Toll-like receptor 3 in liver diseases. Gastroenterol Res Pract. 2010;2010. [PMID: 20936107 PMCID: PMC2948910 DOI: 10.1155/2010/750904]

Effect of Shenlingyigan decoction on inflammatory factors related to liver injury regulated by TLR3 signaling pathway

Background

To investigate the therapeutic effect of Shenlingyigan decoction on acute liver injury. Further explored the mechanisms involved in the therapeutic properties of Shenlingyigan decoction by test several key proteins (TLR3, TRIF, TBK1, IRF3, IFNβ, IL-1 and IL-6) within the TLR3 signaling pathway.

Methods

The mouse acute liver injury model group was established by pretreatment with D-GalN and Poly (I:C) induction. The acute liver injury mouse treatment groups were gavage with different doses of Shenlingyigan decoction for 3 days. The therapeutic effects of Shenlingyigan decoction were preliminarily evaluated using organ indices, tissue images, and HE staining. Furthermore, potential associated signaling pathways and target effects were predicted through network pharmacology. Western blot experiments were conducted to examine the expression of relevant proteins (TLR3, TRIF, TBK1, IRF3, IL-1, and IL-6). In addition, immunofluorescence assays were performed to assess the localization of IRF3 and IFNβ expression in the cytoplasm and nucleus. Finally, the effects of Shenlingyigan decoction on the expression of TLR3, TRIF, TBK1 and IRF3 genes were further studied by QT-PCR.

Results

The liver organ index, the tissue photos and HE staining showed that Shenlingyigan decoction could reduce inflammation by decreasing the presence of inflammatory cells and downregulating the expression of IL-1 and IL-6. The result of network pharmacology showed 709 potential drug and disease overlapping targets. Toll-like receptor signaling pathway was related with these targets through KEGG analysis. Besides, TLR3, TBK1, IRF3, IL6, were important targets associated with viral hepatitis. Westernblot and Immunofluorescence analysis showed that Shenlingyigan decoction reduced the expression of TLR3 and TBK1 in mice with liver injury, while increasing the expression of IRF3. Shenlingyigan decoction does not significantly affect the expression of TRIF and IFNβ; however, it enhances the expression of IRF3 in the nucleus, consequently leading to increased expression of IFNβ in the nucleus. The results of QT-PCR showed that Shenlingyigan decoction could down-regulate the expression of TLR3, TRIF and TBK1 genes, and up-regulate the expression of IRF3 gene.

Conclusions

Shenlingyigan decoction participated in immune responses by effecting the expression of TLR3 signaling pathway-related factors to treat the acute liver injury.

LIGHT Amplification by NF-κB Contributes to TLR3 Signaling Pathway-Induced Acute Hepatitis

LIGHT is a member of the TNF superfamily and a proinflammatory cytokine involved in liver pathogenesis. Many liver diseases involve activation of Toll-like receptor 3 (TLR3), which is activated by double-stranded RNA (dsRNA). However, the involvement of LIGHT in TLR3 implicated liver diseases is not clear. In this study, we investigated the role of LIGHT in TLR3 involved liver pathogenesis by using a mouse model of TLR3 agonist poly(I:C)-induced hepatitis. We found LIGHT expression at both protein and mRNA level in liver tissues is dramatically increased during the course of poly(I:C)-induced liver injury. This induction depends on NF-κB activation as pretreating the mice with a NF-κB inhibitor abrogates LIGHT upregulation. Importantly, blockade of the LIGHT signaling pathway with the recombinant LIGHT receptor HVEM protein ameliorates liver injury in poly(I:C)-induced hepatitis. Conclusions. These results indicate that LIGHT amplification by NF-κB plays a significant role in TLR3 involved hepatitis and points LIGHT to be a potential drug target for liver disease therapy.

Gamma Delta T Cells: Role in Immunotherapy of Hepatocellular Carcinoma

The most typical type of liver cancer or hepatocellular carcinoma (HCC) develops from hepatocyte loss. Non-alcoholic fatty liver disease (NAFLD), viral hepatitis C and cirrhosis are the leading causes of HCC. With the Hepatitis B vaccine and medicines, there are several treatments for HCC, including liver resection, ablation, transplantation, immunotherapy, gene therapy, radiation embolization, and targeted therapy. Currently, a wide range of studies are carried out on gene therapy to identify biomarkers and pathways, which help us identify the exact stage of the disorder and reduce its effects. γδT cells have recently received much interest as a potential cancer treatment method in adaptive immunotherapy. γδT cells can quickly form connections between receptor and ligand activation. They can clonally expand and are a significant source of cytokines and chemokines. The present review provides a comprehensive understanding on the function of γδT cells in immunotherapies and how they are used to treat HCC.

Pathogenesis of Alcohol-Associated Liver Disease

Excessive alcohol consumption is a global healthcare problem with enormous social, economic, and clinical consequences. While chronic, heavy alcohol consumption causes structural damage and/or disrupts normal organ function in virtually every tissue of the body, the liver sustains the greatest damage. This is primarily because the liver is the first to see alcohol absorbed from the gastrointestinal tract via the portal circulation and second, because the liver is the principal site of ethanol metabolism. Alcohol-induced damage remains one of the most prevalent disorders of the liver and a leading cause of death or transplantation from liver disease. Despite extensive research on the pathophysiology of this disease, there are still no targeted therapies available. Given the multifactorial mechanisms for alcohol-associated liver disease pathogenesis, it is conceivable that a multitherapeutic regimen is needed to treat different stages in the spectrum of this disease.

Knowledge-guided deep learning models of drug toxicity improve interpretation

In drug development, a major reason for attrition is the lack of understanding of cellular mechanisms governing drug toxicity. The black-box nature of conventional classification models has limited their utility in identifying toxicity pathways. Here we developed DTox (deep learning for toxicology), an interpretation framework for knowledge-guided neural networks, which can predict compound response to toxicity assays and infer toxicity pathways of individual compounds. We demonstrate that DTox can achieve the same level of predictive performance as conventional models with a significant improvement in interpretability. Using DTox, we were able to rediscover mechanisms of transcription activation by three nuclear receptors, recapitulate cellular activities induced by aromatase inhibitors and pregnane X receptor (PXR) agonists, and differentiate distinctive mechanisms leading to HepG2 cytotoxicity. Virtual screening by DTox revealed that compounds with predicted cytotoxicity are at higher risk for clinical hepatic phenotypes. In summary, DTox provides a framework for deciphering cellular mechanisms of toxicity in silico.

Oral administration of PEGylated TLR7 ligand ameliorates alcohol-associated liver disease via the induction of IL-22

Effective therapies for alcohol-associated liver disease (ALD) are limited; therefore, the discovery of new therapeutic agents is greatly warranted. Toll-like receptor 7 (TLR7) is a pattern recognition receptor for single-stranded RNA, and its activation prevents liver fibrosis. We examined liver and intestinal damage in Tlr7-/- mice to determine the role of TLR7 in ALD pathogenesis. In an alcoholic hepatitis (AH) mouse model, hepatic steatosis, injury, and inflammation were induced by chronic binge ethanol feeding in mice, and Tlr7 deficiency exacerbated these effects. Because these results demonstrated that endogenous TLR7 signaling activation is protective in the AH mouse model, we hypothesized that TLR7 activation may be an effective therapeutic strategy for ALD. Therefore, we investigated the therapeutic effect of TLR7 agonistic agent, 1Z1, in the AH mouse model. Oral administration of 1Z1 was well tolerated and prevented intestinal barrier disruption and bacterial translocation, which thus suppressed ethanol-induced hepatic injury, steatosis, and inflammation. Furthermore, 1Z1 treatment up-regulated the expression of antimicrobial peptides, Reg3b and Reg3g, in the intestinal epithelium, which modulated the microbiome by decreasing and increasing the amount of Bacteroides and Lactobacillus, respectively. Additionally, 1Z1 up-regulated intestinal interleukin (IL)-22 expression. IL-22 deficiency abolished the protective effects of 1Z1 in ethanol-induced liver and intestinal damage, suggesting intestinal IL-22 as a crucial mediator for 1Z1-mediated protection in the AH mouse model. Collectively, our results indicate that TLR7 signaling exerts protective effects in the AH mouse model and that a TLR7 ligand, 1Z1, holds therapeutic potential for the treatment of AH.

Role of γδT cells in liver diseases and its relationship with intestinal microbiota

γδT cells are unconventional T lymphocytes that bridge innate and adaptive immunity. Based on the composition of T cell receptor and the cytokines produced, γδT cells can be divided into diverse subsets that may be present at different locations, including the liver, epithelial layer of the gut, the dermis and so on. Many of these cells perform specific functions in liver diseases, such as viral hepatitis, autoimmune liver diseases, non-alcoholic fatty liver disease, liver cirrhosis and liver cancers. In this review, we discuss the distribution, subsets, functions of γδT cells and the relationship between the microbiota and γδT cells in common hepatic diseases. As γδT cells have been used to cure hematological and solid tumors, we are interested in γδT cell-based immunotherapies to treat liver diseases.

Toll-like receptor 3 activation increases voluntary alcohol intake in C57BL/6J male mice

Many genes differentially expressed in brain tissue from human alcoholics and animals that have consumed large amounts of alcohol are components of the innate immune toll-like receptor (TLR) pathway. TLRs initiate inflammatory responses via two branches: (1) MyD88-dependent or (2) TRIF-dependent. All TLRs signal through MyD88 except TLR3. Prior work demonstrated a direct role for MyD88-dependent signaling in regulation of alcohol consumption. However, the role of TLR3 as a potential regulator of excessive alcohol drinking has not previously been investigated. To test the possibility TLR3 activation regulates alcohol consumption, we injected mice with the TLR3 agonist polyinosinic:polycytidylic acid (poly(I:C)) and tested alcohol consumption in an every-other-day two-bottle choice test. Poly(I:C) produced a persistent increase in alcohol intake that developed over several days. Repeated poly(I:C) and ethanol exposure altered innate immune transcript abundance; increased levels of TRIF-dependent pathway components correlated with increased alcohol consumption. Administration of poly(I:C) before exposure to alcohol did not alter alcohol intake, suggesting that poly(I:C) and ethanol must be present together to change drinking behavior. To determine which branch of TLR signaling mediates poly(I:C)-induced changes in drinking behavior, we tested either mice lacking MyD88 or mice administered a TLR3/dsRNA complex inhibitor. MyD88 null mutants showed poly(I:C)-induced increases in alcohol intake. In contrast, mice pretreated with a TLR3/dsRNA complex inhibitor reduced their alcohol intake, suggesting poly(I:C)-induced escalations in alcohol intake are, at least partially, dependent on TLR3. Together, these results strongly suggest that TLR3-dependent signaling drives excessive alcohol drinking behavior.

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).

Association of Toll-Like Receptor 3 Single-Nucleotide Polymorphisms and Hepatitis C Virus Infection

Toll-like receptor 3 (TLR3) plays a key role in innate immunity by recognizing pathogenic, double-stranded RNAs. Thus, activation of TLR3 is a major factor in antiviral defense and tumor eradication. Although downregulation of TLR3 gene expression has been mainly reported in patients infected with hepatitis C virus (HCV), the influence of TLR3 genotype on the risk of HCV infection, HCV-related cirrhosis, and/or hepatocellular carcinoma (HCC) remains to be determined. Single-nucleotide polymorphisms (SNPs) within the TLR3 gene and their associations with HCV-related disease risk were investigated in a Saudi Arabian population in this study. Eight TLR3 SNPs were analyzed in 563 patients with HCV, which consisted of 437 patients with chronic HCV infections, 88 with HCV-induced liver cirrhosis, and 38 with HCC. A total of 599 healthy control subjects were recruited to the study. Among the eight TLR3 SNPs studied, the rs78726532 SNP was strongly associated with HCV infection when compared to that in healthy control subjects. The rs5743314 was also strongly associated with HCV-related liver disease progression (cirrhosis and HCC). In summary, these results indicate that distinct genetic variants of TLR3 SNPs are associated with HCV infection and HCV-mediated liver disease progression in the Saudi Arabian population.

Toll-like receptors in pathophysiology of liver diseases

Toll-like receptors (TLRs) are pattern recognition receptors that participate in host defense by recognizing pathogen-associated molecular patterns alongside inflammatory processes by recognizing damage associated molecular patterns. Given constant exposure to pathogens from gut, strict control of TLR-associated signaling pathways is essential in the liver, which otherwise may lead to inappropriate production of pro-inflammatory cytokines and interferons and may generate a predisposition to several autoimmune and chronic inflammatory diseases. The liver is considered to be a site of tolerance induction rather than immunity induction, with specificity in hepatic cell functions and distribution of TLR. Recent data emphasize significant contribution of TLR signaling in chronic liver diseases via complex immune responses mediating hepatocyte (i.e., hepatocellular injury and regeneration) or hepatic stellate cell (i.e., fibrosis and cirrhosis) inflammatory or immune pathologies. Herein, we review the available data on TLR signaling, hepatic expression of TLRs and associated ligands, as well as the contribution of TLRs to the pathophysiology of hepatic diseases.

Transglutaminase 2 is dispensable but required for the survival of mice in dextran sulfate sodium-induced colitis

Transglutaminase 2 (TG2) is a ubiquitously expressed enzyme that catalyzes crosslinking, polyamination or deamidation of glutamine residues in proteins. It has been reported that TG2 is involved in the pathogenesis of various inflammatory diseases including celiac disease, pulmonary fibrosis, cystic fibrosis, multiple sclerosis and sepsis. Recently, using a mouse model of bleomycin-induced lung fibrosis, we showed that TG2 is required to trigger inflammation via the induction of T helper type 17 (Th17) cell differentiation in response to tissue damage. However, the role of TG2 in inflammatory bowel disease (IBD), which is thought to be a Th17 cell-associated disease, has remained elusive. In this study, we investigated the role of TG2 in dextran sulfate sodium (DSS)-induced colitis, the most widely used mouse model for IBD. Age- and sex-matched wild-type and TG2^-/- mice were fed 2% DSS for 7 days or 3.5% DSS for 5 days in drinking water. An in situ TG activity assay revealed that DSS treatment activates TG2 in various colon cell types, including columnar absorptive cells and goblet cells. DSS-treated TG2^-/- mice showed lower interleukin (IL)-6, but higher IL-17A and RORγt (retinoic acid receptor-related orphan receptor-γt) expression levels in the colon tissues than that in the wild-type mice. Moreover, TG2^-/- mice showed higher mortality than the wild-type mice because of DSS treatment. Nevertheless, we found no significant differences in changes of body weight, colon length, morphology, immune cell infiltration and in vivo intestinal permeability between DSS-treated wild-type and TG2^-/- mice. These results indicate that TG2-mediated Th17 cell differentiation is not required for the pathogenesis of DSS-induced acute colitis.

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).

Rapidity of fibrosis progression in liver transplant recipients with recurrent hepatitis C is influenced by toll-like receptor 3 polymorphism

Liver transplantation activates the innate immune system through toll-like receptors (TLRs), potentially leading to allograft rejection and graft failure. We evaluated the association of single-nucleotide polymorphisms in TLR genes with the severity of hepatitis C virus recurrence after liver transplantation (LT). This is a two-center study of 176 adult patients who received a first LT from deceased donors for hepatitis C virus (HCV) cirrhosis. Eleven polymorphisms were evaluated by real-time polymerase chain reaction and melting curves analyses: TLR1 (Asp248Ser and Ser602Ile), TLR2 (Arg753Gln), TLR3 (Leu412Phe), TLR4 (Asp299Gly), TLR5 (Arg392Stop), TLR6 (Ser249Pro), TLR7 (Gln11Leu), TLR8 (Met1Val), and TLR9 (-1237T/C and -1486C/T). The CC genotype of TLR3 Leu412Phe in liver recipients was associated with severe recurrence (odds ratio (OR) = 2.01, 95% confidence interval (95% CI) = 1.02-3.93, p = 0.04). We also analyzed this polymorphism in 72 of their donors but no association was found with severity of HCV recurrence (p = 0.89). Multivariate analysis showed donor age older than 40 yr (OR=2.93; 95% CI = 1.49-5.8, p = 0.002) and the TLR3 Leu412Phe CC genotype (OR=2.02, 95%CI=1.01-4.05, p = 0.046) were independently associated with severe HCV recurrence. Our results show that the TLR3 Leu412Phe CC genotype is independently associated with severity of hepatitis C recurrence after LT.

Commensal microbiota is hepatoprotective and prevents liver fibrosis in mice

Translocation of bacteria and their products across the intestinal barrier is common in patients with liver disease, and there is evidence that experimental liver fibrosis depends on bacterial translocation. The purpose of our study was to investigate liver fibrosis in conventional and germ-free (GF) C57BL/6 mice. Chronic liver injury was induced by administration of thioacetamide (TAA) in the drinking water for 21 wk or by repeated intraperitoneal injections of carbon tetrachloride (CCl4). Increased liver fibrosis was observed in GF mice compared with conventional mice. Hepatocytes showed more toxin-induced oxidative stress and cell death. This was accompanied by increased activation of hepatic stellate cells, but hepatic mediators of inflammation were not significantly different. Similarly, a genetic model using Myd88/Trif-deficient mice, which lack downstream innate immunity signaling, had more severe fibrosis than wild-type mice. Isolated Myd88/Trif-deficient hepatocytes were more susceptible to toxin-induced cell death in culture. In conclusion, the commensal microbiota prevents fibrosis upon chronic liver injury in mice. This is the first study describing a beneficial role of the commensal microbiota in maintaining liver homeostasis and preventing liver fibrosis.

Quiescent hepatic stellate cells functionally contribute to the hepatic innate immune response via TLR3

Toll-like Receptor 3 (TLR3) is a pathogen pattern recognition receptor that plays a key role in innate immunity. TLR3 signalling has numerous functions in liver, both in health and disease. Here we report that TLR3 is expressed by quiescent hepatic stellate cells (HSC) where it functions to induce transcription and secretion of functional interferons as well as a number of other cytokines and chemokines. Upon transdifferentiation into myofibroblasts, HSCs rapidly loose the ability to produce interferon gamma (IFNγ). Mechanistically, this gene silencing may be due to Polycomb complex mediated repression via methylation of histone H3 lysine 27. In contrast to wild type, quiescent HSC isolated from tlr3 knockout mice do not produce IFNγ in response to Poly(I∶C) treatment. Therefore, quiescent HSC may contribute to induction of the hepatic innate immune system in response to injury or infection.

Toll like receptor 3 plays a critical role in the progression and severity of acetaminophen-induced hepatotoxicity

Toll-like receptor (TLR) activation has been implicated in acetaminophen (APAP)-induced hepatotoxicity. Herein, we hypothesize that TLR3 activation significantly contributed to APAP-induced liver injury. In fasted wildtype (WT) mice, APAP caused significant cellular necrosis, edema, and inflammation in the liver, and the de novo expression and activation of TLR3 was found to be necessary for APAP-induced liver failure. Specifically, liver tissues from similarly fasted TLR3-deficient (tlr3(-/-) ) mice exhibited significantly less histological and biochemical evidence of injury after APAP challenge. Similar protective effects were observed in WT mice in which TLR3 was targeted through immunoneutralization at 3 h post-APAP challenge. Among three important death ligands (i.e. TNFα, TRAIL, and FASL) known to promote hepatocyte death after APAP challenge, TNFα was the only ligand that was significantly reduced in APAP-challenged tlr3(-/-) mice compared with APAP-challenged WT controls. In vivo studies demonstrated that TLR3 activation contributed to TNFα production in the liver presumably via F4/80(+) and CD11c(+) immune cells. In vitro studies indicated that there was cooperation between TNFα and TLR3 in the activation of JNK signaling in isolated and cultured liver epithelial cells (i.e. nMuLi). Moreover, TLR3 activation enhanced the expression of phosphorylated JNK in APAP injured livers. Thus, the current study demonstrates that TLR3 activation contributes to APAP-induced hepatotoxicity.

Toll-like receptors in liver fibrosis: cellular crosstalk and mechanisms

Toll-like receptors (TLRs) are pattern recognition receptors that distinguish conserved microbial products, also known as pathogen-associated molecular patterns (PAMPs), from host molecules. Liver is the first filter organ between the gastrointestinal tracts and the rest of the body through portal circulation. Thus, the liver is a major organ that must deal with PAMPs and microorganisms translocated from the intestine and to respond to the damage associated molecular patterns (DAMPs) released from injured organs. These PAMPs and DAMPs preferentially activate TLR signaling on various cell types in the liver inducing the production of inflammatory and fibrogenic cytokines that initiate and prolong liver inflammation, thereby leading to fibrosis. We summarize recent findings on the role of TLRs, ligands, and intracellular signaling in the pathophysiology of liver fibrosis due to different etiology, as well as to highlight the potential role of TLR signaling in liver fibrosis associated with hepatitis C infection, non-alcoholic and alcoholic steatoheoatitis, primary biliary cirrhosis, and cystic fibrosis.

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.

Toll-like receptors in secondary obstructive cholangiopathy

Secondary obstructive cholangiopathy is characterized by intra- or extrahepatic bile tract obstruction. Liver inflammation and structural alterations develop due to progressive bile stagnation. Most frequent etiologies are biliary atresia in children, and hepatolithiasis, postcholecystectomy bile duct injury, and biliary primary cirrhosis in adults, which causes chronic biliary cholangitis. Bile ectasia predisposes to multiple pathogens: viral infections in biliary atresia; Gram-positive and/or Gram-negative bacteria cholangitis found in hepatolithiasis and postcholecystectomy bile duct injury. Transmembrane toll-like receptors (TLRs) are activated by virus, bacteria, fungi, and parasite stimuli. Even though TLR-2 and TLR-4 are the most studied receptors related to liver infectious diseases, other TLRs play an important role in response to microorganism damage. Acquired immune response is not vertically transmitted and reflects the infectious diseases history of individuals; in contrast, innate immunity is based on antigen recognition by specific receptors designated as pattern recognition receptors and is transmitted vertically through the germ cells. Understanding the mechanisms for bile duct inflammation is essential for the future development of therapeutic alternatives in order to avoid immune-mediated destruction on secondary obstructive cholangiopathy. The role of TLRs in biliary atresia, hepatolithiasis, bile duct injury, and primary biliary cirrhosis is described in this paper.

Toll-like receptor signaling in liver regeneration, fibrosis and carcinogenesis

Toll-like receptors (TLR) are the germline-coded pattern recognition receptors that sense microbial products. This signaling orchestrates complex signaling pathways that induce expression of inflammatory genes for host defense against invading microorganisms. Recent studies illustrate the role of TLR on non-infectious inflammatory diseases. The liver has a unique anatomy bridging with the intestine by portal vein and bile ducts. This allows delivery of products from intestinal microflora directly into the liver. Subsequently, microbial products cause acute and chronic inflammation through TLR signaling in the liver. Not only exogenous products, but endogenous denatured products released from dying cells also facilitate inflammation even in sterile conditions. Consequently, these responses elicit tissue repairing including liver regeneration and fibrogenesis. An aberrant regenerative response may lead to hepatic carcinogenesis. In this review, we highlight the recently accumulated knowledge about TLR signaling in liver regeneration, fibrosis and carcinogenesis.