Immunohistochemical and molecular biological investigations regarding the pathogenesis of extrahepatic biliary atresia. (Part 1: immunohistochemical studies)

Rotavirus particles in the extrahepatic bile duct in experimental biliary atresia

BACKGROUND

Biliary atresia (BA) is the most common indication for liver transplantation in children. The experimental model of BA, induced by rotavirus infection in neonatal mice, has been widely used to investigate the inflammatory aspects of this disease. We investigated the kinetics and the localization of the viral infection in this murine model.

METHODS

In this study 399 animals were employed for a detailed investigation of rhesus rotavirus (RRV)-induced BA. RRV kinetics was analyzed by rtPCR and its (sub) cellular localization investigated using whole mounts which were further processed for confocal and electron microscopy.

RESULTS

The BA mouse model resulted in up to 100% induction of atresia following RRV injection. The kinetics of RRV infection differed between liver and extrahepatic bile ducts. While the virus peak up to day 10 postinfection was similar in both organs, the virus remained detectable in extrahepatic bile duct cells up to day 21. Interestingly, RRV particles were localized not only in cholangiocytes but also in cells of the subepithelial layers, potentially macrophages.

CONCLUSIONS

RRV remains present in the extrahepatic bile duct cells after an initial virus peak. Viral particles were detected in subepithelial cells in contrast to the described tropism toward cholangiocytes.

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.

Liver fibrosis in biliary atresia

Biliary atresia (BA) is the most common cholestatic liver disorder requiring liver transplantation in children. Hepatic fibrosis is not only a universal and prominent feature of BA, it is also the most important predictor of outcome following portoenterostomy (PE). Without PE, the progression of hepatic fibrosis is quite dramatic, such that liver cirrhosis is established within a few weeks after birth. Etiologies and molecular networks underpinning such an expeditious fibrogenic process have not been well established. However, immune and nonimmune factors implicated in the pathogenesis of BA, and the resultant cholestasis and oxidative stress, appear to be the main triggers of hepatic fibrosis in BA. Owing to a lack of validated noninvasive tools to monitor liver fibrosis, current prognostic models of BA entail clinical and biochemical variables reflecting liver dysfunction rather than hepatic fibrogenesis. Further work is necessary to validate the results of preliminary studies indicating a good relationship between liver fibrosis determined by transient elastography and other clinical and routinely performed biochemical parameters in pediatric patients. Although a prime candidate for a number of antifibrotic therapies on the horizon, owing to poor understanding of molecular mechanisms, a clear framework of antifibrotic targets has not been outlined in BA. Similarly, specific antifibrotic therapies have not yet been incorporated in clinical practice, limiting these measures to prompt diagnosis and PE operation, prevention and treatment of cholangitis and optimal nutritional support including the administration of fat-soluble vitamins.

Biliary atresia: a new immunological insight into etiopathogenesis

Biliary atresia is an idiopathic neonatal cholestatic disease characterized by the destruction of both the intra- and extra-hepatic biliary ducts. There are two clinical manifestations of the disease: an embryonal subtype, which often presents at birth and is associated with congenital malformations, and a 'perinatal' subtype, which is probably an acquired disease due to unknown etiology. Over the last two decades, researchers have focused on activation of the cell-mediated immunity as the mechanism for biliary epithelial cell destruction for the latter subtype. A proposed trigger of this immune response is an initial viral infection, inducing biliary epithelial cells to become antigen-presenting cells and thus instigating immune-mediated destruction of the biliary tract. However, putative viruses have never been confirmed. More recently, a novel hypothesis - that maternal microchimerism may initiate a host immunologic response towards the bile duct epithelia - has been proposed. This paper discusses the etiology of biliary atresia in the context of the current research.

Maternal microchimerism in underlying pathogenesis of biliary atresia: quantification and phenotypes of maternal cells in the liver

OBJECTIVE

The goal was to examine whether microchimerism plays a crucial role in the pathogenesis of biliary atresia; we analyzed the localization of maternal microchimeric cells and their phenotypes.

METHODS

Liver biopsy specimens from 8 male infants with biliary atresia and 6 control subjects with other liver diseases were investigated for maternal chimeric cells and their phenotypes through double-staining fluorescence in situ hybridization and immunohistochemical analyses.

RESULTS

Significantly larger numbers of maternal XX+ cells were found in the portal area and sinusoids of patients with biliary atresia, in comparison with control patients. In phenotypic analyses of XX+ cells, CD8+ T cells, CD45+ cells, and cytokeratin-positive cells were found, and the numbers and proportions among total CD8+ T cells were significantly higher than those in control patients.

CONCLUSIONS

Significantly more maternal chimeric CD8+ T cells in the livers of patients with biliary atresia suggest that maternal immunologic insults represent the underlying pathogenesis in biliary atresia. The findings support the recently postulated mechanisms of alloautoimmune and/or autoalloimmune responses.

Serial circulating markers of inflammation in biliary atresia--evolution of the post-operative inflammatory process

Biliary atresia (BA) may be characterized as an occlusive cholangiopathy affecting both intra- and extra-hepatic parts of the biliary tree, together with a pronounced inflammatory response consisting of hepatic infiltration of (predominantly) CD4+ lymphocytes and macrophages. Soluble cellular adhesion molecules are also known to be raised at the time of portoenterostomy, presumably reflecting intrahepatic disease. We investigated this measurable inflammatory component longitudinally by studying a panel of cellular adhesion molecules (soluble intercellular adhesion molecule-1 [sICAM-1], soluble vascular cell adhesion molecule-1 [sVCAM-1]) and soluble proinflammatory mediators (T helper 1 [interleukin [IL]-2 and interferongamma] and T helper 2 [IL-4 and IL-10]) cytokines and macrophage markers (tumor necrosis factor [TNF] alpha and IL-18) in 21 consecutive infants with BA post-Kasai portoenterostomy (KP). The levels of all adhesion molecules and cytokines (except IL-10) increased progressively by 6 months post-portoenterostomy. The response was non-polarized but with 100-fold increases in IL-2, TNFalpha and IL-18 particularly but only modest elevations in IL-10. When proinflammatory profiles were related to outcome, we found poor discrimination if assessed as clearance of jaundice but markedly higher values for IL-2, interferongamma, IL-4, IL-10, TNFalpha and sICAM-1 for those who would be transplanted by 1 year. Using ROC curve analysis for sICAM-1 levels at 1 month post-KP, a cutoff level of 1,779 ng/ml was determined to predict the need for transplantation at 1 year with 92% specificity and 87% sensitivity.

CONCLUSION

The early circulating inflammatory process in BA is persistent, progressive and involves a non-polarized T cell, macrophage and cell adhesion molecule response only partially ameliorated by KP.

Biliary atresia

Biliary atresia (BA) remains a devastating disease of infants. It is still a disease of largely unknown etiology although many hypotheses such as an aberrant early bile duct development, perinatal viral infection, aberrant immune response, and abnormalities of bile acids have all been suggested as possibly etiologically important. Although recent studies, using the techniques of molecular biology and immunohistochemistry, have improved the understanding of some of the inflammatory elements of BA, there is a lack of understanding of how many such disparate elements interact and relate. Clinically, the management in the majority of cases should consist of a primary portoenterostomy (Kasai procedure) to try and restore bile flow and alleviate jaundice. Transplantation should be reserved for those who develop chronic liver disease and its attendant complications. Recent series would suggest that over 50% of infants in large centers will be able to clear their jaundice and therefore have a reasonable expectation of long-term survival with a good quality-of-life.