Expression of the interferon-induced Mx proteins in biliary atresia

Maternal risk factors associated with offspring biliary atresia: population-based study

BACKGROUND

Biliary atresia (BA) is a progressive, idiopathic, fibro-obliterative disease of the intra and extrahepatic biliary tree. If untreated, it results in severe liver injury and death. The etiology and pathogenesis of BA remain unclear. Few studies have investigated the association between maternal illness/drug use and the occurrence of BA in offspring.

METHODS

We used the data from the Birth Certificate Application of Taiwan and linked to National Health Insurance Research Database and Taiwan Maternal and Child Health Database for the years 2004 to 2017 (N = 1,647,231) on 2022/03, and identified BA cases according to diagnosis and procedure code. A total of 285 BA cases were identified.

RESULTS

Mothers with type 2 diabetes mellitus and non-dependent drug abuse had higher rates having BA children than non-BA children, with an odds ratio of 2.17 (95% confidence interval [CI] = 1.04-4.53) and OR: 3.02 (95% CI = 1.34-6.78), respectively.

CONCLUSION

These results support the notion that BA occurrence is related to maternal reasons. Further studies should be designed to identify additional maternal and pregnancy risk factors and to understand the underlying pathophysiology.

IMPACT

1. The occurrence of offspring biliary atresia may be related to maternal illness/drug use. 2. Maternal drug abuse and type 2 diabetes mellitus pose a high risk for offspring biliary atresia. 3. If maternal etiology is found, biliary atresia might be a preventable disease.

Current Concepts of Biliary Atresia and Matrix Metalloproteinase-7: A Review of Literature

Biliary atresia (BA) is a rare cholangiopathy of infancy in which the bile ducts obliterate, leading to profound cholestasis and liver fibrosis. BA is hypothesized to be caused by a viral insult that leads to over-activation of the immune system. Patients with BA are surgically treated with a Kasai portoenterostomy (KPE), which aims to restore bile flow from the liver to the intestines. After KPE, progressive liver fibrosis is often observed in BA patients, even despite surgical success and clearance of their jaundice. The innate immune response is involved during the initial damage to the cholangiocytes and further differentiation of the adaptive immune response into a T-helper 1 cell (Th1) response. Multiple studies have shown that there is continuing elevation of involved cytokines that can lead to the progressive liver fibrosis. However, the mechanism by which the progressive injury occurs is not fully elucidated. Recently, matrix metalloproteinase-7 (MMP-7) has been investigated to be used as a biomarker to diagnose BA. MMPs are involved in extracellular matrix (ECM) turnover, but also have non-ECM related functions. The role of MMP-7 and other MMPs in liver fibrosis is just starting to be elucidated. Multiple studies have shown that serum MMP-7 measurements are able to accurately diagnose BA in a cohort of cholestatic patients while hepatic MMP-7 expression correlated with BA-related liver fibrosis. While the mechanism by which MMP-7 can be involved in the pathophysiology of BA is unclear, MMP-7 has been investigated in other fibrotic pathologies such as renal and idiopathic pulmonary fibrosis. MMP-7 is involved in Wnt/β-catenin signaling, reducing cell-to-cell contact by shedding of E-cadherin, amplifying inflammation and fibrosis via osteopontin (OPN) and TNF-α while it also appears to play a role in induction of angiogenesis This review aims to describe the current understandings of the pathophysiology of BA. Subsequently, we describe how MMP-7 is involved in other pathologies, such as renal and pulmonary fibrosis. Then, we propose how MMP-7 can potentially be involved in BA. By doing this, we aim to describe the putative role of MMP-7 as a prognostic biomarker in BA and to provide possible new therapeutic and research targets that can be investigated in the future.

Innate Immunity and Pathogenesis of Biliary Atresia

Biliary atresia (BA) is a devastating fibro-inflammatory disease characterized by the obstruction of extrahepatic and intrahepatic bile ducts in infants that can have fatal consequences, when not treated in a timely manner. It is the most common indication of pediatric liver transplantation worldwide and the development of new therapies, to alleviate the need of surgical intervention, has been hindered due to its complexity and lack of understanding of the disease pathogenesis. For that reason, significant efforts have been made toward the development of experimental models and strategies to understand the etiology and disease mechanisms and to identify novel therapeutic targets. The only characterized model of BA, using a Rhesus Rotavirus Type A infection of newborn BALB/c mice, has enabled the identification of key cellular and molecular targets involved in epithelial injury and duct obstruction. However, the establishment of an unleashed chronic inflammation followed by a progressive pathological wound healing process remains poorly understood. Like T cells, macrophages can adopt different functional programs [pro-inflammatory (M1) and resolutive (M2) macrophages] and influence the surrounding cytokine environment and the cell response to injury. In this review, we provide an overview of the immunopathogenesis of BA, discuss the implication of innate immunity in the disease pathogenesis and highlight their suitability as therapeutic targets.

MicroRNA-155 modulates bile duct inflammation by targeting the suppressor of cytokine signaling 1 in biliary atresia

BackgroundBiliary atresia (BA) is an etiologically perplexing disease, manifested by neonatal cholestasis, repeated cholangitis, and progressive biliary fibrosis. MiR-155 has been implicated to modulate the immune response, which contributes to biliary injury. However, its potential role in the pathogenesis of BA has not been addressed so far.MethodsThe microRNA changes from BA patients and controls were identified via microarray. The immunomodulatory function of miR-155 was investigated via cell transfection and reporter assay. The lentiviral vector pL-miR-155 inhibitor was transfected into a mouse model to investigate its role in BA.ResultsThe expression of miR-155 in livers of BA patients was significantly increased, and an inverse correlation between miR-155 and suppressor of cytokine signaling 1 (SOCS1) was detected. MiR-155 overexpression promoted expressions of major histocompatibility complex (MHC) I, MHC II, Chemokine (C-X-C motif) ligand (CXCL) 9, CXCL10, monocyte chemotactic protein 1, and CXCL1 after IFN-γ stimulation, which could be suppressed by SOCS1 overexpression. Moreover, miR-155 overexpression activated JAK2/STAT3, thus enhancing the pro-inflammatory effect. Downregulating miR-155 reduced the incidence of BA in a rhesus monkey rotavirus-induced BA model.ConclusionOur results reveal a vital contribution of miR-155 upregulation and consequent SOCS1 downregulation to an immune response triggered via IFN-γ in BA.

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.

Functional Immune Anatomy of the Liver-As an Allograft

The liver is an immunoregulatory organ in which a tolerogenic microenvironment mitigates the relative "strength" of local immune responses. Paradoxically, necro-inflammatory diseases create the need for most liver transplants. Treatment of hepatitis B virus, hepatitis C virus, and acute T cell-mediated rejection have redirected focus on long-term allograft structural integrity. Understanding of insults should enable decades of morbidity-free survival after liver replacement because of these tolerogenic properties. Studies of long-term survivors show low-grade chronic inflammatory, fibrotic, and microvascular lesions, likely related to some combination of environment insults (i.e. abnormal physiology), donor-specific antibodies, and T cell-mediated immunity. The resultant conundrum is familiar in transplantation: adequate immunosuppression produces chronic toxicities, while lightened immunosuppression leads to sensitization, immunological injury, and structural deterioration. The "balance" is more favorable for liver than other solid organ allografts. This occurs because of unique hepatic immune physiology and provides unintended benefits for allografts by modulating various afferent and efferent limbs of allogenic immune responses. This review is intended to provide a better understanding of liver immune microanatomy and physiology and thereby (a) the potential structural consequences of low-level, including allo-antibody-mediated injury; and (b) how liver allografts modulate immune reactions. Special attention is given to the microvasculature and hepatic mononuclear phagocytic system.

Biliary atresia: Clinical advances and perspectives

Biliary atresia (BA) is a rare and severe inflammatory and obliterative cholangiopathy that affects both extra- and intrahepatic bile ducts. BA symptoms occur shortly after birth with jaundice, pale stools and dark urines. The prognosis of BA has dramatically changed in the last decades: before the Kasai operation most BA patients died, while nowadays with the sequential treatment with Kasai operation±liver transplantation BA patient survival is close to 90%. Early diagnosis is very important since the chances of success of the Kasai procedure decrease with time. The causes of BA remain actually unknown but several mechanisms including genetic and immune dysregulation may probably lead to the obliterative cholangiopathy. Current research focuses on the identification of blood or liver factors linked to the pathogenesis of BA that could become therapeutic targets and avoid the need for liver transplantation. No similar disease leading to total obstruction of the biliary tree exists in older children or adults. But understanding the physiopathology of BA may highlight the mechanisms of other destructive cholangiopathies, such as sclerosing cholangitis.

Pathogenesis of biliary atresia: defining biology to understand clinical phenotypes

Biliary atresia is a severe cholangiopathy of early infancy that destroys extrahepatic bile ducts and disrupts bile flow. With a poorly defined disease pathogenesis, treatment consists of the surgical removal of duct remnants followed by hepatoportoenterostomy. Although this approach can improve the short-term outcome, the liver disease progresses to end-stage cirrhosis in most children. Further improvement in outcome will require a greater understanding of the mechanisms of biliary injury and fibrosis. Here, we review progress in the field, which has been fuelled by collaborative studies in larger patient cohorts and the development of cell culture and animal model systems to directly test hypotheses. Advances include the identification of phenotypic subgroups and stages of disease based on clinical, pathological and molecular features. Stronger evidence exists for viruses, toxins and gene sequence variations in the aetiology of biliary atresia, triggering a proinflammatory response that injures the duct epithelium and produces a rapidly progressive cholangiopathy. The immune response also activates the expression of type 2 cytokines that promote epithelial cell proliferation and extracellular matrix production by nonparenchymal cells. These advances provide insight into phenotype variability and might be relevant to the design of personalized trials to block progression of liver disease.

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.

Toxoplasmosis--a global threat. Correlation of latent toxoplasmosis with specific disease burden in a set of 88 countries

BACKGROUND

Toxoplasmosis is becoming a global health hazard as it infects 30-50% of the world human population. Clinically, the life-long presence of the parasite in tissues of a majority of infected individuals is usually considered asymptomatic. However, a number of studies show that this 'asymptomatic infection' may also lead to development of other human pathologies.

AIMS OF THE STUDY

The purpose of the study was to collect available geoepidemiological data on seroprevalence of toxoplasmosis and search for its relationship with mortality and disability rates in different countries.

METHODS AND FINDINGS

Prevalence data published between 1995-2008 for women in child-bearing age were collected for 88 countries (29 European). The association between prevalence of toxoplasmosis and specific disease burden estimated with age-standardized Disability Adjusted Life Year (DALY) or with mortality, was calculated using General Linear Method with Gross Domestic Product per capita (GDP), geolatitude and humidity as covariates, and also using nonparametric partial Kendall correlation test with GDP as a covariate. The prevalence of toxoplasmosis correlated with specific disease burden in particular countries explaining 23% of variability in disease burden in Europe. The analyses revealed that for example, DALY of 23 of 128 analyzed diseases and disease categories on the WHO list showed correlations (18 positive, 5 negative) with prevalence of toxoplasmosis and another 12 diseases showed positive trends (p<0.1). For several obtained significant correlations between the seroprevalence of toxoplasmosis and specific diseases/clinical entities, possible pathophysiological, biochemical and molecular explanations are presented.

CONCLUSIONS

The seroprevalence of toxoplasmosis correlated with various disease burden. Statistical associations does not necessarily mean causality. The precautionary principle suggests however that possible role of toxoplasmosis as a triggering factor responsible for development of several clinical entities deserves much more attention and financial support both in everyday medical practice and future clinical research.

Participation of natural killer cells in the pathogenesis of bile duct lesions in biliary atresia

Aims

Immunological disturbances including innate immunity after a suspected viral infection are considered important to the pathogenesis of bile duct lesions in cases of biliary atresia (BA). In this study, we tried to evaluate whether natural killer (NK) cells and CX3CL1 (Fractalkine) and its receptor (CX3CR1) are involved in the bile duct injury.

Methods

Using the section of BA (22 cases) and controls, immunohistochemistry for CD56, CD16, CD68, CX3CL1 and CX3CR1 was performed. Moreover, using cultured biliary epithelial cells (BECs) and NK cells, the production of CX3CL1 in BECs and the migration of NK cells were evaluated.

Results

It was found that CD56(−)CD16(+)CD68(−) NK cells were increased around the damaged small and large bile ducts in BA and hepatitis C virus-related chronic hepatitis in comparison with other controls. CX3CL1 was strongly expressed on the damaged bile ducts in BA, while this expression was relatively weak or absent in the bile ducts of normal liver. The results suggest the CD56(−)CD16(+) NK cells to be involved in the development of bile duct injuries in BA. These CD16(+) NK cells were positive for CX3CR1, and attracted by CX3CL1 expressed on bile ducts. Further study revealed that stimulation with poly(I:C) (a synthetic analogue of viral dsRNA) increased the expression of CX3CL1 on cultured BECs followed by increased migrational activity of cultured NK cells.

Conclusions

CD56(−)CD16(+) NK cells with reduced NK activity may be involved in the bile duct damage in BA, and CD16(+) NK cells expressing CX3CR1 may be attracted by and interact with bile ducts expressing CX3CL1.

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.

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 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.

Biliary atresia: will blocking inflammation tame the disease?

Biliary atresia is the most common cholangiopathy of childhood. With complete obstruction of segments or the entire length of extrahepatic bile ducts, the timely pursuit of hepatoportoenterostomy is the best strategy to restore bile drainage. However, even with prompt surgical intervention, ongoing injury of intrahepatic bile ducts and progressive cholangiopathy lead to end-stage cirrhosis. The pace of disease progression is not uniform; it may relate to clinical forms of disease and/or staging of liver pathology at diagnosis. Although the etiology of disease is not yet defined, several biological processes have been linked to pathogenic mechanisms of bile duct injury. Among them, there is increasing evidence that the immune system targets the duct epithelium and disrupts bile flow. We discuss how careful clinical phenotyping, staging of disease, and basic mechanistic research are providing insights into clinical trial designs and directions for development of new therapies to block progression of disease.

Hedgehog activity, epithelial-mesenchymal transitions, and biliary dysmorphogenesis in biliary atresia

Biliary atresia (BA) is notable for marked ductular reaction and rapid development of fibrosis. Activation of the Hedgehog (Hh) pathway promotes the expansion of populations of immature epithelial cells that coexpress mesenchymal markers and may be profibrogenic. We examined the hypothesis that in BA excessive Hh activation impedes ductular morphogenesis and enhances fibrogenesis by promoting accumulation of immature ductular cells with a mesenchymal phenotype. Livers and remnant extrahepatic ducts from BA patients were evaluated by quantitative reverse-transcription polymerase chain reaction (QRT-PCR) and immunostaining for Hh ligands, target genes, and markers of mesenchymal cells or ductular progenitors. Findings were compared to children with genetic cholestatic disease, age-matched deceased donor controls, and adult controls. Ductular cells isolated from adult rats with and without bile duct ligation were incubated with Hh ligand-enriched medium ± Hh-neutralizing antibody to determine direct effects of Hh ligands on epithelial to mesenchymal transition (EMT) marker expression. Livers from pediatric controls showed greater innate Hh activation than adult controls. In children with BA, both intra- and extrahepatic ductular cells demonstrated striking up-regulation of Hh ligand production and increased expression of Hh target genes. Excessive accumulation of Hh-producing cells and Hh-responsive cells also occurred in other infantile cholestatic diseases. Further analysis of the BA samples demonstrated that immature ductular cells with a mesenchymal phenotype were Hh-responsive. Treating immature ductular cells with Hh ligand-enriched medium induced mesenchymal genes; neutralizing Hh ligands inhibited this.

CONCLUSION

BA is characterized by excessive Hh pathway activity, which stimulates biliary EMT and may contribute to biliary dysmorphogenesis. Other cholestatic diseases show similar activation, suggesting that this is a common response to cholestatic injury in infancy.

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.

Inflammation and biliary tract injury

PURPOSE OF REVIEW

Primary biliary cirrhosis, primary sclerosing cholangitis and biliary atresia are thought to be immune-mediated cholangiopathies, however, gaps in knowledge remain with regard to the immunopathogenesis of these diseases.

RECENT FINDINGS

In this review, we highlight recent investigations pertaining to the role of both innate and adaptive immunity in bile duct damage. In innate immunity, evidence is presented for the contribution of cholangiocyte toll-like receptor stimulation promoting the ongoing inflammatory response. Innate-like lymphocytes may also be critical in the early phases of small bile duct injury found in primary biliary cirrhosis. With regard to adaptive immunity, the role of specific gene deficiencies in the susceptibility to immune-mediated cholangiopathies is reviewed. Furthermore, recent work analyzing the effector mechanisms of adaptive immunity leading to bile duct epithelial apoptosis are outlined.

SUMMARY

Understanding the intricacies of the inflammatory mechanisms culminating in bile duct epithelial injury are crucial to the future development of therapies aimed at halting the ongoing biliary tract destruction found in immune-mediated cholangiopathies. A paucity of research studies on primary sclerosing cholangitis was noted in this review and future research efforts should focus on primary sclerosing cholangitis, in addition to primary biliary cirrhosis and biliary atresia.

Incidence of hepatotropic viruses in biliary atresia

Biliary atresia (BA) is the most frequent indication for paediatric liver transplantation. We tested the hypothesis of a viral aetiology of this disease by screening liver samples of a large number of BA patients for the common human hepatotropic viruses. Moreover, we correlated our findings to the expression of Mx protein, which has been shown to be significantly up-regulated during viral infections. Seventy-four liver biopsies (taken during Kasai portoenterostomy) were tested by polymerase chain reaction (PCR) for DNA viruses (herpes simplex virus [HSV], Epstein-Barr virus [EBV], varicella zoster virus [VZV], cytomegalovirus [CMV], adenovirus, parvovirus B19 and polyoma BK) and RNA viruses (enteroviruses, rotavirus and reovirus 3). Mx protein expression was assessed by immunohistochemistry. Virus DNA/RNA was found in less than half of the biopsies (8/74 CMV, 1/74 adenovirus; 21/64 reovirus, 1/64 enterovirus). A limited number presented with double infection. Patients that had detectable viral RNA/DNA in their liver biopsies were significantly older than virus-free patients (P = 0.037). The majority (54/59) of the liver biopsies showed expression of Mx proteins in hepatocytes, bile ducts and epithelium. Our data suggest that the known hepatotropic viruses do not play a major role in the aetiology and progression of BA. Their incidence appears to be, rather, a secondary phenomenon. Nonetheless, the inflammatory response in the livers of BA patients mimics that observed during viral infections.

Biliary atresia: recent progress

Extrahepatic biliary atresia (EHBA), an inflammatory sclerosing cholangiopathy, is the leading indication for liver transplantation in children. The cause is still unknown, although possible infectious, genetic, and immunologic etiologies have received much recent focus. These theories are often dependent on each other for secondary or coexisting mechanisms. Concern for EHBA is raised by a cholestatic infant, but the differential diagnosis is large and the path to diagnosis remains varied. Current treatment is surgical with an overall survival rate of approximately 90%. The goals of this article are to review the important clinical aspects of EHBA and to highlight some of the more recent scientific and clinical developments contributing to our understanding of this condition.

Incidence of hepatotropic viruses in biliary atresia

Biliary atresia (BA) is the most frequent indication for paediatric liver transplantation. We tested the hypothesis of a viral aetiology of this disease by screening liver samples of a large number of BA patients for the common human hepatotropic viruses. Moreover, we correlated our findings to the expression of Mx protein, which has been shown to be significantly up-regulated during viral infections. Seventy-four liver biopsies (taken during Kasai portoenterostomy) were tested by polymerase chain reaction (PCR) for DNA viruses (herpes simplex virus [HSV], Epstein-Barr virus [EBV], varicella zoster virus [VZV], cytomegalovirus [CMV], adenovirus, parvovirus B19 and polyoma BK) and RNA viruses (enteroviruses, rotavirus and reovirus 3). Mx protein expression was assessed by immunohistochemistry. Virus DNA/RNA was found in less than half of the biopsies (8/74 CMV, 1/74 adenovirus; 21/64 reovirus, 1/64 enterovirus). A limited number presented with double infection. Patients that had detectable viral RNA/DNA in their liver biopsies were significantly older than virus-free patients (P = 0.037). The majority (54/59) of the liver biopsies showed expression of Mx proteins in hepatocytes, bile ducts and epithelium. Our data suggest that the known hepatotropic viruses do not play a major role in the aetiology and progression of BA. Their incidence appears to be, rather, a secondary phenomenon. Nonetheless, the inflammatory response in the livers of BA patients mimics that observed during viral infections.

The immunobiology of cholangiocytes

Cholangiocytes, the epithelial cells lining bile ducts, provide the first line of defense against lumenal microbes in the biliary system. Recent advances in biliary immunity indicate that cholangiocytes express a variety of pathogen-recognition receptors and can activate a set of intracellular signaling cascades to initiate a profound antimicrobial defense, including release of proinflammatory cytokines and chemokines, production of antimicrobial peptides and maintenance of biliary epithelial integrity. Cholangiocytes also interact with other cell types in the liver (for example, lymphocytes and Kupffer cells) through expression and release of adhesion molecules and immune mediators. Subsequently, through an intricate feedback mechanism involving both epithelial and other liver cells, a set of intracellular signaling pathways are activated to regulate the functional state of cholangiocyte responses during microbial infection. Thus, cholangiocytes are actively involved in mucosal immunity of the biliary system and represent a fine-tuned, integral component of liver immunity.

Induction of innate immune response and absence of subsequent tolerance to dsRNA in biliary epithelial cells relate to the pathogenesis of biliary atresia

BACKGROUND/AIMS

Biliary epithelial cells (BECs) possess negative regulatory mechanisms of Toll-like receptor (TLR)-based tolerance to bacteria (e.g. endotoxin tolerance). Viral infections of the Reoviridae genus with a dsRNA genome are suspected to be part of the aetiology of biliary atresia (BA), but the negative biliary mechanisms remain unexplored.

METHODS

Cultured human intrahepatic BECs (HIBECs) pretreated with polyinosinic-polycytidylic acid [poly(I:C)] (a synthetic analogue of viral dsRNA) for 24 h were exposed to poly(I:C) in fresh medium. The activation of nuclear factor-kappaB (NF-kappaB) and the expression of myxovirus resistance protein A (MxA) and tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) mRNAs were evaluated. Moreover, after the pretreatment, the transition of these molecules was examined in poly(I:C)-free conditions.

RESULTS

Treatment with poly(I:C) significantly upregulated NF-kappaB activity in fresh HIBECs, and pretreatment failed to show tolerance to poly(I:C). The production of MxA and TRAIL was also preserved. Moreover, upregulation in the pretreated HIBECs was well preserved in poly(I:C)-free medium for at least 72 h.

CONCLUSIONS

BECs fail to show tolerance to poly(I:C), and once innate immunity is activated it is sustained in poly(I:C)-free conditions, suggesting that the initiation of the immune response to dsRNA in HIBECs and its presence after the clearance of virus are closely associated with the progression of BA.

Innate immune response to double-stranded RNA in biliary epithelial cells is associated with the pathogenesis of biliary atresia

Infections of Reoviridae consisting of a double-stranded RNA (dsRNA) genome are a possible cause of biliary atresia (BA). The aim of the present study is to clarify the pathophysiological function of dsRNA viruses in the pathogenesis of BA. The expression of dsRNA pattern-recognizing receptors, Toll-like receptor 3 (TLR3), retinoic acid inducible gene I (RIG-I), melanoma differentiation-associated gene-5 (MDA-5), and dsRNA-activated protein kinase R (PKR) was constitutively detected in cultured human biliary epithelial cells (BECs). Stimulation with polyinosinic-polycytidylic acid [poly(I:C), a synthetic analog of viral dsRNA] induced the activation of transcription factors [nuclear factor (NF)-kappaB and interferon regulatory factor 3 (IRF3)] and the production of interferon-beta1 (IFN-beta1) and MxA as potent antiviral responses. Moreover, poly(I:C) up-regulated the expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), and both poly(I:C) and TRAIL reduced the viability of cultured human BECs by enhancing apoptosis. Experiments in vivo using tissue sections of extrahepatic bile ducts from patients with BA and controls (choledochal cysts and nonbiliary diseases) showed that the activation of NF-kappaB, interferon regulatory factor-3 (IRF-3), and PKR, and the enhancement of TRAIL and single-stranded DNA (ssDNA)-positive apoptosis were significant in BA, although extrahepatic bile ducts diffusely and constantly expressed TLR3 in all diseases.

CONCLUSION

dsRNA viruses could directly induce the expression of TRAIL and apoptosis in human biliary epithelial cells as a result of the biliary innate immune response, supporting the notion that Reoviridae infections are directly associated with the pathogenesis of cholangiopathies in cases of BA.

Cholestasis and cholestatic syndromes

PURPOSE OF REVIEW

This review focuses on the recent advances in cholestatic liver diseases. While there is an emphasis placed on translational and treatment-focused studies, basic science studies with the greatest impact on the field are also covered.

RECENT FINDINGS

Highlights include new discoveries for the role of the farsenoid X receptor and sodium-dependent taurocholate cotransporting polypeptide; new insights into the pathogenesis of progressive familial intrahepatic cholestasis type 1, biliary atresia, intrahepatic cholestasis of pregnancy, and primary biliary cirrhosis; new information for assessing prognosis in biliary atresia and primary biliary cirrhosis; and important clinical trials in intrahepatic cholestasis of pregnancy, primary biliary cirrhosis and primary sclerosing cholangitis.

SUMMARY

The studies of 2006 have furthered our understanding of cholestasis and cholestatic syndromes. While we continue to add to our knowledge of pathogenesis and treatment for many of these diseases, much work remains.