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

Development of liver inflammatory injury in biliary atresia: from basic to clinical research

Biliary atresia (BA) is a severe cholangiopathy in infants. It is characterized by inflammatory fibro-obliteration of the intra- and extrahepatic bile ducts. Although the restoration of bile flow can be successful after Kasai operation, the rapid progression of liver fibrosis can continue, leading to cirrhosis. It is believed that the progression of liver fibrosis in BA is exacerbated by complicated mechanisms other than the consequence of bile duct obstruction. The fibrogenic cascade in BA liver can be divided into three stages, including liver inflammatory injury, myofibroblast activation, and fibrous scar formation. Recent studies have revealed that the activation of an immune response following bile duct injury plays an important role in promoting the inflammatory process, the releasing of inflammatory cytokines, and the development of fibrogenesis in BA liver. In this article, we summarized the evidence regarding liver inflammatory injury and the possible mechanisms that explain the rapid progression of liver fibrosis in BA.

Identification of Hub Genes and Immune Infiltration in Pediatric Biliary Atresia by Comprehensive Bioinformatics Analysis

Background: Biliary atresia (BA) is the leading cause of pediatric liver failure and pediatric liver transplantation worldwide. Evidence suggests that the immune system plays a central role in the pathogenesis of BA. Methods: In this work, the novel immune-related genes between BA and normal samples were investigated based on weighted gene co-expression network analysis (WGCNA) and the deconvolution algorithm of CIBERSORT. Results: Specifically, 650 DEGs were identified between the BA and normal groups. The blue module was the most positively correlated with BA containing 3274 genes. Totally, 610 overlapping BA-related genes of DEGs and WGCNA were further used to identify IRGs. Three IRGs including VCAM1, HLA-DRA, and CD74 were finally identified as the candidate biomarkers. Particularly, the CD74 biomarker was discovered for the first as a potential immune biomarker for BA. Conclusions: Possibly, these 3 IRGs might serve as candidate biomarkers and guide the individualized treatment strategies for BA patients. Our results would provide great insights for a deeper understanding of both the occurrence and the treatment of BA.

Update on Etiology and Pathogenesis of Biliary Atresia

Biliary atresia is a rare inflammatory sclerosing obstructive cholangiopathy that initiates in infancy as complete choledochal blockage and progresses to the involvement of intrahepatic biliary epithelium. Growing evidence shows that biliary atresia is not a single entity with a single etiology but a phenotype resulting from multifactorial events whose common path is obliterative cholangiopathy. The etiology of biliary atresia has been explained as resulting from genetic variants, toxins, viral infection, chronic inflammation or bile duct lesions mediated by autoimmunity, abnormalities in the development of the bile ducts, and defects in embryogenesis, abnormal fetal or prenatal circulation and susceptibility factors. It is increasingly evident that the genetic and epigenetic predisposition combined with the environmental factors to which the mother is exposed are potential triggers for biliary atresia. There is also an indication that a progressive thickening of the arterial middle layer occurs in this disease, suggestive of vascular remodeling and disappearance of the interlobular bile ducts. It is suggested that the hypoxia/ischemia process can affect portal structures in biliary atresia and is associated with both the extent of biliary proliferation and the thickening of the medial layer.

The Role of B Cells in Adult and Paediatric Liver Injury

B lymphocytes are multitasking cells that direct the immune response by producing pro- or anti-inflammatory cytokines, by presenting processed antigen for T cell activation and co-stimulation, and by turning into antibody-secreting cells. These functions are important to control infection in the liver but can also exacerbate tissue damage and fibrosis as part of persistent inflammation that can lead to end stage disease requiring a transplant. In transplantation, immunosuppression increases the incidence of lymphoma and often this is of B cell origin. In this review we bring together information on liver B cell biology from different liver diseases, including alcohol-related and metabolic fatty liver disease, autoimmune hepatitis, primary biliary and primary sclerosing cholangitis, viral hepatitis and, in infants, biliary atresia. We also discuss the impact of B cell depletion therapy in the liver setting. Taken together, our analysis shows that B cells are important in the pathogenesis of liver diseases and that further research is necessary to fully characterise the human liver B cell compartment.

Unique Cholangiocyte-Targeted IgM Autoantibodies Correlate With Poor Outcome in Biliary Atresia

BACKGROUND AND AIMS

The etiology of biliary atresia (BA) is not known and is likely multifactorial, including a genetic predisposition, a viral or environmental trigger, an aberrant autoimmune response targeting cholangiocytes, and unique susceptibilities of the neonatal bile ducts to injury. Damaged cholangiocytes may express neo self-antigens and elicit autoreactive T-cell-mediated inflammation and B-cell production of autoantibodies. The aim of this study was to discover autoantibodies in BA that correlated with outcomes.

APPROACH AND RESULTS

An autoantigen microarray encompassing approximately 9,500 autoantigens was used to screen for serum immunoglobulin M (IgM) and immunoglobulin G (IgG) autoantibodies in patients with BA or other liver disease controls. Validation of candidate autoantibodies by enzyme-linked immunosorbent assay on a second cohort of subjects (6-12 months following Kasai portoenterostomy) and correlations of autoantibodies with outcomes were performed (serum bilirubin levels and need for liver transplant in first 2 years of life). Mean anti-chitinase 3-like 1 (CHI3L1), anti-delta-like ligand (DLL-4), and antisurfactant protein D (SFTPD) IgM autoantibodies in BA were significantly higher compared with controls, and IgM autoantibody levels positively correlated with worse outcomes. Immunofluorescence revealed cholangiocyte-predominant expression of CHI3L1, DLL-4, and SFTPD. The humoral autoantibody response was associated with C3d complement activation and T-cell autoimmunity, based on detection of cholangiocyte-predominant C3d co-staining and peripheral blood autoreactive T cells specific to CHI3L1, DLL-4 and SFTPD, respectively.

CONCLUSIONS

BA is associated with cholangiocyte-predominant IgM autoantibodies in the first year after Kasai portoenterostomy. Anti-CHI3L1, anti-DLL-4, and anti-SFTPD IgM autoantibody correlations with worse outcomes and the detection of C3d on cholangioctyes and antigen-specific autoreactive T cells suggest that autoimmunity plays a role in the ongoing bile duct injury and progression of disease.

Unsupervised Clustering Reveals Distinct Subtypes of Biliary Atresia Based on Immune Cell Types and Gene Expression

BACKGROUND

Biliary atresia (BA) is a severe cholangiopathy of early infancy that destroys cholangiocytes, obstructs ductular pathways and if left untreated, culminates to liver cirrhosis. Mechanisms underlying the etiological heterogeneity remain elusive and few studies have attempted phenotyping BA. We applied machine learning to identify distinct subtypes of BA which correlate with the underlying pathogenesis.

METHODS

The BA microarray dataset GSE46995 was downloaded from the Gene Expression Omnibus (GEO) database. Unsupervised hierarchical cluster analysis was performed to identify BA subtypes. Then, functional enrichment analysis was applied and hub genes identified to explore molecular mechanisms associated with each subtype. An independent dataset GSE15235 was used for validation process.

RESULTS

Based on unsupervised cluster analysis, BA patients can be classified into three distinct subtypes: Autoimmune, Viral and Embryonic subtypes. Functional analysis of Subtype 1 correlated with Fc Gamma Receptor (FCGR) activation and hub gene FCGR2A, suggesting an autoimmune response targeting bile ducts. Subtype 2 was associated with immune receptor activity, cytokine receptor, signaling by interleukins, viral protein interaction, suggesting BA is associated with viral infection. Subtype 3 was associated with signaling and regulation of expression of Robo receptors and hub gene ITGB2, corresponding to embryonic BA. Moreover, Reactome pathway analysis showed Neutrophil degranulation pathway enrichment in all subtypes, suggesting it may result from an early insult that leads to biliary stasis.

CONCLUSIONS

The classification of BA into different subtypes improves our current understanding of the underlying pathogenesis of BA and provides new insights for future studies.

Synthetic retinoid AM80 inhibits IL-17 production of gamma delta T cells and ameliorates biliary atresia in mice

BACKGROUND & AIMS

Recent evidence suggests that Interleukin (IL)-17-producing gamma delta ( γδ ) T cells are the dominant pathogenic cellular component in designated autoimmune or inflammatory diseases, including biliary atresia (BA). We have previously demonstrated that retinoids effectively suppress T-helper cell (Th) 17 differentiation.

METHODS

Here, we established an in vitro system, enabling investigations of the effect of AM80 on the IL-17 production of γδ T cells. Additionally, we tested the therapeutic effect of AM80 in the Rotavirus-induced mouse model of BA. Co-incubation of γδ T cells with IL-23 and anti-CD28 mAb proved most effective in inducing an IL-17 response in vitro. The effect of AM80 on human CCR6+CD26+ V δ 2 cells was assessed by flow cytometry.

RESULTS

AM80 efficiently reduced IL-17 production by murine γδ T cells and the expression of the master transcription factor Retinoid-Orphan-Receptor- γ t (ROR γτ ) in a dose-dependent manner. The fraction of human CCR6+CD26+ V δ 2 cells was significantly reduced by co-incubation with AM80. Moreover, AM80 also inhibited IL-17 production by liver-infiltrating γδ T cells isolated from animals suffering from BA. Intraperitoneal treatment with AM80 ameliorated BA-associated inflammation. However, AM80 treatment was not sufficient to control disease progression in the murine model, despite reduced inflammatory activity in the animals.

CONCLUSIONS

Retinoids are very efficient in down-regulating IL-17 production by γδ T cells in vitro and, to a lesser extent, in the BA mouse model. However, retinoids do not suffice for the control of disease progression. Thus, our data suggest that IL-17 is not the only factor contributing to the pathogenesis of BA.

LAY SUMMARY

Biliary atresia (BA) is a rare disease which affects infants, causing progressive liver failure in most children, and is the most common indication for paediatric liver transplantation. We have previously demonstrated that IL-17, produced by γδ T cells, contributes to hepatic inflammation in the murine model of BA and is increased in the livers of infants suffering from the disease. In the study at hand, we demonstrate that treatment with AM80, a synthetic retinoid with superior pharmacological properties, effectively inhibits the IL-17 production of gamma delta T cells without generating systemic immunosuppression. Although all-trans retinoic acid (ATRA) has been demonstrated to suppress differentiation of IL-17-producing conventional T-helper cells (Th17) in vitro, the therapeutic application of ATRA in vivo is limited by the compound's potential side effects caused by its instability and lack of receptor specificity. Our study is the first to show that AM80 suppresses the IL-17 production of γδ T cells in a very efficient manner and that hepatic inflammation is ameliorated in mice suffering from BA. However, AM80 treatment does not suffice to block the disease progression. We conclude that factors other than IL-17 drive the progressive inflammation in BA. The addition of retinoids to the treatment regime of children suffering from BA might decrease the disease burden; however, further research is needed to clarify the pathomechanism and possible therapeutic interventions in humans.

The relative abundance of monocyte subsets determines susceptibility to perinatal hepatic inflammation

The devastating consequences of perinatal liver inflammation contribute to a pressing need to develop therapeutics for the diseases that underly this condition. Biliary atresia (BA) is a perinatal inflammatory disease of the liver that results in obliterative cholangiopathy and rapidly progresses to liver failure, requiring transplantation. The ability to develop targeted therapies requires an understanding of the immune mechanisms that mitigate perinatal liver inflammation. This article reviews our recent findings demonstrating that in a murine model of perinatal hepatic inflammation, Ly6c^Lo non-classical monocytes express a pro-reparative transcriptomic profile and that the relative abundance of Ly6c^Lo monocytes promotes resolution of perinatal liver inflammation, rendering neonatal pups resistant to disease. We also examine the lineage relationship between monocyte subsets, reviewing data that suggests classical monocytes are a precursor for non-classical monocytes, and the alternative possibility that separate progenitors exist for each subset. Although a precursor-product relationship between classical and non-classical monocytes might exist in certain environments, we argue that they may also arise from separate progenitors, which is evident by sustained Ly6c^Lo non-classical monocyte expansion when Ly6c^Hi monocytes are absent. An improved understanding of monocyte subsets and their developmental trajectories during perinatal hepatic inflammation will provide insight into how therapies directed at controlling monocyte function may help alleviate the devastating consequences of diseases like BA.

Inflammation Drives MicroRNAs to Limit Hepatocyte Bile Acid Transport in Murine Biliary Atresia

BACKGROUND

Biliary atresia (BA) is an inflammatory pediatric cholangiopathy with only surgical means for treatment. Many contributors to bile acid synthesis and transport have previously been reported to be downregulated in patients with BA; yet, the driving factors of the abnormal bile acid synthesis and transport in regard to BA have not been previously studied.

MATERIALS AND METHODS

Wild type or Ig-α^-/- mice were injected with salt solution (control) or rotavirus on day of life 0, and analyses were performed on day of life 14. The mRNA levels of bile acid transporters/nuclear receptors and liver microRNAs (miRNAs) were compared between groups. A mouse hepatocyte cell line was used to examine the effects of innate cytokines on miRNA levels and bile acid transporter/nuclear receptor expression and miRNAs on bile acid transporter/nuclear receptor expression.

RESULTS

BA mice had significantly increased mRNA expression of innate cytokines and miRNAs known to bind bile acid transporters/nuclear receptors (miRNAs -22-5p, -34a-5p, and -222-3p) and decreased mRNA expression of bile acid transporters and nuclear receptors. In vitro, TNF-α and IL-1β decreased BSEP and CYP7A1 while increasing miRNA-34a-5p and miRNA 222-3p. LXR, SHP, CYP7A1, NTCP, and MRP2 were decreased by miRNA-34a-5p, whereas miRNA-222-3p decreased NTCP and MRP4. TNF-α and IL-1β increased expression of miRNAs 34a-5p and 222-3p and these miRNAs then decrease expression of multiple bile acid transporters and nuclear receptors.

CONCLUSIONS

Loss of bile acid transporters increases hepatotoxicity via bile acid retention. Therapeutic agents that increase bile acid transport or nuclear receptor functioning should be investigated in BA.

Rotavirus and autoimmunity

Rotavirus, a major etiological agent of acute diarrhea in children worldwide, has historically been linked to autoimmunity. In the last few years, several physiopathological approaches have been proposed to explain the leading mechanism triggering autoimmunity, from the old concept of molecular mimicry to the emerging theory of bystander activation and break of tolerance. Epidemiological and immunological data indicate a strong link between rotavirus infection and two of the autoimmune pathologies with the highest incidence: celiac disease and diabetes. The role for current oral rotavirus vaccines is now being elucidated, with a so far positive protective association demonstrated.

Ly6cLo non-classical monocytes promote resolution of rhesus rotavirus-mediated perinatal hepatic inflammation

Perinatal hepatic inflammation can have devastating consequences. Monocytes play an important role in the initiation and resolution of inflammation, and their diverse functions can be attributed to specific cellular subsets: pro-inflammatory or classical monocytes (Ly6c^Hi) and pro-reparative or non-classical monocytes (Ly6c^Lo). We hypothesized that inherent differences in Ly6c^Hi classical monocytes and Ly6c^Lo non-classical monocytes determine susceptibility to perinatal hepatic inflammation in late gestation fetuses and neonates. We found an anti-inflammatory transcriptional profile expressed by Ly6c^Lo non-classical monocytes, and a physiologic abundance of these cells in the late gestation fetal liver. Unlike neonatal pups, late gestation fetuses proved to be resistant to rhesus rotavirus (RRV) mediated liver inflammation. Furthermore, neonatal pups were rendered resistant to RRV-mediated liver injury when Ly6c^Lo non-classical monocytes were expanded. Pharmacologic inhibition of Ly6c^Lo non-classical monocytes in this setting restored susceptibility to RRV-mediated disease. These data demonstrate that Ly6c^Lo monocytes promote resolution of perinatal liver inflammation in the late gestation fetus, where there is a physiologic expansion of non-classical monocytes, and in the neonatal liver upon experimental expansion of these cells. Therapeutic strategies directed towards enhancing Ly6c^Lo non-classical monocyte function may mitigate the detrimental effects of perinatal liver inflammation.

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.

The Contribution of B Cells in Autoimmune Liver Diseases

Autoreactive B cells can promote autoimmunity through antigen presentation to autoreactive T cells, production of autoantibodies, generation of cytokines promoting T cell activation and differentiation, and inhibition of regulatory T cells and B cells. Here, the authors highlight studies pertaining to B cell mechanisms associated with disease pathogenesis and outcomes in autoimmune hepatitis and the immune-mediated cholangiopathies (primary biliary cholangitis, primary sclerosing cholangitis, and biliary atresia). The vast majority of investigations focus on autoantibodies and future research endeavors should include deciphering the role of the B cell in T cell activation (through antigen presentation, cytokine/chemokine production, and inhibition of regulation). Targeting B cell mechanisms in the treatment of autoimmune liver diseases is also highlighted.

A Phase I/IIa Trial of Intravenous Immunoglobulin Following Portoenterostomy in Biliary Atresia

OBJECTIVES

Biliary atresia (BA) is a progressive neonatal fibroinflammatory cholangiopathy. We hypothesized that intravenous immunoglobulin (IVIg) would be safe, feasible, acceptable, and efficacious for the treatment of BA. The primary objective of this study was to establish the feasibility, acceptability, and safety profile of IVIg administration after hepatoportoenterostomy (HPE) in BA. The secondary objective was to determine the treatment efficacy of IVIg based on good bile drainage and survival with the native liver.

METHODS

A multicenter, prospective, open-labeled, phase I/IIA trial of IVIg was conducted, with 1 g/kg/dose of IVIg infused at 3-5, 30, and 60 days post-HPE, and subjects followed for 360 days post-HPE. Twenty-nine participants completed the study.

RESULTS

Administration of IVIg infusions was feasible and acceptable in 79%. None of the serious adverse events (SAEs) were directly related to IVIg infusions; however, 90% of participants had an SAE. Compared with a historical placebo-arm group, there was no significant increase in the proportion of IVIg participants with a serum total bilirubin <1.5 mg/dL at 90, 180, or 360 days post-HPE. Survival with the native liver in the IVIg participants showed no significant benefit over the historical placebo arm, with a difference at 360 days of -11.9% (IVIg: 58.6%, placebo: 70.5%; 90% UCB: 2.1%; P > 0.05).

CONCLUSIONS

Although IVIg infusions in infants with BA post-HPE were feasible, acceptable and safe, there was no trend to lower bilirubin levels or improved 360-day survival with the native liver.

CLINICAL TRIAL

Safety Study of Intravenous Immunoglobulin Post-Portoenterostomy in Biliary Atresia; #NCT01854827.

Correlation of Immune Markers With Outcomes in Biliary Atresia Following Intravenous Immunoglobulin Therapy

Biliary atresia is a progressive fibroinflammatory cholangiopathy of infancy that is associated with activation of innate and adaptive immune responses targeting bile ducts. A recently completed multicenter phase I/IIA trial of intravenous immunoglobulin in biliary atresia did not improve serum total bilirubin levels at 90 days after hepatoportoenterostomy or survival with the native liver at 1 year. A mechanistic aim of this trial was to determine if the peripheral blood immunophenotype was associated with clinical outcomes. Flow cytometry of peripheral blood cell markers (natural killer [NK], macrophage subsets, T‐ and B‐cell subsets, regulatory T cells), neutrophils, and activation markers (clusters of differentiation [CD]38, CD69, CD86, human leukocyte antigen‐DR isotype [HLA‐DR]) was performed on 29 patients with biliary atresia at baseline and at 60, 90, 180, and 360 days after hepatoportoenterostomy. Plasma cytokines and neutrophil products were also measured. Spearman correlations of change of an immune marker from baseline to day 90 with change in serum bilirubin revealed that an increase in total bilirubin correlated with 1) increased percentage of HLA‐DR⁺CD38⁺ NK cells and expression of NK cell activation markers CD69 and HLA‐DR, 2) decreased percentage of regulatory T cells, and 3) increased interleukin (IL)‐8 and associated neutrophil products (elastase and neutrophil extracellular traps). Cox modeling revealed that the change from baseline to day 60 of the percentage of HLA‐DR⁺CD38⁺ NK cells and plasma IL‐8 levels was associated with an increased risk of transplant or death by day 360. Conclusion: Poor outcomes in biliary atresia correlated with higher peripheral blood NK cells and IL‐8 and lower regulatory T cells. Future studies should include immunotherapies targeting these pathways in order to protect the biliary tree from ongoing damage.

Oligoclonal immunoglobulin repertoire in biliary remnants of biliary atresia

Biliary atresia (BA) is a neonatal cholestatic liver disease that is the leading cause of pediatric liver transplantation, however, the mechanism of disease remains unknown. There are two major forms of BA: isolated BA (iBA) comprises the majority of cases and is thought to result from an aberrant immune response to an environmental trigger, whereas syndromic BA (BASM) has associated malformations and is thought to arise from a congenital insult. To determine whether B cells in BA biliary remnants are antigen driven, we examined the immunoglobulin (Ig) repertoire of diseased tissue from each BA group. Deep sequencing of the Ig chain DNA was performed on iBA and BASM biliary remnants and lymph nodes obtained from the Childhood Liver Disease Research Network (ChiLDReN) repository. Statistical analysis of the Ig repertoire provided measures of Ig clonality and the Ig phenotype. Our data demonstrate that B cells infiltrate diseased iBA and BASM biliary remnant tissue. The Ig repertoires of iBA and BASM disease groups were oligoclonal supporting a role for an antigen-driven immune response in both sub-types. These findings shift the current understanding of BA and suggest a role for antigen stimulation in early iBA and BASM disease pathogenesis.

Cytokine-Producing B Cells Promote Immune-Mediated Bile Duct Injury in Murine Biliary Atresia

Biliary atresia (BA) is a neonatal T cell-mediated, inflammatory, sclerosing cholangiopathy. In the rhesus rotavirus (RRV)-induced neonatal mouse model of BA (murine BA), mice lacking B cells do not develop BA, and the lack of B cells is associated with loss of T-cell and macrophage activation. The aim of this study was to determine the mechanism of B cell-mediated immune activation (antigen presentation versus cytokine production) in murine BA. Normal neonatal B cells in the liver are predominantly at pro-B and pre-B cellular development. However, BA mice exhibit a significant increase in the number and activation status of mature liver B cells. Adoptively transferred B cells into RRV-infected, B cell-deficient mice were able to reinstate T-cell and macrophage infiltration and biliary injury. Nonetheless, neonatal liver B cells were incompetent at antigen presentation to T cells. Moreover, 3-83 immunoglobulin transgenic mice, in which B cells only present an irrelevant antigen, developed BA, indicating a B-cell antigen-independent mechanism. B cells from BA mice produced a variety of innate and adaptive immune cytokines associated with immune activation. In vitro trans-well studies revealed that BA B cells secreted cytokines that activated T cells based on increased expression of T-cell activation marker cluster of differentiation 69. Conclusion: Neonatal liver B cells are highly activated in murine BA and contribute to immune activation through production of numerous cytokines involved in innate and adaptive immunity; this work provides increased knowledge on the capacity of neonatal B cells to contribute to an inflammatory disease through cytokine-mediated mechanisms, and future studies should focus on targeting B cells as a therapeutic intervention in human BA.

Update on investigations pertaining to the pathogenesis of biliary atresia

Biliary atresia is a devastating biliary disease of neonates that results in liver transplantation for the vast majority. The etiology of biliary atresia is unknown and is likely multifactorial, with components of genetic predisposition, environmental trigger and autoimmunity contributing to disease pathogenesis. This review highlights recent work related to investigations of disease pathogenesis in biliary atresia.

Expression of programmed death-1 and its ligands in the liver of biliary atresia

BACKGROUND

An aberrant immune response is the predominant pathogenetic factor in biliary atresia (BA). Programmed death-1 (PD-1) and its two ligands, programmed death ligand-1 and programmed death ligand-2 (PD-L1 and PD-L2, respectively) play an important inhibitory role in immune reactions. We aimed to illustrate the expression of these molecules in BA.

METHODS

Liver specimens were obtained from infants with BA during the Kasai procedure (early BA) and liver transplantation (late BA). Intrahepatic expression of PD- 1, PD-L1, and PD-L2 were examined by immunostaining and compared with that in patients with neonatal hepatitis syndrome and normal controls. The correlation between the expression levels of these molecules in the liver and clinicopathological parameters was analyzed for each group.

RESULTS

Enhanced expression of PD-1 and its ligands occurred in the livers with early BA. In the BA-affected livers, PD-1 was correlated with the degree of peri-biliary inflammation, while PD-L2 was linked more directly with portal fibrosis. None of the three molecules was correlated with the prognosis of the Kasai procedure in patients with early BA.

CONCLUSIONS

Only PD-1 and PD-L1 are involved in the immune reactions of early BA. Elucidation of the detailed role of PD-L2 in BA requires further research.

Mechanisms by Which B Cells and Regulatory T Cells Influence Development of Murine Organ-Specific Autoimmune Diseases

Experiments with B cell-deficient (B−/−) mice indicate that a number of autoimmune diseases require B cells in addition to T cells for their development. Using B−/− Non-obese diabetic (NOD) and NOD.H-2h4 mice, we demonstrated that development of spontaneous autoimmune thyroiditis (SAT), Sjogren’s syndrome and diabetes do not develop in B−/− mice, whereas all three diseases develop in B cell-positive wild-type (WT) mice. B cells are required early in life, since reconstitution of adult mice with B cells or autoantibodies did not restore their ability to develop disease. B cells function as important antigen presenting cells (APC) to initiate activation of autoreactive CD4+ effector T cells. If B cells are absent or greatly reduced in number, other APC will present the antigen, such that Treg are preferentially activated and effector T cells are not activated. In these situations, B−/− or B cell-depleted mice develop the autoimmune disease when T regulatory cells (Treg) are transiently depleted. This review focuses on how B cells influence Treg activation and function, and briefly considers factors that influence the effectiveness of B cell depletion for treatment of autoimmune diseases.

Biliary atresia and other cholestatic childhood diseases: Advances and future challenges

Biliary Atresia and other cholestatic childhood diseases are rare conditions affecting the function and/or anatomy along the canalicular-bile duct continuum, characterised by onset of persistent cholestatic jaundice during the neonatal period. Biliary atresia (BA) is the most common among these, but still has an incidence of only 1 in 10-19,000 in Europe and North America. Other diseases such as the genetic conditions, Alagille syndrome (ALGS) and Progressive Familial Intrahepatic Cholestasis (PFIC), are less common. Choledochal malformations are amenable to surgical correction and require a high index of suspicion. The low incidence of such diseases hinder patient-based studies that include large cohorts, while the limited numbers of animal models of disease that recapitulate the spectrum of disease phenotypes hinders both basic research and the development of new treatments. Despite their individual rarity, collectively BA and other cholestatic childhood diseases are the commonest indications for liver transplantation during childhood. Here, we review the recent advances in basic research and clinical progress in these diseases, as well as the research needs. For the various diseases, we formulate current key questions and controversies and identify top priorities to guide future research.

Toll-like receptor 3 mediates PROMININ-1 expressing cell expansion in biliary atresia via Transforming Growth Factor-Beta

BACKGROUND

In biliary atresia (BA), epithelial-mesenchymal hepatic progenitor cells (HPC) expressing the stem/progenitor cell marker PROMININ-1 (PROM1) undergo expansion and subsequent transdifferentiation into collagen-producing myofibroblasts within regions of evolving biliary fibrosis under the regulation of Transforming Growth Factor-β (TGFβ) signaling. We hypothesized that pro-inflammatory Toll-like Receptor-3 (TLR3) signal activation promotes the differentiation of PROM1+ HPC via TGFβ pathway activation in vitro.

METHODS

PROM1+ Mat1a(-/-) HPC were treated with a double-stranded RNA analog, polyionosinic-polycytidylic acid (Poly I:C), ± small molecule inhibitors nafamostat, or SB431542.

RESULTS

Poly I:C induced myofibroblastic-like morphologic changes, degradation of IκB-α consistent with TLR3-NFκB activation, a 15-fold increase in the expression of Vimentin, a 9-fold increase in Collagen-1a, a 4.6-fold increase in Snail at 24h (p<0.05), and an 8.2-fold increase in Prom1 at 72h (p<0.0001) by qPCR. Immunofluorescence demonstrated nuclear phosphorylated SMAD3, TLR3, and COLLAGEN-1α staining following Poly I:C treatment. Degradation of IκBα was inhibited by nafamostat. Co-treatment with either nafamostat or SB431542 blocked the morphologic change and abrogated the increased expression of Cd133, Collagen, Vimentin, and Snail1.

CONCLUSIONS

TLR3 activation induces myofibroblastic differentiation of PROM1+ HPC in part via TGFβ pathway activation to promote BA-associated biliary fibrosis.

Identification of a plant isoflavonoid that causes biliary atresia

Biliary atresia (BA) is a rapidly progressive and destructive fibrotic disorder of unknown etiology affecting the extrahepatic biliary tree of neonates. Epidemiological studies suggest that an environmental factor, such as a virus or toxin, is the cause of the disease, although none have been definitively established. Several naturally occurring outbreaks of BA in Australian livestock have been associated with the ingestion of unusual plants by pregnant animals during drought conditions. We used a biliary secretion assay in zebrafish to isolate a previously undescribed isoflavonoid, biliatresone, from Dysphania species implicated in a recent BA outbreak. This compound caused selective destruction of the extrahepatic, but not intrahepatic, biliary system of larval zebrafish. A mutation that enhanced biliatresone toxicity mapped to a region of the zebrafish genome that has conserved synteny with an established human BA susceptibility locus. The toxin also caused loss of cilia in neonatal mouse extrahepatic cholangiocytes in culture and disrupted cell polarity and monolayer integrity in cholangiocyte spheroids. Together, these findings provide direct evidence that BA could be initiated by perinatal exposure to an environmental toxin.

Interleukin 17, Produced by γδ T Cells, Contributes to Hepatic Inflammation in a Mouse Model of Biliary Atresia and Is Increased in Livers of Patients

BACKGROUND & AIMS

Biliary atresia (BA) is a rare disease in infants, with unknown mechanisms of pathogenesis. It is characterized by hepatobiliary inflammatory, progressive destruction of the biliary system leading to liver fibrosis, and deterioration of liver function. Interleukin (IL) 17A promotes inflammatory and autoimmune processes. We studied the role of IL17A and cells that produce this cytokine in a mouse model of BA and in hepatic biopsy samples from infants with BA.

METHODS

We obtained peripheral blood and liver tissue specimens from 20 patients with BA, collected at the time of Kasai portoenterostomy, along with liver biopsies from infants without BA (controls). The tissue samples were analyzed by reverse transcription quantitative polymerase chain reaction (PCR), in situ PCR, and flow cytometry analyses. BA was induced in balb/cAnNCrl mice by rhesus rotavirus infection; uninfected mice were used as controls. Liver tissues were collected from mice and analyzed histologically and by reverse transcriptase PCR; leukocytes were isolated, stimulated, and analyzed by flow cytometry and PCR analyses. Some mice were given 3 intraperitoneal injections of a monoclonal antibody against IL17 or an isotype antibody (control).

RESULTS

Livers from rhesus rota virus-infected mice with BA had 7-fold more Il17a messenger RNA than control mice (P = .02). γδ T cells were the exclusive source of IL17; no T-helper 17 cells were detected in livers of mice with BA. The increased number of IL17a-positive γδ T cells liver tissues of mice with BA was associated with increased levels of IL17A, IL17F, retinoid-orphan-receptor C, C-C chemokine receptor 6, and the IL23 receptor. Mice that were developing BA and given antibodies against IL17 had lower levels of liver inflammation and mean serum levels of bilirubin than mice receiving control antibodies (191 μmol/L vs 78 μmol/L, P = .002). Liver tissues from patients with BA had 4.6-fold higher levels of IL17 messenger RNA than control liver tissues (P = .02).

CONCLUSIONS

In livers of mice with BA, γδ T cells produce IL17, which is required for inflammation and destruction of the biliary system. IL17 is up-regulated in liver tissues from patients with BA, compared with controls, and might serve as a therapeutic target.

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.

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.

Natural killer cells promote long-term hepatobiliary inflammation in a low-dose rotavirus model of experimental biliary atresia

Biliary atresia is a rapidly progressive obstructive cholangiopathy of infants. Mechanistic studies in the mouse model of Rhesus rotavirus (RRV)-induced biliary atresia have linked the importance of effector lymphocytes to the pathogenesis of extrahepatic bile duct (EHBD) injury and obstruction in experimental biliary atresia; however, studies of the progressive liver injury have been limited by early death of newborn mice. Here, we aimed to determine 1) if a lower inoculum of RRV induces obstruction of EHBDs while allowing for ongoing liver inflammation, and 2) if NK cells regulate intrahepatic injury. The administration of 0.25x10⁶ fluorescence forming units of RRV induced an obstructive extrahepatic cholangiopathy, but allowed for restoration of the duct epithelium, increased survival, and the development of a progressive intrahepatic inflammatory injury with molecular and cellular signatures equivalent to the traditional infectious model. Investigating the mechanisms of liver injury, we found that NK cell depletion at the onset of jaundice decreased liver inflammation, suppressed the expression of fibrosis and inflammation/immunity genes, lowered plasma ALT and bilirubin and improved survival.

What Causes Biliary Atresia? Unique Aspects of the Neonatal Immune System Provide Clues to Disease Pathogenesis

Biliary atresia (BA) is the most frequent identifiable cause of neonatal cholestasis and the majority of patients will need liver transplantation for survival. Despite surgical intervention with the Kasai portoenterostomy, significant fibrosis and cirrhosis develops early in life. An increased understanding of what causes this inflammatory fibrosing cholangiopathy will lead to therapies aimed at protecting the intrahepatic biliary system from immune-mediated damage. This review focuses on studies pertaining to the role of the adaptive immune response in bile duct injury in BA, including cellular and humoral immunity. The neonatal presentation of BA begs the question of what are potential modifications of unique aspects of the neonatal immune system that "sets the stage" for the progressive biliary disease? Throughout this article, characteristics of the neonatal immune response are outlined and theories as to how alterations of this response could contribute to the pathogenesis of BA are discussed. These include aberrant Th1 and Th17 responses, deficiencies in regulatory T cells, activation of humoral immunity and autoimmunity. In order to advance our understanding of the etiology of BA, future studies should focus on those unique aspects of the neonatal immune system that have gone awry, as detailed throughout this review.

Rotavirus activates lymphocytes from non-obese diabetic mice by triggering toll-like receptor 7 signaling and interferon production in plasmacytoid dendritic cells

It has been proposed that rotavirus infection promotes the progression of genetically-predisposed children to type 1 diabetes, a chronic autoimmune disease marked by infiltration of activated lymphocytes into pancreatic islets. Non-obese diabetic (NOD) mice provide a model for the human disease. Infection of adult NOD mice with rhesus monkey rotavirus (RRV) accelerates diabetes onset, without evidence of pancreatic infection. Rather, RRV spreads to the pancreatic and mesenteric lymph nodes where its association with antigen-presenting cells, including dendritic cells, induces cellular maturation. RRV infection increases levels of the class I major histocompatibility complex on B cells and proinflammatory cytokine expression by T cells at these sites. In autoimmunity-resistant mice and human mononuclear cells from blood, rotavirus-exposed plasmacytoid dendritic cells contribute to bystander polyclonal B cell activation through type I interferon expression. Here we tested the hypothesis that rotavirus induces bystander activation of lymphocytes from NOD mice by provoking dendritic cell activation and proinflammatory cytokine secretion. NOD mouse splenocytes were stimulated with rotavirus and assessed for activation by flow cytometry. This stimulation activated antigen-presenting cells and B cells independently of virus strain and replicative ability. Instead, activation depended on virus dose and was prevented by blockade of virus decapsidation, inhibition of endosomal acidification and interference with signaling through Toll-like receptor 7 and the type I interferon receptor. Plasmacytoid dendritic cells were more efficiently activated than conventional dendritic cells by RRV, and contributed to the activation of B and T cells, including islet-autoreactive CD8+ T cells. Thus, a double-stranded RNA virus can induce Toll-like receptor 7 signaling, resulting in lymphocyte activation. Our findings suggest that bystander activation mediated by type I interferon contributes to the lymphocyte activation observed following RRV infection of NOD mice, and may play a role in diabetes acceleration by rotavirus.