Interferon gamma accelerates NF-kappaB activation of biliary epithelial cells induced by Toll-like receptor and ligand interaction

HSCs-derived exosomes regulate the levels of inflammatory cytokines in HIBECs through miR-122-5p mediated p38 MAPK signaling pathway

PBC is an autoimmune-mediated liver disease, and intrahepatic biliary epithelial cells (IBECs) are the target cells of early damage. Previous studies found that miRNAs and inflammation is closely related to PBC. In this study, we extracted exosomes from serum and human IBECs supernatant, and RNA-sequence analyzed the expression profiles of miRNAs. Elisa measured the levels of inflammatory cytokines. RT- qPCR and western blot detected the levels of miR-122-5p, p38 and p-p38. The results showed that 263 differentially expressed (DE) miRNAs were identified in serum exosomes of PBC patients. The levels of IL-1β, IL-6, IL-12, IL-17 A, IFN-γ, TNF-α and TGF-β1 in peripheral blood of PBC patients were higher than those of normal controls. According to the validation results and previous literature, exosomal miR-122-5p was finally selected as the study object, and correlated with inflammatory factors. In vitro experiments further found that exosomal miR-122-5p may derive from hepatic stellate cells (HSCs), and can be HIBECs intake, and influence HIBECs inflammatory factor levels though p38 MAPK signaling pathways. This may provide a new strategy for the treatment of PBC.

Primary Biliary Cholangitis: Pathophysiology

Primary biliary cholangitis (PBC) is the most common of the autoimmune liver diseases, in which there is chronic small bile duct inflammation. The pathophysiology of PBC is multifactorial, involving immune dysregulation and damage to biliary epithelial cells, with influences from genetic factors, epigenetics, the gut-liver axis, and environmental exposures.

Is it possible to intervene early cirrhosis by targeting toll-like receptors to rebalance the intestinal microbiome?

Cirrhosis is a progressive chronic liver disease caused by one or more causes and characterized by diffuse fibrosis, pseudolobules, and regenerated nodules. Once progression to hepatic decompensation, the function of the liver and other organs is impaired and almost impossible to reverse and recover, which often results in hospitalization, impaired quality of life, and high mortality. However, in the early stage of cirrhosis, there seems to be a possibility of cirrhosis reversal. The development of cirrhosis is related to the intestinal microbiota and activation of toll-like receptors (TLRs) pathways, which could regulate cell proliferation, apoptosis, expression of the hepatomitogen epiregulin, and liver inflammation. Targeting regulation of intestinal microbiota and TLRs pathways could affect the occurrence and development of cirrhosis and its complications. In this paper, we first reviewed the dynamic change of intestinal microbiota and TLRs during cirrhosis progression. And further discussed the interaction between them and potential therapeutic targets to reverse early staged cirrhosis.

Clonorchis sinensis aggravates biliary fibrosis through promoting IL-6 production via toll-like receptor 2-mediated AKT and p38 signal pathways

Clonorchis sinensis is an important food-borne zoonotic parasite which has been linked to biliary fibrosis and cholangiocarcinoma. However, the details of the pathogenesis of C. sinensis were unclear. To explore the role and regulatory mechanism of toll-like receptor 2 (TLR2) in C. sinensis-induced biliary fibrosis, we established the C. sinensis-infected C57BL/6 mouse model with TLR2-/- and wild type (WT) mice. The mortality rate, liver lesions, TLR2 and TGF-β1 expression, phosphorylation of Smad2/3, AKT, p38, ERK and p65, and cytokine productions were analyzed. Furthermore, similar parameters were examined in mouse biliary epithelial cells (BECs) co-cultured with C. sinensis excretory/secretory proteins (ESPs). The results showed that TLR2 expression was enhanced significantly in C. sinensis-infected WT mice and mouse BECs. C. sinensis-infected TLR2-/- mice exhibited an increased weight and a decreased mortality rate; significantly alleviated liver lesions and biliary fibrosis, reduced numbers of myofibroblasts; decreased expression of TGF-β1 and phosphorylation level of AKT, p38 and Smad2/3; significantly decreased production of IL-6, TNF-α and IL-4, while increased production of IFN-γ compared with C. sinensis-infected WT mice. Furthermore, C. sinensis ESPs could activate TLR2-mediated AKT and p38 pathways to increase the production of IL-6 in mouse BECs. In conclusion, these data indicate that C. sinensis infection activated TGF-β1-Smad2/3 through TLR2-mediated AKT and p38 pathways to promote IL-6 production, which resulted in myofibroblast activation and aggravating biliary fibrosis in mice.

Apoptotic biliary epithelial cells and gut dysbiosis in the induction of murine primary biliary cholangitis

Primary biliary cholangitis (PBC) is a female-predominant liver autoimmune disease characterized by the specific immune-mediated destruction of the intrahepatic small bile duct. Although apoptosis of biliary epithelial cells (BECs) and alterations in gut microbiota are observed in patients with PBC, it is still unclear whether these events happen in the early stage and cause the breakdown of tolerance in PBC. In this study, we examined the early events in the loss of tolerance in our well-defined 2-OA-OVA-induced murine autoimmune cholangitis (AIC) model. We report herein that apoptosis of BECs was notable in the early stage of murine AIC. An altered gut microbiota, in particular, an increased percentage of gram-positive Firmicutes in AIC mice was also observed. BECs in AIC mice expressed adhesion molecule ICAM-1, cytokines/chemokines TNF-α, CCL2, CXCL9, CXCL10, and toll-like receptor (TLR) 2. Moreover, BECs treated with TLR2 ligand had elevated apoptosis and CXCL10 production. These data collectively suggest a new mechanism of tolerance breakdown in AIC. Altered gut microbiota induces apoptosis of BECs through TLR2 signaling. BECs secrete chemokines to recruit CD8 T cells to damage BECs further.

Cellular Homeostasis and Repair in the Biliary Tree

During biliary tree homeostasis, BECs are largely in a quiescent state and their turnover is slow for maintaining normal tissue homeostasis. BTSCs continually replenish new BECs in the luminal surface of EHBDs. In response to various types of biliary injuries, distinct cellular sources, including HPCs, BTSCs, hepatocytes, and BECs, repair or regenerate the injured bile duct. BEC, biliary epithelial cell; BTSC, biliary tree stem/progenitor cell; EHBD, extrahepatic bile ducts; HPC, hepatic progenitor cell.The biliary tree comprises intrahepatic bile ducts and extrahepatic bile ducts lined with epithelial cells known as biliary epithelial cells (BECs). BECs are a common target of various cholangiopathies for which there is an unmet therapeutic need in clinical hepatology. The repair and regeneration of biliary tissue may potentially restore the normal architecture and function of the biliary tree. Hence, the repair and regeneration process in detail, including the replication of existing BECs, expansion and differentiation of the hepatic progenitor cells and biliary tree stem/progenitor cells, and transdifferentiation of the hepatocytes, should be understood. In this paper, we review biliary tree homeostasis, repair, and regeneration and discuss the feasibility of regenerative therapy strategies for cholangiopathy treatment.

Primary Biliary Cholangitis and Primary Sclerosing Cholangitis: Current Knowledge of Pathogenesis and Therapeutics

Cholangiopathies encompass various biliary diseases affecting the biliary epithelium, resulting in cholestasis, inflammation, fibrosis, and ultimately liver cirrhosis. Primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) are the most important progressive cholangiopathies in adults. Much research has broadened the scope of disease biology to genetic risk, epigenetic changes, dysregulated mucosal immunity, altered biliary epithelial cell function, and dysbiosis, all of which interact and arise in the context of ill-defined environmental triggers. An in-depth understanding of the molecular pathogenesis of these cholestatic diseases will help clinicians better prevent and treat diseases. In this review, we focus on the main underlying mechanisms of disease initiation and progression, and novel targeted therapeutics beyond currently approved treatments.

The pathogenesis, models and therapeutic advances of primary biliary cholangitis

Primary biliary cholangitis (PBC) is an autoimmune disease characterized by the destruction of intrahepatic small bile ducts and the presence of antimitochondrial antibody (AMA), eventually progresses to liver fibrosis and cirrhosis. Genetic predisposition and environmental factors are involved in the occurrence of PBC, and the epitopes exposure and the imbalance of autoimmune tolerance are the last straw. The apoptosis of biliary epithelial cell (BEC) leads to the release of autoantigen epitopes, which activate the immune system, and the disorder of innate and adaptive immunity eventually leads to the start of disease. Animal models have unique advantages in investigating the pathogenesis and drug exploitation of PBC. Multiple models have been reported, and spontaneous model and induced model have been widely used in relevant research of PBC in recent years. Currently, the only drugs licensed for PBC are ursodesoxycholic acid (UDCA) and obeticholic acid (OCA). In the last few years, as the learned more about the pathogenesis of PBC, more and more targets have been discovered, and multiple targeted drugs are being in developed. In this review, the pathogenesis, murine models and treatment strategies of PBC were summarized, and the current research status was discussed to provide insights for the further study of PBC.

Immune system and cholangiocytes: A puzzling affair in primary biliary cholangitis

Primary biliary cholangitis (PBC) is a cholestatic liver disease characterized by the destruction of the small and medium bile ducts. Its pathogenesis is still unknown. Despite the genome wide association study findings, the therapies targeting the cytokines pathway, tested so far, have failed. The concept of the biliary epithelium as a key player of the PBC pathogenesis has emerged over the last few years. It is now well accepted that the biliary epithelial cells (BECs) actively participate to the genesis of the damage. The chronic stimulation of BECs via microbes and bile changes the cell phenotype toward an active state, which, across the production of proinflammatory mediators, can recruit, retain, and activate immune cells. The consequent immune system activation can in turn damage BECs. Thus, the crosstalk between both innate and adaptive immune cells and the biliary epithelium creates a paracrine loop responsible for the disease progression. In this review, we summarize the evidence provided in literature about the role of BECs and the immune system in the pathogenesis of PBC. We also dissect the relationship between the immune system and the BECs, focusing on the unanswered questions and the future potential directions of the translational research and the cellular therapy in this area.

Primary biliary cholangitis: pathogenesis and therapeutic opportunities

Primary biliary cholangitis is a chronic, seropositive and female-predominant inflammatory and cholestatic liver disease, which has a variable rate of progression towards biliary cirrhosis. Substantial progress has been made in patient risk stratification with the goal of personalized care, including early adoption of next-generation therapy with licensed use of obeticholic acid or off-label fibrate derivatives for those with insufficient benefit from ursodeoxycholic acid, the current first-line drug. The disease biology spans genetic risk, epigenetic changes, dysregulated mucosal immunity and altered biliary epithelial cell function, all of which interact and arise in the context of ill-defined environmental triggers. A current focus of research on nuclear receptor pathway modulation that specifically and potently improves biliary excretion, reduces inflammation and attenuates fibrosis is redefining therapy. Patients are benefiting from pharmacological agonists of farnesoid X receptor and peroxisome proliferator-activated receptors. Immunotherapy remains a challenge, with a lack of target definition, pleiotropic immune pathways and an interplay between hepatic immune responses and cholestasis, wherein bile acid-induced inflammation and fibrosis are dominant clinically. The management of patient symptoms, particularly pruritus, is a notable goal reflected in the development of rational therapy with apical sodium-dependent bile acid transporter inhibitors.

Evaluation of the Combined Use of Saccharomyces Cerevisiae and Aspergillus Oryzae with Phytase Fermentation Products on Growth, Inflammatory, and Intestinal Morphology in Broilers

Saccharomyces cerevisiae and Aspergillus oryzae are both ancient probiotic species traditionally used as microbes for brewing beer and soy sauce, respectively. This study investigated the effect of adding these two probiotics with phytase fermentation products to the broilers diet. Fermented products possess protease and cellulase, and the activities were 777.1 and 189.5 U/g dry matter (DM) on S. cerevisiae fermented products (SCFP) and 190 and 213.4 U/g DM on A. oryzae fermented products (AOFP), respectively. Liposaccharides stimulated PBMCs to produce nitric oxide to 120 μmol. Both SCFP and AOFP reduced lipopolysaccharides stimulated peripheral blood mononuclear cells (PBMCs) nitric oxide release to 40 and 60 μmol, respectively. Nevertheless, in an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, SCFP and AOFP also increased the survival rate of lipopolysaccharides stimulated PBMCs by almost two-fold compared to the negative control. A total of 240 broilers were divided into four groups as Control, SCFP 0.1% (SCFP), SCFP 0.05% + AOFP 0.05% (SAFP), and AOFP 0.1% (AOFP) groups, respectively. Each group had 20 broilers, and three replicate pens. The results showed that the addition of SCFP, SAFP, and AOFP groups did not affect the growth performances, but increased the jejunum value of villus height and villus: crypt ratio on SAFP and AOFP groups compared to the control and SCFP groups. Furthermore, adding SCFP, SAFP, and AOFP significantly reduced the number of Clostridium perfringens in ileum chyme. SCFP, SAFP, and AOFP significantly reduced the amount of interleukin-1β, inducible nitric oxide synthases, interferon-γ, and nuclear factor kappa B mRNA expression in PBMCs, especially in the AOFP group. In summary, all the SCFP, SAFP, and AOFP groups can be suggested as a functional feed additive since they enhanced villus: crypt ratio and decreased inflammation-related mRNA expression, especially for AOFP group in broilers.

Multiple innate antibacterial immune defense elements are correlated in diverse ungulate species

In this study, we aimed to evaluate to what extent different assays of innate immunity reveal similar patterns of variation across ungulate species. We compared several measures of innate antibacterial immune function across seven different ungulate species using blood samples obtained from captive animals maintained in a zoological park. We measured mRNA expression of two receptors involved in innate pathogen detection, toll-like receptors 2 and 5 (TLR2 and 5), the bactericidal capacity of plasma, as well as the number of neutrophils and lymphocytes. Species examined included aoudad (Ammotragus lervia), American bison (Bison bison bison), yak (Bos grunniens), Roosevelt elk (Cervus canadensis roosevelti), fallow deer (Dama dama), sika deer (Cervus nippon), and Damara zebra (Equus quagga burchellii). Innate immunity varied among ungulate species. However, we detected strong, positive correlations between the different measures of innate immunity-specifically, TLR2 and TLR5 were correlated, and the neutrophil to lymphocyte ratio was positively associated with TLR2, TLR5, and bacterial killing ability. Our results suggest that ecoimmunological study results may be quite robust to the choice of assays, at least for antibacterial innate immunity; and that, despite the complexity of the immune system, important sources of variation in immunity in natural populations may be discoverable with comparatively simple tools.

Progress in research of mechanism of biliary epithelial cell injury in primary biliary cholangitis

Primary biliary cholangitis (PBC) is an autoimmune liver disease characterized by chronic biliary cholestasis and progressive intrahepatic and small bile duct non- suppurative inflammation with early infiltration of inflammatory cells around biliary epithelial cells (BECs). BECs lining the bile duct express multiple receptors for pathogen-associated molecular patterns and can activate intracellular signaling pathways and participate in immune regulation. The etiology and pathogenesis of PBC are not fully understood yet, but the key step found in its pathogenesis is the targeted destruction of biliary cells. Since bile duct epithelial cells participate in a series of intrahepatic immune regulation processes, bile duct epithelial cell injury is an important mechanism involved in the development of intrahepatic inflammation in PBC. Therefore, understanding the mechanism of BEC injury can help us find some new targets for the treatment of PBC. This article briefly reviews the progress in the research of mechanism of biliary epithelial cell injury in PBC.

Cytotoxic activity and molecular targets of atractylodin in cholangiocarcinoma cells

Objectives

To evaluate the cytotoxic activity of atractylodin and its potential effects on heme oxygenase (HO)-1 production, STAT1/3 phosporylation and major NF-κB protein expression in the cholangiocarcinoma-associated cell line CL-6.

Methods

Standard MTT assay was used for accessing antiproliferative activity on CL-6 cells. Normal human embryonic fibroblast (OUMS) cell was taken as control cell line. Colony formation and wound healing assay were conducted to access the effects of atractylodin on cell proliferation and directional migration activity of CL-6 cells. Western blot was used for evaluating levels of protein expression and phosphorylation.

Key findings

Atractylodin exhibited selective cytotoxicity towards CL-6 as compared with OUMS with IC50 of 216.8 (212.4-233.8) and 351.2 (345.7-359.5) μm [median (range)], respectively. Exposure to the compound dose-dependently inhibited colony formation ability and decreased wound closure potential of CL-6 cells. Atractylodin treatment suppressed HO-1 production in CL-6 cells. It dose-dependently inhibited STAT1/3 protein phosphorylation and moderately inhibited NF-κB (p50), NF-κB (p52), and NF-κB (p65) protein expression in both dose- and time-dependent manner.

Conclusions

Atractylodin exerts significant cytotoxic activity against CL-6 cells which may be linked to its suppressive effect on HO-1 production, STAT1/3 phosphorylation and expression of key NF-κB proteins.

Pathophysiology of primary biliary cholangitis

Primary biliary cholangitis is a prototypical autoimmune disease characterized by an overwhelming female predominance, a distinct clinical phenotype, and disease specific anti-mitochondrial antibodies targeted against a well-defined auto-antigen. In a genetically susceptible host, multi-lineage loss of tolerance to the E2 component of the 2-oxo-dehydrogenase pathway and dysregulated immune pathways directed at biliary epithelial cells leads to cholestasis, progressive biliary fibrosis, and cirrhosis in a subset of patients. Several key insights have shed light on the complex pathogenesis of disease. First, characteristic anti-mitochondrial antibodies (AMAs) target lipoic acid containing immunodominant epitopes, particularly pyruvate dehydrogenase complex (PDC-E2), on the inner mitochondrial membrane of BECs. Next, breakdown of the protective apical bicarbonate rich umbrella may sensitize BECs to aberrant apoptotic pathways leaving the antigenic PDC-E2 epitope immunologically tact within an apoptotic bleb. A multi-lineage immune response ensues characterized by an imbalance between effector and regulatory activity resulting in progressive and self-perpetuating biliary injury. Genome wide studies shed light on important pathways involved in disease, key among them being IL-12. Epigenetic mechanisms and microRNAs may play help shed light on the missing heritability and female preponderance of disease. Taken together, these findings have dramatically advanced our understanding of disease and may lead to important therapeutic advances.

Sclerosing and obstructive cholangiopathy in biliary atresia: mechanisms and association with biliary innate immunity

Biliary atresia (BA) is histologically characterized by a progressive, sclerosing cholangitis and the obstruction of extrahepatic bile ducts. In terms of the etiology and pathogenesis of BA, several viral infections consisting of dsRNA, including Reoviridae, have been implicated. Human biliary epithelial cells (BECs) possess an innate immune system consisting of Toll-like receptors (TLRs). BECs have negative regulatory mechanisms of TLR tolerance to avoid an excessive inflammatory response to lipopolysaccharide (LPS), a TLR4 ligand; however, they lack the tolerance to poly(I:C) (a synthetic analog of viral dsRNA), a TLR3 ligand. Treatment with poly(I:C) induces the expression of the apoptosis-inducer TNF-related apoptosis-inducing ligand (TRAIL), along with the antiviral molecule IFN-β1, and reduces the viability of BECs by enhancing apoptosis. In response, surviving BECs increase their expression of various markers, including basic FGF [an epithelial-mesenchymal transition (EMT)-inducer], S100A4 (a mesenchymal marker), and Snail (a transcriptional factor), and decrease that of epithelial markers such as CK19 and E-cadherin before undergoing EMT. Extrahepatic bile ducts in BA infants frequently show a lack of epithelial markers and an aberrant expression of vimentin, in addition to the enhancement of TRAIL and apoptosis. dsRNA viruses may directly induce apoptosis and EMT in human BECs as a result of the biliary innate immune response, supporting the notion that Reoviridae infections may be directly associated with the pathogenesis of cholangiopathies in BA.

Growth inhibitory effect of β-eudesmol on cholangiocarcinoma cells and its potential suppressive effect on heme oxygenase-1 production, STAT1/3 activation, and NF-κB downregulation

Cholangiocarcinoma (CCA) is a progressively fatal form of cancer originating from the malignant transformation of hepatic biliary cholangiocytes. The present study reports for the first time in vitro growth inhibitory activities of β-eudesmol, the bioactive sesquiterpenoid present in the rhizome of Atractylodes lancea (Thunb) DC., with respect to its underlying potential effects on heme oxygenase-1 (HO-1) production, STAT1/3 phosphorylation, and NF-κB protein expression in human CCA cell line CL-6. The cytotoxic effect of β-eudesmol on CL-6 cells was evaluated by MTT assay using normal human embryonic fibroblast (OUMS) as a control cell line. Results indicated that β-eudesmol exhibited selective cytotoxicity towards CL-6 compared to OUMS with mean (±SD) IC₅₀ (concentration that inhibits cell growth by 50%) values of 166.75 ± 3.69 and 240.01 ± 16.54 μmol/L, respectively. In addition, it also significantly suppressed colony forming and wound healing ability of CL-6 cells in a concentration-dependent manner. Western blot analysis indicated that β-eudesmol treatment resulted in significant suppression of HO-1 production in CL-6 cells. Its inhibitory effects on the phosphorylation of STAT1/3 proteins and expression of NF-κB (p65 and p50) proteins were concentration-dependent. Taken together, these results suggest that β-eudesmol exerts significant growth inhibitory activity on CL-6 cells that may be linked to its inhibitory effect on the production of HO-1, phosphorylation of STAT1/3, and expression of major NF-κB proteins.

How the biliary tree maintains immune tolerance?

The liver is a vital organ with distinctive anatomy, histology and heterogeneous cell populations. These characteristics are of particular importance in maintaining immune homeostasis within the liver microenvironments, notably the biliary tree. Cholangiocytes are the first line of defense of the biliary tree against foreign substances, and are equipped to participate through various immunological pathways. Indeed, cholangiocytes protect against pathogens by TLRs-related signaling; maintain tolerance by expression of IRAK-M and PPARγ; limit immune response by inducing apoptosis of leukocytes; present antigen by expressing human leukocyte antigen molecules and costimulatory molecules; recruit leukocytes to the target site by expressing cytokines and chemokines. However, breach of tolerance in the biliary tree results in various cholangiopathies, exemplified by primary biliary cholangitis, primary sclerosing cholangitis and biliary atresia. Lessons learned from immune tolerance of the biliary tree will provide the basis for the development of effective therapeutic approaches against autoimmune biliary tract diseases. This article is part of a Special Issue entitled: Cholangiocytes in Health and Disease edited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

The role of macrophages in the development of biliary injury in a lipopolysaccharide-aggravated hepatic ischaemia-reperfusion model

INTRODUCTION

Endotoxins, in the form of lipopolysaccharides (LPS), are potent inducers of biliary injury. However the mechanism by which injury develops remains unclear. We hypothesized that hepatic macrophages are pivotal in the development of endotoxin-induced biliary injury and that no injury would occur in their absence.

MATERIAL AND METHODS

Clodronate liposomes were used to deplete macrophages from the liver. Forty-eight rats were equally divided across six study groups: sham operation (sham), liposome treatment and sham operation (liposomes+sham), 1mg/kg LPS i.p. (LPS), liposome treatment and LPS administration (liposomes+LPS), hepatic ischaemia-reperfusion injury with LPS administration (IRI+LPS) and liposome treatment followed by IRI+LPS (liposomes+IRI+LPS). Following 6h of reperfusion, blood, bile, and liver tissue was collected for further analysis. Small bile duct injury was assessed, serum liver tests were performed and bile composition was evaluated. The permeability of the blood-biliary barrier (BBB) was assessed using intravenously administered horseradish peroxidase (HRP).

RESULTS

The presence of hepatic macrophages was reduced by 90% in LPS and IRI+LPS groups pre-treated with clodronate liposomes (P<0.001). Severe small bile duct injury was not affected by macrophage depletion, and persisted in the liposomes+IRI+LPS group (50% of animals) and liposomes+LPS group (75% of animals). Likewise, BBB impairment persisted following macrophage depletion. LPS-induced elevation of the chemokine Mcp-1 in bile was not affected by macrophage depletion.

CONCLUSIONS

Depletion of hepatic macrophages did not prevent development of biliary injury following LPS or LPS-enhanced IRI. Cholangiocyte activation rather than macrophage activation may underlie this injury. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

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.

Oridonin derivative ameliorates experimental colitis by inhibiting activated T-cells and translocation of nuclear factor-kappa B

OBJECTIVE

To confirm the potential therapeutic efficacy of HAO472 against inflammatory bowel disease (IBD), we investigated the modulatory functions of HAO472 in a mouse model of trinitrobenzene sulfonic acid (TNBS)-induced colitis.

METHODS

Colitis was induced via an intrarectal injection of TNBS in mice. HAO472 (5.0 mg/kg or 7.5 mg/kg) or 1 mg/kg dexamethasone (DX) was injected intraperitoneally into the mice after the TNBS administration. Behavioral and weight changes, macroscopic and histological assessments of colon, the expressions of tumor necrosis factor (TNF)-α, interferon (IFN)-γ and interleukin (IL)-17A, cyclooxygenase (COX)-2, inducible nitric oxide synthase (iNOS) and nuclear factor-kappa B (NF-κB) in the colonic tissues were evaluated. The effect of HAO472 on NF-κB signaling pathway in lymphocytes was also invesigated.

RESULTS

HAO472 significantly ameliorated the clinical symptoms, reduced the severity of the inflammation and decreased mortality in the mouse model. HAO472 also reduced TNF-α, IFN-γ, IL-17A, iNOS/COX-2 and lymphocyte proliferation. These changes were associated with a significant decrease in NF-κB p65 expression and activity.

CONCLUSION

HAO472 has positive effects on TNBS-induced colitis by modulating the subsets and functions of lymphocytes, suppressing inflammation and inhibiting the nuclear translocation of NF-κB p65 subunits.

The Riddle of Nonalcoholic Fatty Liver Disease: Progression From Nonalcoholic Fatty Liver to Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver (NAFL) is an emerging global epidemic which progresses to nonalcoholic steatohepatitis (NASH) and cirrhosis in a subset of subjects. Various reviews have focused on the etiology, epidemiology, pathogenesis and treatment of NAFLD. This review highlights specifically the triggers implicated in disease progression from NAFL to NASH. The integrating role of genes, dietary factors, innate immunity, cytokines and gut microbiome have been discussed.

Lipopolysaccharide (LPS)-Induced Biliary Epithelial Cell NRas Activation Requires Epidermal Growth Factor Receptor (EGFR)

Cholangiocytes (biliary epithelial cells) actively participate in microbe-induced proinflammatory responses in the liver and contribute to inflammatory and infectious cholangiopathies. We previously demonstrated that cholangiocyte TLR-dependent NRas activation contributes to proinflammatory/ proliferative responses. We test the hypothesis that LPS-induced activation of NRas requires the EGFR. SV40-transformed human cholangiocytes (H69 cells), or low passage normal human cholangiocytes (NHC), were treated with LPS in the presence or absence of EGFR or ADAM metallopeptidase domain 17 (TACE) inhibitors. Ras activation assays, quantitative RT-PCR, and proliferation assays were performed in cells cultured with or without inhibitors or an siRNA to Grb2. Immunofluorescence for phospho-EGFR was performed on LPS-treated mouse samples and specimens from patients with primary sclerosing cholangitis, primary biliary cirrhosis, hepatitis C, and normal livers. LPS-treatment induced an association between the TLR/MyD88 and EGFR/Grb2 signaling apparatus, NRas activation, and EGFR phosphorylation. NRas activation was sensitive to EGFR and TACE inhibitors and correlated with EGFR phosphorylation. The TACE inhibitor and Grb2 depletion prevented LPS-induced IL6 expression (p<0.05) and proliferation (p<0.01). Additionally, cholangiocytes from LPS-treated mouse livers and human primary sclerosing cholangitis (PSC) livers exhibited increased phospho-EGFR (p<0.01). Moreover, LPS-induced mouse cholangiocyte proliferation was inhibited by concurrent treatment with the EGFR inhibitor, Erlotinib. Our results suggest that EGFR is essential for LPS-induced, TLR4/MyD88-mediated NRas activation and induction of a robust proinflammatory cholangiocyte response. These findings have implications not only for revealing the signaling potential of TLRs, but also implicate EGFR as an integral component of cholangiocyte TLR-induced proinflammatory processes.

Autophagy and senescence in fibrosing cholangiopathies

Fibrosing cholangiopathy such as primary sclerosing cholangitis (PSC) and biliary atresia (BA) is characterized by biliary epithelial injuries and concentric fibrous obliteration of the biliary tree together with inflammatory cell infiltration. In these diseases, inappropriate innate immunity is reported to contribute more to bile duct pathology as compared with various aspects of "classical" autoimmune diseases. Primary biliary cirrhosis (PBC) is characterized by chronic cholangitis with bile duct loss and classical autoimmune features. Cellular senescence of cholangiocytes and a senescence-associated secretory phenotype lead to the production of proinflammatory cytokines and chemokines that may modify the milieu of the bile duct and then trigger fibroinflammatory responses in PSC and PBC. Furthermore, deregulated autophagy might be involved in cholangiocyte senescence and possibly in the autoimmune process in PBC, and the deregulated innate immunity against enteric microbes or their products that is associated with cholangiocyte senescence might result in the fibrosing cholangitis that develops in PBC and PSC. In BA, innate immunity against double-stranded RNA viruses might be involved in cholangiocyte apoptosis and also in the development of the epithelial-mesenchymal transition of cholangiocytes that results in fibrous obliteration of bile ducts. These recent advances in the understanding of immune-mediated biliary diseases represent a paradigm shift: the cholangiocyte is no longer viewed merely as a passive victim of injury; it is now also considered to function as a potential effector in bile duct pathology.

Immune function of biliary epithelial cells

Biliary epithelial cells (BECs) are the epithelial cells lining the bile duct, constituting the biliary system's first line of defense against pathogenic microorganisms. BECs can express many kinds of pathogen recognition receptors, activate intracellular signal transduction pathways, initiate the internal microbial defense system, including the release of pro-inflammatory cytokines and chemokines and antibacterial peptide synthesis, and maintain the integrity of the biliary epithelium. By expressing and releasing adhesion molecules and immune mediators, BECs interact with other cells in the liver, such as lymphocytes and Kupffer's cells. BECs are involved in a complex feedback mechanism of liver cells and thereby regulate the response to microbial infection. BECs actively participate in the biliary duct mucosal immunity and form an important component of liver immunity.

Mechanisms of tissue injury in autoimmune liver diseases

Autoimmune diseases affecting the liver are mainly represented by autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC). The characteristic morphologic patterns of injury are a chronic hepatitis pattern of damage in AIH, destruction of small intrahepatic bile ducts in PBC and periductal fibrosis and inflammation involving larger bile ducts in PSC. The factors responsible for initiation and perpetuation of the injury in all the three autoimmune liver diseases are not understood completely but are likely to be environmental triggers on the background of genetic variation in immune regulation. In this review, we summarise the current understanding of the mechanisms underlying the breakdown of self-tolerance in autoimmune liver diseases.

Role of cholangiocytes in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by selective destruction of intrahepatic cholangiocytes. Mechanisms underlying the development and progression of the disease are still controversial and largely undefined. Evidence suggests that PBC results from an articulated immunologic response against an immunodominant mitochondrial autoantigen, the E2 component of the pyruvate dehydrogenase complex (PDC-E2); characteristics of the disease are also the presence of disease-specific antimitochondrial autoantibodies (AMAs) and autoreactive CD4 and CD8 T cells. Recent evidence suggests that cholangiocytes show specific immunobiological features that are responsible for the selective targeting of those cells by the immune system. The immune reaction in PBC selectively targets small sized, intrahepatic bile ducts; although a specific reason for that has not been defined yet, it has been established that the biliary epithelium displays a unique heterogeneity, for which the physiological and pathophysiological features of small and large cholangiocytes significantly differ. In this review article, the authors provide a critical overview of the current evidence on the role of cholangiocytes in the immune-mediated destruction of the biliary tree that characterizes PBC.

Role of innate immune response in non-alcoholic Fatty liver disease: metabolic complications and therapeutic tools

Non-alcoholic fatty liver disease (NAFLD) is currently the most common liver disease worldwide, both in adults and children. It is characterized by an aberrant lipid storage in hepatocytes, named hepatic steatosis. Simple steatosis remains a benign process in most affected patients, while some of them develop superimposed necroinflammatory activity with a non-specific inflammatory infiltrate and a progression to non-alcoholic steatohepatitis with or without fibrosis. Deep similarity and interconnections between innate immune cells and those of liver parenchyma have been highlighted and showed to play a key role in the development of chronic liver disease. The liver can be considered as an “immune organ” because it hosts non-lymphoid cells, such as macrophage Kupffer cells, stellate and dendritic cells, and lymphoid cells. Many of these cells are components of the classic innate immune system, enabling the liver to play a major role in response to pathogens. Although the liver provides a “tolerogenic” environment, aberrant activation of innate immune signaling may trigger “harmful” inflammation that contributes to tissue injury, fibrosis, and carcinogenesis. Pathogen recognition receptors, such as toll-like receptors and nucleotide oligomerization domain-like receptors, are responsible for the recognition of immunogenic signals, and represent the major conduit for sensing hepatic and non-hepatic noxious stimuli. A pivotal role in liver inflammation is also played by cytokines, which can initiate or have a part in immune response, triggering hepatic intracellular signaling pathways. The sum of inflammatory signals and deranged substrate handling induce most of the metabolic alteration traits: insulin resistance, obesity, diabetes, hyperlipidemia, and their compounded combined effects. In this review, we discuss the relevant role of innate immune cell activation in relation to NAFLD, the metabolic complications associated to this pathology, and the possible pharmacological tools.

Toll-like receptors and liver disease

Toll-like receptors (TLRs) are pattern recognition receptors that play an important role in host defence by recognizing pathogen-associated molecular patterns (PAMP). Recent studies indicate that TLR signalling plays an important role in progression of chronic liver diseases. Ongoing clinical trials suggest that therapeutic manipulation of TLR pathways may offer novel means of reversing chronic liver diseases. Upon activation by their respective ligands, TLRs initiate an intracellular pro-inflammatory/anti-inflammatory signalling cascade via recruitment of various adaptor proteins. TLR associated signalling pathways are tightly regulated to keep a check on inappropriate production of pro-inflammatory cytokines and interferons thereby preventing various autoimmune and inflammatory processes. Herein, we review the current state of knowledge of hepatic distribution, signalling pathways and therapeutic modulation of TLRs in chronic liver diseases.

Apotopes and innate immune system: novel players in the primary biliary cirrhosis scenario

Our understanding of primary biliary cirrhosis has been rapidly growing over the past decade and the disease is now regarded as a model for other female-predominant, organ-specific autoimmune conditions. Primary biliary cirrhosis ensues from a multi-lineage loss of tolerance to the E2 component of the pyruvate dehydrogenase complex. One of the major unanswered questions in the pathogenesis of primary biliary cirrhosis is the specificity of small intrahepatic bile ducts attack while PDC-E2 is present in mitochondria of all nucleated cells. Recent findings suggest that the uniqueness of the primary target tissue, biliary epithelium, may be of considerable importance for understanding primary biliary cirrhosis and that the biliary epithelial cell is more than an innocent victim. Rather, it attracts an immune attack by virtue of the unique apoptotic mechanisms and by the way it handles PDC-E2. Moreover, recent evidence suggests that apoptotic bodies of biliary epithelial cell are able to activate the innate immune system in the presence of anti-mitochondrial antibodies. This review article is intended to provide a critical overview of the role of apoptosis in biliary epithelial cells, the activation of the innate immune system, and its biological and clinical significance in primary biliary cirrhosis.

The immunophysiology and apoptosis of biliary epithelial cells: primary biliary cirrhosis and primary sclerosing cholangitis

Biliary epithelial cells (BECs) provide the first line of defense against lumenal microbes in the biliary system. BECs express a variety of pathogen recognition receptors and can activate several intracellular signaling cascades to initiate antimicrobial defenses, including production of several anti-microbial peptides, cytokines, chemokines, and adhesion molecules. BECs also secrete immunoglobulin A and interact with other cells through expression and release of adhesion molecules and immune mediators. Recently, several reports suggest a correlation between apoptosis and autoimmunity through ineffective clearance of self-antigens. Primary biliary cirrhosis (PBC) is a slowly progressive, autoimmune cholestatic liver disease characterized by highly specific antimitochondrial antibodies (AMAs) and the specific immune-mediated destruction of BECs. We have demonstrated that the AMA self-antigen, namely the E2 subunit of the pyruvate dehydrogenase complex, is detectable in its antigenically reactive form within apoptotic blebs from human intrahepatic biliary epithelial cells and activates innate immune responses. Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease characterized by inflammation and the presence of concentric fibrosis of intrahepatic and/or extrahepatic bile ducts, eventually leading to cirrhosis. However, apoptosis does not appear to play a central role in PSC. Despite both diseases involving immune-mediated injury to bile ducts, apoptosis occurs more commonly overall in PBC where it likely plays a unique role.

The dynamic biliary epithelia: molecules, pathways, and disease

Cholangiocytes, the cells lining bile ducts, are a heterogenous, highly dynamic population of epithelial cells. While these cells comprise a small fraction of the total cellular component of the liver, they perform the essential role of bile modification and transport of biliary and blood constituents. From a pathophysiological standpoint, cholangiocytes are the target of a diverse group of biliary disorders, collectively referred to as the cholangiopathies. To date, the cause of most cholangiopathies remains obscure. It is known, however, that cholangiocytes exist in an environment rich in potential mediators of cellular injury, express receptors that recognize potential injurious insults, and participate in portal tract repair processes following hepatic injury. As such, cholangiocytes may not be only a passive target, but are likely directly and actively involved in the pathogenesis of cholangiopathies. Here, we briefly summarize the characteristics of the reactive cholangiocyte and cholangiocyte responses to potentially injurious endogenous and exogenous molecules, and in addition, present emerging concepts in our understanding of the etiopathogenesis of several cholangiopathies.

Advances in cholangiocyte immunobiology

Cholangiocytes, or bile duct epithelia, were once thought to be the simple lining of the conduit system comprising the intra- and extrahepatic bile ducts. Growing experimental evidence demonstrated that cholangiocytes are in fact the first line of defense of the biliary system against foreign substances. Experimental advances in recent years have unveiled previously unknown roles of cholangiocytes in both innate and adaptive immune responses. Cholangiocytes can release inflammatory modulators in a regulated fashion. Moreover, they express specialized pattern-recognizing molecules that identify microbial components and activate intracellular signaling cascades leading to a variety of downstream responses. The cytokines secreted by cholangiocytes, in conjunction with the adhesion molecules expressed on their surface, play a role in recruitment, localization, and modulation of immune responses in the liver and biliary tract. Cholangiocyte survival and function is further modulated by cytokines and inflammatory mediators secreted by immune cells and cholangiocytes themselves. Because cholangiocytes act as professional APCs via expression of major histocompatibility complex antigens and secrete antimicrobial peptides in bile, their role in response to biliary infection is critical. Finally, because cholangiocytes release mediators critical to myofibroblastic differentiation of portal fibroblasts and hepatic stellate cells, cholangiocytes may be essential in the pathogenesis of biliary cirrhosis.

Cutting-edge issues in primary biliary cirrhosis

Several crucial issues remain open in our understanding of primary biliary cirrhosis (PBC), an autoimmune liver disease targeting the small- and medium-sized intrahepatic bile ducts. These issues include the high tissue specificity of the autoimmune injury despite the nontraditional autoantigens found in all mitochondria recognized by PBC-associated autoantibodies, the causes of the commonly observed pruritus, and the disease etiology per se. In all these fields, there has been recent interest secondary to the use of large-scale efforts (such as genome-wide association studies) that were previously considered poorly feasible in a rare disease such as PBC as well as other intuitions. Accordingly, there are now fascinating theories to explain the onset and severity of pruritus due to elevated autotaxin levels, the peculiar apoptotic features of bile duct cells to explain the tissue specificity, and genomic and epigenetic associations contributing to disease susceptibility. We have arbitrarily chosen these four aspects as the most promising in the PBC recent literature and will provide herein a discussion of the recent data and their potential implications.

Etiopathogenesis of primary biliary cirrhosis: an overview of recent developments

Substantial advancements in the field of primary biliary cirrhosis (PBC) research have broadened our understanding of this enigmatic disease. Genome-wide studies have identified several new candidate genes involved in the immunoregulatory process, particularly those responsible for antigen presentation and lymphocyte signaling. Examples include the HLA class-II region and genes implicated in IL12-JAK/STAT signaling, and the NF-κB and TNF signaling pathways. Environmental triggers appear to disrupt the pre-existing, unstable immune tolerance in genetically susceptible individuals, and molecular mimics of the PBC-specific autoantigen (PDC) may be derived from microbes or xenobiotic compounds, which modify native proteins, making them immunogenic. Although the vast majority of patients with PBC are AMA-positive, a variety of disease-specific antinuclear antibodies have been recognized in conferring a worse clinical outcome. There has also been a revived interest in the role of antibody-secreting B cells in murine models suggesting that depletion of these cells paradoxically exacerbates cholangiopathy. Biliary specificity in PBC is most likely driven by the uniqueness of cholangiocyte apoptosis in which the PDC-E2 autoantigen undergoes differential glutathiolation. Cholangiocytes also possess the ability to phagocytose neighboring apoptotic cells, present intact immunoreactive antigen, and undergo attack from autoantibodies, the innate immune system, and autoreactive lymphocytes. Cellular senescence and a lack of functioning T-regulatory cells are proposed mechanisms by which this multi-lineage process is thought to be enhanced. This review summarizes these key advances as the true complexities of the disease process begin to be unraveled.

HIV Infection and TLR Signalling in the Liver

Despite the availability of effective combination antiretroviral therapy (cART), liver disease is one of the leading causes of morbidity and mortality in Human Immunodeficiency Virus (HIV)-infected individuals, specifically, in the presence of viral hepatitis coinfection. HIV, a single stranded RNA virus, can bind to and activate both Toll-like receptor (TLR)7 and TLR8 in circulating blood mononuclear cells, but little is known about the effect of HIV on TLRs expressed in the liver. HIV can directly infect cells of the liver and HIV-mediated depletion of CD4+ T-cells in the gastrointestinal tract (GI tract) results in increased circulating lipopolysaccharide (LPS), both of which may impact on TLR signaling in the liver and subsequent liver disease progression. The potential direct and indirect effects of HIV on TLR signaling in the liver will be explored in this paper.

Cholangiopathy with respect to biliary innate immunity

Biliary innate immunity is involved in the pathogenesis of cholangiopathies in cases of biliary disease. Cholangiocytes possess Toll-like receptors (TLRs) which recognize pathogen-associated molecular patterns (PAMPs) and play a pivotal role in the innate immune response. Tolerance to bacterial PAMPs such as lipopolysaccharides is also important to maintain homeostasis in the biliary tree, but tolerance to double-stranded RNA (dsRNA) is not found. Moreover, in primary biliary cirrhosis (PBC) and biliary atresia, biliary innate immunity is closely associated with the dysregulation of the periductal cytokine milieu and the induction of biliary apoptosis and epithelial-mesenchymal transition (EMT), forming in disease-specific cholangiopathy. Biliary innate immunity is associated with the pathogenesis of various cholangiopathies in biliary diseases as well as biliary defense systems.

Enhanced innate immune responsiveness and intolerance to intestinal endotoxins in human biliary epithelial cells contributes to chronic cholangitis

BACKGROUND

Pattern recognition receptors (PRRs) orchestrate the innate immune defence in human biliary epithelial cells (BECs). Tight control of PRR signalling provides tolerance to physiological amounts of intestinal endotoxins in human bile to avoid constant innate immune activation in BECs.

AIMS

We wanted to determine whether inappropriate innate immune responses to intestinal endotoxins contribute to the development and perpetuation of chronic biliary inflammation.

METHODS

We examined PRR-mediated innate immune responses and protective endotoxin tolerance in primary BECs isolated from patients with primary sclerosing cholangitis (PSC), alcoholic liver disease and patients without chronic liver disease. Expression studies comprised northern blots, RT-PCR, Western blots and immunocytochemistry. Functional studies comprised immuno-precipitation Western blots, FACS for endotoxin uptake, and NF-κB activation assays and ELISA for secreted IL-8 and tumour necrosis factor (TNF)-α.

RESULTS

Primary BECs from explanted PSC livers showed reversibly increased TLR and NOD protein expression and activation of the MyD88/IRAK signalling complex. Consecutively, PSC BECs exhibited inappropriate innate immune responses to endotoxins and did not develop immune tolerance after repeated endotoxin exposures. This endotoxin hyper-responsiveness was probably because of the stimulatory effect of abundantly expressed IFN-γ and TNF-α in PSC livers, which stimulated TLR4-mediated endotoxin signalling in BECs, leading to increased TLR4-mediated endotoxin incorporation and impaired inactivation of the TLR4 signalling cascade. As TNF-α inhibition partly restored protective innate immune tolerance, endogenous TNF-α secretion probably contributed to inappropriate endotoxin responses in BECs.

CONCLUSION

Inappropriate innate immune responses to intestinal endotoxins and subsequent endotoxin intolerance because of enhanced PRR signalling in BECs probably contribute to chronic cholangitis.

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.

Toll-like receptors in acute liver injury and regeneration

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

Significance of periductal Langerhans cells and biliary epithelial cell-derived macrophage inflammatory protein-3α in the pathogenesis of primary biliary cirrhosis

BACKGROUND/AIMS

To clarify the primary biliary cirrhosis (PBC)-specific antigen-presenting mechanism, we examined the distribution and phenotypic characteristics of infiltrating dendritic cells (DCs) with respect to bile ducts and the mechanism of migration in terms of the periductal cytokine milieu and biliary innate immunity.

METHODS AND RESULTS

Immunohistochemistry using liver sections from patients with PBC and controls revealed that blood dendritic cell antigen (BDCA)-2(+) plasmacytoid DCs were found mainly in the portal tracts in PBC and the controls, but their distribution was not related to bile ducts. BDCA-1(+) and CD19(-) myeloid DCs were also found in portal tracts in PBC and the controls and, in particular, Langerin+Langerhans cells (LCs) were dominantly scattered around or within biliary epithelial layers of the damaged bile ducts in PBC. Moreover, experiments with cultured human biliary epithelial cells (BECs) showed that an LC-attracting chemokine, macrophage inflammatory protein-3α, was produced by BECs in the response to cytokines [interleukin (IL)-1β, tumour necrosis factor-α and IL-17] and pathogen-associated molecular patterns.

CONCLUSIONS

LCs existing around or within biliary epithelial layers are important as periductal antigen-presenting cells in PBC and the migration of LCs into bile ducts is closely associated with the periductal cytokine milieu and biliary innate immunity in PBC.