Involvement of natural killer cells in PolyI:C-induced liver injury

Photophosphatidylserine Guides Natural Killer Cell Photoimmunotherapy via Tim-3

Natural killer (NK) cells, in addition to their cytotoxicity function, harbor prominent cytokine production capabilities and contribute to regulating autoimmune responses. T-cell immunoglobulin and mucin domain containing protein-3 (Tim-3) is one of the inhibitory receptors on NK cells and a promising immune checkpoint target. We recently found that phosphatidylserine (PS) binding to Tim-3 can suppress NK cell activation. Therefore, based on the therapeutic potential of Tim-3 in NK-cell-mediated diseases, we developed a photoswitchable ligand of Tim-3, termed photophosphatidylserine (phoPS), that mimics the effects of PS. Upon 365 or 455 nm light irradiation, the isomer of phoPS cyclically conversed the cis/trans configuration, resulting in an active/inactive Tim-3 ligand, thus modulating the function of NK cells in vitro and in vivo. We also demonstrated that reversible phoPS enabled optical control of acute hepatitis. Together, phoPS may be an appealing tool for autoimmune diseases and cytokine storms in the future.

Pathogenesis of Autoimmune Hepatitis-Cellular and Molecular Mechanisms

Pediatric autoimmune liver disorders include autoimmune hepatitis (AIH), autoimmune sclerosing cholangitis (ASC), and de novo AIH after liver transplantation. AIH is an idiopathic disease characterized by immune-mediated hepatocyte injury associated with the destruction of liver cells, causing inflammation, liver failure, and fibrosis, typically associated with autoantibodies. The etiology of AIH is not entirely unraveled, but evidence supports an intricate interaction among genetic variants, environmental factors, and epigenetic modifications. The pathogenesis of AIH comprises the interaction between specific genetic traits and molecular mimicry for disease development, impaired immunoregulatory mechanisms, including CD4+ T cell population and Treg cells, alongside other contributory roles played by CD8+ cytotoxicity and autoantibody production by B cells. These findings delineate an intricate pathway that includes gene to gene and gene to environment interactions with various drugs, viral infections, and the complex microbiome. Epigenetics emphasizes gene expression through hereditary and reversible modifications of the chromatin architecture without interfering with the DNA sequence. These alterations comprise DNA methylation, histone transformations, and non-coding small (miRNA) and long (lncRNA) RNA transcriptions. The current first-line therapy comprises prednisolone plus azathioprine to induce clinical and biochemical remission. Further understanding of the cellular and molecular mechanisms encountered in AIH may depict their impact on clinical aspects, detect biomarkers, and guide toward novel, effective, and better-targeted therapies with fewer side effects.

The role of natural killer cells in liver inflammation

The liver is an important immunological site that can promote immune tolerance or activation. Natural killer (NK) cells are a major immune subset within the liver, and therefore understanding their role in liver homeostasis and inflammation is crucial. Due to their cytotoxic function, NK cells are important in the immune response against hepatotropic viral infections but are also involved in the inflammatory processes of autoimmune liver diseases and fatty liver disease. Whether NK cells primarily promote pro-inflammatory or tolerogenic responses is not known for many liver diseases. Understanding the involvement of NK cells in liver inflammation will be crucial in effective treatment and future immunotherapeutic targeting of NK cells in these disease settings. Here, we explore the role that NK cells play in inflammation of the liver in the context of viral infection, autoimmunity and fatty liver disease.

Intrahepatic TLR3 and IFNL3 Expressions Are Associated with Stages of Fibrosis in Chronic Hepatitis C

An inefficient immune response against the hepatitis C virus (HCV), combined with viral evasion mechanisms, is responsible for the chronicity of infection. The need to evaluate the innate mechanisms of the immune response, such as TLR3 and IFN-λ3, and their relationship with the virus-host interaction is important for understanding the pathogenesis of chronic hepatitis C. The present study aimed to investigate the gene expressions of TRL3 and IFNL3 in liver tissue, seeking to evaluate whether these could be potential biomarkers of HCV infection. A total of 23 liver biopsy samples were collected from patients with chronic HCV, and 8 biopsies were collected from healthy control patients. RNA extraction, reverse transcription and qPCR were performed to quantify the relative gene expressions of TLR3 and IFNL3. Data on the viral load; AST, ALT, GGT and AFP levels; and the viral genotype were collected from the patients' medical records. The intrahepatic expression of TLR3 (p = 0.0326) was higher in chronic HCV carriers than in the control group, and the expression of IFNL3 (p = 0.0037) was lower in chronic HCV carriers than in the healthy control group. The expression levels of TLR3 (p = 0.0030) and IFNL3 (p = 0.0036) were higher in the early stages of fibrosis and of necroinflammatory activity in the liver; in contrast, TLR3 and IFNL3 expressions were lower in the more advanced stages of fibrosis and inflammation. There was no correlation between the gene expression and the serum viral load. Regarding the initial METAVIR scale scores, liver transaminase levels were lower in patients with advanced fibrosis when correlated with TLR3 and IFNL3 gene expressions. The results suggest that in the early stages of the development of hepatic fibrosis, TLR3 and IFN-λ3 play important roles in the antiviral response and in the modulation of the tolerogenic liver environment because there is a decrease in the intrahepatic expressions of TLR3 and IFNL3 in the advanced stages of fibrosis, probably due to viral evasion mechanisms.

NK Cells in Autoimmune Diseases: Protective or Pathogenic?

Autoimmune diseases generally result from the loss of self-tolerance (i.e., failure of the immune system to distinguish self from non-self), and are characterized by autoantibody production and hyperactivation of T cells, which leads to damage of specific or multiple organs. Thus, autoimmune diseases can be classified as organ-specific or systemic. Genetic and environmental factors contribute to the development of autoimmunity. Recent studies have demonstrated the contribution of innate immunity to the onset of autoimmune diseases. Natural killer (NK) cells, which are key components of the innate immune system, have been implicated in the development of multiple autoimmune diseases such as systemic lupus erythematosus, type I diabetes mellitus, and autoimmune liver disease. However, NK cells have both protective and pathogenic roles in autoimmunity depending on the NK cell subset, microenvironment, and disease type or stage. In this work, we review the current knowledge of the varied roles of NK cell subsets in systemic and organic-specific autoimmune diseases and their clinical potential as therapeutic targets.

Paeoniflorin mitigates PBC-induced liver fibrosis by repressing NLRP3 formation

Purpose:

To delve into the influence of paeoniflorin (PA) on abating primary biliary cholangitis (PBC)-induced liver fibrosis and its causative role.

Methods:

Our team allocated the mice to control group, PA group, PBC group and PBC+PA group. We recorded the weight change of mice in each group. We used Masson staining for determining liver fibrosis, immunofluorescence staining for measuring tumor necrosis factor-α (TNF-α) expression, quantitative real-time polymerase chain reaction (qRT-PCR) for assaying related gene expression, as well as Western blot for testing related protein expression.

Results:

The weight of PBC model mice declined. Twenty-four weeks after modeling, the positive rate of anti-mitochondrial antibody-M2 (AMA-M2) in PBC mice reached 100%. Alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), hydroxyproline (HYP), laminin (LN), procollagen type III (PC III), and malondialdehyde (MDA) contents saliently waxed (p<0.01). Meanwhile, superoxide dismutase (SOD) and glutathione peroxidase (GSH-px) activity patently waned (p<0.01). Liver fibrosis levels were flagrantly higher (p<0.01), and TNF-α, NOD-like receptor protein 3 (NLRP3), caspase-1, interleukin-18 (IL-18), and interleukin-1β (IL-1β) protein or gene expression were manifestly up-regulated (p<0.01). PA could restore the weight of PBC mice, strikingly restrain the positive expression of AMA-M2, and down-regulate serum ALP, ALT, AST, HYP, LN, PC III, MDA in PBC mice (p<0.01). PA could also significantly up-regulate SOD and GSH-px levels (p<0.01), down-regulate IL-1β, IL-18, caspase-1, NLRP3, and TNF-α protein or gene expression in PBC mice (p<0.01) and inhibit liver fibrosis levels (p<0.01).

Conclusions:

PA can reduce PBC-induced liver fibrosis in mice and may function by curbing the formation of NLRP3.

The Toll-Like Receptor 3 Agonist Polyriboinosinic Polyribocytidylic Acid Increases the Numbers of NK Cells with Distinct Phenotype in the Liver of B6 Mice

One of the activating factors of the cells of the innate immune system is the agonists of toll-like receptors (TLRs). Our earlier publications detailed how poly(I:C), a TLR3 agonist, elevates the NK cell population and the associated antigen-specific CD8⁺ T cell responses. This study involved a single treatment of the B6 mice with poly(I:C) intraperitoneally. To perform a detailed phenotypic analysis, mononuclear cells were prepared from each of the liver, peripheral blood, and spleen. These cells were then examined for their NK cell population by flow cytometric analysis following cell staining with indicated antibodies. The findings of the study showed that the NK cell population of the liver with an NK1.1^highCD11b^highCD11c^high B220⁺Ly6G^- phenotype was elevated following the treatment with poly(I:C). In the absence of CD11b molecule (CR3^-/- mice), poly(I:C) can still increase the remained numbers of NK cells with NK1.1⁺CD11b^- and NK1.1⁺Ly6G^- phenotypes in the liver while their numbers in the blood decrease. After the treatment with anti-AGM1 Ab, which induced depletion of NK1.1⁺CD11b⁺ cells and partial depletion of CD3⁺NK1.1⁺ and NK1.1⁺CD11b^- cell populations, poly(I:C) normalized the partial decreases in the numbers of NK cells concomitant with increased numbers of NK1.1^-CD11b⁺ cell population in both liver and blood. Regarding mice with a TLR3^-/- phenotype, their injection with poly(I:C) resulted in the partial elevation in the NK cell population as compared to wild-type B6 mice. To summarise, the TLR3 agonist poly(I:C) results in the elevation of a subset of liver NK cells expressing the two myeloid markers CD11c and CD11b. The effect of poly(I:C) on NK cells is partially dependent on TLR3 and independent of the presence of CD11b.

Organ-Specific Expression of IL-1 Receptor Results in Severe Liver Injury in Type I Interferon Receptor Deficient Mice

Upon treatment with polyinosinic:polycytidylic acid [poly(I:C)], an artificial double-stranded RNA, type I interferon receptor-deficient (IFNAR^−/−) mice develop severe liver injury seen by enhanced alanine aminotransferase (ALT) activity in the serum that is not observed in their wildtype (WT) counterparts. Recently, we showed that liver injury is mediated by an imbalanced expression of interleukin (IL)-1β and its receptor antagonist (IL1-RA) in the absence of type I IFN. Here we show that despite comparable expression levels of IL-1β in livers and spleens, spleens of poly(I:C)-treated IFNAR^−/− mice show no signs of injury. In vitro analyses of hepatocytes and splenocytes revealed that poly(I:C) had no direct toxic effect on hepatocytes. Furthermore, expression levels of cytokines involved in other models for liver damage or protection such as interferon (IFN)-γ, transforming growth factor (TGF)-β, IL-6, IL-10, IL-17, and IL-22 were comparable for both organs in WT and IFNAR^−/− mice upon treatment. Moreover, flow cytometric analyses showed that the composition of different immune cells in livers and spleens were not altered upon injection of poly(I:C). Finally, we demonstrated that the receptor binding IL-1β, IL1R1, is specifically expressed in livers but not spleens of WT and IFNAR^−/− mice. Accordingly, mice double-deficient for IFNAR and IL1R1 developed no liver injury upon poly(I:C) treatment and showed ALT activities comparable to those of WT mice. Collectively, liver injury is mediated by the organ-specific expression of IL1R1 in the liver.

Cellular and Molecular Mechanisms of Autoimmune Hepatitis

Autoimmune hepatitis is an uncommon idiopathic syndrome of immune-mediated destruction of hepatocytes, typically associated with autoantibodies. The disease etiology is incompletely understood but includes a clear association with human leukocyte antigen (HLA) variants and other non-HLA gene variants, female sex, and the environment. Pathologically, there is a CD4+ T cell-rich lymphocytic inflammatory infiltrate with variable hepatocyte necrosis and subsequent hepatic fibrosis. Attempts to understand pathogenesis are informed by several monogenetic syndromes that may include autoimmune liver injury, by several drug and environmental agents that have been identified as triggers in a minority of cases, by human studies that point toward a central role for CD4+ effector and regulatory T cells, and by animal models of the disease. Nonspecific immunosuppression is the current standard therapy. Further understanding of the disease's cellular and molecular mechanisms may assist in the design of better-targeted therapies, aid the limitation of adverse effects from therapy, and inform individualized risk assessment and prognostication.

NK cells in liver homeostasis and viral hepatitis

As an important member of the innate immune system, natural killer (NK) cells are well known for their rapid and efficient immune responses against infectious agents and tumors. NK cells are widely distributed throughout the body and are particularly enriched within the liver, where they display unique phenotypic and functional properties, playing important roles in various liver diseases. Herein, we present an overview of liver NK cell properties with regard to phenotype, function, and subset composition at steady state, and we also summarize the complex reciprocal interactions between liver NK cells and other cell types within the local environment of the liver. We also provide an overview of recent advances demonstrating the roles of NK cells in viral hepatitis, including a discussion of NK cell altered states and their beneficial versus harmful effects during hepatitis B virus and hepatitis C virus infection.

Hepatoprotective Effect of San-Cao Granule on Con A-Induced Liver Injury in Mice and Mechanisms of Action Exploration

Objective: San-Cao granule (SCG), a traditional Chinese herb formula, has been used for treating autoimmune hepatitis (AIH) in our clinics for a long time. However, its active ingredients and mechanisms of action were still unknown due to its complicated chemical compositions. In the present study, the pharmacological study of SCG on acute liver injury induced by Concanavalin A (Con A) was performed to provide a scientific evidence for SCG against liver injury. Methods: In order to screen active components and predicate mechanisms of action, an "ingredients-target-disease" interaction network was constructed by network pharmacology. Then, the pharmacological study was performed to evaluate the therapeutic effect and the underlying mechanisms of SCG on Con A-induced liver injury in mice. Results: This research demonstrated the pharmacological effect of SCG on Con A-induced liver injury, which was through improving the liver function, relieving the pathological changes of liver tissue, decreasing the level of pro-inflammatory cytokines, and thus balancing the pro- and anti-inflammatory cytokines. And the anti-inflammatory of SCG may advantage over the ursodeoxycholic acid (UDCA). Network pharmacology analysis revealed that the pharmacological effect of SCG might be related to its active ingredients of taraxanthin, dihydrotanshinone I, isotanshinone I, γ-sitosterol, 3β-acetyl-20,25-epoxydammarane-24α, and δ-7-stigmastenol. The hepatoprotective effect of SCG was reflected by suppressing Con A-induced apoptosis which was mediated by TRAIL and FASL. Conclusion: The combination of network pharmacology and experimental data has revealed the anti-apoptotic effect of SCG against Con A-induced liver injury.

Recent advances in the discovery and development of TLR ligands as novel therapeutics for chronic HBV and HIV infections

INTRODUCTION

Toll-like receptor (TLR) ligands remain as promising antiviral drug candidates for the treatment of chronic viral infections. Basic research on the mechanisms of antiviral activity of TLR ligands in preclinical animal models and clinical testing of drug candidates have been carried out in recent years. Areas covered: This review provides an overview of the preclinical and clinical testing of TLR ligands in two major viral infections: hepatitis B virus (HBV) and human immunodeficiency virus (HIV). Recent results have further demonstrated the potent antiviral activity of various TLR ligands . A TLR7 agonist is in clinical trials for the treatment of chronic HBV infection while a HBV vaccine using a TLR9 ligand as an adjuvant has proven to be superior to conventional HBV vaccines and has been approved for clinical use. Generally, TLR activation may achieve viral control mainly by promoting adaptive immunity to viral proteins. Expert opinion: Recent research in this field indicates that TLR ligands could be developed as clinically effective drugs if the obstacles concerning toxicity and application routes are overcome. TLR-mediated promotion of adaptive immunity is a major issue for future studies and will determine the future development of TLR ligands as drugs for immunomodulation.

Inducible disruption of the c-myb gene allows allogeneic bone marrow transplantation without irradiation

Allogeneic bone marrow (BM) transplantation enables the in vivo functional assessment of hematopoietic cells. As pre-conditioning, ionizing radiation is commonly applied to induce BM depletion, however, it exerts adverse effects on the animal and can limit experimental outcome. Here, we provide an alternative method that harnesses conditional gene deletion to ablate c-myb and thereby deplete BM cells, hence allowing BM substitution without other pre-conditioning. The protocol results in a high level of blood chimerism after allogeneic BM transplantation, whereas immune cells in peripheral tissues such as resident macrophages are not replaced. Further, mice featuring a low chimerism after initial transplantation can undergo a second induction cycle for efficient deletion of residual BM cells without the necessity to re-apply donor cells. In summary, we present an effective c-myb-dependent genetic technique to generate BM chimeras in the absence of irradiation or other methods for pre-conditioning.

Differential gene expression following TLR stimulation in rag1-/- mutant zebrafish tissues and morphological descriptions of lymphocyte-like cell populations

In the absence of lymphocytes, rag1-/- mutant zebrafish develop protective immunity to bacteria. In mammals, induction of protection by innate immunity can be mediated by macrophages or natural killer (NK) cells. To elucidate potential responsive cell populations, we morphologically characterized lymphocyte-like cells (LLCs) from liver, spleen and kidney hematopoietic tissues. In fish, these cells include NK cells and Non-specific cytotoxic cells (NCCs). We also evaluated the transcriptional expression response of select genes that are important indicators of NK and macrophage activation after exposure to specific TLR ligands. The LLC cell populations could be discriminated by size and further discriminated by the presence of cytoplasmic granules. Expression levels of mx, tnfα, ifnγ, t-bet and nitr9 demonstrated dynamic changes in response to intra-coelomically administered β glucan (a TLR2/6 ligand), Poly I:C (a TLR3 ligand) and resiquimod (R848) (a TLR7/8 ligand). Following TLR 2/6 stimulation, there was a greater than 100 fold increase in ifnγ in liver, kidney and spleen and moderate increases in tnfα in liver and kidney. TLR3 stimulation caused broad up regulation of mx, down-regulation of tnfα in kidney and spleen tissues and up regulation of nitr9 in the kidney. Following TLR 7/8 stimulation, there was a greater than 100 fold increase in ifnγ in liver and kidney and t-bet in liver. Our gene expression findings suggest that LLCs and macrophages are stimulated following β glucan exposure. Poly I:C causes type I interferon response and mild induction of LLC in the kidney and R-848 exposure causes the strongest LLC stimulation. Overall, the strongest NK like gene expression occurred in the liver. These differential effects of TLR ligands in rag1-/- mutant zebrafish shows strong NK cell-like gene expression responses, especially in the liver, and provides tools to evaluate the basis for protective immunity mediated by the innate immune cells of fish.

Association of Toll-Like Receptor 3 and Toll-Like Receptor 9 Single Nucleotide Polymorphisms with Hepatitis C Virus Infection and Hepatic Fibrosis in Egyptian Patients

Toll-like receptors (TLRs) are recognized as fundamental contributors to the immune system function against infections. Hepatitis C virus (HCV) infection represents a global health problem especially in Egypt having the highest HCV prevalence worldwide where HCV infection is a continuing epidemic. The aim of the present study was to investigate the possible association between genetic variation in TLR-3 and TLR-9 and HCV infection and hepatic fibrosis in chronic HCV-positive Egyptian patients. The present study included 100 naïve chronic HCV-positive patients and 100 age- and sex-matched healthy controls. Genotyping of TLR-3 (_7 C/A [rs3775296]), TLR-3 (c.1377C/T [rs3775290]) and TLR-9 (1237T/C [rs5743836]) were done by polymerase chain reaction restriction fragment length polymorphism technique. Frequency of polymorphic genotypes in TLR-3 (_7 C/A), TLR-3 (c.1377C/T) and TLR-9 (1237T/C) were not significantly different between studied HCV-positive patients and controls with P values 0.121, 0.112, and 0.683, respectively. TLR-3 c.1377 T-allele was associated with advanced stage of hepatic fibrosis (P = 0.003).

Exosomes derived from human menstrual blood-derived stem cells alleviate fulminant hepatic failure

Background

Human menstrual blood-derived stem cells (MenSCs) are a novel source of MSCs that provide the advantage of being easy to collect and isolate. Exosomes contain some mRNAs and adhesion molecules that can potentially impact cellular and animal physiology. This study aimed to investigate the therapeutic potential of MenSC-derived exosomes (MenSC-Ex) on AML12 cells (in vitro) and D-GalN/LPS-induced FHF mice (in vivo).

Methods

Transmission electron microscopy and Western blot were used to identify MenSC-Ex. Antibody array was used to examine cytokine levels on MenSC-Ex. MenSC-Ex were treated in D-GalN/LPS-induced AML12 in vitro. Cell proliferation and apoptosis were measured. MenSC-Ex were injected into the tail veins of mice 24 h before treatment with D-GalN/LPS. Blood and liver tissues served as physiological and biochemical indexes. The number of liver mononuclear cells (MNCs) and the amount of the active apoptotic protein caspase-3 were determined to elaborate the mechanism of hepatoprotective activity.

Results

Human menstrual blood-derived stem cell-derived exosomes (MenSC-Ex) are bi-lipid membrane vesicles that have a round, ball-like shape with a diameter of approximately 30–100 nm. Cytokine arrays have shown that MenSC-Ex expressed cytokines, including ICAM-1, angiopoietin-2, Axl, angiogenin, IGFBP-6, osteoprotegerin, IL-6, and IL-8. MenSC-Ex markedly improved liver function, enhanced survival rates, and inhibited liver cell apoptosis at 6 h after transplantation. MenSC-Ex migrated to sites of injury and to AML12 cells (a mouse hepatocyte cell line), respectively. Moreover, MenSC-Ex reduced the number of liver mononuclear cells (MNCs) and the amount of the active apoptotic protein caspase-3 in injured livers.

Conclusions

In conclusion, our results provide preliminary evidence for the anti-apoptotic capacity of MenSC-Ex in FHF and suggest that MenSC-Ex may be an alternative therapeutic approach to treat FHF.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0453-6) contains supplementary material, which is available to authorized users.

Inhibition of Sophocarpine on Poly I: C/D-GalN-Induced Immunological Liver Injury in Mice

Increasing evidence has suggested that natural killer (NK) cells contribute to the pathogenesis of human immunological liver injury (ILI). Previous studies have demonstrated that Sophocarpine exerts activity in immune modulation. It also has a therapeutic effect on liver protection in that it can alleviate liver fibrosis by suppressing both the activation of hepatic stellate cells and the proliferation of the activated hepatic stellate cells. However, whether Sophocarpine protects the liver by regulating NK cell activity remains unclear. In this study, the modulating effect of Sophocarpine on NK cells in the liver was investigated. The results showed that Sophocarpine dramatically decreased the production of pro-inflammatory cytokines and attenuated the liver injury induced by Poly I: C/D-GalN in C57BL/6- mice. More importantly, Sophocarpine pre-treatment significantly suppressed NK cell activation and downregulated the expression of NKG2D, a receptor responsible for NK cell activation. Moreover, the protein levels of DAP12, ZAP76 and Syk decreased, as did their corresponding mRNA levels. Overall, our study demonstrates that Sophocarpine inhibits NK cell activity, thus making it a promising therapy for ILI.

Exosome-mediated activation of toll-like receptor 3 in stellate cells stimulates interleukin-17 production by γδ T cells in liver fibrosis

During liver injury, hepatocytes secrete exosomes that include diverse types of self-RNAs. Recently, self-noncoding RNA has been recognized as an activator of Toll-like receptor 3 (TLR3). However, the roles of hepatic exosomes and TLR3 in liver fibrosis are not yet fully understood. Following acute liver injury and early-stage liver fibrosis induced by a single or 2-week injection of carbon tetrachloride (CCl4 ), increased interleukin (IL)-17A production was detected primarily in hepatic γδ T cells in wild-type (WT) mice. However, liver fibrosis and IL-17A production by γδ T cells were both significantly attenuated in TLR3 knockout (KO) mice compared with WT mice. More interestingly, IL-17A-producing γδ T cells were in close contact with activated hepatic stellate cells (HSCs), suggesting a role for HSCs in IL-17A production by γδ T cells. In vitro treatments with exosomes derived from CCl4 -treated hepatocytes significantly increased the expression of IL-17A, IL-1β, and IL-23 in WT HSCs but not in TLR3 KO HSCs. Furthermore, IL-17A production by γδ T cells was substantially increased upon coculturing with exosome-treated WT HSCs or conditioned medium from TLR3-activated WT HSCs. However, similar increases were not detected when γδ T cells were cocultured with exosome-treated HSCs from IL-17A KO or TLR3 KO mice. Using reciprocal bone marrow transplantation between WT and TLR3 KO mice, we found that TLR3 deficiency in HSCs contributed to decreased IL-17A production by γδ T cells, as well as liver fibrosis.

CONCLUSION

In liver injury, the exosome-mediated activation of TLR3 in HSCs exacerbates liver fibrosis by enhancing IL-17A production by γδ T cells, which might be associated with HSC stimulation by unknown self-TLR3 ligands from damaged hepatocytes. Therefore, TLR3 might be a novel therapeutic target for liver fibrosis. (Hepatology 2016;64:616-631).

Characterization of SIGIRR/IL-1R8 Homolog from Zebrafish Provides New Insights into Its Inhibitory Role in Hepatic Inflammation

Single Ig IL-1R-related molecule (SIGIRR, also called IL-1R8 or Toll/IL-1R [TIR]8), a negative regulator for Toll/IL-1R signaling, plays critical roles in innate immunity and various diseases in mammals. However, the occurrence of this molecule in ancient vertebrates and its function in liver homeostasis and disorders remain poorly understood. In this study, we identified a SIGIRR homology from zebrafish (Danio rerio [DrSIGIRR]) by using a number of conserved structural and functional hallmarks to its mammalian counterparts. DrSIGIRR was highly expressed in the liver. Ablation of DrSIGIRR by lentivirus-delivered small interfering RNA in the liver significantly enhanced hepatic inflammation in response to polyinosinic-polycytidylic acid [poly(I:C)] stimulation, as shown by the upregulation of inflammatory cytokines and increased histological disorders. In contrast, depletion of TIR domain-containing adaptor inducing IFN-β (TRIF) or administration of TRIF signaling inhibitor extremely abrogated the poly(I:C)-induced hepatic inflammation. Aided by the zebrafish embryo model, overexpression of DrSIGIRR in vivo significantly inhibited the poly(I:C)- and TRIF-induced NF-κB activations; however, knockdown of DrSIGIRR promoted such activations. Furthermore, pull-down and Duolink in situ proximity ligation assay assays showed that DrSIGIRR can interact with the TRIF protein. Results suggest that DrSIGIRR plays an inhibitory role in TRIF-mediated inflammatory reactions by competitive recruitment of the TRIF adaptor protein from its TLR3/TLR22 receptor. To our knowledge, this study is the first to report a functional SIGIRR homolog that existed in a lower vertebrate. This molecule is essential to establish liver homeostasis under inflammatory stimuli. Overall, the results will enrich the current knowledge about SIGIRR-mediated immunity and disorders in the liver.

Involvement of LSECtin in the hepatic natural killer cell response

Accumulating evidence has indicated that natural killer cells (NK cells) play an important role in immune responses generated in the liver. However, the underlying molecular basis for local immune regulation is poorly understood. Mice were intraperitoneally injected with polyinosinic-polycytidylic acid (PolyI:C) at a dose of 20 mg/kg body wt. The percentage and absolute number of NK cells in the liver were analysed with flow cytometry. LSECtin knockout mice and LSECtin cDNA plasmids were used for analyze the role of LSECtin in hepatic NK cell regulation in vivo. Here, we show that the C-type lectin LSECtin, a member of the DC-SIGN family, is a novel liver regulator for NK cells. LSECtin could bind to NK cells in a carbohydrate-dependent manner and could regulate the number of hepatic NK cells. In the NK cell-mediated acute liver injury model induced with PolyI:C, the exogenous expression of LSECtin accelerated NK cell-induced liver injury, whereas the absence of LSECtin ameliorated this condition. Our results reveal that LSECtin is a novel, liver-specific NK cell regulator that may be a target for the treatment of inflammatory diseases in the liver.

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Liver-specific C-type lectin, LSECtin, binds to NK cells.

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LSECtin expression in vivo accelerates inflammatory liver injury induced by polyI:C.

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Absence of LSECtin in vivo decreased the member of hepatic NK cells.

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LSECtin is not only an activated T cells but also a NK cells modulator in the liver.

Liver natural killer cells: subsets and roles in liver immunity

The liver represents a frontline immune organ that is constantly exposed to a variety of gut-derived antigens as a result of its unique location and blood supply. With a predominant role in innate immunity, the liver is enriched with various innate immune cells, among which natural killer (NK) cells play important roles in host defense and in maintaining immune balance. Hepatic NK cells were first described as 'pit cells' in the rat liver in the 1970s. Recent studies of NK cells in mouse and human livers have shown that two distinct NK cell subsets, liver-resident NK cells and conventional NK (cNK) cells, are present in this organ. Here, we review liver NK cell subsets in different species, revisiting rat hepatic pit cells and highlighting recent progress related to resident NK cells in mouse and human livers, and also discuss the dual roles of NK cells in liver immunity.

Immunity, tolerance and autoimmunity in the liver: A comprehensive review

The hepatic immune system is constantly exposed to a massive load of harmless dietary and commensal antigens, to which it must remain tolerant. Immune tolerance in the liver is mediated by a number of specialized antigen-presenting cells, including dendritic cells, Kupffer cells, liver sinusoidal endothelial cells and hepatic stellate cells. These cells are capable of presenting antigens to T cells leading to T cell apoptosis, anergy, or differentiation into regulatory T cells. However, the hepatic immune system must also be able to respond to pathogens and tumours and therefore must be equipped with mechanisms to override immune tolerance. The liver is a site of accumulation of a number of innate lymphocyte populations, including natural killer cells, CD56(+) T cells, natural killer T cells, γδ T cells, and mucosal-associated invariant T cells. Innate lymphocytes recognize conserved metabolites derived from microorganisms and host cells and respond by killing target cells or promoting the differentiation and/or activation of other cells of the immune system. Innate lymphocytes can promote the maturation of antigen-presenting cells from their precursors and thereby contribute to the generation of immunogenic T cell responses. These cells may be responsible for overriding hepatic immune tolerance to autoantigens, resulting in the induction and maintenance of autoreactive T cells that mediate liver injury causing autoimmune liver disease. Some innate lymphocyte populations can also directly mediate liver injury by killing hepatocytes or bile duct cells in murine models of hepatitis, whilst other populations may protect against liver disease. It is likely that innate lymphocyte populations can promote or protect against autoimmune liver disease in humans and that these cells can be targeted therapeutically. Here I review the cellular mechanisms by which hepatic antigen-presenting cells and innate lymphocytes control the balance between immunity, tolerance and autoimmunity in the liver.

Bone marrow-derived mesenchymal stem cells suppress NK cell recruitment and activation in PolyI:C-induced liver injury

Mesenchymal stem cells (MSCs) have been shown to have an immunomodulatory capability and clinical potential in immune diseases. However, it is unknown how MSCs may affect immunity in liver injury. This study was designed to explore the effect of bone marrow-derived MSCs (BM-MSCs) on hepatic natural killer (NK) cells in polyinosinic-polycytidylic acid (PolyI:C)-induced liver injury. Unlike in controls, adoptive transfer of BM-MSCs in mice ameliorated PolyI:C-induced liver injury, as shown by lower alanine aminotransferase levels and decreased lymphocyte infiltration in the liver. Importantly, BM-MSCs suppress NK cell accumulation and activation in the liver, which plays an important role in PolyI:C-induced liver injury. Furthermore, NK cells co-cultured with BM-MSCs reduced expression of sphingosine-1-phosphate receptor type 5 (S1PR5), an important receptor required for NK cell trafficking in vivo. BM-MSC administration suppressed the elevation of expression of S1PR5 in the liver induced by PolyI:C injection. Accordingly, BM-MSCs inhibited the chemotactic activity of NK cells induced by sphingosine-1-phosphate (S1P, the ligand of S1PR5). Our results provide an additional mechanism for the immunosuppressive effect of BM-MSCs on NK cells, which further supports the therapeutic potential of BM-MSCs in immune-mediated disorders, including those in which NK cells play a major role.

A new mouse model of mild ornithine transcarbamylase deficiency (spf-j) displays cerebral amino acid perturbations at baseline and upon systemic immune activation

Ornithine transcarbamylase deficiency (OTCD, OMIM# 311250) is an inherited X-linked urea cycle disorder that is characterized by hyperammonemia and orotic aciduria. In this report, we describe a new animal model of OTCD caused by a spontaneous mutation in the mouse Otc gene (c.240T>A, p.K80N). This transversion in exon 3 of ornithine transcarbamylase leads to normal levels of mRNA with low levels of mature protein and is homologous to a mutation that has also been described in a single patient affected with late-onset OTCD. With higher residual enzyme activity, spf-J were found to have normal plasma ammonia and orotate. Baseline plasma amino acid profiles were consistent with mild OTCD: elevated glutamine, and lower citrulline and arginine. In contrast to WT, spf-J displayed baseline elevations in cerebral amino acids with depletion following immune challenge with polyinosinic:polycytidylic acid. Our results indicate that the mild spf-J mutation constitutes a new mouse model that is suitable for mechanistic studies of mild OTCD and the exploration of cerebral pathophysiology during acute decompensation that characterizes proximal urea cycle dysfunction in humans.

Liver myofibroblasts from hepatitis B related liver failure patients may regulate natural killer cell function via PGE2

BACKGROUND

Natural killer (NK) cells are abundant in the liver and constitute a major innate immune component that contributes to immune-mediated liver injury. However, few studies have investigated the phenotypes and functions of NK cells involved in hepatitis B related liver failure (LF), and the precise mechanism underlying NK cell regulation is not fully understood.

METHODS

We detected the percentage and function of peripheral NK cells both in hepatitis B related LF patients and healthy volunteers by flow cytometry and isolated the liver myofibroblasts (LMFs) from hepatitis B related LF livers. To determine the possible effects of LMFs on NK cells, mixed cell cultures were established in vitro.

RESULTS

We found a down-regulated percentage of peripheral NK cells in hepatitis B related LF patients, and their NK cells also displayed decreased activated natural cytotoxicity receptors (NCRs) and cytokine production. In a co-culture model, LMFs sharply attenuated IL-2-induced NK cell triggering receptors, cytotoxicity, and cytokine production. The inhibitory effect of LMFs on NK cells correlated with their ability to produce prostaglandin (PG) E2.

CONCLUSION

These data suggest that LMFs may protect against immune-mediated liver injury in hepatitis B related LF patients by inhibiting NK cell function via PGE2.

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.

Hepcidin induction by pathogens and pathogen-derived molecules is strongly dependent on interleukin-6

Hepcidin, the iron-regulatory hormone, is increased during infection or inflammation, causing hypoferremia. This response is thought to be a host defense mechanism that restricts iron availability to invading pathogens. It is not known if hepcidin is differentially induced by bacterial versus viral infections, whether the stimulation of pattern recognition receptors directly regulates hepcidin transcription, or which of the proposed signaling pathways are essential for hepcidin increase during infection. We analyzed hepcidin induction and its dependence on interleukin-6 (IL-6) in response to common bacterial or viral infections in mice or in response to a panel of pathogen-derived molecules (PAMPs) in mice and human primary hepatocytes. In wild-type (WT) mice, hepcidin mRNA was induced several hundred-fold both by a bacterial (Streptococcus pneumoniae) and a viral infection (influenza virus PR8) within 2 to 5 days. Treatment of mice and human primary hepatocytes with most Toll-like receptor ligands increased hepcidin mRNA within 6 h. Hepcidin induction by microbial stimuli was IL-6 dependent. IL-6 knockout mice failed to increase hepcidin in response to S. pneumoniae or influenza infection and had greatly diminished hepcidin response to PAMPs. In vitro, hepcidin induction by PAMPs in primary human hepatocytes was abolished by the addition of neutralizing IL-6 antibodies. Our results support the key role of IL-6 in hepcidin regulation in response to a variety of infectious and inflammatory stimuli.

CRACC-CRACC interaction between Kupffer and NK cells contributes to poly I:C/D-GalN induced hepatitis

CD2-like receptor activating cytotoxic cells (CRACC) is known as a critical activating receptor of natural killer (NK) cells. We have previously reported that NK cells contribute to Poly I:C/D-galactosamine (D-GalN)-induced fulminant hepatitis. Since natural killer group 2, member D (NKG2D) is considered critical but not the only activating receptor for NK cells, we investigated the role of CRACC in this model. We found that CRACC was abundant on hepatic NK cells but with low expression levels on Kupffer cells under normal conditions. Expression of CRACC on NK cells and Kupffer cells was remarkably upregulated after poly I:C injection. Hepatic CRACC mRNA levels were also upregulated in Poly I:C/D-GalN-treated mice, and correlated positively with the serum alanine aminotransferase (ALT) levels. CRACC expression on Kupffer cells was specifically silenced by nano-particle encapsulated siRNA in vivo, which significantly reduced Poly I:C/D-GalN-induced liver injury. In co-culture experiments, it was further verified that silencing CRACC expression or blockade of CRACC activation by mAb reduced the production of interferon (IFN)-γ and tumor necrosis factor (TNF)-α. Collectively, our findings suggest that CRACC-CRACC interaction between NK cells and resident Kupffer cells contributes to Poly I:C/D-GalN-induced fulminant hepatitis.

Pathological role of interleukin-17 in poly I:C-induced hepatitis

Immune-mediated responses were the main causes of liver damage during viral hepatitis, and recently viral RNA mimetic Poly I:C was used to induce a NK cell-dominated acute hepatitis. Interleukin-17A (IL-17A), the cytokine tightly associated with various autoimmune diseases, was known to play protective or pathological roles in LPS and ConA-induced hepatitis. However, its role in NK cell-mediated acute hepatitis remains unknown. Here we demonstrated that Poly I:C treatment triggered IL-17A production from hepatic γδT cells. Neutralizing IL-17A by monoclonal antibodies reduced Poly I:C-induced intrahepatic inflammatory responses and the liver injury through decreased accumulation, activation and cytolytic activity of NK cells in the liver. Furthermore, Poly I:C didn't trigger IL-17A secretion from γδT cells directly, and Kuppfer cells were demonstrated to be the accessory cell that can secrete IL-23. Finally, our findings demonstrated a pathological role of IL-17A and γδT cells in Poly I:C-induced acute hepatitis, which provides novel insights into viral infection-induced hepatitis and may serve as potential target in clinic immunotherapy against these disease.

IL-12-based vaccination therapy reverses liver-induced systemic tolerance in a mouse model of hepatitis B virus carrier

Liver-induced systemic immune tolerance that occurs during chronic hepadnavirus infection is the biggest obstacle for effective viral clearance. Immunotherapeutic reversal of this tolerance is a promising strategy in the clinic but remains to be explored. In this study, using a hepatitis B virus (HBV)-carrier mouse model, we report that IL-12-based vaccination therapy can efficiently reverse systemic tolerance toward HBV. HBV-carrier mice lost responsiveness to hepatitis B surface Ag (HBsAg) vaccination, and IL-12 alone could not reverse this liver-induced immune tolerance. However, after IL-12-based vaccination therapy, the majority of treated mice became HBsAg(-) in serum; hepatitis B core Ag was also undetectable in hepatocytes. HBV clearance was dependent on HBsAg vaccine-induced anti-HBV immunity. Further results showed that IL-12-based vaccination therapy strongly enhanced hepatic HBV-specific CD8(+) T cell responses, including proliferation and IFN-γ secretion. Systemic HBV-specific CD4(+) T cell responses were also restored in HBV-carrier mice, leading to the arousal of HBsAg-specific follicular Th-germinal center B cell responses and anti-hepatitis B surface Ag Ab production. Recovery of HBsAg-specific responses also correlated with both reduced CD4(+)Foxp3(+) regulatory T cell frequency and an enhanced capacity of effector T cells to overcome inhibition by regulatory T cells. In conclusion, IL-12-based vaccination therapy may reverse liver-induced immune tolerance toward HBV by restoring systemic HBV-specific CD4(+) T cell responses, eliciting robust hepatic HBV-specific CD8(+) T cell responses, and facilitating the generation of HBsAg-specific humoral immunity; thus, this therapy may become a viable approach to treating patients with chronic hepatitis B.

Natural killer cells: multifaceted players with key roles in hepatitis C immunity

Natural killer cells (NKs) are involved in every stage of hepatitis C viral (HCV) infection, from protection against HCV acquisition and resolution in the acute phase to treatment-induced clearance. In addition to their direct antiviral actions, NKs are involved in the induction and priming of appropriate downstream T-cell responses. In the setting of chronic HCV, overall NK cell levels are decreased, subset distribution is altered, and changes in NK receptor (NKR) expression have been demonstrated, although the contribution of individual NKRs to viral clearance or persistence remains to be clarified. Enhanced NK cell cytotoxicity accompanied by insufficient interferon-γ production may promote liver damage in the setting of chronic infection. Treatment-induced clearance is associated with activation of NK cells, and it will be of interest to monitor NK cell responses to triple therapy. Activated NK cells also have anti-fibrotic properties, and the same hepatic NK cell populations that are actively involved in control of HCV may also be involved in control of HCV-associated liver damage. We still have much to learn, in particular: how do liver-derived NKs influence the outcome of HCV infection? Do NK receptors recognize HCV-specific components? And, are HCV-specific memory NK populations generated?

NK cells in immunotolerant organs

Organs such as the liver, uterus and lung possess hallmark immunotolerant features, making these organs important for sustaining self-homeostasis. These organs contain a relatively large amount of negative regulatory immune cells, which are believed to take part in the regulation of immune responses. Because natural killer cells constitute a large proportion of all lymphocytes in these organs, increasing attention has been given to the roles that these cells play in maintaining immunotolerance. Here, we review the distribution, differentiation, phenotypic features and functional features of natural killer cells in these immunotolerant organs, in addition to the influence of local microenvironments on these cells and how these factors contribute to organ-specific diseases.

Natural killer cells in liver disease

Natural killer (NK) cells are enriched in lymphocytes within the liver and have unique phenotypic features and functional properties, including tumor necrosis factor-related apoptosis-inducing ligand-dependent cytotoxicity and specific cytokine profiles. As a key component of innate immunity in the liver, NK cells perform critical roles in host defense against pathogens and tumors through their natural cytotoxicity and cytokine production, and they also act as regulatory cells by engaging in reciprocal interactions with other types of liver cells through cell-to-cell contact and the production of cytokines. Accumulating evidence from the last decade suggests that NK cells play an important role in controlling viral hepatitis, liver fibrosis, and liver tumorigenesis, but also contribute to the pathogenesis of liver injury and inflammation. The characterization of intrahepatic NK cell functions has not only helped us to better understand the pathogenesis of liver disease, but has also revealed new therapeutic targets for managing this disease.

CD62L is critical for maturation and accumulation of murine hepatic NK cells in response to viral infection

NK cells play critical roles in the first line of defense against viruses and other pathogens. However, the factors that control NK cell recruitment into local sites to exert effector functions during viral infection remain poorly understood. In this study, we found that murine NK cells in various organs could be divided into CD62L(-) and CD62L(+) subsets, the latter of which were less abundant in the liver and exhibited a relatively mature NK cell phenotype and a stronger cytotoxic function. Moreover, NK cells acquired CD62L expression after birth, and the frequency of CD62L(+) NK cells gradually increased during postnatal development. In models of polyinosinic-polycytidylic acid administration and adenovirus infection in vivo, CD62L(+) NK cell frequency and absolute numbers in the liver rapidly and markedly increased as a result of the augmented differentiation of CD62L(-) to CD62L(+) NK cells and recruitment of peripheral mature NK cells to the liver. However, blocking CD62L prior to administering viral stimuli in vivo abolished viral stimulation-induced NK cell accumulation and maturation in the liver. Collectively, these data suggest that CD62L marks a mature NK cell subset, as well as affects the magnitude of the local NK cell response to viral infection.

Liver restores immune homeostasis after local inflammation despite the presence of autoreactive T cells

The liver must keep equilibrium between immune tolerance and immunity in order to protect itself from pathogens while maintaining tolerance to food antigens. An imbalance between these two states could result in an inflammatory liver disease. The aims of this study were to identify factors responsible for a break of tolerance and characterize the subsequent restoration of liver immune homeostasis. A pro-inflammatory environment was created in the liver by the co-administration of TLR ligands CpG and Poly(I:C) in presence or absence of activated liver-specific autoreactive CD8(+) T cells. Regardless of autoreactive CD8(+) T cells, mice injected with CpG and Poly(I:C) showed elevated serum ALT levels and a transient liver inflammation. Both CpG/Poly(I:C) and autoreactive CD8(+)T cells induced expression of TLR9 and INF-γ by the liver, and an up-regulation of homing and adhesion molecules CXCL9, CXCL10, CXCL16, ICAM-1 and VCAM-1. Transferred CFSE-labeled autoreactive CD8(+) T cells, in presence of TLR3 and 9 ligands, were recruited by the liver and spleen and proliferated. This population then contracted by apoptosis through intrinsic and extrinsic pathways. Up-regulation of FasL and PD-L1 in the liver was observed. In conclusion, TLR-mediated activation of the innate immune system results in a pro-inflammatory environment that promotes the recruitment of lymphocytes resulting in bystander hepatitis. Despite this pro-inflammatory environment, the presence of autoreactive CD8(+) T cells is not sufficient to sustain an autoimmune response against the liver and immune homeostasis is rapidly restored through the apoptosis of T cells.

Two cases of food additive-induced severe liver damage associated with positive results on lymphocyte stimulation test and for antinuclear antibodies

Two cases of severe liver injury and positive result for antinuclear antibodies induced by food additives are reported. The first patient reported long-term intake of Mabo Ramen(®) noodle soup, nutritional supplements, and over-the-counter drugs. Total bilirubin, aspartate aminotransferase, and alanine aminotransferase were 9.6 mg/dL, 1,048, and 1,574 IU/L, respectively. Antinuclear antibody was 80×. The drug-induced lymphocyte stimulation test (DLST) was positive for Mabo Ramen(®) and its additives such as Xanthan gum, guar gum, and Doubanjiang. Histologic examination of a liver biopsy specimen showed lymphocyte infiltration and necrosis. The autoimmune hepatitis score was 3. The second patient reported intake of dietary supplements, including Bimore C(®) and Chokora BB(®). Laboratory tests revealed that total bilirubin was 9.8 mg/dL, aspartate aminotransferase was 1,130 IU/L, and alanine aminotransferase was 1,094 IU/L. Antinuclear antibody was 320×. Co-existing pancreatic damage was confirmed by the findings on abdominal CT and elevation of serum lipase, span-1, and DUPAN-2. DLSTs were positive for both supplements. These two supplements contained additives such as titanium oxide, magnesium stearate, and hydroxypropylcellulose. DLSTs for all three additives were positive. Histologic examination revealed periportal necrosis and lymphocyte infiltration of lobular and portal areas. These two cases demonstrate that repeating DLSTs is useful for identifying causative constituents in foods and supplements.

The role of innate immunity in HBV infection

Hepatitis B virus (HBV) infection is one of the main causes of chronic liver diseases. Whether HBV infection is cleared or persists is determined by both viral factors and host immune responses. It becomes clear that innate immunity is of importance in protecting the host from HBV infection and persistence. However, HBV develops strategies to suppress the antiviral immune responses. A combined therapeutic strategy with both viral suppression and enhancement of antiviral immune responses is needed for effective long-term clearance and cure for chronic HBV infection. We and others confirmed that bifunctional siRNAs with both gene silencing and innate immune activation properties are beneficial for inhibition of HBV and represent a potential approach for treatment of viral infection. Understanding the nature of liver innate immunity and their roles in chronic HBV progression and HBV clearance may aid in the design of novel therapeutic strategies for chronic HBV infection.

Regulatory NK cells in autoimmune disease

As major components of innate immunity, NK cells not only exert cell-mediated cytotoxicity against tumor cells or infected cells, but also act to regulate the function of other immune cells by secretion of cytokines and chemokines, thus providing surveillance in early defense against viruses, intracellular bacteria and cancer cells. However, the effector function of NK cells must be exquisitely controlled in order to prevent inadvertent attack against self normal cells. The activity of NK cells is defined by integration of signals coming from inhibitory and activation receptors. Inhibitory receptors not only distinguish healthy from diseased cells by recognize self-MHC class I molecules on cell surfaces with "missing-self" model, but also provide an educational signal that generates functional NK cells. NK cells enrich in immunotolerance organ and recent findings of different regulatory NK cell subsets have indicated the unique role of NK cells in maintenance of homeostasis. Once the self-tolerance is broken, autoimmune response may occur. Although data has demonstrated that NK cells play important role in autoimmune disorders, NK cells seemed to act as a two edged weapon and play opposite roles with both regulatory and inducer activity even in the same disease. The precise role and regulatory mechanisms need to be further determined. In this review, we focus on recent research on the association of NK cells and antoimmune diseases, particularly the genetic correlation, the immune tolerance and misrecognition of NK cells, the regulatory function of NK cells, and their potential role in autoimmunity.

Tyrosine kinase Btk is required for NK cell activation

Bruton tyrosine kinase (Btk) is not only critical for B cell development and differentiation but is also involved in the regulation of Toll-like receptor-triggered innate response of macrophages. However, whether Btk is involved in the regulation of natural killer (NK) cell innate function remains unknown. Here, we show that Btk expression is up-regulated during maturation and activation of mouse NK cells. Murine Btk(-/-) NK cells have decreased innate immune responses to the TLR3 ligand, with reduced expressions of IFN-γ, perforin, and granzyme-B and decreased cytotoxic activity. Furthermore, Btk is found to promote TLR3-triggered NK cell activation mainly by activating the NF-κB pathway. Poly(I:C)-induced NK cell-mediated acute hepatitis was observed to be attenuated in Btk(-/-) mice or the mice with in vivo administration of the Btk inhibitor. Correspondingly, liver damage was aggravated in Btk(-/-) mice after the adoptive transfer of Btk(+/+) NK cells, further indicating that Btk-mediated NK cell activation contributes to TLR3-triggered acute liver injury. Importantly, reduced TLR3-triggered activation of human NK cells was observed in Btk-deficient patients with X-linked agammaglobulinemia, as evidenced by the reduced IFN-γ, CD69, and CD107a expression and cytotoxic activity. These results indicate that Btk is required for activation of NK cells, thus providing insight into the physiological significance of Btk in the regulation of immune cell functions and innate inflammatory response.

The multi-hit hypothesis of primary biliary cirrhosis: polyinosinic-polycytidylic acid (poly I:C) and murine autoimmune cholangitis

A void in understanding primary biliary cirrhosis (PBC) is the absence of appropriate animal models. Our laboratory has studied a murine model of autoimmune cholangitis induced following immunization with 2-octynoic acid (2OA), an antigen identified following extensive quantitative structural activity relationship (QSAR) analysis, using human autoantibodies and three-dimensional analysis of the mitochondrial autoantigen, the E2 subunit of the pyruvate dehydrogenase complex (PDC-E2). Mice immunized with 2OA coupled to bovine serum albumin (BSA) develop anti-mitochondrial antibodies (AMAs) of the identical specificity as humans with PBC, and in addition develop inflammatory portal cell infiltrates in liver. However, the natural history of disease is less severe than in humans and does not include fibrosis. Data from human and autoimmune murine models suggest that environmental and/or infectious agents can exacerbate autoimmune reactions, and a model of PBC has been described in which polyinosinic-polycytidylic acid (poly I:C), a viral RNA mimetic and Toll-like receptor 3 (TLR-3) agonist induces low-titre AMAs and in mild portal infiltrates. We took advantage of our established model to determine whether immunization with 2OA-BSA coupled with poly I:C alters the disease process. Indeed, the addition of poly I:C produces a profound exacerbation of autoimmune cholangitis, including a significant increase in CD8(+) infiltrating T cells, as well as a marked increase of proinflammatory cytokines. In addition, mice have evidence of fibrosis. These findings lend support to the concept that besides breakdown of self-tolerance, there is a requirement of a second 'hit' during the breakdown process that leads to disease which more faithfully mimics human PBC.

Mitochondrial antiviral signaling protein defect links impaired antiviral response and liver injury in steatohepatitis in mice

Mitochondrial dysfunction is a pathogenic feature of nonalcoholic steatohepatitis (NASH). NASH complicates hepatotropic viral disease. The mitochondrial antiviral signaling protein (MAVS) is the adapter of helicase receptors involved in sensing double-stranded RNA (dsRNA). We hypothesized that impaired MAVS function may contribute to insufficient antiviral response and liver damage in steatohepatitis. We identified reduced MAVS protein levels and increased MAVS association with the proteasome subunit alpha type 7 (PSMA7) in livers from mice given a methionine-choline-deficient (MCD) diet. Decreased association of MAVS with mitochondria and increased cytosolic cytochrome c indicated mitochondrial damage in steatohepatitis. In vivo administration of the synthetic dsRNA polyinosinic:polycytidylic acid [poly(I:C)], but not lipopolysaccharide or cytidine-phosphate-guanosine-rich DNA, resulted in impaired induction of type I interferons (IFNs) and proinflammatory cytokines in steatohepatitis. Consistent with a defect in helicase receptor-induced signaling, there was loss of poly(I:C)-induced translocation of MAVS to the cytosol and decreased IFN regulatory factor 3 phosphorylation. Caspases 1 and 8, both of which cleave MAVS, were increased in MCD diet-fed mice. At baseline, steatohepatitis was associated with increased serum alanine aminotransferase (ALT), apoptosis and caspase 3 activation compared with controls. In contrast to apoptosis in controls, necrosis was induced by poly(I:C) stimulation in steatohepatitis. Hepatocyte necrosis was indicated by elevated serum high-mobility group box protein-1 and ALT and was correlated with increased expression of receptor-interacting protein 3 (RIP3), a master regulator of necrosis. Increased expression of MAVS, PSMA7, and RIP3 messenger RNA was also present in human NASH livers.

CONCLUSION

Our novel findings suggest that mitochondrial damage in steatohepatitis extends to MAVS, an adapter of helicase receptors, resulting in inefficient type I IFN and inflammatory cytokine response but increased hepatocyte necrosis and RIP3 induction in response to a dsRNA viral challenge. These mechanisms may contribute to progressive liver damage and impaired viral clearance in NASH.

Toll-like receptors in acute liver injury and regeneration

Liver is the lymphoid organ with an overwhelming innate immune system, which functions as a filter organ at the first line between the digestive tract and the rest of the body, with receiving 80% of the blood supply through portal vein. TLRs are widely expressed on parenchymal and non-parenchymal cells in the liver, which play critical roles for the liver health. Recent studies indicate that TLR-medicated signals have been involved in almost all liver diseases such as acute and chronic hepatitis, liver fibrosis and cirrhosis, alcoholic and non-alcoholic liver disease, ischemia/reperfusion liver injury, liver regeneration and hepatocellular carcinoma. In this review, the expressions of TLRs in hepatic cell populations including hepatocytes, LSECs, Kupffer cells, lymphocytes, DCs, biliary epithelial cells and HSCs, and TLR ligands and signaling in the liver are summarized. Further, recent advances in the roles of TLRs in acute liver injury and regeneration as mediator and regulator, and their potential therapeutic targets are discussed.

NK cells suppress experimental cholestatic liver injury by an interleukin-6-mediated, Kupffer cell-dependent mechanism

BACKGROUND & AIMS

Natural killer (NK) cells are innate immune effector cells first characterized by their ability to lyse susceptible tumor cells. Recent studies demonstrated their role in initiating and modulating adaptive immunity. NK cells represent a larger percentage of the lymphoid population in liver than other organs, suggesting that hepatic NK cells express some unique function. Here, we examined the response of NK cells to liver injury that occurs in a mouse model of biliary obstruction.

METHODS

Bile duct ligations (BDL) were performed in mice previously depleted or not depleted of NK cells. NK cell activation, interleukin (IL)-6 mRNA expression and protein production by Kupffer cells, and the ability of exogenous IL-6 to ameliorate liver injury in NK cell-depleted mice, were determined.

RESULTS

The number of activated hepatic NK cells increased markedly following BDL. Activation was suppressed in mice rendered Kupffer cell-depleted prior to ligation. Increased liver injury occurred in NK cell-depleted mice correlating with a reduction in IL-6 production. Purified Kupffer cells, obtained from NK cell-depleted or anti-interferon (IFN)-γ monoclonal antibody-pretreated mice following BDL, produced less IL-6 in culture than did Kupffer cells derived from control animals. In culture, hepatic NK cells derived from BDL mice stimulated IFN-γ-dependent IL-6 production by Kupffer cells; splenic NK cells obtained from the same animals had a negligible effect. Treatment with recombinant murine IL-6 reduced liver injury in BDL, NK cell-depleted mice.

CONCLUSIONS

Hepatic NK cells suppress cholestatic liver injury by stimulating Kupffer cell-dependent IL-6 production.