Cytomegalovirus-specific T-cell reactivity in biliary atresia at the time of diagnosis is associated with deficits in regulatory T cells

Cytomegalovirus-associated biliary atresia: An aetiological and prognostic subgroup

BACKGROUND AND AIMS

Perinatal cytomegalovirus (CMV) infection is a possible cause or trigger of biliary atresia though clinical evidence is scant. We hypothesised that CMV IgM+ve biliary atresia is a separate clinical entity compared to CMV IgM-ve biliary atresia.

METHODS

Prospective single-centre study. 210 infants with histologically confirmed biliary atresia were treated in our institution (Jan. 2004 to Dec. 2011); of these 20 (9.5%) were CMV IgM+ve at presentation. We compared these with 111 infants who were CMV IgM-ve (controls) for clinical features, biochemistry at presentation and outcome following Kasai portoenterostomy (KPE). A blinded comparison of age-matched liver histology was also performed. Data are quoted as median (interquartile range). A P value ≤ 0.05 was regarded as significant.

RESULTS

Infants with CMV IgM+ve biliary atresia were older at Kasai portoenterostomy (or laparotomy) [70 (60-80) days vs. 56 (44-75)days; P = 0.003] and were more jaundiced [175 (147-224) vs. 140 (121-181) μmol/L; P = 0.002+ with higher AST*287 (157-403) vs. 180 (133-254) IU/L; P = 0.005] and aspartate aminotransferase-to-platelet ratio index [1.1 (0.79-3.0) vs. 0.63 (0.43-0.95)] levels. Liver histology: CMV IgM+ve biliary atresia was characterised by a greater degree of inflammation (P < 0.0001) and fibrosis (P = 0.02), whereas CMV IgM-ve isolated biliary atresia had a higher degree of lobular cholestasis (P = 0.001). This effect was independent of the effects of age at KPE.

OUTCOME

CMV IgM+ve biliary atresia had a poorer outcome with a reduced clearance of jaundice (15% vs. 52.2%; P = 0.002), native liver survival (P < 0.0001) and increased mortality (P = 0.002).

CONCLUSIONS

CMV IgM+ve biliary atresia is a distinct clinical and pathological entity with a diminished response to Kasai portoenterostomy.

Dendritic Cells Regulate Treg-Th17 Axis in Obstructive Phase of Bile Duct Injury in Murine Biliary Atresia

Several cell types are considered to be effector cells in bile duct injury in rhesus rotavirus (RRV)-induced experimental biliary atresia (BA). Here, we identified an increased T helper 17 (Th17) cell population in a BA mode. By depleting the Th17 cells, the BA symptoms (onset of jaundice, acholic stools and retarded growth) were attenuated and the survival rate was improved. Furthermore, we found that in mice with BA, the percentage of CD4⁺CD25^highFoxp3⁺ T regulatory (Treg) cells decreased along with the increased percentage of Th17 cells. However, the absolute numbers of Treg and Th17 cells were both increased in liver of RRV-injected mice compared to saline-injected mice. The proportion of Th17 cells at 7 days post-infection was decreased if Treg cells isolated from normal adult mice, but not Treg cells from the livers of mice with BA, were intraperitoneally transferred on day 5 of life. In vitro experiments also showed that Treg cells from mice with BA had a diminished suppressive effect on Th17 cell generation. To determine the mechanisms, we investigated the production of cytokines in the liver. The level of IL-6, which has been shown to be abundantly secreted by activated dendritic cells (DCs), was remarkably elevated. Importantly, in a Treg/Th17 cell suppression assay, IL-6 was demonstrated to paralyze the Treg cells’ suppressive effect on Th17 cells and eventually the unrestrained increase of Th17 cells contributed to bile duct injury. In conclusion, the DC-regulated Treg-Th17 axis, probably in conjunction with other effector T cells, aggravates progressive inflammatory injury at the time of ductal obstruction.

Biliary Atresia: Clinical Lessons Learned

Biliary atresia is a rare disease of unclear etiology, in which obstruction of the biliary tree causes severe cholestasis leading to cirrhosis and ultimately death if left untreated. Biliary atresia is the leading cause of neonatal cholestasis and the most frequent indication for pediatric liver transplantation. Any infant with persistent jaundice beyond 2 weeks of life needs to be evaluated for biliary atresia with fractionation of the bilirubin into conjugated and unconjugated portions. Early performance of a hepatoportoenterostomy in the first 45 days of life to restore bile flow and lessen further damage to the liver is thought to optimize outcome. Despite surgery, progressive liver scarring occurs, and 80% of patients with biliary atresia will require liver transplantation during childhood.

Th-17 cells infiltrate the liver in human biliary atresia and are related to surgical outcome

BACKGROUND

Biliary atresia (BA), a cholangiopathy of unknown etiology is associated with intrahepatic mononuclear cell infiltrate. An abnormal reaction to viral exposure has been hypothesized in some cases. We aimed to investigate the nature of the CD4+ hepatic infiltrate in defined clinical variants of BA by quantification of inflammatory cell components.

METHODS

Liver biopsies of infants obtained at Kasai portoenterostomy (KPE) were stained immunohistochemically using monoclonal antibodies to Tbet, GATA-3, FOXP3 and interleukin (IL) 17, identifying Th-1, Th-2, Tregs and Th-17 cells respectively. T cells were counted with the aid of a graticule. Data are reported as median (range) of cells per high-power-field (×400) and compared using nonparametric statistical tests with P≤0.05 regarded as significant.

RESULTS

Liver biopsies from BA (n=37) and age-matched cholestatic controls (e.g. alpha-1-anti trypsin deficiency, Alagilles syndrome, n=12) were investigated. BA infants were divided into three groups: cytomegalovirus IgM +ve (CMV; n=9); BA splenic malformation (BASM; n=9) and isolated BA (IBA; n=19). All T-cell subsets were present in the portal tracts, with an overrepresentation of Th-1 (P<0.001) and Th-17 (P<0.03), but not Th-2 (P=0.94) or Tregs (P=0.15), compared to controls. Th-1 cells predominated in the CMV group; (18 [7-37] vs. 3 [0-14] [BASM] and vs. 5 [3-23] [IBA]; P<0.01 both), while no subgroup differences were seen for Th-17 cells. The degree of Th-1 cell infiltrate inversely correlated with platelet count (rS=-0.49; P<0.01). Th-17 cells were fewer (6 [2-11] vs. 11 [8-20]; P=0.02) in infants who cleared their jaundice (n=15, <20μmol/L) although this did not translate to improved native liver survival (P=0.17).

CONCLUSIONS

Th-17 cells infiltrate the liver in BA and are associated with a worse surgical outcome; a Th-1 profile predominates in CMV-associated BA.

Evidence for viral infection as a causative factor of human biliary atresia

OBJECTIVES

To explore the evidence for viral infections triggering human biliary atresia (BA) by reviewing archival original articles that analyzed human samples via polymerase chain reaction (PCR) experiments, considering the recent experimental trend of extensive use of rotaviral BA animal models.

METHODS

A PubMed search retrieved original articles that reported the results of PCR experiments for detecting viral DNA or RNA in patient samples as proof of past infection. Search terms included the often-debated DNA or RNA viruses and BA. Special focus was directed toward PCR analyses that targeted reovirus and rotavirus, where PCR accuracy, specimen characteristics and their interpretations were compared.

RESULTS

Nineteen studies were conducted on 16 different kinds of viruses using PCR, with 5 studies on reovirus, 3 on rotavirus, 10 on cytomegalovirus, 5 on Epstein-Barr virus, 4 on parvovirus B19, and so on. Among the papers suggesting a possible viral link to only BA, there was no study on reovirus, 1 on rotavirus, 3 on cytomegalovirus, 1 on EB virus, and 1 on papillomavirus. Of the 6 PCR studies on Reoviridae, 3 on reovirus and 2 on rotavirus were evaluated rigorously for experimental accuracy, including their sensitivity. Two research groups analyzed preoperative stool samples in addition to generic hepatobiliary tissue obtained at surgery. Sample collection timing varied widely, with storage period prior to PCR experimentation not revealed in most reports on Reoviridae.

CONCLUSION

Although a considerable number of PCR studies have sought to clarify a viral role in the pathogenesis of BA using human samples, the findings have been contradictory and have not succeeded in achieving an obvious differentiation between causative and accidental infection of the focused virus. Reproducible and convincing evidence for a causative Reoviridae infection has been lacking based on objective data from highly sensitive PCR experiments. Even though the possibility remains of viral disappearance at the timing of collection, to avoid further ambiguous interpretations of PCR results, rigorous and meticulous collection of large numbers of specimens at carefully planned timing, along with a strictly adjusted and finely tuned PCR system, is strongly recommended for obtaining more reliable and consistent results.

Recent advances in the pathogenesis and management of biliary atresia

PURPOSE OF REVIEW

The purpose of this study is to review advances in both the pathogenesis and clinical management of biliary atresia.

RECENT FINDINGS

Immunologic studies have further characterized roles of helper T-cells, B-cells, and natural killer cells in the immune dysregulation following viral replication within and damage of biliary epithelium. Prominin-1-expressing portal fibroblasts may play an integral role in the biliary fibrosis associated with biliary atresia. A number of genetic polymorphisms have been characterized as leading to susceptibility for biliary atresia. Postoperative corticosteroid therapy is not associated with greater transplant-free survival. Newborn screening may improve outcomes of infants with biliary atresia and may also provide a long-term cost benefit.

SUMMARY

Although recent advances have enhanced our understanding of pathogenesis and clinical management, biliary atresia remains a significant challenge requiring further investigation.

The Cholangiopathies

Cholangiocytes (ie, the epithelial cells that line the bile ducts) are an important subset of liver cells. They are actively involved in the modification of bile volume and composition, are activated by interactions with endogenous and exogenous stimuli (eg, microorganisms, drugs), and participate in liver injury and repair. The term cholangiopathies refers to a category of chronic liver diseases that share a central target: the cholangiocyte. The cholangiopathies account for substantial morbidity and mortality given their progressive nature, the challenges associated with clinical management, and the lack of effective medical therapies. Thus, cholangiopathies usually result in end-stage liver disease requiring liver transplant to extend survival. Approximately 16% of all liver transplants performed in the United States between 1988 and 2014 were for cholangiopathies. For all these reasons, cholangiopathies are an economic burden on patients, their families, and society. This review offers a concise summary of the biology of cholangiocytes and describes a conceptual framework for development of the cholangiopathies. We also present the recent progress made in understanding the pathogenesis of and how this knowledge has influenced therapies for the 6 common cholangiopathies-primary biliary cirrhosis, primary sclerosing cholangitis, cystic fibrosis involving the liver, biliary atresia, polycystic liver disease, and cholangiocarcinoma-because the latest scientific progress in the field concerns these conditions. We performed a search of the literature in PubMed for published papers using the following terms: cholangiocytes, biliary epithelia, cholestasis, cholangiopathy, and biliary disease. Studies had to be published in the past 5 years (from June 1, 2009, through May 31, 2014), and non-English studies were excluded.

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.

Immunosenescence: Implications for response to infection and vaccination in older people

People aged 60 and older represent over 11% of the world population and it is expected to rise 22% by 2050. Population aging is associated to an increased frequency of age-related diseases including higher susceptibility to infections, cancer, cardiovascular and neurodegenerative diseases. Immunosenescence refers to the decline of the immune system associated to aging. It affects both, innate and adaptive immunity limiting the response to pathogens and to vaccines. The analyses of the immune system in elderly individuals determined several immune signatures constituting an immune risk phenotype that predicts mortality. An inverse CD4/CD8 ratio, loss of naïve T cells, increased numbers of terminally-differentiated T cells and oligoclonal expansions of virus-specific T cells constitute hallmarks of immunosenescence. Natural killer (NK) cells are also found severely altered in the elderly. The contribution of latent cytomegalovirus infection to immunosenescence of T and NK cells has been shown. Considering the worldwide ageing of the population in the next decades, the impact of infections will be a real health problem for older individuals requiring preventive strategies. Thus, further studies are required to analyse the bases of immunosenescence and to establish protocols to overcome the age-associated alterations of the immune response in order to define effective vaccines against those pathogens, such as influenza, contributing to increased morbidity and mortality in the elderly.

Low doses of CMV induce autoimmune-mediated and inflammatory responses in bile duct epithelia of regulatory T cell-depleted neonatal mice

Recent studies have indicated that perinatal infection with cytomegalovirus (CMV) may promote bile duct damage in biliary atresia (BA) and that the decreased regulatory T cell (Treg) percentage associated with BA may further amplify the bile duct damage. Although a majority of BA patients have had previous CMV infections and lower percentages of Tregs, it is unknown whether an initial exposure to a low dose of CMV could induce exaggerated and progressive biliary injury. A Treg-depleted neonatal mouse was infected with low-dose CMV (LD-CMV) as a model to study BA patients. LD-CMV infection in Treg-depleted mice induced extensive inflammation in both the intrahepatic and extrahepatic bile ducts, accompanied with injury to and atresia of intrahepatic bile ducts and partial obstruction of the extrahepatic bile ducts. Serum total and direct bilirubin amounts were also elevated. Evidence for the involvement of cellular and humoral autoimmune responses in LD-CMV-infection of Treg-depleted mice was also obtained through detection of increased percentages of CD3 and CD8 mononuclear cells and serum autoantibodies reactive to bile duct epithelial proteins, one of which was identified as α-enolase. Depletion of Tregs that can lead to the decreased inhibition of aberrantly activated hepatic T-lymphocytes and generation of autoantibodies may lead to further injury. Increased hepatic expression of Th1-related genes (TNF-α), IFN-γ-activated genes (STAT-1) and Th1 cytokines (TNF-α, lymphotactin, IL-12p40 and MIP -1γ) were also identified. In conclusion, autoimmune-mediated and inflammatory responses induced by LD-CMV infection in Treg-depleted mice results in increased intrahepatic and extrahepatic bile duct injury and contributed to disease progression.

Role of viruses and bacteria-virus interactions in autoimmunity

A potential role for viral and bacterial-viral interactions in the pathogenesis of autoimmune disease has been long recognized. Recently, intensive investigation has begun to decipher interactions between specific microbes with the host that contribute toward autoimmunity. This work has primarily focused on known viral and bacterial pathogens. A major challenge is to determine the role of bacteria that are typically considered as commensals as well as chronic viruses. Furthermore, equally challenging is to prove causality given the potential complexity of microbe-microbe interactions. Important initial contributions to this field have shown that specific interactions of microbes with hosts that contain a background of genetic susceptibility can play a role in autoimmune pathogenesis. In this review, we describe principles of immune tolerance with a focus on its breakdown during pathogenic as well as commensal relationships between the host and the microbial world.

Preliminary exploration of HLA-A 1101-restricted human cytomegalovirus glycoprotein B-specific CD8⁺ T cells in allogeneic stem-cell transplant recipients

T-cell responses directed against human cytomegalovirus (HCMV) glycoprotein B (gB) contribute to protective immunity against HCMV infection in both animal models and humans. However, the gB-specific human CD8(+) T cell responses remain poorly understood. gB antigen-specific CD8(+) T cells were stained with seven major histocompatibility complex (MHC)-peptide pentamers in 16 human leukocyte antigen (HLA)-A 1101-positive, HCMV-seropositive patients following hematopoietic stem cell transplantation (HSCT). Of these seven pentamers, the most frequent CD8(+) T-cell responses were directed against the gB332-340 peptide. These gB332-340-specific CD8(+) T cells were strongly associated with the presence of plasma HCMV immunoglobulin M in all HSCT recipients and exhibited a probable causal relationship with the level of pp65 antigenemia. Together, these data suggest a role for gB332-340-specific CD8(+) T cells in HCMV reactivation after HSCT. Furthermore, the pentamer assay may be valuable in detecting antigen-specific CD8(+) T cells.

High-dose IgG therapy mitigates bile duct-targeted inflammation and obstruction in a mouse model of biliary atresia

BACKGROUND

A proposed etiology of biliary atresia (BA) entails a virus-induced, progressive immune-mediated injury of the biliary system. Intravenous Ig (IVIg) has demonstrated clinical benefit in several inflammatory diseases. The aim of this study was to determine the therapeutic effects of high-dose IgG treatment in the rhesus rotavirus (RRV)-induced mouse model of BA.

METHODS

Newborn mice were infected with RRV, and jaundiced mice were given high-dose IgG or albumin control. Survival, histology, direct bilirubin, liver immune cell subsets, and cytokine production were analyzed.

RESULTS

There was no difference in overall survival between RRV-infected groups, however high-dose IgG resulted in decreased bilirubin, bile duct inflammation, and increased extrahepatic bile duct patency. High-dose IgG decreased vascular cell adhesion molecule-1, resulting in limited migration of immune cells to portal tracts. High-dose IgG significantly decreased CD4(+) T cell production of interleukin (IL)-2, interferon (IFN)-γ, and tumor necrosis factor (TNF)-α and CD8(+) T cell production of IFN-γ, as well as increased levels of regulatory T cells.

CONCLUSION

High-dose IgG therapy in murine BA dramatically decreased Th1 cell-mediated inflammation and biliary obstruction. This study lends support for consideration of IVIg clinical trials in infants with BA, to diminish the progressive intrahepatic bile duct injury.

Maternal microchimerism in biliary atresia: are maternal cells effector cells, targets, or just bystanders?

The etiology of biliary atresia (BA) is unknown; however, the liver histology is similar to that observed in immune-mediated hepatic disorders. Liver fibrosis in BA progresses even after bile drainage has been achieved by the Kasai operation. Maternal microchimerism has been purported to play a part in the pathogenesis of BA as well as certain autoimmune diseases. However, the role of maternal cells has not yet been determined in BA. Specifically, it is unknown whether these maternal cells function as maternal effector T lymphocytes, or targets or bystanders. We currently hypothesize that the first hit is due to GvHD interaction by engrafted maternal effector T lymphocytes. Furthermore, we suggest that the secondary effects that are manifested by progressive cirrhosis are caused either by maternal chimeric effector T lymphocytes (e.g., GvHD interaction) or targets (e.g., HvGD interaction). Based on our hypothesis, mixed lymphocyte reactions between patients and their mothers might shed light on the etiopathogenesis and prognostic indicators.

Elevated Th17 cells accompanied by decreased regulatory T cells and cytokine environment in infants with biliary atresia

PURPOSE

The aim of this study was to investigate the role of Th17 and T reg cells in biliary atresia (BA) and to assess the liver cytokine environment in BA patients.

METHODS

The percentages of Th17 and T reg cells in peripheral blood mononuclear cells (PBMCs) of BA patients and healthy controls (HC) were evaluated. The serum concentrations of IL-17a and IL-23 as well as Foxp3, IL-17a, ROR-γt, IL-6, IL-1β and TGF-β1 m-RNA and protein expressions in liver tissues and the number of Foxp3, IL-17a, ROR-γt, CD4 expressing cells which infiltrated the hepatic tissues were determined.

RESULTS

The Th17/T reg cell ratio (P < 0.001) and blood concentrations of IL-17a and IL-23 (P < 0.05) were increased in the BA as compared to the HC group. Expressions of Foxp3, ROR-γt, IL-17a, IL-1β, IL-6 as well as TGF-β1 mRNA and proteins were significantly increased in BA as compared to HC livers (P < 0.01, P < 0.05). High levels of IL-17a/ROR-γt-positive and moderate levels of Foxp3-positive cells infiltrated damaged BA bile ducts and the ratio of FoxP3+ T to CD4+ T cells was significantly lower in BA than in HC samples (P < 0.01).

CONCLUSION

Cytokine-induced imbalance between Th17 and T reg cells in BA livers may be involved in bile duct damage.

Regulatory T cells inhibit Th1 cell-mediated bile duct injury in murine biliary atresia

BACKGROUND & AIMS

Biliary atresia (BA) is a pediatric inflammatory disease of the biliary system which leads to cirrhosis and the need for liver transplantation. One theory regarding etiology is that bile duct injury is due to virus-induced autoreactive T cell-mediated inflammation. Regulatory T cell (Treg) abnormalities in BA could result in unchecked bystander inflammation and autoimmunity targeting bile ducts. The aim of this study was to determine if Tregs are dysfunctional in the rotavirus-induced mouse model of BA (murine BA).

METHODS

Murine BA resulted from infection of BALB/c neonates with Rhesus rotavirus (RRV).

RESULTS

Liver Tregs from BA mice were decreased in number, activation marker expression, and suppressive function. Adoptive transfer studies revealed that RRV-infected mice that received Tregs had significantly increased survival (84%) compared to controls (12.5%). In addition, ablation of Tregs in older mice, followed by RRV infection, resulted in increased bile duct injury.

CONCLUSIONS

These studies demonstrate that dysregulation of Tregs is present in murine BA and that diminished Treg function may be implicated in the pathogenesis of human BA.

Aetiology of biliary atresia: what is actually known?

Biliary atresia (BA) is a rare disease of unknown etiology and unpredictable outcome, even when there has been timely diagnosis and exemplary surgery. It has been the commonest indication for liver transplantation during childhood for the past 20 years. Hence much clinical and basic research has been directed at elucidating the origin and pathology of BA. This review summarizes the current clinical variations of BA in humans, its occasional appearance in animals and its various manifestations in the laboratory as an experimental model.

B cell deficient mice are protected from biliary obstruction in the rotavirus-induced mouse model of biliary atresia

A leading theory regarding the pathogenesis of biliary atresia (BA) is that bile duct injury is initiated by a virus infection, followed by an autoimmune response targeting bile ducts. In experimental models of autoimmune diseases, B cells have been shown to play an important role. The aim of this study was to determine the role of B cells in the development of biliary obstruction in the Rhesus rotavirus (RRV)-induced mouse model of BA. Wild-type (WT) and B cell-deficient (Ig-α(-/-)) mice received RRV shortly after birth. Ig-α(-/-) RRV-infected mice had significantly increased disease-free survival rate compared to WT RRV-infected BA mice (76.8% vs. 17.5%). In stark contrast to the RRV-infected BA mice, the RRV-infected Ig-α(-/-) mice did not have hyperbilirubinemia or bile duct obstruction. The RRV-infected Ig-α(-/-) mice had significantly less liver inflammation and Th1 cytokine production compared to RRV-infected WT mice. In addition, Ig-α(-/-) mice had significantly increased numbers of regulatory T cells (Tregs) at baseline and after RRV infection compared to WT mice. However, depletion of Tregs in Ig-α(-/-) mice did not induce biliary obstruction, indicating that the expanded Tregs in the Ig-α(-/-) mice were not the sole reason for protection from disease. Conclusion : B cell deficient Ig-α(-/-) mice are protected from biliary obstruction in the RRV-induced mouse model of BA, indicating a primary role of B cells in mediating disease pathology. The mechanism of protection may involve lack of B cell antigen presentation, which impairs T-cell activation and Th1 inflammation. Immune modulators that inhibit B cell function may be a new strategy for treatment of BA.

Prevention of cholestasis in the murine rotavirus-induced biliary atresia model using passive immunization and nonreplicating virus-like particles

Biliary atresia (BA) is a neonatal cholangiopathy of unknown etiology that results in obliteration of bile ducts and is the primary indication for liver transplant in children. A murine model of BA, which involves infecting newborn mice with rhesus rotavirus (RRV) and leads to development of an obstructive cholangiopathy, has provided a model to assess measures to prevent and treat BA. We used this mouse model of RRV-induced BA to determine if passive immunization of pups using maternal immunization [injection of dams with non-replicating rotavirus (RV) virus-like particles (VLPs) or live RRV] or injection of pups with RV immune serum would protect these RRV-infected neonates from developing BA (measured using cholestasis). Parenteral immunization of mouse dams with two formulations of VLPs (containing viral proteins 2/6 or 2/6/7) resulted in a significant increase in serum RV antibody, and pups born to these immunized dams were protected from developing cholestasis following neonatal infection with RRV. Serum RV-specific antibody with titers of ≥400-800 in dams significantly protected pups from developing cholestasis, and a significant trend of increasing protection with high titers was observed (p<0.0001). Cholestatic pups had lower levels of RV serum antibody and higher serum (p<0.01) and liver (p<0.05) RV antigen compared to healthy pups. Passive transfer of low-titer (1600; p<0.05) or high-titer (25,600; p<0.01) RV immune serum to neonatal pups prior to RRV infection also protected them from developing cholestasis. Together, these findings indicate that passively acquired, neutralizing or non-neutralizing RV serum antibody attenuates viral replication and protects pups against disease in the RRV BA model. Early reduction of viral load by clearance with RV-specific antibody is likely a critical determinant of disease in this model.

Lack of HLA predominance and HLA shared epitopes in biliary Atresia

Biliary atresia (BA) is characterized by progressive inflammation and fibrosis of bile ducts. A theory of pathogenesis entails autoimmune-mediated injury targeting bile duct epithelia. One of the strongest genetic associations with autoimmunity is with HLA genes. In addition, apparently dissimilar HLA alleles may have similar antigen-binding sites, called shared epitopes, that overlap in their capacity to present antigens. In autoimmune disease, the incidence of the disease may be related to the presence of shared epitopes, not simply the HLA allelic association. Aim: To determine HLA allele frequency (high-resolution genotyping) and shared epitope associations in BA. Results: Analysis of every allele for HLA-A, -B, -C, -DRB1, -DPB1 and -DQB1 in 180 BA and 360 racially-matched controls did not identify any significant HLA association with BA. Furthermore, shared epitope analysis of greater than 10 million possible combinations of peptide sequences was not different between BA and controls. Conclusions: This study encompasses the largest HLA allele frequency analysis for BA in the United States and is the first study to perform shared epitope analysis. When controlling for multiple comparisons, no HLA allele or shared epitope association was identified in BA. Future studies of genetic links to BA that involve alterations of the immune response should include investigations into defects in regulatory T cells and non-HLA linked autoinflammatory diseases.

Clues to the etiology of bile duct injury in biliary atresia

Biliary atresia (BA) is an infantile obstructive cholangiopathy of unknown etiology with suboptimal therapy, which is responsible for 40 to 50% of all pediatric liver transplants. Although the etiology of bile duct injury in BA in unknown, it is postulated that a pre- or perinatal viral infection initiates cholangiocyte apoptosis and release of antigens that trigger a Th1 immune response that leads to further bile duct injury, inflammation, and obstructive fibrosis. Humoral immunity and activation of the innate immune system may also play key roles in this process. Moreover, recent investigations from the murine BA model and human data suggest that regulatory T cells and genetic susceptibility factors may orchestrate autoimmune mechanisms. What controls the coordination of these events, why the disease only occurs in the first few months of life, and why a minority of infants with perinatal viral infections develop BA are remaining questions to be answered.

Biliary atresia: cellular dynamics and immune dysregulation

The cause of biliary atresia is unknown; in the past few decades, the majority of investigations related to its pathogenesis have centered on viral infections and immunity. The acquired or perinatal form of biliary atresia entails a progressive inflammatory injury of bile ducts, leading to fibrosis and obliteration of both the extrahepatic and intrahepatic bile ducts. Theories of pathogenesis include viral infection, chronic inflammatory or autoimmune-mediated bile duct injury, and abnormalities in bile duct development. This review will focus solely on human studies pertaining to a potential viral trigger of bile duct injury at diagnosis and provide insight into the interplay of the innate and adaptive immune responses in the pathogenesis of disease.

Regulatory T cells control the CD8 adaptive immune response at the time of ductal obstruction in experimental biliary atresia

CD8 T-lymphocytes are effector cells of cholangiocyte injury in human and in rhesus rotavirus (RRV)-induced experimental biliary atresia (BA). Here we hypothesize that neonatal deficiency in CD25(+) CD4(+) regulatory T cells (Tregs) leads to aberrant activation of hepatic T-lymphocytes in BA. We found that adoptive transfer of total CD4 cells, but not of CD25-depleted CD4 cells, prior to RRV inoculation reduced expansion of CD8 cells, plasma bilirubin levels, ductal inflammation, and bile duct epithelial injury at 7 days postinfection (dpi) compared with age-matched infected controls without adoptive transfer. Searching for mechanisms, we found that in vitro production of interferon-gamma (IFN-γ) by naïve CD8 cells upon polyclonal stimulation was enhanced in coculture with hepatic dendritic cells (DCs) from RRV-infected, but not with DCs from noninfected mice, which was correlated with an increased proportion of CD11b(+) myeloid (m)DCs and up-regulation of the costimulatory molecule CD86 on RRV-primed DCs. Furthermore, DC-dependent T-lymphocyte activation was blocked by anti-CD86 antibody in dose-dependent fashion. Importantly, expression of CD86 on mDCs was down-regulated by Tregs in vitro, and adoptive transfer of Treg-containing CD4 cells decreased expression of CD86 on hepatic mDCs at 7 dpi. On the contrary, in mice resistant to experimental BA, CD25+ cell depletion aggravated bile duct injury at 12 dpi after RRV inoculation, as plasma bilirubin levels were elevated by >20-fold compared with nondepleted infected controls. Increased susceptibility to hepatobiliary injury in Treg-depleted mice was linked to hepatic CD8 expansion and enhanced stimulatory capacity of hepatic DCs.

CONCLUSION

Activation of hepatic T-lymphocytes driving biliary obstruction in BA is regulated by mDCs by way of CD86-dependent costimulation and is susceptible to inhibition by Tregs.