Toll-like receptor 3 in liver diseases

Toll-like receptor 3 (TLR3) is a member of the TLR family that can recognize double-stranded RNA (dsRNA), playing an important role in antiviral immunity. Recent studies have shown that TLR3 is also expressed on parenchymal and nonparenchymal cells in the liver as well as on several types of immune cells. In this review, we summarize the role of TLR3 in liver injury, inflammation, regeneration, and liver fibrosis, and discuss the implication of TLR3 in the pathogenesis of human liver diseases including viral hepatitis and autoimmune liver disease.

Therapeutic vaccination in chronic hepatitis B: preclinical studies in the woodchuck

Recommended treatment of chronic hepatitis B with interferon-α and/or nucleos(t)ide analogues does not lead to a satisfactory result. Induction of HBV-specific T cells by therapeutic vaccination or immunotherapies may be an innovative strategy to overcome virus persistence. Vaccination with commercially available HBV vaccines in patients did not result in effective control of HBV infection, suggesting that new formulations of therapeutic vaccines are needed. The woodchuck (Marmota monax) is a useful preclinical model for developing the new therapeutic approaches in chronic hepadnaviral infections. Several innovative approaches combining antiviral treatments with nucleos(t)ide analogues, DNA vaccines, and protein vaccines were tested in the woodchuck model. In this paper we summarize the available data concerning therapeutic immunization and gene therapy using recombinant viral vectors approaches in woodchucks, which show encouraging results. In addition, we present potential innovations in immunomodulatory strategies to be evaluated in this animal model.

Toll-like receptors in the pathogenesis of alcoholic liver disease

In the multifactorial pathophysiology of alcoholic liver disease (ALD), inflammatory cascade activation plays a central role. Recent studies demonstrated that Toll-like Receptors, the sensors of microbial and endogenous danger signals, are expressed and activated in innate immune cells as well as in parenchymal cells in the liver and thereby contribute to ALD. In this paper, we discuss the importance of gut-derived endotoxin and its recognition by TLR4. The significance of TLR-induced intracellular signaling pathways and cytokine production as well as the contribution of reactive oxygen radicals is evaluated. The contribution of TLR signaling to induction of liver fibrosis and hepatocellular cancer is reviewed in the context of alcohol-induced liver disease.

Hepatitis B virus X protein suppresses virus-triggered IRF3 activation and IFN-beta induction by disrupting the VISA-associated complex

Viral RNAs produced during viral infection are recognized by the cytoplasmic RNA helicases retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5). A central adapter protein downstream of RIG-I and MDA5 is the mitochondrial membrane protein virus-induced signaling adaptor (VISA), which mediates the induction of type I interferons (IFNs) through the activation of transcription factors such as nuclear factor-kappaB (NF-kappaB) and IFN-regulatory factor-3 (IRF3). Here we found that hepatitis B virus (HBV)-encoded X protein (HBx) acts as an inhibitor of virus-triggered IRF3 activation and IFN-beta induction. Reporter and plaque assays indicate that HBx inhibits signaling by components upstream but not downstream of VISA. Immunoprecipitation experiments indicate that HBx interacts with VISA and disrupts the association of VISA with its upstream and downstream components. These findings suggest that HBx acts as a suppressor of virus-triggered induction of type I IFNs, which explains the observation that HBV causes transient and chronic infection in hepatocytes but fails to activate the pattern recognition receptor-mediated IFN induction pathways.

Toll-like receptor signaling and liver fibrosis

Liver fibrosis occurs as a wound-healing scar response following acute and chronic liver inflammation including alcoholic liver disease, non-alcoholic steatohepatitis, hepatitis B and C, and autoimmune hepatitis. Myofibroblasts, mainly transdifferentiated from hepatic stellate cells, are pivotal cell types that produce fibrillar collagen. The activation of inflammatory cells, including Kupffer cells, is a crucial step for activating hepatic stellate cells. Toll-like receptors (TLRs) are pattern recognition receptors that sense pathogen-associated molecular patterns (PAMPs), which discriminate the products of microorganisms from the host. TLRs are expressed on Kupffer cells, endothelial cells, dendritic cells, biliary epithelial cells, hepatic stellate cells, and hepatocytes in the liver. TLR signaling induces potent innate immune responses in these cell types. The liver is constantly exposed to PAMPs, such as LPS and bacterial DNA through bacterial translocation because there is a unique anatomical link, the portal vein system between liver and intestine. Recent evidence demonstrates the role of TLRs in the activation of hepatic immune cells and stellate cells during liver fibrosis. Moreover, crosstalk between TLR4 signaling and TGF-β signaling in hepatic stellate cells has been reported. This paper highlights the role of TLR signaling in stellate cell activation and the progression of liver fibrosis.

Immunotherapy of viral infections

Among the microorganisms that cause diseases of medical or veterinary importance, the only group that is entirely dependent on the host, and hence not easily amenable to therapy via pharmaceuticals, is the viruses. Since viruses are obligate intracellular pathogens, and therefore depend a great deal on cellular processes, direct therapy of viral infections is difficult. Thus, modifying or targeting nonspecific or specific immune responses is an important aspect of intervention of ongoing viral infections. However, as a result of the unavailability of effective vaccines and the extended duration of manifestation, chronic viral infections are the most suitable for immunotherapies. We present an overview of various immunological strategies that have been applied for treating viral infections after exposure to the infectious agent.

Hepatitis B virus polymerase blocks pattern recognition receptor signaling via interaction with DDX3: implications for immune evasion

Viral infection leads to induction of pattern-recognition receptor signaling, which leads to interferon regulatory factor (IRF) activation and ultimately interferon (IFN) production. To establish infection, many viruses have strategies to evade the innate immunity. For the hepatitis B virus (HBV), which causes chronic infection in the liver, the evasion strategy remains uncertain. We now show that HBV polymerase (Pol) blocks IRF signaling, indicating that HBV Pol is the viral molecule that effectively counteracts host innate immune response. In particular, HBV Pol inhibits TANK-binding kinase 1 (TBK1)/IkappaB kinase-epsilon (IKKepsilon), the effector kinases of IRF signaling. Intriguingly, HBV Pol inhibits TBK1/IKKepsilon activity by disrupting the interaction between IKKepsilon and DDX3 DEAD box RNA helicase, which was recently shown to augment TBK1/IKKepsilon activity. This unexpected role of HBV Pol may explain how HBV evades innate immune response in the early phase of the infection. A therapeutic implication of this work is that a strategy to interfere with the HBV Pol-DDX3 interaction might lead to the resolution of life-long persistent infection.

Plasma membrane calcium ATPase isoform 3 expression in single cells isolated from rat liver

The plasma membrane Ca(2+)-ATPase (PMCA) located in the hepatocyte is a controversial molecule in itself since it displays different features to those regarded as canonical for P-type Ca(2+)-ATPases, and from which transcript expression as well as catalytic activity continues to be under active investigation. Our aim in this study was to explore at a first glance, pmca isoform distribution using isolated parenchymal and non-parenchymal cells from rat liver tissue. Expression of pmca transcripts was analyzed in fresh or cell-enriched culture preparations, confirming pmca1 and pmca4 as the housekeeping isoforms in all cell types studied (hepatocytes, Kupffer cells, and stellate cells). However, for the first time we show expression of pmca3 transcripts edited at two different sites in both hepatocytes and non-parenchymal cells. Interestingly, employing non-parenchymal cells we demonstrate the specific expression of pmca3e transcripts previously considered nearly exclusive of excitable tissues. Real-time PCR quantification shows a significant decrease of pmca3 transcripts in cultured Kupffer and hepatic stellate cells in comparison with fresh cells. The presence of pmca2 along with pmca3 in all liver cell types studied suggests that high affinity isoforms are relevant to the adequate management of calcium in liver tissue, particularly when hepatic cells become activated by diverse stimuli.

Innate antiviral immune responses to hepatitis B virus

Hepatitis B virus (HBV) is a major cause of acute and chronic hepatitis in humans. As HBV itself is currently viewed as a non-cytopathic virus, the liver pathology associated with hepatitis B is mainly thought to be due to immune responses directed against HBV antigens. The outcome of HBV infection is the result of complex interactions between replicating HBV and the immune system. While the role of the adaptive immune response in the resolution of HBV infection is well understood, the contribution of innate immune mechanisms remains to be clearly defined. The innate immune system represents the first line of defense against viral infection, but its role has been difficult to analyze in humans due to late diagnosis of HBV infection. In this review, we discuss recent advances in the field of innate immunity to HBV infection.

Increased immunogenicity of tumor-associated antigen, mucin 1, engineered to express alpha-gal epitopes: a novel approach to immunotherapy in pancreatic cancer

Mucin 1 (MUC1), a bound mucin glycoprotein, is overexpressed and aberrantly glycosylated in >80% of human ductal pancreatic carcinoma. Evidence suggests that MUC1 can be used as a tumor marker and is a potential target for immunotherapy of pancreatic cancer. However, vaccination with MUC1 peptides fails to stimulate the immune response against cancer cells because immunity toward tumor-associated antigens (TAA), including MUC1, in cancer patients is relatively weak, and the presentation of these TAAs to the immune system is poor due to their low immunogenicity. We investigated whether vaccination with immunogenetically enhanced MUC1 (by expressing alpha-gal epitopes; Galalpha1-3Galbeta1-4GlcNAc-R) can elicit effective antibody production for MUC1 itself as well as certain TAAs derived from pancreatic cancer cells and induced tumor-specific T-cell responses. We also used alpha1,3galactosyltransferase (alpha1,3GT) knockout mice that were preimmunized with pig kidney and transplanted with B16F10 melanoma cells transfected with MUC1 expression vector. Vaccination of these mice with alpha-gal MUC1 resulted in marked inhibition of tumor growth and significant improvement of overall survival time compared with mice vaccinated with MUC1 alone (P = 0.003). Furthermore, vaccination with pancreatic cancer cells expressing alpha-gal epitopes induced immune responses against not only differentiated cancer cells but also cancer stem cells. The results suggested that vaccination using cells engineered to express alpha-gal epitopes is a novel strategy for treatment of pancreatic cancer.

Hepatocyte death: a clear and present danger

The hepatocyte is especially vulnerable to injury due to its central role in xenobiotic metabolism including drugs and alcohol, participation in lipid and fatty acid metabolism, its unique role in the enterohepatic circulation of bile acids, the widespread prevalence of hepatotropic viruses, and its existence within a milieu of innate immune responding cells. Apoptosis and necrosis are the most widely recognized forms of hepatocyte cell death. The hepatocyte displays many unique features regarding cell death by apoptosis. It is quite susceptible to death receptor-mediated injury, and its death receptor signaling pathways involve the mitochondrial pathway for efficient cell killing. Also, death receptors can trigger lysosomal disruption in hepatocytes which further promote cell and tissue injury. Interestingly, hepatocytes are protected from cell death by only two anti-apoptotic proteins, Bcl-x(L) and Mcl-1, which have nonredundant functions. Endoplasmic reticulum stress or the unfolded protein response contributes to hepatocyte cell death during alterations of lipid and fatty acid metabolism. Finally, the current information implicating RIP kinases in necrosis provides an approach to more fully address this mode of cell death in hepatocyte injury. All of these processes contributing to hepatocyte injury are discussed in the context of potential therapeutic strategies.

A single nucleotide polymorphism of Toll-like receptor 4 identifies the risk of developing graft failure after liver transplantation

BACKGROUND & AIMS

While studies in animal models have linked Toll-like receptor (TLR) 4 signaling to the pathophysiology of ischemia/reperfusion (IR) injury and liver fibrosis, the relevance of TLR4 activation after human liver transplantation is unknown. The TLR4 single nucleotide polymorphism (SNP) D299G is situated within the extracellular domain and diminishes receptor binding to danger-associated molecular patterns.

METHODS

We studied the influence of TLR4 D299G on IR injury and graft survival in 430 deceased donor LT recipients. Compared with livers expressing wild-type (WT) alleles, livers with a TLR4 loss-of-function allele were significantly more likely to have initial good graft function (IGGF) (OR 2.20, p=0.01). In contrast, there was no effect of recipient TLR4 genotype on the rate of IGGF.

RESULTS

The effect of TLR4 D299G on long-term graft survival was analyzed based on hepatitis C virus (HCV) serostatus. In HCV infected recipients, multivariate Cox regression analysis demonstrated a significant association between the presence of recipient, but not donor TLR4 D299G and long-term graft failure (HR 2.48, CI 1.28-4.81; p=0.007). There was no difference in graft survival between TLR4 mutant and WT recipients among non-HCV infected recipients.

CONCLUSIONS

Collectively, these results demonstrate the differential effects of donor and recipient TLR4 signaling in human liver transplantation. Donor TLR4 contributed to sterile injury following cold preservation and the recipient TLR4 genotype was linked with poor allograft survival among HCV infected recipients.

Program death-1 signaling and regulatory T cells collaborate to resist the function of adoptively transferred cytotoxic T lymphocytes in advanced acute myeloid leukemia

Tumor-induced immune defects can weaken host immune response and permit tumor cell growth. In a systemic model of murine acute myeloid leukemia (AML), tumor progression resulted in increased regulatory T cells (Treg) and elevation of program death-1 (PD-1) expression on CD8(+) cytotoxic T cells (CTLs) at the tumor site. PD-1 knockout mice were more resistant to AML despite the presence of similar percentage of Tregs compared with wild type. In vitro, intact Treg suppression of CD8(+) T-cell responses was dependent on PD-1 expression by T cells and Tregs and PD-L1 expression by antigen-presenting cells. In vivo, the function of adoptively transferred AML-reactive CTLs was reduced by AML-associated Tregs. Anti-PD-L1 monoclonal antibody treatment increased the proliferation and function of CTLs at tumor sites, reduced AML tumor burden, and resulted in long-term survivors. Treg depletion followed by PD-1/PD-L1 blockade showed superior efficacy for eradication of established AML. These data demonstrated that interaction between PD-1 and PD-L1 can facilitate Treg-induced suppression of T-effector cells and dampen the antitumor immune response. PD-1/PD-L1 blockade coupled with Treg depletion represents an important new approach that can be readily translated into the clinic to improve the therapeutic efficacy of adoptive AML-reactive CTLs in advanced AML disease.

Toll-like receptors as therapeutic targets in gastrointestinal diseases

IMPORTANCE OF THE FIELD

Toll-like receptors (TLRs) are innate immunity receptors that recognize several different antigens, initiating immunological/inflammatory responses. Recent evidence associates numerous pathophysiological processes and diseases with dysregulated activation of these receptors, conferring a potential therapeutic value to their modulation.

AREAS COVERED IN THIS REVIEW

The aim of this systematic review that covers literature from the past 10 years is to address the role of TLRs in the pathophysiology of gastrointestinal (GI) diseases as well as the therapeutic potential of modulating TLRs' signaling pathways in GI pathology.

WHAT THE READER WILL GAIN

This review shows that TLRs play an important role in the pathophysiology of several GI diseases and that modulating TLRs signaling pathways may have an enormous therapeutic potential. Different methods for modulation of TLRs' activity in GI tract, with direct agonists/antagonists but also with non-specific substances, like antibiotics or probiotics, are presented.

TAKE HOME MESSAGE

Even though TLRs modulators have been used for therapy in some GI diseases, further research, particularly in humans, is needed in order to establish the precise role of the different TLRs in the diverse GI diseases and to motivate clinical trials that consider TLRs as therapeutic targets in GI pathology.

Langerhans cells as targets for immunotherapy against skin cancer

Cancer is the second most common cause of death in the world. Treatment of cancer is very challenging and immunotherapy has been developed as a potential way to fight cancer. The main obstacle with immunotherapy is that cancer cells evolve from healthy body cells in response to an accumulation of genetic mutations. As a consequence, the immune system struggles to detect the abnormal cells as they are mainly recognized as self. This implies that equipping the immune system to eliminate cancer cells is tricky, yet represents a very efficient way to constrain the growth of tumors. We became interested in developing immunotherapeutical strategies against skin cancer in the context of our observations that Langerhans cells (LC) are very potent antigen presenting cells and are able to incorporate protein antigens and present them to CD4(+) and CD8(+) T cells in the skin-draining lymph nodes. As a consequence, we developed an immunization strategy through the skin, termed epicutaneous immunization. Protein antigen applied onto barrier-disrupted skin induces long-lasting cytotoxic T-cell responses, potent enough to control and inhibit tumor growth. In this review, we suggest that immunization strategies through the skin could be a promising new approach for the treatment of skin cancer.

The molecular basis of the failed immune response in chronic HBV: therapeutic implications

There is a pressing need to develop new immunotherapeutic interventions in chronic hepatitis B virus (HBV) infection in order to limit the high costs and risks of toxicity or viral resistance associated with maintenance antiviral treatment. Here we review recent advances in our understanding of the molecular defects underlying the profound T cell depletion characteristic of these patients. We propose that T cells are driven to apoptosis by the combination of a persistent, high antigen load and excessive inhibitory signals encountered in the hepatic microenvironment. The feasibility of boosting sustained antiviral control by targeted reversal of key tolerising mechanisms is discussed.

Effect of dipterinyl calcium pentahydrate on hepatitis B virus replication in transgenic mice

Background

Dipterinyl calcium pentahydrate (DCP) has previously been shown to inhibit MDA-MB-231 human breast cancer xenographs in nude mice in a manner correlated with increases in plasma IL-12 and IL-4 concentrations, and decreases in plasma IL-6 levels. DCP also inhibits indoleamine 2,3-dioxygenase (IDO), an immuno-inhibitory enzyme, in human PBMCs (Peripheral Blood Mononuclear Cells).

Methods

In the present study, DCP was administered per os, once daily for 14 days to hepatitis B virus (HBV) transgenic mice at 23, 7.3, and 2.3 mg/(kg d). Multivariate stepwise regression and MANOVA analyses, by gender and treatment, of liver HBV DNA and RNA measures, liver core and serum HBe antigen assays, serum cytokine/chemokine profiles, and IDO metabolite measurements were performed.

Results

DCP caused a significant dose-response reduction of log liver HBV DNA as measured by PCR in the female HBV mice. The gender dependence of the anti-HBV DNA activity was explained by the DCP Effects Model (DCP-EM) (p = .001) which includes three serum biomarker changes caused by DCP: 1) decreased MCP-1; 2) decreased Kyn/Trp (an estimation of IDO activity); and 3) increased GM-CSF.

Conclusions

Immunomodulation via IDO or TDO (tryptophan 2,3-dioxygenase) pathways, along with serum MCP-1 and GM-CSF are proposed to play roles in the anti-HBV mechanism of DCP based upon their coordinated modulation in the reduction of viral DNA replication in HBV mice.

Virulence factor p60 of Listeria monocytogenes modulates innate immunity by inducing tumor necrosis factor alpha

We investigated the effect of p60, a virulence factor of Listeria monocytogenes, on host immune response in vitro and in vivo. Administration of p60 before a sublethal infection with L. monocytogenes enhanced innate host resistance in naïve mice. Mouse macrophage RAW264.7 cells produced tumor necrosis factor (TNF)-alpha in response to stimulation with recombinant p60. Toll-like receptor 4 may be involved in TNF-alpha production from RAW264.7 cells and enhanced host resistance induced by p60 administration. Our findings demonstrated that p60 modulates innate immune responses against L. monocytogenes infection.

TLRs antiviral effect on hepatitis B virus in HepG2 cells

AIMS

A hepatoma cell line, HepG2, was used as a model system to detect Toll-like receptor (TLR) expression in hepatocytes and examine the antiviral effect on hepatitis B virus (HBV).

METHODS AND RESULTS

Toll-like receptor expression was detected in HepG2 cells by RT-PCR. The TLRs, which were strongly expressed in HepG2 cells, were stimulated with specific ligands. Interferon (IFN) response was evaluated poststimulation with Western blotting for signal transduction and activators of transcription-1. Furthermore, HepG2 cells were transiently transfected with wild-type HBV 1.3-fold over-length plasmid and treated with specific ligands at indicated times. Replication of HBV DNA, transcription of HBV RNA intermediate and expression of HBV antigens were respectively detected by Southern blotting, real time PCR, ELISA and Western blotting. Activation of different TLRs induced antiviral effects on HBV to varying degrees.

CONCLUSIONS

The TLRs, which were strongly expressed in HepG2 cells, could be stimulated with specific ligands. Activation of TLRs induced apparent production of antiviral cytokines such as IFN-alpha/beta and inhibited HBV lifecycle in the hepatocyte cell model.

SIGNIFICANCE AND IMPACT OF THE STUDY

Expression of TLRs in hepatocytes may be related to local immunity of liver and participate in the outcome of viral hepatitis.

Toll-like receptor 3 ligand dampens liver inflammation by stimulating Valpha 14 invariant natural killer T cells to negatively regulate gammadeltaT cells

Valpha14 invariant natural killer T (Valpha14iNKT) cells are at the interface between the innate and adaptive immune responses and are thus critical for providing full engagement of host defense. We investigated the role of polyriboinosinic:polycytidylic acid (poly I:C), a replication-competent viral double-stranded RNA mimic and a specific agonist that recognizes the cellular sensor Toll-like receptor 3 (TLR3), in regulating Valpha14iNKT cell activation. We established for the first time that hepatic Valpha14iNKT cells up-regulate TLR3 extracellularly after poly I:C treatment. Notably, activation of TLR3-expressing hepatic Valpha14iNKT cells by a TLR3 ligand was suppressed by TLR3 deficiency. Our studies also revealed that Valpha14iNKT cell activation in response to poly I:C administration uniquely suppressed the accumulation and activation of intrahepatic gammadeltaT cells (but not natural killer cells) by inducing apoptosis. Furthermore, we established that activated hepatic Valpha14iNKT cells (via cytokines and possibly reactive oxygen species) influenced the frequency and absolute number of intrahepatic gammadeltaT cells, as evidenced by increased hepatic gammadeltaT cell accumulation in Valpha14iNKT cell-deficient mice after poly I:C treatment relative to wild-type mice. Thus, hepatic Valpha14iNKT cells and intrahepatic gammadeltaT cells are functionally linked on application of TLR3 agonist. Overall, our results demonstrate a novel and previously unrecognized anti-inflammatory role for activated hepatic Valpha14iNKT cells in negatively regulating intrahepatic gammadeltaT cell accumulation (probably through TLR3 signaling) and thereby preventing potentially harmful activation of intrahepatic gammadeltaT cells.

Pathogenesis of hepatitis B virus infection

The adaptive immune response is thought to be responsible for viral clearance and disease pathogenesis during hepatitis B virus infection. It is generally acknowledged that the humoral antibody response contributes to the clearance of circulating virus particles and the prevention of viral spread within the host while the cellular immune response eliminates infected cells. The T cell response to the hepatitis B virus (HBV) is vigorous, polyclonal and multispecific in acutely infected patients who successfully clear the virus and relatively weak and narrowly focussed in chronically infected patients, suggesting that clearance of HBV is T cell dependent. The pathogenetic and antiviral potential of the cytotoxic T lymphocyte (CTL) response to HBV has been proven by the induction of a severe necroinflammatory liver disease following the adoptive transfer of HBsAg specific CTL into HBV transgenic mice. Remarkably, the CTLs also purge HBV replicative intermediates from the liver by secreting type 1 inflammatory cytokines thereby limiting virus spread to uninfected cells and reducing the degree of immunopathology required to terminate the infection. Persistent HBV infection is characterized by a weak adaptive immune response, thought to be due to inefficient CD4+ T cell priming early in the infection and subsequent development of a quantitatively and qualitatively ineffective CD8+ T cell response. Other factors that could contribute to viral persistence are immunological tolerance, mutational epitope inactivation, T cell receptor antagonism, incomplete down-regulation of viral replication and infection of immunologically privileged tissues. However, these pathways become apparent only in the setting of an ineffective immune response, which is, therefore, the fundamental underlying cause. Persistent infection is characterized by chronic liver cell injury, regeneration, inflammation, widespread DNA damage and insertional deregulation of cellular growth control genes, which, collectively, lead to cirrhosis of the liver and hepatocellular carcinoma.

Kupffer cell activation by ambient air particulate matter exposure may exacerbate non-alcoholic fatty liver disease

Owing to increased obesity, non-alcoholic fatty liver disease (NAFLD) is now the most prevalent liver disease in the United States. NAFLD is considered a component of metabolic syndrome, a cluster of disorders that also includes diabetes mellitus, dyslipidemia, arteriosclerosis, and hypertension. Exposure to ambient air particulate matter with aerodynamic diameters < 2.5 microm (PM(2.5)) is a risk factor for arteriosclerosis and lung disease, but its effect on NAFLD is unknown. PM(2.5) induces pulmonary dysfunction via Toll-like receptor (TLR) activation on alveolar macrophages. TLR activation of Kupffer cells, resident hepatic macrophages, and subsequent pro-inflammatory cytokine production have been shown to play a key role in NAFLD progression. We hypothesized that PM(2.5) exposure is a significant risk factor for the progression of NAFLD. Thus, following exposure of male C57BL/6 mice fed high fat chow (HFC) to concentrated air particulate matter (CAPs) or filtered air for 6 weeks, progression of NAFLD was evaluated by standardized histological assessment of hepatic inflammation and fibrosis. In mice fed HFC, the hepatic inflammatory grade (3.00 +/- 0.00 vs. 1.50 +/- 0.71, P < 0.001) and fibrosis stage (1.00 +/- 0.00 vs. 0.60 +/- 0.52, P = 0.023) were both significantly higher in mice exposed to CAPs versus filtered air, respectively. Increased numbers of Kupffer cells contained PM in CAPs-exposed mice scores of (2.00 +/- 0.94 vs. 0.20 +/- 0.42, respectively, P < 0.001). PM exposure increased IL-6 secretion up to seven-fold in a dose-dependent manner by isolated wild-type but not TLR4(-/-) Kupffer cells (P < 0.050). In conclusion, ambient PM(2.5) exposure may be a significant risk factor for NAFLD progression.

Kupffer cell activation by ambient air particulate matter exposure may exacerbate non-alcoholic fatty liver disease

Owing to increased obesity, non-alcoholic fatty liver disease (NAFLD) is now the most prevalent liver disease in the United States. NAFLD is considered a component of metabolic syndrome, a cluster of disorders that also includes diabetes mellitus, dyslipidemia, arteriosclerosis, and hypertension. Exposure to ambient air particulate matter with aerodynamic diameters < 2.5 microm (PM(2.5)) is a risk factor for arteriosclerosis and lung disease, but its effect on NAFLD is unknown. PM(2.5) induces pulmonary dysfunction via Toll-like receptor (TLR) activation on alveolar macrophages. TLR activation of Kupffer cells, resident hepatic macrophages, and subsequent pro-inflammatory cytokine production have been shown to play a key role in NAFLD progression. We hypothesized that PM(2.5) exposure is a significant risk factor for the progression of NAFLD. Thus, following exposure of male C57BL/6 mice fed high fat chow (HFC) to concentrated air particulate matter (CAPs) or filtered air for 6 weeks, progression of NAFLD was evaluated by standardized histological assessment of hepatic inflammation and fibrosis. In mice fed HFC, the hepatic inflammatory grade (3.00 +/- 0.00 vs. 1.50 +/- 0.71, P < 0.001) and fibrosis stage (1.00 +/- 0.00 vs. 0.60 +/- 0.52, P = 0.023) were both significantly higher in mice exposed to CAPs versus filtered air, respectively. Increased numbers of Kupffer cells contained PM in CAPs-exposed mice scores of (2.00 +/- 0.94 vs. 0.20 +/- 0.42, respectively, P < 0.001). PM exposure increased IL-6 secretion up to seven-fold in a dose-dependent manner by isolated wild-type but not TLR4(-/-) Kupffer cells (P < 0.050). In conclusion, ambient PM(2.5) exposure may be a significant risk factor for NAFLD progression.

The host-pathogen interaction during HBV infection: immunological controversies

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

Control of hepatitis B virus replication by innate response of HepaRG cells

Hepatitis B virus (HBV) is currently viewed as a stealth virus that does not elicit innate immunity in vivo. This assumption has not yet been challenged in vitro because of the lack of a relevant cell culture system. The HepaRG cell line, which is physiologically closer to differentiated hepatocytes and permissive to HBV infection, has opened new perspectives in this respect.HBV baculoviruses were used to initiate an HBV replication in both HepG2 and HepaRG cells. To monitor HBV replication, the synthesis of encapsidated DNA, and secretion of hepatitis B surface antigen (HBsAg), was respectively analyzed by southern blot and enzyme-linked immunosorbent assay. The induction of a type I interferon (IFN) response was monitored by targeted quantitative reverse transcription polymerase chain reaction (qRT-PCR), low-density arrays, and functional assays. The invalidation of type I IFN response was obtained by either antibody neutralization or RNA interference. We demonstrate that HBV elicits a strong and specific innate antiviral response that results in a noncytopathic clearance of HBV DNA in HepaRG cells. Challenge experiment showed that transduction with Bac-HBV-WT, but not with control baculoviruses, leads to this antiviral response in HepaRG cells, whereas no antiviral response is observed in HepG2 cells. Cellular gene expression analyses showed that IFN-beta and other IFN-stimulated genes were up-regulated in HepG2 and HepaRG cells, but not in cells transduced by control baculoviruses. Interestingly, a rescue of viral replication was observed when IFN-beta action was neutralized by antibodies or RNA interference of type I IFN receptor.

CONCLUSION

Our data suggest that a strong HBV replication is able to elicit a type I IFN response in HepaRG-transduced cells.

Immune effectors required for hepatitis B virus clearance

To better define the mechanism(s) likely responsible for viral clearance during hepatitis B virus (HBV) infection, viral clearance was studied in a panel of immunodeficient mouse strains that were hydrodynamically transfected with a plasmid containing a replication-competent copy of the HBV genome. Neither B cells nor perforin were required to clear the viral DNA transcriptional template from the liver. In contrast, the template persisted for at least 60 days at high levels in NOD/Scid mice and at lower levels in the absence of CD4(+) and CD8(+) T cells, NK cells, Fas, IFN-gamma (IFN-gamma), IFN-alpha/beta receptor (IFN-alpha/betaR1), and TNF receptor 1 (TNFR1), indicating that each of these effectors was required to eliminate the transcriptional template from the liver. Interestingly, viral replication was ultimately terminated in all lineages except the NOD/Scid mice, suggesting the existence of redundant pathways that inhibit HBV replication. Finally, induction of a CD8(+) T cell response in these animals depended on the presence of CD4(+) T cells. These results are consistent with a model in which CD4(+) T cells serve as master regulators of the adaptive immune response to HBV; CD8(+) T cells are the key cellular effectors mediating HBV clearance from the liver, apparently by a Fas-dependent, perforin-independent process in which NK cells, IFN-gamma, TNFR1, and IFN-alpha/betaR play supporting roles. These results provide insight into the complexity of the systems involved in HBV clearance, and they suggest unique directions for analysis of the mechanism(s) responsible for HBV persistence.

Stimulation of the interleukin-1 receptor and Toll-like receptor 2 inhibits hepatitis B virus replication in hepatoma cell lines in vitro

BACKGROUND

Toll-like receptors (TLRs) are a key component of the innate immune system and TLR2 has been shown to be involved in the immunopathogenesis of hepatitis B virus (HBV) infection in vivo. We investigated the role of TLR2 stimulation of virus-infected hepatocyte cell lines as a potential antiviral mechanism in vitro.

METHODS

The hepatoblastoma cell line HepG2 was transduced with recombinant HBV baculoviruses and the hepatoma cell line Huh-7 was transiently transfected with complimentary DNA clones of HBV. HBV viral replication was quantified after stimulation with interleukin (IL)-1beta and Pam-2-Cys, a synthetic TLR2 ligand, by measuring intracellular core-associated single-stranded HBV DNA using Southern blot hybridization, as well as viral nucleocapsid formation using a non-denaturing immunoblot method.

RESULTS

Stimulation of both cell lines in vitro with IL-1beta and Pam-2-Cys, both known to induce expression of the pro inflammatory cytokines tumour necrosis factor-alpha and IL-8 via a nuclear factor-kappaB dependent pathway, resulted in the inhibition of HBV DNA replication in the transduced HepG2 cells by up to 90% and nucleocapsid formation in the transiently transfected Huh-7 cells by up to 30%, when compared with mock-treated cells.

CONCLUSIONS

Hepatoma cell lines expressed functional IL-1 receptor and TLR2 receptors, which when stimulated led to a signalling cascade that inhibited HBV replication. These data support an active role for hepatocytes in inhibiting HBV replication and provide a rationale for the development of TLR agonists as potentially novel antiviral agents.

Inhibitory role of toll-like receptors agonists in Plasmodium yoelii liver stage development

It is well known that innate immune plays an important role in controlling the development of Plasmodium liver stage. However, little is known about the role of toll-like receptors (TLR) signalling in the pre-erythrocytic immunity against Plasmodium. Here, we found that pre-treatment with individual TLR agonist pam3CSK4 (TLR2), poly(I:C) (TLR3), LPS (TLR4) and CpG (TLR9) could decrease significantly the liver malaria parasite load in mice for 58%, 63%, 75% and 88% respectively. Moreover, no parasitaemia was observed within 14 days in CpG group mice challenged with 100 sporozoites. At 24 h prior to CpG injection, administration of gadolinium chloride (GdCl(3)) led to the rebound of liver Plasmodium load through inhibiting selectively Kupffer cells (KC) phagocytosis capacity but failed to neutralize completely CpG-induced immunity against malaria liver stage. Compared with the control, pre-treatment of CpG up-regulated hepatic pro-inflammatory cytokines IL-12, IFN-gamma and TNF-alpha, but down-regulated anti-inflammatory cytokines IL-10 and TGF-beta. Hence, our data demonstrated the inhibitory role of diverse TLR agonists in the Plasmodium development during pre-erythrocytic stage. As the most robust agonist, CpG might inhibit the development of Plasmodium liver stage through regulation of intrahepatic inflammatory cytokines and enhancement of KC cells phagocytosis capacity.

Toll-like receptor activated human and murine hepatic stellate cells are potent regulators of hepatitis C virus replication

BACKGROUND/AIMS

While hepatic stellate cells (HSC) are known to be key mediators of liver fibrosis, only little is known about their functional role in the innate immune system of the liver.

METHODS

To address this question, murine HSC were isolated from livers of C57BL/6J mice and human HSC were isolated from liver samples obtained from resections and liver explants. HSC were stimulated with Toll-like receptor (TLR) 1-9 ligands for 20 h. Supernatants were harvested and used in virus protection assays (encephalomyocarditis virus, EMCV) as well as in human and murine hepatitis C virus (HCV) replicon systems. Expression of interferon (IFN), retinoic acid-inducible gene-I (RIG-I), and interferon-stimulated genes (ISGs) was assessed by quantitative reverse transcription polymerase chain reaction.

RESULTS

While all TLRs were detectable in HSC, in murine HSC only TLR 3 and -4 agonists could induce cytokines that had an antiviral effect upon EMCV and HCV replication. IFN-beta was the main cytokine mediating the antiviral activity of TLR 3-stimulated HSC whereas other cytokines of undefined nature were involved in TLR 4-mediated antiviral effects. In human HSC, only TLR 3 stimulation led to production of antiviral cytokines. The antiviral effect was related to the up-regulation of ISGs and RIG-I in target cells.

CONCLUSIONS

These data demonstrate that murine and human HSC have as yet unrecognized antiviral properties when activated through the TLR-system and TLR 3/HCV in particular. This sheds new light on their role in the innate immune system of the liver and their participation in the control of HCV replication.

Not interferon, but interleukin-6 controls early gene expression in hepatitis B virus infection

With about 350 million virus carriers, hepatitis B virus (HBV) infection remains a major health problem. HBV is a noncytopathic virus causing persistent infection, but it is still unknown whether host recognition of HBV may activate an innate immune response. We describe that upon infection of primary human liver cells, HBV is recognized by nonparenchymal cells of the liver, mainly by liver macrophages (Kupffer cells), although they are not infected. Within 3 hours, this recognition leads to the activation of nuclear factor kappa B (NF-kappaB) and subsequently to the release of interleukin-6 (IL-6) and other proinflammatory cytokines (IL-8, TNF-alpha, IL-1beta), but does not induce an interferon response. The activation of proinflammatory cytokines, however, is transient, and even inhibits responsiveness toward a subsequent challenge. IL-6 released by Kupffer cells after activation of NF-kappaB controls HBV gene expression and replication in hepatocytes at the level of transcription shortly after infection. Upon binding to its receptor complex, IL-6 activates the mitogen-activated protein kinases exogenous signal-regulated kinase 1/2, and c-jun N-terminal kinase, which inhibit expression of hepatocyte nuclear factor (HNF) 1alpha and HNF 4alpha, two transcription factors essential for HBV gene expression and replication.

CONCLUSION

Our results demonstrate recognition of HBV patterns by nonparenchymal liver cells, which results in IL-6-mediated control of HBV infection at the transcriptional level. Thus, IL-6 ensures early control of the virus, limiting activation of the adaptive immune response and preventing death of the HBV-infected hepatocyte. This pattern recognition may be essential for a virus, which infects a new host with only a few virions. Our data also indicate that therapeutic neutralization of IL-6 for treatment of certain diseases may represent a risk if the patient is HBV-infected.

Correlation of circulating TLR2/4 expression with CD3+/4+/8+ T cells and Treg cells in HBV-related liver cirrhosis

Toll-like receptors (TLRs) 2 and 4 play a key role in chronic hepatitis B virus (HBV) infection. However, the role of TLRs in the pathogenesis of HBV-related liver cirrhosis and their regulation of the innate immune response of patients with liver cirrhosis remain unknown. To assess the contribution of TLR2/4 in HBV-related liver cirrhosis, we examined the expression of circulating TLR2 and TLR4 on peripheral blood mononuclear cells (PBMCs), CD4(+)CD25(+)CD127(low/-) Treg proportions, and CD3(+)/CD4(+)/CD8(+) T-cell counts in 30 liver cirrhosis patients, 21 chronic hepatitis B (CHB) patients, and 16 normal controls (NC). Furthermore, we analyzed the relationship between TLR2/4 expression and Treg proportions and T-cell counts. We show that the expression of TLR2 and TLR4 was significantly upregulated in patients with liver cirrhosis compared to NC. TLR4 expression was significantly increased in patients with liver cirrhosis compared to patients with CHB, and for TLR2 expression there were no differences between them. TLR4 expression showed a significant positive correlation with the frequency of Tregs in liver cirrhosis patients. TLR2 expression negatively correlated with CD3(+)/CD4(+)/CD8(+) T-cell counts and HBV viral load in patients with liver cirrhosis. These findings indicate that TLR may be involved in the pathogenesis of HBV-related liver cirrhosis, and may interact with Tregs and CD3(+)/CD4(+)/CD8(+) T cells in the immune response during HBV-related liver cirrhosis.

Costimulatory molecule programmed death-1 in the cytotoxic response during chronic hepatitis C

Hepatitis C virus (HCV)-specific CD8⁺ T cells play an important role in the resolution of HCV infection. Nevertheless, during chronic hepatitis C these cells lack their effector functions and fail to control the virus. HCV has developed several mechanisms to escape immune control. One of these strategies is the up-regulation of negative co-stimulatory molecules such us programmed death-1 (PD-1). This molecule is up-regulated on intrahepatic and peripheral HCV-specific cytotoxic T cells during acute and chronic phases of the disease, whereas PD-1 expression is low in resolved infection. PD-1 expressing HCV-specific CD8⁺ T cells are exhausted with impairment of several effector mechanisms, such as: type-1 cytokine production, expansion ability after antigen encounter and cytotoxic ability. However, PD-1 associated exhaustion can be restored by blocking the interaction between PD-1 and its ligand (PD-L1). After this blockade, HCV-specific CD8⁺ T cells reacquire their functionality. Nevertheless, functional restoration depends on PD-1 expression level. High PD-1-expressing intrahepatic HCV-specific CD8⁺ T cells do not restore their effector abilities after PD-1/PD-L1 blockade. The mechanisms by which HCV is able to induce PD-1 up-regulation to escape immune control are unknown. Persistent TCR stimulation by a high level of HCV antigens could favour early PD-1 induction, but the interaction between HCV core protein and gC1q receptor could also participate in this process. The PD-1/PD-L1 pathway modulation could be a therapeutic strategy, in conjunction with the regulation of others co-stimulatory pathways, in order to restore immune response against HCV to succeed in clearing the infection.

Liver is able to activate naïve CD8+ T cells with dysfunctional anti-viral activity in the murine system

The liver possesses distinct tolerogenic properties because of continuous exposure to bacterial constituents and nonpathogenic food antigen. The central immune mediators required for the generation of effective immune responses in the liver environment have not been fully elucidated. In this report, we demonstrate that the liver can indeed support effector CD8⁺ T cells during adenovirus infection when the T cells are primed in secondary lymphoid tissues. In contrast, when viral antigen is delivered predominantly to the liver via intravenous (IV) adenovirus infection, intrahepatic CD8⁺ T cells are significantly impaired in their ability to produce inflammatory cytokines and lyse target cells. Additionally, intrahepatic CD8⁺ T cells generated during IV adenovirus infection express elevated levels of PD-1. Notably, lower doses of adenovirus infection do not rescue the impaired effector function of intrahepatic CD8⁺ T cell responses. Instead, intrahepatic antigen recognition limits the generation of potent anti-viral responses at both priming and effector stages of the CD8⁺ T cell response and accounts for the dysfunctional CD8⁺ T cell response observed during IV adenovirus infection. These results also implicate that manipulation of antigen delivery will facilitate the design of improved vaccination strategies to persistent viral infection.

Impaired TLR3/IFN-beta signaling in monocyte-derived dendritic cells from patients with acute-on-chronic hepatitis B liver failure: relevance to the severity of liver damage

Toll-like receptors (TLRs) are a class of proteins that play key roles in innate immunity through recognition of microbial components. TLR3 is expressed abundantly in dendritic cells, and is responsible for recognizing viral pathogens and inducing interferon beta (IFN-beta) production. Although TLR3 has been reported to be involved in several diseases caused by viral infections, its role in hepatitis B virus (HBV)-induced hepatitis is still largely unknown. We found that expression of TLR3 and IFN-beta was decreased significantly in monocyte-derived dendritic cells (MoDCs) from patients with chronic hepatitis B (CHB, n=40) or acute-on-chronic hepatitis B liver failure (ACHBLF, n=60), compared with normal controls (n=20). We observed a further decrease in TLR3 and IFN-beta in ACHBLF compared to CHB patients. Compared with surviving patients, TLR3 and IFN-beta expression was significantly lower in non-surviving ACHBLF patients, which strongly indicated a correlation between TLR3 signaling impairment in MoDCs and disease severity in ACHBLF patients. Further linear correlation analysis demonstrated significant correlations between expression of TLR3 signaling components (TLR3 and IFN-beta) and disease severity markers (prothrombin activity and total bilirubin) for individual ACHBLF patients. To the best of our knowledge, this is the first study to show that MoDC impairment is correlated with severe liver damage in ACHBLF patients, which suggests the potential of TLR3/IFN-beta expression in MoDCs as a diagnostic marker.

Host immunity influences disease progression and antiviral efficacy in humans infected with hepatitis B virus

Hepatitis B virus (HBV) infection can lead to several severe liver diseases, including hepatitis, cirrhosis and hepatocellular carcinoma, although the underlying mechanisms responsible for the clinical outcome have not been well characterized. In this review, we retrospectively examine the history of immunological responses to HBV infection and summarize the current understanding of innate and adaptive immunity in the context of HBV-associated liver disease. Recent data indicate that the interaction between HBV and the host immune response not only substantially drives disease progression, but also significantly influences antiviral efficacy in HBV-infected individuals. Advances in the field have provided insight into the immunopathology of HBV infection. Based on the characteristics of host immune responses in patients with HBV infection, a 'climbing slope hypothesis' is proposed to suggest that therapeutic strategies aimed at modulating the immune activity of the host may represent a complementary approach to antiviral drug treatment for the management of chronically HBV-infected patients.

The size of the viral inoculum contributes to the outcome of hepatitis B virus infection

The impact of virus dose on the outcome of infection is poorly understood. In this study we show that, for hepatitis B virus (HBV), the size of the inoculum contributes to the kinetics of viral spread and immunological priming, which then determine the outcome of infection. Adult chimpanzees were infected with a serially diluted monoclonal HBV inoculum. Unexpectedly, despite vastly different viral kinetics, both high-dose inocula (10(10) genome equivalents [GE] per animal) and low-dose inocula (10 degrees GE per animal) primed the CD4 T-cell response after logarithmic spread was detectable, allowing infection of 100% of hepatocytes and requiring prolonged immunopathology before clearance occurred. In contrast, intermediate (10(7) and 10(4) GE) inocula primed the T-cell response before detectable logarithmic spread and were abruptly terminated with minimal immunopathology before 0.1% of hepatocytes were infected. Surprisingly, a dosage of 10(1) GE primed the T-cell response after all hepatocytes were infected and caused either prolonged or persistent infection with severe immunopathology. Finally, CD4 T-cell depletion before inoculation of a normally rapidly controlled inoculum precluded T-cell priming and caused persistent infection with minimal immunopathology. These results suggest that the relationship between the kinetics of viral spread and CD4 T-cell priming determines the outcome of HBV infection.

Cytokine expression during chronic versus occult hepatitis B virus infection in HIV co-infected individuals

Chronic hepatitis B virus infection is characterized by persistent detectable levels of hepatitis B surface antigen (HBsAg) and HBV DNA in the serum. In contrast, HBsAg is not detectable during occult HBV infection, despite the presence of HBV DNA. An altered host immune response could play a role in the development of occult HBV infection; however, potential differences in immune responses among chronic and occult HBV-infected patients have not been evaluated in vivo. In the current study, we evaluated serum levels of regulatory, apoptotic, and fibrotic/anti-fibrotic cytokines/markers as indicators of immune responses in 25 chronic and 12 occult HBV-infected patients. More than half of the patients in both chronic and occult HBV infection groups had IL-2, IL-4, IL-13, and IFN-gamma levels below detectable limits. In contrast, most patients had detectable levels of IL-8, IL-10, IP-10, sFas, sFasL, and TGF-beta1. Of these, only sFas was significantly different between the two groups, with lower levels observed during occult compared to chronic HBV infection (p=0.01). As a surrogate marker of apoptotic inhibition, decreased sFas during occult HBV infection suggests that apoptosis occurs at different rates in occult compared to chronic HBV infection and therefore, may contribute to persistence of occult HBV infection.

Galactosylated LDL nanoparticles: a novel targeting delivery system to deliver antigen to macrophages and enhance antigen specific T cell responses

We aim to define the role of Kupffer cells in intrahepatic antigen presentation, using the selective delivery of antigen to Kupffer cells rather than other populations of liver antigen-presenting cells. To achieve this we developed a novel antigen delivery system that can target antigens to macrophages, based on a galactosylated low-density lipoprotein nanoscale platform. Antigen was delivered via the galactose particle receptor (GPr), internalized, degraded and presented to T cells. The conjugation of fluoresceinated ovalbumin (FLUO-OVA) and lactobionic acid with LDL resulted in a substantially increased uptake of FLUO-OVA by murine macrophage-like ANA1 cells in preference to NIH3T3 cells, and by primary peritoneal macrophages in preference to primary hepatic stellate cells. Such preferential uptake led to enhanced proliferation of OVA specific T cells, showing that the galactosylated LDL nanoscale platform is a successful antigen carrier, targeting antigen to macrophages but not to all categories of antigen presenting cells. This system will allow targeted delivery of antigen to macrophages in the liver and elsewhere, addressing the question of the role of Kupffer cells in liver immunology. It may also be an effective way of delivering drugs or vaccines directly at macrophages.

Tripartite motif-containing 22 inhibits the activity of hepatitis B virus core promoter, which is dependent on nuclear-located RING domain

Members of the tripartite motif (TRIM) family are a part of the innate immune system to counter intracellular pathogens. TRIM22 has been reported to possess antiretroviral activity. Here we report that TRIM22 is involved in antiviral immunity against hepatitis B virus (HBV). Our results showed that TRIM22, being a strongly induced gene by interferons in human hepatoma HepG2 cells, could inhibit HBV gene expression and replication in a cell culture system as well as in a mouse model system. Importantly, it was found that TRIM22 could inhibit the activity of HBV core promoter (CP) in a dose-dependent manner. However, TRIM22 lacking the C terminal SPRY domain lost this activity. Further study showed that the SPRY domain deletion mutant was localized exclusively to the cytoplasm of HepG2 cells. In contrast, the wild-type TRIM22 was localized to the nucleus, as expected for a transcriptional suppressor. Interestingly, although RING domain mutants of TRIM22 were localized to the nucleus, they could not inhibit HBV CP activity, indicating that TRIM22-mediated anti-HBV activity was dependent on the nuclear-located RING domain.

CONCLUSION

These findings suggest that TRIM22, which exhibits anti-HBV activity by acting as a transcriptional suppressor, may play an important role in the clearance of HBV.

HBV-Specific Adaptive Immunity

The successful control of HBV infection requires an efficient expansion of distinct elements of the adaptive immune system (B cells, helper and cytotoxic T cells) that, due to the hepatotropic nature of HBV, need to operate in the liver parenchyma. In this respect, we will discuss broad features of HBV immunity in patients with resolved or chronic HBV infection and analyze how the liver environment can directly modulate HBV-immunity.

Lipopolysaccharide-induced innate immune responses in primary hepatocytes downregulates woodchuck hepatitis virus replication via interferon-independent pathways

Our previous studies have shown that Toll-like receptor (TLR) ligands, Poly I:C and lipopolysaccharide (LPS), are able to activate non-parenchymal liver cells and trigger the production of interferon (IFN) to inhibit hepatitis B virus replication in vivo and in vitro. However, little is known about TLR-mediated cellular responses in primary hepatocytes. By the model of woodchuck hepatitis virus (WHV) infected primary woodchuck hepatocytes (PWHs), Poly I:C and LPS stimulation resulted in upregulation of cellular antiviral genes and relevant TLRs mRNA expression respectively. LPS stimulation led to a pronounced reduction of WHV replicative intermediates without a significant IFN induction. Poly I:C transfection resulted in the production of IFN and a highly increased expression of antiviral genes in PWHs and slight inhibitory effect on WHV replication. LPS could activate nuclear factor kappa B, MAPK and PI-3k/Akt pathways in PWHs. Further, inhibitors of MAPK-ERK and PI-3k/Akt pathways, but not that of IFN signalling pathway, were able to block the antiviral effect of LPS. These results indicate that IFN- independent pathways which activated by LPS are able to downregulate hepadnaviral replication in hepatocytes.

Advance in molecular mechanism of interferon to treat chronic hepatitis B

The antiviral efficacy of interferon-α (IFN-α) therapy for chronic hepatitis B (CHB) is not only related to DNA load and genetype of HBV before treatment, gene mutation of HBV and polymorphism of type II HLA in the host, but also depends on the immunity of CHB patients. Researchers pay more and more attention to the mutant strain of virus and phenotypes of genes. However, the mechanism of interferon to resist HBV and the escape mechanism of HBV against the IFN therapy have not been clarified yet. This paper reviews the mechanism of IFN therapy and the influencing factors at molecular and genetic levels.

Toll-like receptors in liver ischemia reperfusion injury: a novel target for therapeutic modulation?

BACKGROUND

There is increasing evidence that Toll-like receptors (TLRs) sense host tissue damage by engaging with endogenous ligands. TLRs are considered to be involved in many primarily non-immune-related diseases. Hepatic ischemia reperfusion injury (IRI) represents one of these disorders.

OBJECTIVE

To present the latest findings supporting the involvement of TLRs in liver IRI and to explore their role as potential targets for therapeutic intervention.

METHODS

A review of the literature summarizing the latest advances in TLR signaling, the role of TLRs in each hepatic cell population and the involvement of TLRs in the pathophysiology of hepatic IRI. The potential role of TLR-targeting treatment strategies in liver IRI is discussed.

CONCLUSIONS

Recent experimental evidence suggests that TLR activation on Kupffer cells provides the triggering signal for pro-inflammatory responses that lead to liver IRI. Modulating TLR signaling could have a beneficial effect in patients with liver IRI.

Drug targets in hepatitis B virus infection

Hepatitis B virus infection (HBV) is a significant global health problem. Despite the success of universal hepatitis B vaccination in many countries, more than 350 million individuals worldwide are chronically infected and 15- 40% of those will develop cirrhosis and/or hepatocellular carcinoma if left untreated. Available therapies for chronic hepatitis B (CHB) infection are effective at decreasing viremia and improving measured clinical outcomes, however, no single therapy is optimal. As such, alternative drug therapies and the investigation of their role in the management of CHB are warranted. Significant improvements in the understanding of the HBV life cycle, viral genomics, and virus-host interactions continue to lead to the development of novel viral targets and immune modulators. Currently, two major classes of agents are utilized in CHB: the interferons and the nucleos(t)ide analogues. Each agent has individual advantages and drawbacks. The development of specific antiviral therapy has led to the emergence of HBV drug-resistant strains that has limited the long-term therapeutic potential of available agents. This necessitates the development of new agents that target both wild-type and drug-resistant strains. Further understanding of the basic mechanisms and clinical nuances of drug therapy is warranted. As most novel therapies are in the earliest stages of clinical development and testing, in the near future, treatment will continue to be long-term and likely involve the use of combination therapies to prevent viral resistance. In this review, we will highlight the HBV life cycle and genome, focusing in on current and potential novel antiviral drug targets as well as the benefits and clinical challenges with these therapies.

Expression of toll-like receptor 9 in peripheral blood mononuclear cells from patients with different hepatitis B and C viral loads

The aim of the present study was to investigate the expression of toll-like receptors (TLR) 9 in peripheral blood mononuclear cells (PBMC) of patients with chronic hepatitis B and C with different virus copies. The study group included 90 patients (60 with chronic hepatitis B, and 30 with chronic hepatitis C), and 20 healthy people served as control group. The protein and mRNA levels of TLR9 were detected by using flow cytometry and real-time PCR. The serum viral copies of HBV and HCV were measured in all patients, and the correlation between HBV-DNA copies or HCV-RNA copies and the TLR9 expression was analyzed. Our results demonstrated that HBV or HCV infection led to a decreased expression of TLR9 mRNA and protein compared to the control group (P<0.05). The TLR9 protein and mRNA levels were negatively correlated with serum viral copies of HBV and HCV (r=-0.632, r=-0.909, P<0.01). It was concluded that TLR9 mRNA and protein are down-regulated in PBMC of HBV-infected or HCV-infected patients, and they are negatively correlated with serum viral copies and play an important role in detecting viral replication of HBV and HCV.