Enhanced expression of type I interferon and toll-like receptor-3 in primary biliary cirrhosis

The liver as a central "hub" of the immune system: pathophysiological implications

The purpose of this review is to describe the immune function of the liver, guiding the reader from the homeostatic tolerogenic status to the aberrant activation demonstrated in chronic liver disease. An extensive description of the pathways behind the inflammatory modulation of the healthy liver will be provided focusing on the complex immune cell network residing within the liver. The limit of tolerance will be presented in the context of organ transplantation, seizing the limits of homeostatic mechanisms that fail in accepting the graft, progressing eventually toward rejection. The triggers and mechanisms behind chronic activation in metabolic liver conditions and viral hepatitis will be discussed. The last part of the review will be dedicated to one of the greatest paradoxes for a tolerogenic organ, developing autoimmunity. Through the description of the three most common autoimmune liver diseases, the autoimmune reaction against hepatocytes and biliary epithelial cells will be dissected.

Functional Polarization of Liver Macrophages by Glyco Gold Nanoparticles

Macrophages are crucial drivers of innate immunity. Reprogramming macrophages to a restorative phenotype in cancer or autoimmune diseases can stop their cancer-promoting activity or trigger anti-inflammatory immunity. Glycans have emerged as key components for immunity as they are involved in many pathophysiological disorders. Previous studies have demonstrated that supraphysiological amounts of mannose (Man) or sialic acid (Sia) can inhibit tumor growth and stimulate differentiation of regulatory T cells. Man is known to affect glucose metabolism in glycolysis by competing for the same intracellular transporters and affecting macrophage polarization, whereas Sia alters macrophage differentiation via signaling through Siglec-1. Herein, this work describes a macrophage targeting platform using gold nanoparticles (GNPs) functionalized with Man and Sia monosaccharides which exhibit high liver tropism. A single dose of glyco-GNPs can convert macrophages to a restorative phenotype in two completely different immune environments. Man promotes tumor-associated macrophages toward an antitumorigenic activity in a MC38 liver colorectal cancer model by secretion of TNF-α, IL -1β, and IL -6 in the tumor microenvironment. However, in a proinflammatory environment, as observed in a mouse model of autoimmune disease, primary biliary cholangitis, Man impairs the production of TNF-α, IL-1β, Arg1, and IL-6 cytokines. The results probe the dual role of Man in macrophage repolarization in response to the immune system. This study is a proof-of-concept that demonstrates that nanomedicine using specific glycans designed to target other immune cells such as myeloid cells, are a promising strategy not only against cancer but also against other pathologies such as autoimmune diseases.

Increased type-I interferon level is associated with liver damage and fibrosis in primary sclerosing cholangitis

BACKGROUND

The level of type-I interferons (IFNs) in primary sclerosing cholangitis (PSC) was investigated to evaluate its association with disease activity and progression.

METHODS

Bioactive type-I IFNs were evaluated in a murine model of PSC and human patients' sera using a cell-based reporter assay and ELISA techniques. In total, 57 healthy participants, 71 PSC, and 38 patients with primary biliary cholangitis were enrolled in this study.

RESULTS

Bioactive type-I IFNs were elevated in the liver and serum of multidrug resistance protein 2-deficient animals and showed a correlation with the presence of CD45+ immune cells and serum alanine transaminase levels. Concordantly, bioactive type-I IFNs were elevated in the sera of patients with PSC as compared to healthy controls (sensitivity of 84.51%, specificity of 63.16%, and AUROC value of 0.8267). Bioactive IFNs highly correlated with alkaline phosphatase (r=0.4179, p<0.001), alanine transaminase (r=0.4704, p<0.0001), and gamma-glutamyl transpeptidase activities (r=0.6629, p<0.0001) but not with serum bilirubin. In addition, patients with PSC with advanced fibrosis demonstrated significantly higher type-I IFN values. Among the type-I IFN subtypes IFNα, β and IFNω could be detected in patients with PSC with IFNω showing the highest concentration among the subtypes and being the most abundant among patients with PSC.

CONCLUSIONS

The selectively elevated bioactive type-I IFNs specifically the dominating IFNω could suggest a novel inflammatory pathway that might also have a hitherto unrecognized role in the pathomechanism of PSC.

Regulation of CD47 expression on CD14+ monocytes by interferon-α in PBC patients

Background

Primary biliary cholangitis (PBC) is a chronic intrahepatic cholestatic autoimmune liver disease characterized by inflammatory injury of small and medium-sized bile ducts in the liver. The pathogenesis of PBC has yet to be entirely understood. CD47/signal-regulatory protein alpha (SIRPα) is closely related to developing autoimmune diseases by promoting inflammatory response. However, the effect of CD47/SIRPα on inflammatory response in PBC patients is still unclear.

Objective

We investigated the expression of CD47/SIRPα and the effect of inflammatory cytokines on the CD47 expression, analyzed potential autoantibodies against CD47 and the effect of anti-CD47 antibody on the inflammatory response in PBC, provided laboratory basis for the study of the pathogenesis and targets for non-invasive diagnosis and treatment on PBC.

Methods

The expression levels of CD47 and SIRPα on peripheral blood mononuclear cells (PBMC) were measured in 14 patients with PBC (the PBC group) and 13 healthy subjects (the Control group) by flow cytometry (FCM). The PBMC derived from healthy subjects were stimulated with healthy subjects' serum, PBC patients' serum, IFN-α or TNF-α, and the CD47 expression level on CD14+ monocytes was detected by FCM. The level of serum anti-CD47 antibody or IFN-α in PBC patients and healthy subjects was analyzed by ELISA. FCM was used to examine the TNF-α expression level in CD14+ monocytes of healthy subjects stimulated with isotype control antibody, anti-CD47 antibody, LPS or LPS combined with CD47 antibody.

Results

The CD47 expression level on the CD14+ monocytes in PBC patients was statistically higher than that in the Control group (P<0.01). Compared with the Control group (PBMC+healthy serum), the CD47 expression on CD14+ monocyte stimulated with the PBC patients' serum (PBMC+PBC patients' serum) was increased (P<0.001); the CD47 expression on CD14+ monocyte stimulated with IFN-α (PBMC + IFN-α) increased gradually with the increased concentration of IFN-α (P<0.05). However, there was no similar trend on CD14+ monocyte stimulated with the TNF-α (PBMC+TNF-α) (P>0.05). The levels of serum anti-CD47 antibody and IFN-α in the PBC patients were higher than those in healthy subjects (P<0.05). The TNF-α expression level in CD14+ monocyte stimulated with the LPS (PBMC+LPS) or anti-CD47 antibody+LPS group (PBMC+LPS+anti-CD47 antibody) was significantly increased than that in the Control group (PBMC+isotype control antibody) (P<0.01 and P<0.001, respectively). The TNF-α expression level in CD14+ monocyte stimulated with the anti-CD47 antibody + LPS was higher than that with the LPS (P< 0.05).

Conclusion

The CD47 may be related to the pathogenesis of PBC by inflammatory response. The CD47/SIRPα signal were imbalanced in PBC patients. The presence of serum anti-CD47 antibodies in PBC patients provides a laboratory basis for clinical diagnosis and treatment.

The Genetics of Primary Biliary Cholangitis: A GWAS and Post-GWAS Update

Primary biliary cholangitis (PBC) is a chronic, progressive cholestatic liver disease in which the small intrahepatic bile ducts are destroyed by autoimmune reactions. Among autoimmune diseases, which are polygenic complex traits caused by the combined contribution of genetic and environmental factors, PBC exhibits the strongest involvement of genetic heritability in disease development. As at December 2022, genome-wide association studies (GWASs) and associated meta-analyses identified approximately 70 PBC susceptibility gene loci in various populations, including those of European and East Asian descent. However, the molecular mechanisms through which these susceptibility loci affect the pathogenesis of PBC are not fully understood. This study provides an overview of current data regarding the genetic factors of PBC as well as post-GWAS approaches to identifying primary functional variants and effector genes in disease-susceptibility loci. Possible mechanisms of these genetic factors in the development of PBC are also discussed, focusing on four major disease pathways identified by in silico gene set analyses, namely, (1) antigen presentation by human leukocyte antigens, (2) interleukin-12-related pathways, (3) cellular responses to tumor necrosis factor, and (4) B cell activation, maturation, and differentiation pathways.

Liver immunity, autoimmunity, and inborn errors of immunity

The liver is the front line organ of the immune system. The liver contains the largest collection of phagocytic cells in the body that detect both pathogens that enter through the gut and endogenously produced antigens. This is possible by the highly developed differentiation capacity of the liver immune system between self-antigens or non-self-antigens, such as food antigens or pathogens. As an immune active organ, the liver functions as a gatekeeping barrier from the outside world, and it can create a rapid and strong immune response, under unfavorable conditions. However, the liver's assumed immune status is anti-inflammatory or immuno-tolerant. Dynamic interactions between the numerous populations of immune cells in the liver are key for maintaining the delicate balance between immune screening and immune tolerance. The anatomical structure of the liver can facilitate the preparation of lymphocytes, modulate the immune response against hepatotropic pathogens, and contribute to some of its unique immunological properties, particularly its capacity to induce antigen-specific tolerance. Since liver sinusoidal endothelial cell is fenestrated and lacks a basement membrane, circulating lymphocytes can closely contact with antigens, displayed by endothelial cells, Kupffer cells, and dendritic cells while passing through the sinusoids. Loss of immune tolerance, leading to an autoaggressive immune response in the liver, if not controlled, can lead to the induction of autoimmune or autoinflammatory diseases. This review mentions the unique features of liver immunity, and dysregulated immune responses in patients with autoimmune liver diseases who have a close association with inborn errors of immunity have also been the emphases.

Treatment with a JAK1/2 inhibitor ameliorates murine autoimmune cholangitis induced by IFN overexpression

The interferon (IFN) signaling pathways are major immunological checkpoints with clinical significance in the pathogenesis of autoimmunity. We have generated a unique murine model named ARE-Del, with chronic overexpression of IFNγ, by altering IFNγ metabolism. Importantly, these mice develop an immunologic and clinical profile similar to patients with primary biliary cholangitis, including high titers of autoantibodies and portal inflammation. We hypothesized that the downregulation of IFN signaling pathways with a JAK1/2 inhibitor would inhibit the development and progression of cholangitis. To study this hypothesis, ARE-Del+/- mice were treated with the JAK1/2 inhibitor ruxolitinib and serially studied. JAK inhibition resulted in a significant reduction in portal inflammation and bile duct damage, associated with a significant reduction in splenic and hepatic CD4+ T cells and CD8+ T cells. Functionally, ruxolitinib inhibited the secretion of the proinflammatory cytokines IFNγ and TNF from splenic CD4+ T cells. Additionally, ruxolitinib treatment also decreased the frequencies of germinal center B (GC B) cells and T follicular helper (Tfh) cells and led to lower serological AMA levels. Of note, liver and peritoneal macrophages were sharply decreased and polarized from M1 to M2 with a higher level of IRF4 expression after ruxolitinib treatment. Mechanistically, ruxolitinib inhibited the secretion of IL-6, TNF and MCP1 and the expression of STAT1 but promoted the expression of STAT6 in macrophages in vitro, indicating that M1 macrophage polarization to M2 occurred through activation of the STAT6-IRF4 pathway. Our data highlight the significance, both immunologically and clinically, of the JAK/STAT signaling pathway in autoimmune cholangitis.

The Proinflammatory Cytokines IL-18, IL-21, and IFN-γ Differentially Regulate Liver Inflammation and Anti-Mitochondrial Antibody Level in a Murine Model of Primary Biliary Cholangitis

Primary biliary cholangitis (PBC) is a cholestatic liver disease primarily featured by autoimmune-mediated damage of intrahepatic small- and medium-sized bile ducts. Elevated serum proinflammatory cytokines, serum anti-mitochondrial antibodies (AMAs), liver inflammation, and fibrosis are also hallmarks of PBC disease. However, whether the elevated proinflammatory cytokines play a role in autoimmune cholangitis remains unknown. Herein, we utilized the p40-/-IL-2Rα-/- PBC mouse model to investigate the roles of proinflammatory cytokines IL-18, IL-21, and IFN-γ in the onset and progression of PBC. IL-18-/-, IFN-γ-/-, and IL-21-/- mice were crossed with p40-/-IL-2Ra+/- mice, respectively, to produce corresponding cytokine-deficient PBC models. Autoantibody level, liver inflammation, and bile duct injury were analyzed. We found that livers from p40-/-IL-2Rα-/- mice exhibit similar transcriptomic characters of PBC patients. In p40-/-IL-2Rα-/- mice, deletion of IL-18 has no remarkable effect on disease progression, while deletion of IL-21 indicates that it is necessary for AMA production but independent of liver inflammation and cholangitis. IFN-γ is responsible for both AMA production and liver inflammation in our model. Our results demonstrate that different proinflammatory cytokines can regulate different effector functions in PBC pathogenesis and need to be considered in PBC treatment.

Joint Analysis of Genetic Correlation, Mendelian Randomization and Colocalization Highlights the Bi-Directional Causal Association Between Hypothyroidism and Primary Biliary Cirrhosis

Background: Hypothyroidism and primary biliary cirrhosis (PBC) are often co-existed in observational epidemiological studies. However, the causal relationship between them remains unclear.

Methods: Genetic correlation, Mendelian randomization (MR) and colocalization analysis were combined to assess the potential causal association between hypothyroidism and PBC by using summary statistics from large-scale genome-wide association studies. Various sensitivity analyses had been conducted to assess the robustness and the consistency of the findings.

Results: The linkage disequilibrium score regression demonstrated significant evidence of shared genetic architecture between hypothyroidism and PBC, with the genetic correlation estimated to be 0.117 (p = 0.006). The OR of hypothyroidism on PBC was 1.223 (95% CI, 1.072–1.396; p = 2.76 × 10⁻³) in MR analysis with inverse variance weighted (IVW) method. More importantly, the results from other 7MR methods with different model assumptions, were almost identical with that of IVW, suggesting the findings were robust and convincing. On the other hand, PBC was also causally associated with hypothyroidism (OR, 1.049; 95% CI, 1.010–1.089; p = 0.012), and, again, similar results can also be obtained from other MR methods. Various sensitivity analyses regarding the outlier detection and leave-one-out analysis were also performed. Besides, colocalization analysis suggested that there existed shared causal variants between hypothyroidism and PBC, further highlighting the robustness of the results.

Conclusion: Our results suggest evidence for the bi-directional causal association between hypothyroidism and PBC, which may provide insights into the etiology of hypothyroidism and PBC as well as inform prevention and intervention strategies directed toward both diseases.

Type I interferon detection in autoimmune diseases: challenges and clinical applications

INTRODUCTION

Accumulating data highlights that the dysregulation of type I interferon (IFN) pathways plays a central role in the pathogenesis of several systemic and organ-specific autoimmune diseases. Advances in understanding the role of type I IFNs in these disorders can lead to targeted drug development as well as establishing potential disease biomarkers.

AREAS COVERED

Here, we summarize current knowledge regarding the role of type I IFNs in the major systemic, as well as organ-specific, autoimmune disorders, including prominent inflammatory CNS disorders like multiple sclerosis.

EXPERT OPINION

Type I IFN involvement and its clinical associations in a wide spectrum of autoimmune diseases represents a promising area for research aiming to unveil common pathogenetic pathways in systemic and organ-specific autoimmunity.

Interferon-induced protein with tetratricopeptide repeats 3 may be a key factor in primary biliary cholangitis

Accumulating studies suggest that senescent biliary epithelial cells (BECs) produce senescence-associated secretory phenotypes (SASPs) and play various roles in the pathogenesis of primary biliary cholangitis (PBC) and other cholangiopathies. We examined comprehensive profiles of senescent BECs and its contribution to the pathogenesis of PBC taking advantage of microarray analysis. cDNA microarray analysis revealed that 1841 genes including CCL2, IFIT3, CPQ were commonly up-regulated in senescent BECs cultured in serum depleted media or media with glycochenodeoxycholic acid. Knockdown of IFIT3 significantly suppressed cellular senescence (p < 0.01) and significantly increased apoptosis (p < 0.01) in BECs treated with serum depletion or glycochenodeoxycholic acid. Significantly increased expression of IFIT3 was seen in senescent BECs in small bile ducts showing cholangitis and in ductular reactions in PBC, compared to control livers (p < 0.01). An inadequate response to UDCA was inversely correlated to the increased expression of IFIT3 in small bile duct in PBC (p < 0.05). In conclusion, the expression of various genes related to immunity and inflammation including SASPs were increased in senescent BECs. Upregulated IFIT3 in senescent BECs may be associated with the pathogenesis of PBC and may be a possible therapeutic target in 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.

Integrated GWAS and mRNA Microarray Analysis Identified IFNG and CD40L as the Central Upstream Regulators in Primary Biliary Cholangitis

Genome‐wide association studies (GWASs) in European and East Asian populations have identified more than 40 disease‐susceptibility genes in primary biliary cholangitis (PBC). The aim of this study is to computationally identify disease pathways, upstream regulators, and therapeutic targets in PBC through integrated GWAS and messenger RNA (mRNA) microarray analysis. Disease pathways and upstream regulators were analyzed with ingenuity pathway analysis in data set 1 for GWASs (1,920 patients with PBC and 1,770 controls), which included 261 annotated genes derived from 6,760 single‐nucleotide polymorphisms (P < 0.00001), and data set 2 for mRNA microarray analysis of liver biopsy specimens (36 patients with PBC and 5 normal controls), which included 1,574 genes with fold change >2 versus controls (P < 0.05). Hierarchical cluster analysis and categorization of cell type–specific genes were performed for data set 2. There were 27 genes, 10 pathways, and 149 upstream regulators that overlapped between data sets 1 and 2. All 10 pathways were immune‐related. The most significant common upstream regulators associated with PBC disease susceptibility identified were interferon‐gamma (IFNG) and CD40 ligand (CD40L). Hierarchical cluster analysis of data set 2 revealed two distinct groups of patients with PBC by disease activity. The most significant upstream regulators associated with disease activity were IFNG and CD40L. Several molecules expressed in B cells, T cells, Kupffer cells, and natural killer–like cells were identified as potential therapeutic targets in PBC with reference to a recently reported list of cell type–specific gene expression in the liver. Conclusion: Our integrated analysis using GWAS and mRNA microarray data sets predicted that IFNG and CD40L are the central upstream regulators in both disease susceptibility and activity of PBC and identified potential downstream therapeutic targets.

Toll-like receptor 3 downregulation is an escape mechanism from apoptosis during hepatocarcinogenesis

BACKGROUND & AIMS

Low levels of toll-like receptor 3 (TLR3) in patients with hepatocellular carcinoma (HCC) are associated with poor prognosis, primarily owing to the loss of inflammatory signaling and subsequent lack of immune cell recruitment to the liver. Herein, we explore the role of TLR3-triggered apoptosis in HCC cells.

METHODS

Quantitative reverse transcription PCR, western blotting, immunohistochemistry and comparative genomic hybridization were used to analyze human and mouse HCC cell lines, as well as surgically resected primary human HCCs, and to study the impact of TLR3 expression on patient outcomes. Functional analyses were performed in HCC cells, following the restoration of TLR3 by lentiviral transduction. The role of TLR3-triggered apoptosis in HCC was analyzed in vivo in a transgenic mouse model of HCC.

RESULTS

Lower expression of TLR3 in tumor compared to non-tumor matched tissue was observed at both mRNA and protein levels in primary HCC, and was predictive of shorter recurrence-free survival after surgical resection in both univariate (hazard ratio [HR] 1.79; 95% CI 1.04-3.06; p = 0.03) and multivariate analyses (HR 1.73; CI 1.01-2.97; p = 0.04). Immunohistochemistry confirmed frequent downregulation of TLR3 in human and mouse primary HCC cells. None of the 6 human HCC cell lines analyzed expressed TLR3, and ectopic expression of TLR3 following lentiviral transduction not only restored the inflammatory response but also sensitized cells to TLR3-triggered apoptosis. Lastly, in the transgenic mouse model of HCC, absence of TLR3 expression was accompanied by a lower rate of preneoplastic hepatocyte apoptosis and accelerated hepatocarcinogenesis without altering the tumor immune infiltrate.

CONCLUSION

Downregulation of TLR3 protects transforming hepatocytes from direct TLR3-triggered apoptosis, thereby contributing to hepatocarcinogenesis and poor patient outcome.

LAY SUMMARY

Hepatocellular carcinoma (HCC) is a heterogeneous disease associated with a poor prognosis. In patients with HCC, TLR3 downregulation is associated with reduced survival. Herein, we show that the absence of TLR3 is associated with a lower rate of apoptosis, and subsequently more rapid hepatocarcinogenesis, without any change to the immune infiltrate in the liver. Therefore, the poor prognosis associated with low TLR3 expression in HCC is likely linked to tumors ability to escape apoptosis. TLR3 may become a promising therapeutic target in TLR3-positive HCC.

Immunological abnormalities in patients with primary biliary cholangitis

Primary biliary cholangitis (PBC), an autoimmune liver disease occurring predominantly in women, is characterized by high titers of serum anti-mitochondrial antibodies (AMAs) and progressive intrahepatic cholestasis. The immune system plays a critical role in PBC pathogenesis and a variety of immune cell subsets have been shown to infiltrate the portal tract areas of patients with PBC. Amongst the participating immune cells, CD4 T cells are important cytokine-producing cells that foster an inflammatory microenvironment. Specifically, these cells orchestrate activation of other immune cells, including autoreactive effector CD8 T cells that cause biliary epithelial cell (BEC) injury and B cells that produce large quantities of AMAs. Meanwhile, other immune cells, including dendritic cells (DCs), natural killer (NK) cells, NKT cells, monocytes, and macrophages are also important in PBC pathogenesis. Activation of these cells initiates and perpetuates bile duct damage in PBC patients, leading to intrahepatic cholestasis, hepatic damage, liver fibrosis, and eventually cirrhosis or even liver failure. Taken together, the body of accumulated clinical and experimental evidence has enhanced our understanding of the immunopathogenesis of PBC and suggests that immunotherapy may be a promising treatment option. Herein, we summarize current knowledge regarding immunological abnormalities of PBC patients, with emphasis on underlying pathogenic mechanisms. The differential immune response which occurs over decades of disease activity suggests that different therapies may be needed at different stages of disease.

Primary biliary cholangitis: A tale of epigenetically-induced secretory failure?

Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease associated with autoimmune-related destruction of small to medium size intrahepatic bile ducts. The aetiology of PBC is unknown and its pathogenesis remains obscure. Both genetic variants and environmental factors have been linked to increased PBC susceptibility, with other alterations known to cooperate in disease pathobiology. Increasing evidence indicates the presence of epigenetic abnormalities in PBC, particularly alterations of cholangiocellular microRNAs (miRNAs or miRs). This review highlights and discusses the most relevant epigenetic alterations found in patients with PBC, focusing on the role of miR-506 in the promotion of cholestasis and immune activation.

Association of Toll-like receptor 3 and Toll-like receptor 9 single-nucleotide polymorphisms with hepatitis C virus persistence among Egyptians

Toll-like receptors (TLRs) give the innate immune system a considerable specificity for a large range of pathogens. TLR3 detects dsRNA of viruses while TLR9 recognizes bacterial and viral unmethylated CpG motifs. This study examined whether there is a potential association between single-nucleotide polymorphisms (SNPs) in the TLR3.rs3775290 (c.1377C/T), TLR9.rs5743836 (-1237T→C) and TLR9.rs352140 (G2848A) genes and HCV infection among Egyptian patients and healthcare workers (HCWs). We enrolled 546 subjects (409 HCWs and 137 patients) divided into four groups: group 1 included 265 seronegative, aviremic subjects; group 2 included 25 seronegative, viremic subjects; group 3 included 87 subjects with spontaneously resolved HCV infection; and group 4 included 169 chronic HCV patients. All subjects were genotyped for TLR3.rs3775290, TLR9.rs5743836 and TLR9.rs352140 SNPs by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analysis. TLR3.rs3775290 "CC" genotype was associated with chronic HCV infection, where there was a significantly greater frequency of this genotype among chronic patients when compared to subjects with spontaneously resolved infection (63.9% vs. 51.9%; p = 0.033; OR = 1.639 and 95% CI = 0.94-2.84). However, this SNP did not correlate with the HCV RNA load among the chronic subjects (p > 0.05). There was no significant difference in TLR9.rs5743836 and TLR9.rs352140 genotype distribution between groups (p > 0.05). Lack of association between the three SNPs was found, as the three SNPs are located on two different chromosomes. In conclusion, the TLR3.rs3775290 "CC" genotype was associated with HCV chronicity, while the TLR9 gene may not play a major role in HCV infection.

Interferon alpha: The key trigger of type 1 diabetes

IFNα is a cytokine essential to a vast array of immunologic processes. Its induction early in the innate immune response provides a priming mechanism that orchestrates numerous subsequent pathways in innate and adaptive immunity. Despite its beneficial effects in viral infections IFNα has been reported to be associated with several autoimmune diseases including autoimmune thyroid disease, systemic lupus erythematosus, rheumatoid arthritis, primary biliary cholangitis, and recently emerged as a major cytokine that triggers Type 1 Diabetes. In this review, we dissect the role of IFNα in T1D, focusing on the potential pathophysiological mechanisms involved. Evidence from human and mouse studies indicates that IFNα plays a key role in enhancing islet expression of HLA-I in patients with T1D, thereby increasing autoantigen presentation and beta cell activation of autoreactive cytotoxic CD8 T-lymphocytes. The binding of IFNα to its receptor induces the secretion of chemokines, attracting monocytes, T lymphocytes, and NK cells to the infected tissue triggering autoimmunity in susceptible individuals. Furthermore, IFNα impairs insulin production through the induction of endoplasmic reticulum stress as well as by impairing mitochondrial function. Due to its central role in the early phases of beta cell death, targeting IFNα and its pathways in genetically predisposed individuals may represent a potential novel therapeutic strategy in the very early stages of T1D.

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.

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.

Pathophysiologic implications of innate immunity and autoinflammation in the biliary epithelium

The most studied physiological function of biliary epithelial cells (cholangiocytes) is to regulate bile flow and composition, in particular the hydration and alkalinity of the primary bile secreted by hepatocytes. After almost three decades of studies it is now become clear that cholangiocytes are also involved in epithelial innate immunity, in inflammation, and in the reparative processes in response to liver damage. An increasing number of evidence highlights the ability of cholangiocyte to undergo changes in phenotype and function in response to liver damage. By participating actively to the immune and inflammatory responses, cholangiocytes represent a first defense line against liver injury from different causes. Indeed, cholangiocytes express a number of receptors able to recognize pathogen- or damage-associated molecular patterns (PAMPs/DAMPs), such as Toll-like receptors (TLR), which modulate their pro-inflammatory behavior. Cholangiocytes can be both the targets and the initiators of the inflammatory process. Derangements of the signals controlling these mechanisms are at the basis of the pathogenesis of different cholangiopathies, both hereditary and acquired, such as cystic fibrosis-related liver disease and sclerosing cholangitis. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

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.

Protective Effects of S-Adenosylmethionine and Its Combinations With Taurine and/or Betaine Against Lipopolysaccharide or Polyinosinic-polycytidylic Acid-induced Acute Hepatotoxicity

BACKGROUND

Several mechanisms for the pathogenesis of many liver diseases are related with oxidative stress, endotoxins, and infections by many microorganisms. These can lead to chronic hepatitis, cirrhosis, and even liver cancer. The aim of this study was to evaluate the effects of S-adenosylmethionine (SAMe) and its combinations with taurine and/or betaine against hepatotoxicites induced by lipopolysaccharide (LPS) or polyinosinic-polycytidylic acid (polyI:C).

METHODS

RAW 264.7 macrophage cells and seven-week-old male C57BL/6 mice were pretreated with SAMe (SAM or AdoMet), taurine, and/or betaine. In order to mimic hepatic injury like endotoxemia or viral infection, cells and mice were treated with LPS or polyI:C. Concentrations of glutathione (GSH), mRNA expressions of GSH synthesizing enzymes, and inflammatory markers were measured by biochemical assays and quantitative real-time PCR.

RESULTS

In RAW 264.7 cells and mice, pretreatment of SAMe alone or SAMe with taurine and/or betaine attenuated the decrease in GSH levels and mRNA expressions of GSH synthesizing enzymes. In addition, pretreatment of SAMe with taurine and/or betaine prevented the excessive increase in inflammatory mediators produced by LPS or polyI:C treatment.

CONCLUSIONS

Treatment with SAMe in combination with taurine and betaine, would have anti-oxidant functions in addition to anti-inflammatory action against bacterial and/or viral inflammation.

Elevation of Vδ1 T cells in peripheral blood and livers of patients with primary biliary cholangitis

Primary biliary cholangitis (PBC), hitherto called primary biliary cirrhosis, is a cholestatic liver disease of unclear aetiology with autoimmune features. Accumulating evidence revealed that γδ T cells were involved in the development of autoimmune diseases. As one of γδ T cells subsets, however, the role of Vδ1 T cells in the immunopathogenesis of PBC is poorly understood. We analysed peripheral blood Vδ1 T cells in PBC patients in active stage (ASP, n = 18), adequate responders (AR, n = 10) and inadequate responders (IAR, n = 4) to ursodeoxycholic acid (UDCA) and an age-matched healthy control group (n = 16) by flow cytometric analysis. The ASP group exhibited a significantly higher proportion and absolute number of Vδ1 T cells, which were also observed in immunofluorescence staining of liver biopsy specimens of PBC patients. Moreover, these Vδ1 T cells expressed a series of activation markers and intracellular cytokines, which may contribute to the immunopathogenesis of PBC. Our study will help to clarify the role of Vδ1 T cells in the development of PBC.

The protective effects of bone marrow-derived mesenchymal stem cell (BMSC) on LPS-induced acute lung injury via TLR3-mediated IFNs, MAPK and NF-κB signaling pathways

The study attempted to clarify the protective role of bone marrow-derived mesenchymal stem cell (BMSC) transplantation on LPS-induced acute lung injury (ALI) of rats. BMSC were obtained from bone marrow of rat, cultured and proliferated in vitro. Rats of ALI were established through lipopolysaccharide (LPS) administration. Male rats were allocated to control group, ALI group and BMSC, transplantation group. Rats were sacrificed after BMSC injection after 12h, 24h and 48h. Here we investigated the role of BMSC in LPS-induced alveolar macrophages to further demonstrate the mechanism of BMSC to lung injury. TLR3, a member of Toll-like receptor family, has been found in macrophages and the cell surface. In our study, first BMSC successfully reversed LPS-induced lung injury by hematoxylin-eosin (H&E) staining, ameliorated apoptosis via TUNEL and flow cytometer analysis, as well as improved cell structure. And then, western blot, quantitative real-time PCR, immunohistochemistry and immunofluorescence analysis were used to confirm that TLR3 was significantly down-regulated for BMSC treatment. Subsequently, TRIF and RIP1, down-streaming signals of TLR3, were inhibited greatly, leading to TRAF3, MAPK as well as NF-κB inactivity. Our results indicated that BMSC transplantation group displayed inhibitory effects on interferon (IFNs) levels via TLR3 in LPS-induced ALI and preventive effects on inflammation response via TLR3-regualted MAPK and NF-κB signaling pathway in LPS-induced lung injury. The present study indicated that BMSC could display protective effects on LPS-induced ALI and provide an experimental basis for clinical therapy.

Expression and functionality of Toll- and RIG-like receptors in HepaRG cells

BACKGROUND & AIMS

HepaRG cells are considered as the best surrogate model to primary human hepatocyte (PHH) culture to investigate host-pathogen interactions. Yet their innate immune functions remain unknown. In this study, we explored the expression and functionality of Toll-like (TLR) and retinoic acid-inducible gene-1 (RIG-I)-like receptors (RLR) in these cells.

METHODS

Gene and protein expression levels of TLR-1 to 9 and RLR in HepaRG were mainly compared to PHH, by RT-qPCR, FACS, and Western blotting. Their functionality was assessed, by measuring the induction of toll/rig-like themselves and several target innate gene expressions, as well as the secretion of IL-6, IP-10, and type I interferon (IFN), upon agonist stimulation. Their functionality was also shown by measuring the antiviral activity of some TLR/RLR agonists against hepatitis B virus (HBV) infection.

RESULTS

The basal gene and protein expression profile of TLR/RLR in HepaRG cells was similar to PHH. Most receptors, except for TLR-7 and 9, were expressed as proteins and functionally active as shown by the induction of some innate genes, as well as by the secretion of IL-6 and IP-10, upon agonist stimulation. The highest levels of IL-6 and IP-10 secretion were obtained by TLR-2 and TLR-3 agonist stimulation respectively. The highest preventive anti-HBV activity was obtained following TLR-2, TLR-4 or RIG-I/MDA-5 stimulations, which correlated with their high capacity to produce both cytokines.

CONCLUSIONS

Our results indicate that HepaRG cells express a similar pattern of functional TLR/RLR as compared to PHH, thus qualifying HepaRG cells as a surrogate model to study pathogen interactions within a hepatocyte innate system.

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.

Expression pattern of Toll-like receptors (TLRs) in different organs and effects of lipopolysaccharide on the expression of TLR 2 and 4 in reproductive organs of female rabbit

Toll-like receptors (TLRs) are vital for innate immunity, and they were expressed in various immune cells, tissues and organs. Moreover, TLRs specific expression pattern in different cells, tissue and organs have been confirmed to have correlation with the ability to resistance to pathogenic challenges. The present study aimed to determine the expression profiles and levels of TLR2, 3, 4, 5, 6, 8 and 10 in the lung, trachea, intestine, stomach, liver, spleen, uterine horn and body, cervix, ovary, oviduct and hypothalamus of female rabbits, and whether the expression level of TLR2 and 4 in the ovary, oviduct, uterine horn and body, and cervix were affected by lipopolyasaccharide (LPS). The tissues of the lung, trachea, intestine, stomach, liver, spleen, uterine horn and body, cervix, ovary, oviduct and hypothalamus were collected from four rabbits which didn't be treated as 0 h. 16 rabbits in LPS group were injected with LPS (according to 0.5mg/kg body weight) and 16 rabbits in control group were injected with saline (LPS carrier), hereafter the tissues of the uterine horn and body, cervix, ovary and oviduct from 32 rabbits were collected after 1.5, 3, 6, and 12h (n=4 each group) postinjection. The expression profiles of TLRs were analyzed by reverse transcriptase polymerase chain reaction (RT-PCR), and expression level of TLRs were examined using quantitative real-time PCR (qRT-PCR). The results shown: TLR2, 3, 4, 5, 6, 8 and 10 were expressed in lung, trachea, intestine, stomach, liver, spleen, uterine horn and body, cervix, ovary, oviduct and hypothalamus of female rabbits, but their expression level had great difference in the same organs, and each TLR has different expression level in the different organs. After LPS-stimulation, the expression of TLR2 in the uterine body and horn was significantly higher than that in control group by 3h and 12h of postinjection (P<0.05) respectively. The expression of TLR4 in ovary and uterine body was significantly higher than that in control group by 3 and 12h of postinjection (P<0.05), and the expression of TLR4 in uterine body was greater than that in control by 3h postinjection (P<0.05). The results suggested LPS upregulated the expression of TLR2 and 4 in uterine body and horn, and the expression of TLR4 in ovary.

Systemic and local expression levels of TNF-like ligand 1A and its decoy receptor 3 are increased in primary biliary cirrhosis

BACKGROUND & AIMS

Through a genome-wide association study of a Japanese population, we recently identified TNFSF15, a gene encoding TNF-like ligand 1A (TL1A), as a susceptibility gene for primary biliary cirrhosis (PBC). We investigated the clinical significance of TL1A and one of its receptors, decoy receptor 3 (DcR3), in PBC.

METHODS

We analysed the systemic and local expression of TL1A and DcR3 in 110 PBC patients and 46 healthy controls using enzyme-linked immunosorbent assay, quantitative polymerase chain reaction and immunohistochemical staining.

RESULTS

Serum TL1A levels were significantly increased in PBC patients at both early and late stages as compared with healthy controls, and its levels were significantly decreased in early-stage PBC patients after ursodeoxycholic acid (UDCA) treatment. TL1A was immunohistochemically localized to biliary epithelial cells, Kupffer cells, blood vessels and infiltrating mononuclear cells in the PBC liver. In addition, TL1A messenger RNA expression was increased in the PBC liver as compared with the non-diseased liver. Serum DcR3 levels were also significantly increased in PBC patients, and were significantly decreased after UDCA treatment in early-stage PBC patients.

CONCLUSIONS

These results indicate that TL1A and DcR3 may play an important role in the pathogenesis of PBC.

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.

Kupffer Cells in Health and Disease

Kupffer cells (KC), the resident macrophages of the liver, represent the largest population of mononuclear phagocytes in the body. Phenotypic, developmental, and functional aspects of these cells in steady state and in different diseases are the focus of this review. Recently it has become evident that KC precursors seed the liver already early in fetal development, and the population can be maintained independently from circulating monocytes. However, inflammatory conditions allow rapid differentiation of monocytes into mature cells that are indistinguishable from genuine KC. KC are located in the lumen of sinusoids that receive blood both from the portal vein, carrying nutrients and microbial products from the gut, and from the hepatic artery. This positions KC ideally for their prime function, namely surveillance and clearance of the circulation. As such, they are important in iron recycling by phagocytosing effete erythrocytes, for instance. The immunophenotype of KC, characterized by a wide variety of endocytic receptors, is indicative of this scavenger function. In maintaining homeostasis, KC have an ambivalent response to exogenous triggers. On the one hand, their surveillance function requires alert responses to potentially hazardous substances. On the other hand, continuous exposure of the cells to the trigger-rich content of blood originating from the gut dampens their responsiveness to further stimuli. This ambivalence is also reflected in their diverse roles in disease pathogenesis. For the latter, we sketch the contribution of KC by giving examples of their role in metabolic disease, infections, and liver injury.

The role of vitamin d in primary biliary cirrhosis: possible genetic and cell signaling mechanisms

Primary biliary cirrhosis (PBC) is an immune-mediated chronic inflammatory disease of the liver of unknown etiology. Vitamin D deficiency is highly prevalent in patients with PBC, and many studies have demonstrated the significant effect of calcitriol on liver cell physiology. Vitamin D has antiproliferative and antifibrotic effects on liver fibrosis. Genetic studies have provided an opportunity to determine which proteins link vitamin D to PBC pathology (e.g., the major histocompatibility complex class II molecules, the vitamin D receptor, toll-like receptors, apolipoprotein E, Nramp1, and cytotoxic T lymphocyte antigen-4). Vitamin D also exerts its effect on PBC through cell signaling mechanisms, that is, matrix metalloproteinases, prostaglandins, reactive oxygen species, and the transforming growth factor betas. In conclusion, vitamin D may have a beneficial role in the treatment of PBC. The best form of vitamin D for use in the PBC is calcitriol because it is the active form of vitamin D3 metabolite, and its receptors are present in the sinusoidal endothelial cells, Kupffer cells, and stellate cells of normal livers, as well as in the biliary cell line.

Role of gut microbiota in liver diseases

The liver constantly encounters food-derived antigens and bacterial components such as lipopolysaccharide translocated from the gut into the portal vein. Bacterial components stimulate Toll-like receptors (TLR), which are expressed on Kupffer cells, biliary epithelial cells, hepatocytes, hepatic stellate cells, endothelial cells and dendritic cells and recognize specific pathogen-associated molecular patterns. The signaling of TLR to its main ligand triggers inflammation. Usually, in order to protect against hyperactivation of the immune system and to prevent organ failure by persistent inflammation, TLR tolerance to repeated stimuli is induced. In chronic liver diseases, a breakdown in TLR tolerance occurs. Furthermore, Kupffer cells, hepatic stellate cells and natural killer T cells are key components of innate immunity. Decreased numbers and impaired ability of these cells lead to failures in immune tolerance, resulting in persistent inflammation. Recently, the activation of inflammasome was revealed to control the secretion of pro-inflammatory cytokines such as interleukin-1β in response to bacterial pathogens. Innate immunity seems to be an important contributor to the pathogenesis of fatty liver disease and autoimmune liver disease. Recently, probiotics were reported to affect various liver diseases via shifts in gut microbiota and the stability of intestinal permeability. However, many unresolved questions remain. Further analysis will be needed to gain a more comprehensive understanding of the association of innate immunity with the pathogenesis of various liver diseases.

Toll-like receptor 3 polymorphism and its association with hepatitis B virus infection in Saudi Arabian patients

Hepatitis B virus (HBV) is the major causative agent of chronic liver complications including cirrhosis and hepatocellular carcinoma (HCC). Individuals infected with HBV show a wide spectrum of disease manifestations ranging from asymptomatic carriers to HCC. TLR3 is part of the innate immune system that recognizes double-stranded RNA (dsRNA) and provides early immune response to exogenous antigens. The genetic polymorphisms such as single nucleotide polymorphisms (SNPs) in the TLR3 could be considered as factors for the susceptibility to viral pathogens including HBV. Due to lack of knowledge on the role of TLR3 polymorphisms in HBV infection, this study investigated the distribution of nine SNPs in the TLR3 gene and its association with Saudi Arabian patients infected with HBV. A total of 707 patients and 600 uninfected controls were examined for different parameters including the nine SNPs (rs5743311, rs5743312, rs1879026, rs5743313, rs5743314, rs5743315, rs111611328, rs78726532 and a newly identified SNP located at position 184322913 of chr4). The association analysis confirmed that only one SNP, rs1879026 (G/T), showed a significant difference (P = 0.0480; OR = 0.809, 95% CI = 0.655-0.999) in the distribution between HBV carriers and uninfected controls. While, the rest of the SNPs showed no significant association with regards to HBV infection or in the progression to cirrhosis of the liver and HCC. Furthermore, haplotype analysis revealed that one haplotype GCGA (rs1879026, rs5743313, rs5743314, and rs5743315, respectively), was associated significantly with HBV infection in this population. These findings indicate that genetic variations in the TLR3 gene could affect the outcome of HBV infection among Saudis.

Hepatic expression of toll-like receptors 3, 4, and 9 in primary biliary cirrhosis and chronic hepatitis C

Toll-like receptors (TLRs) may play a role in the inflammatory patterns observed in primary biliary cirrhosis (PBC) and chronic hepatitis C (CHC). We investigated TLR 3, 4 and 9 expression in PBC and CHC using immunohistochemical staining.

METHODS

Patient biopsies of PBC (N=11) and CHC (N=15) were compared to disease free livers (n=7). The extent of TLR staining was assessed separately according to a semi-quantitative scale for hepatocytes, cholangiocytes and portal mononuclear cells (PMC).

RESULTS

In hepatocytes, TLR4 expression was increased (PBC; P=0.019), as was TLR9 (PBC; P=0.006, CHC; P=0.001). Cholangiocyte expression of TLRs 4 and 3 was reduced in both PBC (TLR4; P<0.0001, TLR3; P=0.006) and CHC (TLR4; P<0.0001, TLR3; P=0.014). Cholangiocyte expression of TLR9 was elevated for both groups and was significant in CHC (P=0.0115). PMCs showed up-regulation of TLR9 in PBC (P=0.022) and CHC (P=0.0001), with almost no expression of TLR 3 or 4.

CONCLUSIONS

In PBC and CHC, hepatocytes showed increased TLR 4 and 9 expression without change in TLR3. Cholangiocytes showed increased TLR9 expression as opposed to down-regulation of TLRs 3 and 4. PMCs in both diseases had significantly increased TLR 9 expression perhaps implicating TLR9 expression in chronic liver inflammation.

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.

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.

Toll-like receptor mRNA expression in liver tissue from patients with biliary atresia

BACKGROUND AND AIM

Inappropriate host immunological reactions against unknown ligands via the Toll-like receptor (TLR) cascades may trigger progressive inflammatory biliary destruction that manifests as biliary atresia (BA) in newborns or infants. The aim of the study was to clarify the role of the innate immune system in the development of BA.

PATIENTS AND METHODS

Liver tissue was obtained from 49 patients with pediatric hepatobiliary diseases: 19 with BA, 21 with choledochal cysts, and 9 with other hepatobiliary diseases. BA samples obtained during the initial portoenterostomy and reoperation or liver transplantation (LT) were classified as early and late BA groups, respectively. Of the early BA group, those requiring LT were designated as the LT group, and the others were designated as the non-LT group. The mRNA expression levels of TLRs 2, 3, 4, 7, and 8 were determined by real-time quantitative reverse transcription-polymerase chain reaction and were compared between groups. The correlation between TLR mRNA expression level and age at sampling was examined for each TLR in the patients with BA.

RESULTS

TLR8 mRNA, encoding the receptor for single-stranded RNA, was significantly higher in the early BA group, compared with non-BA groups (P = 0.008). Within the BA group, mRNA levels of TLRs 2 and 8 were significantly higher in the early group than in the late group (P = 0.02 and 0.006, respectively), despite there being no significant correlation between TLR mRNA expression and age at sampling, except for TLR7 (r = 0.77, P = 0.001). Compared with the non-LT group, the LT group demonstrated significantly higher mRNA expression of TLRs 3 and 7 (P = 0.02 and 0.01, respectively).

CONCLUSIONS

Innate immune responses may contribute to the initiation and progression of BA. Severe inflammation characteristic of BA around the time of the first operation may abate postoperatively, but determination of selected TLR mRNA expression levels in the liver at the time of Kasai portoenterostomy may assist in predicting the prognosis of patients with BA.

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.

Corticosteroids shift the Toll-like receptor response pattern of primary-isolated murine liver cells from an inflammatory to an anti-inflammatory state

OBJECTIVE

Only little is known about the mechanisms of action of corticosteroids in the treatment of inflammatory liver diseases. As there is increasing evidence that stimulation of the innate immune system plays an important pathogenetic role in these conditions, we hypothesized that steroids may interfere with the activation of the Toll-like receptor (TLR) system of the liver.

METHODS

To test this hypothesis, murine non-parenchymal liver cells (Kupffer cells, liver sinusoidal endothelial cells) and primary hepatocytes were stimulated with TLR 1-9 ligands in the presence or absence of dexamethasone. Expression of pro- and anti-inflammatory cytokines was determined by quantitative reverse transcription-PCR or ELISA, respectively. Nuclear factor 'kappa-light-chain-enhancer' of activated B-cells (NF-κB) activation was assessed by western blot analysis.

RESULTS

TLR agonists induced the expression of pro- [tumor necrosis factor-α (TNF-α), IL-6, IL-1β, IFN-β] and anti-inflammatory cytokines [IL-10, transforming growth factor-β (TGF-β)], which was differentially modulated by steroid treatment. TNF-α and IL-6 expression was suppressed by dexamethasone, while IL-10 but not TGF-β was enhanced after TLR stimulation. IFN-β production induced by TLR 4 agonists but not TLR 3 agonists was inhibited by dexamethasone. TLR expression itself was down-regulated by steroid treatment in a cell type-specific manner. These effects were associated with suppression of the TLR-mediated activation of NF-κB.

CONCLUSIONS

TLR signaling is modulated by corticosteroids in a cell type-specific fashion resulting in down-regulation of TLR expression, suppression of pro-inflammatory and up-regulation of anti-inflammatory cytokines. This represents an as yet unknown mechanism of action for corticosteroids that may at least in part explain their therapeutic effects in inflammatory liver diseases.

Interaction between Toll-like receptors and natural killer cells in the destruction of bile ducts in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is characterized by chronic nonsuppurative destructive cholangitis (CNSDC) associated with destruction of small bile ducts. Although there have been significant advances in the dissection of the adaptive immune response against the mitochondrial autoantigens, there are increasing data that suggest a contribution of innate immune mechanisms in inducing chronic biliary pathology. We have taken advantage of our ability to isolate subpopulations of liver mononuclear cells (LMC) and examined herein the role of Toll-like receptors (TLRs), their ligands, and natural killer (NK) cells in modulating cytotoxic activity against biliary epithelial cells (BECs). In particular, we demonstrate that Toll-like receptor 4 ligand (TLR4-L)-stimulated NK cells destroy autologous BECs in the presence of interferon alpha (IFN-α) synthesized by TLR 3 ligand (TLR3-L)-stimulated monocytes (Mo). Indeed, IFN-α production by hepatic Mo is significantly increased in patients with PBC compared to disease controls. There were also marked increases in the cytotoxic activity of hepatic NK cells from PBC patients compared to NK cells from controls but only when the NK cells were prepared following ligation of both TLR3-L- and TLR4-L-stimulated LMC. These functional data are supported by the immunohistochemical observation of an increased presence of CD56-positive NK cells scattered around destroyed small bile ducts more frequently in liver tissues from PBC patients than controls.

CONCLUSION

These data highlight critical differences in the varied roles of Mo and NK cells following TLR3-L and TLR4-L stimulation.

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.

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.

Biliary innate immunity: function and modulation

Biliary innate immunity is involved in the pathogenesis of cholangiopathies in patients with primary biliary cirrhosis (PBC) and biliary atresia. Biliary epithelial cells possess an innate immune system consisting of the Toll-like receptor (TLR) family and recognize pathogen-associated molecular patterns (PAMPs). 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. In PBC, CD4-positive Th17 cells characterized by the secretion of IL-17 are implicated in the chronic inflammation of bile ducts and the presence of Th17 cells around bile ducts is causally associated with the biliary innate immune responses to PAMPs. Moreover, a negative regulator of intracellular TLR signaling, peroxisome proliferator-activated receptor-γ (PPARγ), is involved in the pathogenesis of cholangitis. Immunosuppression using PPARγ ligands may help to attenuate the bile duct damage in PBC patients. In biliary atresia characterized by a progressive, inflammatory, and sclerosing cholangiopathy, dsRNA viruses are speculated to be an etiological agent and to directly induce enhanced biliary apoptosis via the expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Moreover, the epithelial-mesenchymal transition (EMT) of biliary epithelial cells is also evoked by the biliary innate immune response to dsRNA.

Defining a new molecular basis of systemic lupus erythematosus through transcriptional profiling

Data generated using high-throughput DNA microarrays are changing the way we think about systemic lupus erythematosus (SLE). The identification of an interferon gene-expression signature in the majority of patients with SLE, especially those with severe SLE, has stimulated substantial interest in targeting the interferon pathway for the treatment SLE and has catalyzed new inquiries into the utility of interferon signaling as a diagnostic and prognostic biomarker for SLE. As these genomic datasets enlarge and mature, new signatures are being identified that implicate other pathways dysregulated in SLE, including oxidative phosphorylation, immunoglobulin production and granulocyte maturation. Highly anticipated longitudinal studies will be important in defining how this information will ultimately change the way SLE is managed in the clinical setting.

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.