cells were observed in Atb-treated mice, and these Kupffer cells produced higher interleukin-12, which then functioned to activate hepatic NKT cells. Interleukin-12p40 deficiency or treatment with an anti-interleukin-12 antibody significantly inhibited NKT cell overactivation and recovered liver regeneration in Atb-treated mice.

CONCLUSION

Commensal bacteria play a critical role in maintaining Kupffer cells in a tolerant state, preventing subsequent NKT cell overactivation during liver regeneration. Moreover, our data suggest that long-term Atb use, which can impair the gut microbiota, may influence liver function by retarding liver regeneration.

Tim-3 induces Th2-biased immunity and alternative macrophage activation during Schistosoma japonicum infection

T cell immunoglobulin- and mucin-domain-containing molecule 3 (Tim-3) has been regarded as an important regulatory factor in both adaptive and innate immunity. Recently, Tim-3 was reported to be involved in Th2-biased immune responses in mice infected with Schistosoma japonicum, but the exact mechanism behind the involvement of Tim-3 remains unknown. The present study aims to understand the role of Tim-3 in the immune response against S. japonicum infection. Tim-3 expression was determined by flow cytometry, and increased Tim-3 expression was observed on CD4(+) and CD8(+) T cells, NK1.1(+) cells, and CD11b(+) cells from the livers of S. japonicum-infected mice. However, the increased level of Tim-3 was lower in the spleen than in the liver, and no increase in Tim-3 expression was observed on splenic CD8(+) T cells or CD11b(+) cells. The schistosome-induced upregulation of Tim-3 on natural killer (NK) cells was accompanied by reduced NK cell numbers in vitro and in vivo. Tim-3 antibody blockade led to upregulation of inducible nitric oxide synthase and interleukin-12 (IL-12) mRNA in CD11b(+) cells cocultured with soluble egg antigen and downregulation of Arg1 and IL-10, which are markers of M2 macrophages. In summary, we observed schistosome-induced expression of Tim-3 on critical immune cell populations, which may be involved in the Th2-biased immune response and alternative activation of macrophages during infection.

Mathematical models of the interrelated dynamics of hepatitis D and B

The hepatitis delta virus (HDV) is a rarest form of viral hepatitis, but has the worst outcomes for patients.It is a subviral satellite dependent on coinfection with hepatitis B (HBV) to replicate within the host liver.To date, there has been little to no modeling effort for HDV. Deriving and analyzing such a mathematical model poses difficulty as it requires the inclusion of (HBV). Here we begin with a well-studied HBV model from the literature and expand it to incorporate HDV. We investigate two models, one with and one without infected hepatocyte replication. Additionally, we consider treatment by the drug lamivudine. Comparison of model simulations with experimental results of lamivudine treatment indicate that infected cell proliferation may play a significant role in chronic HDV infection. Our results also shed light on several questions surrounding HDV and illustrate the need for more data.

TIGIT safeguards liver regeneration through regulating natural killer cell-hepatocyte crosstalk

Overactivation of innate immunity, particularly natural killer (NK) cells, is harmful to liver regeneration; however, the molecular mechanisms that limit NK cell overactivation during liver regeneration are still elusive. Here we show that a coinhibitory receptor, T cell Ig and ITIM domain (TIGIT), was selectively up-regulated on NK cells, along with high expression of its ligand, poliovirus receptor (PVR/CD155), on hepatocytes during liver regeneration. The absence of TIGIT impaired liver regeneration in vivo, along with overactivation of NK cells and higher NK-derived interferon-gamma (IFN-γ) production. We also show that both depletion of NK cells and deficiency of IFN-γ, but not deficiency of RAG1, rescued impaired liver regeneration caused by the absence of TIGIT. Adoptive transfer of Tigit(-/-) NK cells into NK-deficient Nfil3(-/-) mice sufficiently led to impairment of liver regeneration. On the other hand, silencing PVR in hepatocytes rescued impaired liver regeneration caused by TIGIT deficiency in vivo, while blockade of TIGIT in NK-hepatocyte coculture increased IFN-γ production by NK cells in vitro.

CONCLUSION

TIGIT is a safeguard molecule to improve liver regeneration through negatively regulating NK-hepatocyte crosstalk. This finding suggests a novel mechanism of NK cell self-tolerance towards regenerative hyperplasia of the host.

Activation of invariant natural killer T cells impedes liver regeneration by way of both IFN-γ- and IL-4-dependent mechanisms

Invariant natural killer T (iNKT) cells are a major subset of lymphocytes found in the liver. These cells mediate various functions, including hepatic injury, fibrogenesis, and carcinogenesis. However, the function of iNKT cells in liver regeneration remains unclear. In the present study, partial hepatectomy (PHx) was used to study liver regeneration. α-Galactosylceramide (α-GalCer), a specific ligand for iNKT cells, was used to induce iNKT cell activation. After PHx, two strains of iNKT cell-deficient mice, CD1d(-/-) and Jα281(-/-) mice, showed normal liver regeneration. Injection of α-GalCer before or after PHx, which rapidly stimulated interferon-gamma (IFN-γ) and interleukin (IL)-4 production by iNKT cells, markedly inhibited liver regeneration. In vitro treatment with IFN-γ inhibited hepatocyte proliferation. In agreement with this in vitro finding, genetic disruption of IFN-γ or its downstream signaling molecule signal transducer and activator of transcription (STAT)1 significantly abolished the α-GalCer-mediated inhibition of liver regeneration. In vitro exposure to IL-4 did not affect hepatocyte proliferation, but surprisingly, genetic ablation of IL-4 or its downstream signaling molecule STAT6 partially eliminated the inhibitory effect of α-GalCer on liver regeneration. Further studies revealed that IL-4 contributed to α-GalCer-induced iNKT cell expansion and IFN-γ production, thereby inhibiting liver regeneration.

CONCLUSION

iNKT cells play a minor role in controlling liver regeneration after PHx under healthy conditions. Activation of iNKT cells by α-GalCer induces the production of IFN-γ, which directly inhibits liver regeneration, and IL-4, which indirectly attenuates liver regeneration by stimulating iNKT cell expansion and IFN-γ production.

Interleukin 17-producing γδT cells promote hepatic regeneration in mice

BACKGROUND & AIMS

Subsets of leukocytes synergize with regenerative growth factors to promote hepatic regeneration. γδT cells are early responders to inflammation-induced injury in a number of contexts. We investigated the role of γδT cells in hepatic regeneration using mice with disruptions in Tcrd (encodes the T-cell receptor δ chain) and Clec7a (encodes C-type lectin domain family 7 member a, also known as DECTIN1).

METHODS

We performed partial hepatectomies on wild-type C57BL/6, CD45.1, Tcrd(-/-), or Clec7a(-/-) mice. Cells were isolated from livers of patients and mice via mechanical and enzymatic digestion. γδT cells were purified by fluorescence-activated cell sorting.

RESULTS

In mice, partial hepatectomy up-regulated expression of CCL20 and ligands of Dectin-1, which was associated with recruitment and activation of γδT cells and their increased production of interleukin (IL)-17 family cytokines. Recruited γδT cells induced production of IL-6 by antigen-presenting cells and suppressed expression of interferon gamma by natural killer T cells, promoting hepatocyte proliferation. Absence of IL-17-producing γδT cells or deletion of Dectin-1 prevented development of regenerative phenotypes in subsets of innate immune cells. This slowed liver regeneration and was associated with reduced expression of regenerative growth factors and cell cycle regulators. Conversely, exogenous administration of IL-17 family cytokines or Dectin-1 ligands promoted regeneration. More broadly, we found that γδT cells are required for inflammatory responses mediated by IL-17 and Dectin-1.

CONCLUSIONS

γδT cells regulate hepatic regeneration by producing IL-22 and IL-17, which have direct mitogenic effects on hepatocytes and promote a regenerative phenotype in hepatic leukocytes, respectively. Dectin-1 ligation is required for γδT cells to promote hepatic regeneration.

The Tim-3/galectin-9 pathway involves in the homeostasis of hepatic Tregs in a mouse model of concanavalin A-induced hepatitis

T cell immunoglobulin- and mucin-domain-containing molecule-3 (Tim-3) is a negative regulator of interferon (IFN)-γ-secreting CD4(+) Th1 cells and plays a key role in autoimmune diseases. Here, we report that galectin-9 expression was increased in hepatic CD4(+)CD25(+) T cells in a mouse model of concanavalin A (Con A)-induced hepatitis. Moreover, Tim-3 showed increased levels in CD4(+)CD25(+) Foxp3(+) regulatory T cells (Tregs). Further analyses showed that blocking the Tim-3/galectin-9 pathway resulted in the suppression of Tregs in vitro, thereby significantly increasing interferon (IFN)-γ production from hepatic Teffs. Moreover, blockade of Tim-3 in vivo with an anti-Tim-3 antibody exacerbated the acute hepatitis, possibly by increased IFN-γ production. Furthermore, we found that in vitro activation of CD4(+)CD25(-) T cells with the T cell receptor (TCR) plus interleukin 2 (IL-2) up-regulated Tim-3 expression. And the induced Tim-3 interacted with galectin-9 to induce CD4(+) T cell apoptosis which could be partly reversed by blocking Tim-3 signaling. Our results suggested that the Tim-3/galectin-9 pathway plays a critical role in the homeostasis of hepatic Tregs through the elimination induction in Teffs and the inhibition of IFN-γ release, which contributes to the pathogenesis of liver damage and constitutes at least part of the mechanism underlying the induction of hepatitis by Con A.

Decreased Vδ2 γδ T cells associated with liver damage by regulation of Th17 response in patients with chronic hepatitis B

BACKGROUND

 γδ T cells comprise a small subset of T cells and play a protective role against cancer and viral infections; however, their precise role in patients with chronic hepatitis B remains unclear.

METHODS

 Flow cytometry and immunofunctional assays were performed to analyze the impact of Vδ2 γδ (Vδ2) T cells in 64 immune-activated patients, 22 immune-tolerant carriers, and 30 healthy controls.

RESULTS

 The frequencies of peripheral and hepatic Vδ2 T cells decreased with disease progression from immune tolerant to immune activated. In the latter group of patients, the decreases in peripheral and intrahepatic frequencies of Vδ2 T cells reversely correlated with alanine aminotransferase levels and histological activity index. These activated terminally differentiated memory phenotypic Vδ2 T cells exhibited impaired abilities in proliferation and chemotaxis, while maintained a relative intact interferon (IFN) γ production. Importantly, Vδ2 T cells, in vitro, significantly suppressed the production of cytokines associated with interleukin 17-producing CD4+ T (Th17) cells through both cell contact-dependent and IFN-γ-dependent mechanisms.

CONCLUSIONS

 Inflammatory microenvironment in IA patients result in decreased numbers of Vδ2 T cells, which play a novel role by regulating the pathogenic Th17 response to protect the liver in patients with chronic hepatitis B.

Characterization of the liver-draining lymph nodes in mice and their role in mounting regional immunity to HBV

The lymphatic system is important in mounting an immune response to foreign antigens and tumors in humans and animal models. The liver produces a large amount of lymph, and its lymphatic system is divided into three major components: the portal, sublobular and superficial lymphatic vessels. Despite the fact that mice are the most commonly used laboratory animals, detailed descriptions of the anatomical location and function of the lymph nodes (LNs) that drain the liver are surprisingly absent. In this study, we found that the portal and celiac LNs adjacent to mouse liver were stained with Evans blue within 5-8 min. Enhanced green fluorescence protein (EGFP)-positive cells from the liver also drained into the two aforementioned LNs. These data indicate that the portal and celiac LNs drain the mouse liver. Lymphadenectomy of the identified liver-draining LNs resulted in hepatitis B virus (HBV) persistence in immunocompetent mice compared with the sham group. In addition, the frequencies of CD8(+) T cells and dendritic cells (DCs) increased significantly in the liver-draining LNs after hydrodynamic injection of HBV plasmid. Liver-draining LN cells in HBV plasmid-injected mice also showed significant antigen-specific proliferation in response to stimulation with recombinant hepatitis B core antigen in vitro. Adoptive transfer of these cells into Rag1(-/-) mice induced a reduction in the serum concentration of hepatitis B surface antigen (HBsAg) compared to liver-draining LN cells in uninjected mice. Altogether our data characterize the liver-draining LNs and provide evidence that the liver-draining LNs induce an anti-HBV-specific immune response responsible for HBV clearance.

Characterization of transcriptional profiling of Kupffer cells during liver regeneration in rats

KCs (Kupffer cells), as an important hepatic immunoregulatory cells, play a key role in LR (liver regeneration). Uncovering the transcriptional profiling of KCs after PH (partial hepatectomy) would likely clarify its implication in LR. Here, we isolated KCs by methods of Percoll density gradient centrifugation and immunomagnetic beads. Transcriptional profiles of KCs were monitored up to 168 h post-PH using microarray. By comparing the expression profile of KCs at 2-168 h post-PH with that of the control and applying the statistical and bioinformatics criteria, we found 1407 known and 927 unknown genes related to LR. K-means clustering analysis grouped these 1407 genes into robust 14 time-course clusters representing distinct patterns of regulation. Based on gene-set enrichment analysis, genes encoding products involved in cytokine signalling, inflammatory response and cell chaemotaxis were highly enriched in the cluster characterized by gradual up-regulation and then return; genes in defence response and immune response were enriched in clusters 'the general down-regulation during LR'; genes in fatty acid synthesis and sterol metabolism were preferentially distributed in the cluster 'gradual increase'; whereas genes in the categories 'lipid catabolism' and 'glycolysis' were enriched in cluster 'decrease at two intervals'. According to the above analysis, KCs were seemingly sensitive to operative stimulus; immune defence and detoxification function of KCs obviously dropped post-operatively; fatty acid synthesis were enhanced, whereas lipid catabolism and glycolysis were reduced after PH. This study provides a detailed in vivo gene expression profile of KCs, providing a framework to better understand the molecular mechanisms underlying the regeneration process at cellular level.

Consequences of TCDD treatment on intra-hepatic lymphocytes during liver regeneration

Increasing evidence demonstrates a physiological role for the aryl hydrocarbon receptor (AhR) in regulating hepatocyte cell cycle progression. Previous studies have used a murine model of liver regeneration to show that exposure to the potent exogenous AhR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), suppresses hepatocyte proliferation in vivo. Based on recent reports that natural killer (NK) cells negatively regulate liver regeneration, coupled with the well-established immunomodulatory effects of TCDD, it was hypothesized that alterations in lymphocyte activation contribute to the suppression of liver regeneration in TCDD-treated mice. To test this, mice were treated with TCDD (20 μg/kg) 1 day prior to 70% partial hepatectomy (PH), in which two-thirds of the liver was surgically resected. Lymphocytes were collected from the remnant liver and analyzed by flow cytometry. Whereas exposure to TCDD did not alter the number of NK cells or CD3(+) T-cells recovered from the regenerating liver, it reduced the percentage and number of intra-hepatic NKT cells 42 h after PH. With regard to lymphocyte activation, TCDD treatment transiently increased CD69 expression on NK and NKT cells 12 h after PH, but had no effect on intracellular levels of IFNγ in NK, NKT, or CD3(+) T-cells. To determine the relevance of NK cells to the suppression of liver regeneration by TCDD, mice were treated with anti-Asialo GM-1 (ASGM-1) antibody to deplete NK cells prior to TCDD treatment and PH, and hepatocyte proliferation was measured using bromodeoxyuridine incorporation. Exposure to TCDD was found to inhibit hepatocyte proliferation in the regenerating liver of NK cell-depleted mice and control mice to the same extent. Hence, it is unlikely that enhanced numbers or increased activation of NK cells contribute to the suppression of liver regeneration in TCDD-treated mice.

A complement-IL-4 regulatory circuit controls liver regeneration

The involvement of IL-4 in liver regeneration has not yet been recognized. In this article, we show that IL-4, produced by NKT cells that accumulate in regenerating livers after partial hepatectomy, contributes to this process by regulating the activation of complement after liver resection in mice. The mechanism of this regulation was associated with the maintenance of an appropriate level of IgM in mouse blood, because IgM deposited in liver parenchyma most likely initiated complement activation during liver regeneration. By controlling complement activation, IL-4 regulated the induction of IL-6, thereby influencing a key pathway involved in regenerating liver cell proliferation and survival. Furthermore, the secretion of IL-4 was controlled by complement through the recruitment of NKT cells to regenerating livers. Our study thus reveals the existence of a regulatory feedback mechanism involving complement and IL-4 that controls liver regeneration.

Restored circulating invariant NKT cells are associated with viral control in patients with chronic hepatitis B

Invariant NKT (iNKT) cells are involved in the pathogenesis of various infectious diseases. However, their role in hepatitis B virus (HBV) infection is not fully understood, especially in human species. In this study, 35 chronic hepatitis B (CHB) patients, 25 inactive carriers (IC) and 36 healthy controls (HC) were enrolled and the proportions of circulating iNKT cells in fresh isolated peripheral blood mononuclear cells (PBMC) were detected by flow cytometry. A longitudinal analysis was also conducted in 19 CHB patients who received antiviral therapy with telbivudine. Thereafter, the immune functions of iNKT cells were evaluated by cytokine secretion and a two-chamber technique. The median frequency of circulating iNKT cells in CHB patients (0.13%) was lower than that in HC (0.24%, P = 0.01) and IC (0.19%, P = 0.02), and increased significantly during antiviral therapy with telbivudine (P = 0.0176). The expressions of CC chemokine receptor 5 (CCR5) and CCR6 were dramatically higher on iNKT cells (82.83%±9.87%, 67.67%±16.83% respectively) than on conventional T cells (30.5%±5.65%, 14.02%±5.92%, both P<0.001) in CHB patients. Furthermore, iNKT cells could migrate toward the CC chemokine ligand 5. Patients with a high ratio (≥1.0) of CD4−/CD4+ iNKT cells at baseline had a higher rate (58.33%) of HBeAg seroconversion than those with a low ratio (<1.0, 0%, P = 0.0174). In conclusion, there is a low frequency of peripheral iNKT cells in CHB patients, which increases to normal levels with viral control. The ratio of CD4−/CD4+ iNKT cells at baseline may be a useful predictor for HBeAg seroconversion in CHB patients on telbivudine therapy.

New insights into liver regeneration

Even if the Greeks probably anticipated rather than discovered the extraordinary regenerative capacity of the liver with the Prometheus myth, this phenomenon still fascinates scientists nowadays with the same enthusiasm. There are good reasons to decipher this process other than to find an answer to our fantasy of immortality: it could indeed help patients needing large liver resections or living-donor liver transplantation, it could increase our understanding of liver pathology and finally it could enable novel cell-therapy approaches. For decades, most of our knowledge about the mechanisms involved in liver regeneration came from the classic two-thirds partial hepatectomy (PH) model. In this scenario, hepatocytes play the leading role, which raises the question of the simple existence of a stem cell population. Recently however, hepatic progenitor cells come again under the limelight, seeming to play a role in liver physiology and in various liver diseases such as steatosis or cirrhosis. Excellent reviews have recently addressed liver regeneration. Our goal is therefore to focus on recent improvements in the field, highlighting data mostly published in the last two years in order to draw a putative picture of what the future research axes on liver regeneration might look like.

Regulation of hepatocyte fate by interferon-γ

Interferon (IFN)-γ is a cytokine known for its immunomodulatory and anti-proliferative action. In the liver, IFN-γ can induce hepatocyte apoptosis or inhibit hepatocyte cell cycle progression. This article reviews recent mechanistic reports that describe how IFN-γ may direct the fate of hepatocytes either towards apoptosis or a cell cycle arrest. This review also describes a probable role for IFN-γ in modulating hepatocyte fate during liver regeneration, transplantation, hepatitis, fibrosis and hepatocellular carcinoma, and highlights promising areas of research that may lead to the development of IFN-γ as a therapy to enhance recovery from liver disease.

Activation of natural killer cells inhibits liver regeneration in toxin-induced liver injury model in mice via a tumor necrosis factor-alpha-dependent mechanism

Liver lymphocytes are enriched in natural killer (NK) cells, and activation of NK cells by injection of polyinosinic-polycytidylic acid (poly I:C) inhibits liver regeneration in the partial hepatectomy model via production of IFN-gamma. However, the role of NK cells in liver regeneration in a model of carbon tetrachloride (CCl(4))-induced liver injury remains unknown. In this study, we investigated the effect of activation of NK cells induced by poly I:C on liver regeneration in the CCl(4) model. Administration of poly I:C suppressed liver regeneration in CCl(4)-treated mice. Depletion of NK cells but not Kupffer cells or T cells restored liver regeneration in poly I:C/CCl(4)-treated mice. Poly I:C and CCl(4) cotreatment synergistically induced accumulation of NK cells in the liver and NK cell production of IFN-gamma and tumor necrosis factor (TNF)-alpha. Serum levels of these two cytokines were also synergistically induced after poly I:C and CCl(4) treatment. Finally, blockage of TNF-alpha but not IFN-gamma restored liver regeneration in poly I:C/CCl(4)-treated mice. Taken together, these findings suggest that poly I:C treatment inhibits liver regeneration in the CCl(4)-induced liver injury model via induction of NK cell production of TNF-alpha.

T cell immunoglobulin- and mucin-domain-containing molecule-3 (Tim-3) mediates natural killer cell suppression in chronic hepatitis B

BACKGROUND & AIMS

T cell immunoglobulin- and mucin-domain-containing molecule-3 (Tim-3) has been shown to influence autoimmune diseases; however, its function in viral infection has not been well-defined. We therefore investigated the expression and regulatory function of Tim-3 in natural killer (NK) cells in chronic Hepatitis B (CHB) infection.

METHODS

Seventy-six CHB patients, 38 healthy controls, and 18 patients with fatty liver disease (FLD) were tested for Tim-3 expression on peripheral blood mononuclear cells (PBMCs) and in the liver tissue by flow cytometry and immunohistochemical stainning. The effects of HBV infection on Tim-3 expression in NK cells and the roles of Tim-3 in regulation of NK-cell function were also studied.

RESULTS

There was a significant increase of Tim-3 expression in PBMCs, circulating NK cells and liver infiltrating lymphocytes (LILs) from CHB patients compared to that of healthy controls and FLD patients. Increased Tim-3 expression was also detected in NK92 cells that had been transfected with a HBV expression vector and NK cells isolated from the liver of HBV transgenic mice. Importantly, blockage of Tim-3 signaling with anti-Tim-3 antibodies or Tim-3-Fc fusion proteins resulted in an increased cytotoxicity for NK92 cells compared to HepG2 and HepG2.2.15 cells, as well as an elevated interferon-gamma (IFN-gamma) production. Similarly, enhanced cytotoxicity was also observed in PBMCs or NK cells from CHB patients treated with the Tim-3 blockade ex vivo.

CONCLUSION

HBV infection can up-regulate Tim-3 expression in NK cells, which may in turn suppress NK-cell functions in CHB patients.

Signal molecule-mediated hepatic cell communication during liver regeneration

Liver regeneration is a complex and well-orchestrated process, during which hepatic cells are activated to produce large signal molecules in response to liver injury or mass reduction. These signal molecules, in turn, set up the connections and cross-talk among liver cells to promote hepatic recovery. In this review, we endeavor to summarize the network of signal molecules that mediates hepatic cell communication in the regulation of liver regeneration.

Liver natural killer and natural killer T cells: immunobiology and emerging roles in liver diseases

Hepatic lymphocytes are enriched in NK and NKT cells that play important roles in antiviral and antitumor defenses and in the pathogenesis of chronic liver disease. In this review, we discuss the differential distribution of NK and NKT cells in mouse, rat, and human livers, the ultrastructural similarities and differences between liver NK and NKT cells, and the regulation of liver NK and NKT cells in a variety of murine liver injury models. We also summarize recent findings about the role of NK and NKT cells in liver injury, fibrosis, and repair. In general, NK and NKT cells accelerate liver injury by producing proinflammatory cytokines and killing hepatocytes. NK cells inhibit liver fibrosis via killing early-activated and senescent-activated stellate cells and producing IFN-gamma. In regulating liver fibrosis, NKT cells appear to be less important than NK cells as a result of hepatic NKT cell tolerance. NK cells inhibit liver regeneration by producing IFN-gamma and killing hepatocytes; however, the role of NK cells on the proliferation of liver progenitor cells and the role of NKT cells in liver regeneration have been controversial. The emerging roles of NK/NKT cells in chronic human liver disease will also be discussed.Understanding the role of NK and NKT cells in the pathogenesis of chronic liver disease may help us design better therapies to treat patients with this disease.

Rich dynamics of a hepatitis B viral infection model with logistic hepatocyte growth

Chronic hepatitis B virus (HBV) infection is a major cause of human suffering, and a number of mathematical models have examined within-host dynamics of the disease. Most previous HBV infection models have assumed that: (a) hepatocytes regenerate at a constant rate from a source outside the liver; and/or (b) the infection takes place via a mass action process. Assumption (a) contradicts experimental data showing that healthy hepatocytes proliferate at a rate that depends on current liver size relative to some equilibrium mass, while assumption (b) produces a problematic basic reproduction number. Here we replace the constant infusion of healthy hepatocytes with a logistic growth term and the mass action infection term by a standard incidence function; these modifications enrich the dynamics of a well-studied model of HBV pathogenesis. In particular, in addition to disease free and endemic steady states, the system also allows a stable periodic orbit and a steady state at the origin. Since the system is not differentiable at the origin, we use a ratio-dependent transformation to show that there is a region in parameter space where the origin is globally stable. When the basic reproduction number, R (0), is less than 1, the disease free steady state is stable. When R (0) > 1 the system can either converge to the chronic steady state, experience sustained oscillations, or approach the origin. We characterize parameter regions for all three situations, identify a Hopf and a homoclinic bifurcation point, and show how they depend on the basic reproduction number and the intrinsic growth rate of hepatocytes.

Diverse roles of invariant natural killer T cells in liver injury and fibrosis induced by carbon tetrachloride

Liver fibrosis is a common scarring response to all forms of chronic liver injury and is always associated with inflammation that contributes to fibrogenesis. Although a variety of cell populations infiltrate the liver during inflammation, it is generically clear that CD8 T lymphocytes promote while natural killer (NK) cells inhibit liver fibrosis. However, the role of invariant natural killer T (iNKT) cells, which are abundant in the liver, in hepatic fibrogenesis, remains obscure. Here we show that iNKT-deficient mice are more susceptible to carbon tetrachloride (CCl(4))-induced acute liver injury and inflammation. The protective effect of naturally activated iNKT in this model is likely mediated via suppression of the proinflammatory effect of activated hepatic stellate cells. Interestingly, strong activation of iNKT through injection of iNKT activator alpha-galactosylceramide (alpha-GalCer) accelerates CCl(4)-induced acute liver injury and fibrosis. In contrast, chronic CCl(4) administration induces a similar degree of liver injury in iNKT-deficient and wild-type mice, and only a slightly higher grade of liver fibrosis in iNKT-deficient mice than wild-type mice 2 weeks but not 4 weeks after CCl(4) injection, although iNKT cells are able to kill activated stellate cells. An insignificant role of iNKT in chronic liver injury and fibrosis may be attributable to hepatic iNKT cell depletion. Finally, chronic alpha-GalCer treatment had little effect on liver injury and fibrosis, which is attributable to iNKT tolerance after alpha-GalCer injection.

CONCLUSION

Natural activation of hepatic iNKT cells inhibits, whereas strong activation of iNKT cells by alpha-GalCer accelerates CCl(4)-induced acute liver injury, inflammation, and fibrosis. During chronic liver injury, hepatic iNKT cells are depleted and play a role in inhibiting liver fibrosis in the early stage but not the late stage of fibrosis.

NKT cell immune responses to viral infection

BACKGROUND

Natural killer T (NKT) cells are a heterogeneous population of innate T cells that have attracted interest because of their potential to regulate immune responses to a variety of pathogens. The most widely studied NKT cell subset is the invariant (i)NKT cells that recognize glycolipids in the context of the CD1d molecule. The multifaceted methods of activation iNKT cells possess and their ability to produce regulatory cytokines has made them a primary target for studies.

OBJECTIVE/METHODS

To give insights into the roles of iNKT cells during infectious diseases, particularly viral infections. We also highlight mechanisms leading to iNKT cell activation in response to pathogens.

CONCLUSIONS

iNKT cell's versatility allows them to detect and respond to several viruses. Therapeutic approaches to specifically target iNKT cells will require additional research. Notably, the roles of non-invariant NKT cells in response to pathogens warrant further investigation.

Biological features of hepatitis B virus isolates from patients based on full-length genomic analysis

The mechanisms for HBV persistence and the pathogenesis of chronic HB have been shown mainly due to defects in host immune responses. However, HBV isolates with different biological features may also contribute to different clinical outcomes and epidemiological implications in viral hepatitis B (HB). This review presents interesting biological features of HBV isolates based on the structural and functional analysis of full-length HBV isolates from various patients. Among isolates from children after failure of HB vaccination, 129L mutant at the 'a' determinant was found with normal binding efficiency to anti-HBs, but with reduced immunogenicity, which could initiate persistent HBV infections. Isolates from fulminant hepatitis (FH) B patients were not all highly replicative, but differences in capacities of anti-HBs induction could be involved in the pathogenesis of FH. The high replicative competency of isolates from hepatocellular carcinoma (HCC) patients could result in enhanced immune-mediated cytopathic effects against HBV viral proteins, and increased transactivating activity by the X protein. The mechanism of a double-spliced variant in enhancing replication of the wild-type virus is presented. The importance of integrating structural and functional analysis to reveal biological features of HBV isolates in viral pathogenesis is discussed.

Hepatocytes proteomic alteration and seroproteome analysis of HBV-transgenic mice

Hepatitis B is the most common and serious liver disease, especially in developing countries. Although HBV pathogenesis has been extensively investigated, the proteomic alteration of hepatocytes during HBV chronic infection is still unclear. Using the purified hepatocytes, we compared the protein profiles by 2-DE and LC-MS between HBV-transgenic (Tg) and corresponding background mice. Twenty-seven altered proteins were identified in hepatocytes from HBV-Tg mice, among which 13 proteins were involved in mitochondrion metabolism pathway including tricarboxylic acid (TCA) cycle and oxidative response; four proteins (SELENBP, SCP2, RGN and PRDX1) were also dramatically changed in liver samples from HBV-infected patients. Important genes (gpx, sod, ogg et al.) correlated to oxidative damage were up-regulated in the liver of HBV-Tg mice. Reactive oxygen species production was significantly increased while ATP production was decreased in liver mitochondria from HBV-Tg mice. Moreover, hepatocytes of HBV-Tg mice were more sensitive to hydrogen peroxide-induced cell death than that of wild-type control. Using 2-D Western blotting analysis, eight hepatocyte proteins were found to react with sera of HBV-Tg mice but not with that of background mice. Interestingly, two (Etfa and Dmgdh) of the eight reactive proteins were overexpressed in HBV-Tg mice. We believe this study is the first proteomic and seroproteome analysis of HBV-infected mammalian hepatocyte and provides insightful links between HBV infection and HBV-induced liver diseases.

T cell-derived lymphotoxin regulates liver regeneration

BACKGROUND & AIMS

The ability of the liver to regenerate hepatic mass is essential to withstanding liver injury. The process of liver regeneration is tightly regulated by distinct signaling cascades involving components of the innate immune system, cytokines, and growth factors. However, the role of the adaptive immune system in regulation of liver regeneration is not well-defined. The role of adaptive immune system in liver regeneration was investigated in lymphocyte-deficient mice and in conditional lymphotoxin-deficient mice.

METHODS

A model of liver regeneration after 70% partial hepatectomy was used, followed by examination of liver pathology, survival, DNA synthesis, and cytokine expression.

RESULTS

We found that mice deficient in T cells show a reduced capacity for liver regeneration following partial hepatectomy. Furthermore, surface lymphotoxin, provided by T cells, is critical for liver regeneration. Mice specifically deficient in T-cell lymphotoxin had increased liver damage and a reduced capacity to initiate DNA synthesis after partial hepatectomy. Transfer of splenocytes from wild-type but not lymphotoxin-deficient mice improved liver regeneration in T cell-deficient mice. We found that an agonistic antibody against the lymphotoxin beta receptor was able to facilitate liver regeneration by reducing liver injury, increasing interleukin-6 production, hepatocyte DNA synthesis, and survival of lymphocyte-deficient (Rag) mice after partial hepatectomy.

CONCLUSIONS

The adaptive immune system directly regulates liver regeneration via a T cell-derived lymphotoxin axis, and pharmacological stimulation of lymphotoxin beta receptor might represent a novel therapeutic approach to improve liver regeneration.

Role of natural killer T cells in liver diseases

Natural killer T (NKT) cells are a unique subset of lymphocytes, which express both T and NK cell surface markers as well as functional characteristics. They connect innate and acquired immunity, and restrictedly recognize glycolipid antigens presented by CD1d molecule. NKT cells secrete a great quantity of cytokines rapidly which regulate human immune response after being activated. For there are abundant NKT cells in human liver, researchers have a great interest in their roles.

Innate immunity and alcoholic liver fibrosis

The hepatic innate immune system consists of predominant innate immunity, which plays an important role in innate defense against infection and tumor transformation. Emerging evidence suggests that innate immunity also contributes to liver injury, repair, and fibrosis. The present review summarizes the recent findings on the role of innate immunity in liver fibrosis. In general, Kupffer cells stimulate liver fibrosis via production of reactive oxygen species and pro-inflammatory cytokines, whereas natural killer (NK) cells inhibit liver fibrosis by directly killing activated hepatic stellate cells and production of gamma-interferon (IFN-gamma). Complement components, interferons, and Toll-like receptors have also been shown to regulate liver fibrosis. Recent evidence also suggests that modulation of innate immunity by alcohol plays an important role in the pathogenesis of alcoholic liver fibrosis. These include alcohol amplification of the profibrotic effects of Kupffer cells and suppression of the antifibrotic effects of NK/IFN-gamma.