Cara L. Mack

Pathogenesis and outcome of biliary atresia : current concepts

Neonatal cholestatic disorders are a group of hepatobiliary diseases occurring within the first 3 months of life. Bile flow is impaired, and patients have conjugated hyperbilirubinemia, acholic stools, and hepatomegaly. Overall, 1 in 2,500 live births is affected with a neonatal cholestatic disorder (1). The two most common causes of neonatal cholestasis are biliary atresia and idiopathic neonatal hepatitis, accounting for up to 50% to 70% of cases. Other causes include a variety of neonatal infections (viral, toxoplasmosis, syphilis, bacterial), metabolic and genetic diseases, progressive familial intrahepatic cholestatic disorders (PFIC), paucity of interlobular bile duct disorders (e.g., Alagille syndrome), choledochal cyst, ischemia–reperfusion injury, association with parenteral nutrition administration, and other conditions (Table 1). Despite clinical improvement after the portoenterostomy procedure, approximately 70% to 80% of children with biliary atresia will eventually require liver transplantation; thus, biliary atresia alone accounts for almost 50% of all liver transplants performed in children (1). It should be noted that

Biliary Atresia Is Associated with CD4 + Th1 Cell–Mediated Portal Tract Inflammation

77 million is spent each year in the United States on liver transplantation for children and the ensuing hospitalizations (2). This sum of money covers 0.2% of total health care expenditures related to children, even though these children represent 0.0006% of the total pediatric population. Importantly, this disproportionate expenditure for liver transplantation in children could be cut in half if improved therapies for biliary atresia were developed that could abrogate or further delay the need for liver transplantation. Remarkably, little is known about the etiopathogenesis of biliary atresia; consequently, there has been slow progress in developing improved therapies or preventative strategies during the past decade. The purpose of this review is to summarize recent advances in the diagnosis and management of biliary atresia, examine the clinical outcome, describe the evolving theories of the etiology and pathogenesis of this disorder, and highlight gaps in our current knowledge.

Microglia are activated to become competent antigen presenting and effector cells in the inflammatory environment of the Theiler's virus model of multiple sclerosis

A proposed mechanism in the pathogenesis of biliary atresia involves an initial virus-induced, progressive T cell–mediated inflammatory obliteration of bile ducts. The aim of this study was to characterize the inflammatory environment present within the liver of infants with biliary atresia to gain insight into the role of a primary immune-mediated process versus a nonspecific secondary response to biliary obstruction. Frozen liver tissue obtained from patients with biliary atresia, neonatal giant cell hepatitis, total parenteral nutrition (TPN)–related cholestasis, choledochal cysts, and normal control subjects was used for fluorescent immunohistochemistry studies of cellular infiltrates, cytokine mRNA expression, and in situ hybridization for localization of cytokine-producing cells. Immunohistochemistry revealed increases in CD8+ and CD4+ T cells and Kupffer cells (CD68+) in the portal tracts of biliary atresia. Reverse transcription–PCR analysis of biliary atresia tissue showed a Th1-type cytokine profile with expression of IL-2, interferon-γ, tumor necrosis factor-α, and IL-12. This profile was not seen in normal, neonatal hepatitis or choledochal cyst livers but was present in TPN-related cholestasis. In situ hybridization revealed that the Th1 cytokine–producing cells were located in the portal tracts in biliary atresia and in the parenchyma of TPN-related cholestasis. A distinctive portal tract inflammatory environment is present in biliary atresia, involving CD4+ Th1 cell–mediated immunity. The absence of similar inflammation in other pediatric cholestatic conditions suggests that the portal tract inflammation in biliary atresia is not a secondary response to cholestasis but rather indicates a specific immune response involved in the pathogenesis of biliary atresia.

NASPGHAN Practice Guidelines: Diagnosis and Management of Hepatitis C Infection in Infants, Children, and Adolescents

Theilers murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD) is a well-characterized murine model of the chronic-progressive form of human multiple sclerosis (MS) characterized by the activation of myelin-specific autoreactive CD4 Th1 cells via epitope spreading. To gain an understanding of the potential role of central nervous system (CNS)-resident cells in the presentation of endogenous myelin epitopes, we determined the individual antigen presentation and effector potential of resident microglia vs. infiltrating macrophages in the CNS of mice with ongoing TMEV-IDD by performing functional analysis of these populations separated to high purity by flow cytometric sorting based on their level of CD45 expression. Unlike microglia from nai;ve mice, peptide-pulsed CD45(lo) microglia isolated at the onset of clinical disease were as efficient as CNS-infiltrating CD45(hi) macrophages in activating proliferation and IFN-gamma production by myelin-peptide specific Th1 cells. In contrast, during the chronic stages of TMEV-IDD, CNS-infiltrating macrophages were more highly activated than the resident microglia as reflected both by higher expression of cell surface molecules associated with APC function and enhanced functional ability of spinal cord-infiltrating macrophages to stimulate T cell proliferation in vitro. Interestingly, both microglia and infiltrating macrophages expressed similar profiles of effector molecules such as IL-1, IL-6, IL-12 p40, TNF-alpha, and iNOS. Collectively, this is the first report comparing the antigen-presenting phenotype and function of microglia and infiltrating macrophages in a virus-induced model of CNS demyelination demonstrating that the resident microglia are capable APCs and may play an important role in antigen presentation at the onset of clinical disease and contribute to effector myelin destruction.

Cellular and humoral autoimmunity directed at bile duct epithelia in murine biliary atresia

Hepatitis C virus (HCV) is an RNA virus that affects >180 million individuals worldwide with a high propensity for chronic infection. Children with HCV infection differ from adults in several ways including some modes of transmission, rates of clearance, progression of fibrosis, and the duration of potential chronic infection when acquired at birth. Since the discovery of HCV in 1989, there have been significant advances in the understanding of the virology and natural history of chronic HCV infection in children. In addition, there are now several treatment options for children with chronic hepatitis C infection and many new therapies on the horizon. As a consequence, the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition brought together experts in pediatric hepatology to review the available data in children and provide clinicians with approaches to the diagnosis, management, and prevention of HCV infection in children and adolescents. The guideline details the epidemiology and natural history of HCV infection in children, the diagnostic workup, monitoring and treatment of disease, and provides an update on future treatment options and areas of research.

Treatment of Neonatal Hemochromatosis with Exchange Transfusion and Intravenous Immunoglobulin

Biliary atresia is an inflammatory fibrosclerosing lesion of the bile ducts that leads to biliary cirrhosis and is the most frequent indication for liver transplantation in children. The pathogenesis of biliary atresia is not known; one theory is that of a virus‐induced, subsequent autoimmune‐mediated injury of bile ducts. The aim of this study was to determine whether autoreactive T cells and autoantibodies specific to bile duct epithelia are present in the rotavirus (RRV)‐ induced murine model of biliary atresia and whether the T cells are sufficient to result in bile duct inflammation. In vitro analyses showed significant increases in IFN‐γ–producing T cells from RRV‐diseased mice in response to bile duct epithelial autoantigen. Adoptive transfer of the T cells from RRV‐diseased mice into naïve syngeneic SCID recipients resulted in bile duct–specific inflammation. This induction of bile duct pathology occurred in the absence of detectable virus, indicating a definite response to bile duct autoantigens. Furthermore, periductal immunoglobulin deposits and serum antibodies reactive to bile duct epithelial protein were detected in RRV‐diseased mice. In conclusion, both cellular and humoral components of autoimmunity exist in murine biliary atresia, and the progressive bile duct injury is due in part to a bile duct epithelia–specific T cell–mediated immune response. The role of cellular and humoral autoimmunity in human biliary atresia and possible interventional strategies therefore should be the focus of future research. (HEPATOLOGY 2006;44:1231–1239.)

Unraveling the Pathogenesis and Etiology of Biliary Atresia

OBJECTIVE To determine if immunomodulatory treatment including intravenous immunoglobulin (IVIG) can favorably affect survival in neontatal hemochromatosis (NH) diagnosed postnatally because it can effectively prevent occurrence of NH when applied during gestations at risk. STUDY DESIGN We treated 16 newborn infants with liver failure due to NH with high-dose IVIG, in combination with exchange transfusion in 13 (ET/IVIG), and compared the outcome with 131 historical controls treated conventionally. RESULTS The severity of liver disease as estimated by prothrombin time was similar in the subjects receiving ET/IVIG and the historical controls, and the medical therapy was equivalent with the exception of the ET/IVIG therapy. Twelve subjects (75%) had good outcome, defined as survival without liver transplantation, whereas good outcome was achieved in only 17% (23/131) of historical control patients (P < .001). Four subjects died, 2 without and 2 after liver transplant. Survivors were discharged 6 to 90 days after receiving ET/IVIG therapy, and those followed for more than 1 year are within normal measures for growth, development, and liver function. CONCLUSIONS Immune therapy with ET/IVIG appears to improve the outcome and reduce the need for liver transplantation in patients with NH.

Coordinate expression of regulatory genes differentiates embryonic and perinatal forms of biliary atresia

Biliary atresia (BA) is the most common and important neonatal hepatobiliary disorder. Because current treatment is inadequate, there is an urgent need to better understand the etiology and pathogenesis of BA. Two major forms of BA are recognized: an embryonic form associated with other congenital anomalies and a perinatal form in which bile ducts were presumably formed normally but underwent fibro-obliteration in the perinatal period. There are currently several proposed pathogenic pathways leading to the phenotype of BA, including an immune or autoimmune response to a perinatal insult (e.g. cholangiotropic viral infection) and dysregulated embryonic development of the extra- or intrahepatic biliary system. Recent advances in developmental biology, genomics and genetics, and cell immunology and biology, coupled with the development of appropriate animal models, have provided support for these postulated mechanisms. Future investigations combining animal model work and evaluation of clinical specimens holds the promise of identifying the etiology of BA and providing a scientific basis for treatment and preventative interventions.

Surgically restoring portal blood flow to the liver in children with primary extrahepatic portal vein thrombosis improves fluid neurocognitive ability.

The molecular basis for the embryonic and perinatal clinical forms of biliary atresia is largely undefined. In this study, we aimed to: 1) determine if the clinical forms can be differentiated at the transcriptional level, and 2) search for molecular mechanisms underlying phenotypic differences. To this end, we generated biotinylated cRNA probes from livers of age‐matched infants with the embryonic (n = 5) and perinatal (n = 6) forms of biliary atresia at the time of diagnosis and hybridized them against the Affymetrix human HG‐U133 A and B microarrays containing 44,760 gene products. Data filtering and two‐way cluster analysis of the gene expression platform identified 230 genes with an expression profile that is highly distinctive of the clinical phenotypes. Functionally, the profile did not reveal a higher‐order function for a specific cell type; instead, it uncovered a coordinated expression of regulatory genes. These regulatory genes were predominantly represented in the embryonic form (45% of genes), with a unique pattern of expression of genes involved in chromatin integrity/function (Smarca‐1, Rybp, and Hdac3) and the uniform overexpression of five imprinted genes (Igf2, Peg3, Peg10, Meg3, and IPW), implying a failure to downregulate embryonic gene programs. In conclusion, embryonic and perinatal forms of biliary atresia are distinguished by gene expression profiling. The coordinate expression of regulators of chromatin structure/function and of imprinted genes provides evidence for a transcriptional basis for the pathogenesis of the embryonic form of biliary atresia. Further studies exploring these biological processes are required to determine the significance of these findings. Supplementary material for this article can be found at http://genet.cchmc.org. (HEPATOLOGY 2004;39:954–962.)

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

OBJECTIVES. Children with primary extrahepatic portal vein thrombosis (EHPVT) have portal-systemic shunting, which may lead to disturbed neurocognitive function similar to portal-systemic encephalopathy (PSE) seen with chronic liver disease and cirrhosis. The functions most affected are those involving fluid cognitive ability, which comprise neurocognitive domains such as attention, processing speed, and short-term memory, that are particularly vulnerable to systemic illness or diffuse neurologic insult. We determined the fluid cognitive ability of children with EHPVT and whether surgically restoring portal blood flow by mesenteric left portal vein bypass (MLPVB) improved it. DESIGN. Twelve children with EHPVT and no overt PSE underwent comprehensive neurocognitive testing before and 1 year after undergoing surgery with intent to perform MLPVB. The evaluations sampled 4 functional domains at both time points: (1) neurobehavioral (behavior, emotional, executive functioning); (2) broad cognitive (intelligence, achievement); (3) fluid ability (attention, mental speed, working memory, memory encoding); and (4) visual motor (drawing, fine motor). Tasks in the fluid-ability and visual-motor domains were expected to be especially sensitive to adverse effects of EHPVT and to be most likely to show improvement with MLPVB. The test group consisted of 8 subjects who underwent successful MLPVB, and the comparison group was composed of 3 patients who received distal splenorenal shunts and one whose MLPVB failed. RESULTS. Both groups demonstrated similar fluid cognitive ability at initial evaluation. Successful MLPVB resulted in significantly improved fluid cognitive function: in the fluid cognitive domain, significant improvements were seen for the hit reaction time variability in the Conners Continuous Performance Test, the attention scale of the Cognitive Assessment System, and immediate verbal memory in the Childrens Memory Scale. In the visual-motor domain, z scores on the Grooved Pegboard Test improved. No improvement was observed in the comparison group. DISCUSSION. The results show that surgically restoring portal flow to the liver in children with primary EHPVT results in improved fluid cognitive ability. Subjects showed some neurocognitive abnormalities involving mainly fluid cognitive ability consistent with minimal PSE seen in adults with chronic liver disease. Cognitive defects in patients with minimal PSE seem to relate primarily to attention and fine motor skill, and although affected patients can function in everyday life, they are at risk for performance deficits in educational and vocational situations requiring the ability to pay close attention and react quickly (eg, driving, employment in manufacturing). The tests we administered in these domains are pediatric equivalents to measures used to detect minimal PSE in adults and should detect abnormalities in the same functional domains. Our results suggest that a narrow battery of tests could be used to detect minimal PSE in children in a manner similar to the 5-test battery used in adults, eliminating the need for the comprehensive and broad testing we performed. Our findings suggest that shunting of portal blood from the liver in primary EHPVT can result in PSE and question whether it is as benign a disease as previously thought. The importance of our findings is twofold. For understanding the pathophysiology of PSE, we have shown that restoring blood flow to the liver improves cognitive function in children with EHPVT. For therapy for EHPVT, it becomes clear that MLPVB is an excellent treatment option. It is effective for treating the complications of portal hypertension and provides effective portal blood flow that other medical and surgical therapies do not. The findings provide additional evidence that primary EHPVT should be considered curable by MLPVB. However, comparison of overall risks and benefits of MLPVB with those of other therapeutic options and longer-term outcome studies must be completed before MLPVB can be fully endorsed as the best treatment for EHPVT in children. CONCLUSIONS. Surgical restoration of portal venous flow to the liver in children with primary EHPVT by MLPVB improves fluid cognitive ability. MLPVB should be considered in treating primary EHPVT, because it corrects portal blood flow and could optimize learning potential.