Yasuni Nakanuma

Primary biliary cirrhosis: an orchestrated immune response against epithelial cells

Summary: Primary biliary cirrhosis (PBC) is an organ‐specific autoimmune disease that predominantly affects women and is characterized by chronic progressive destruction of small intrahepatic bile ducts with portal inflammation and ultimately fibrosis. The serologic hallmark of PBC is the presence of antibodies to mitochondria, especially to the E2 component of the pyruvate dehydrogenase complex. The mechanisms by which (and if) such antibodies produce liver tissue injury are unknown. However, the presence of these antibodies has allowed detailed immunological definition of the antigenic epitopes, the nature of reactive autoantibodies and the characterization of T‐cell responses. Several mechanisms may now be proposed regarding the immune‐mediated bile duct damage in PBC, including the possible role of T‐cell‐mediated cytotoxicity and intracellular interaction between the IgA class of antimitochondrial antibodies and mitochondrial autoantigens. There are major questions which remain unanswered, including, of course, etiology, but also the reasons for female predominance, the absence of PBC in children, the relative ineffectiveness of immunosuppressive drugs, and the specific role of mitochondrial antigens. The data so far provide suggestive evidence that PBC is a mucosal disease; this thesis provides a basis for discussion of etiology via the enterohepatic circulation of toxins and/or infection.

Biliary epithelial expression of pyruvate dehydrogenase complex in primary biliary cirrhosis : an immunohistochemical and immunoelectron microscopic study

It has been reported recently that there is a unique distribution of the E2 subunit of the pyruvate dehydrogenase complex (PDC-E2) on biliary epithelial cells in patients with primary biliary cirrhosis (PBC) but not primary sclerosing cholangitis. This distribution has been demonstrated using a mouse monoclonal antibody, coined C355.1. The epitope recognized by C355.1 is near the lipoic acid binding site of PDC-E2. C355.1 inhibits PDC-E2 activity in vitro and, unlike a panel of other monoclonal antibodies against different regions of PDC-E2, appears to bind not only to mitochondria but also to a unique antigen expressed predominantly on the luminal side of biliary epithelial cells in PBC. We have extended these observations by studying the subcellular reactivity of C355.1 using postembedding immunoelectron microscopy on the intrahepatic small bile ducts of PBC livers, extrahepatic biliary obstruction (EBO) livers, and normal livers. We report that the reactivity of C355.1 can be classified into two categories. The first category is characterized by small foci of reaction products that were randomly dispersed in cytoplasm, particularly in supranuclear areas; the ultrastructural characterization of these foci was impossible to define but was similar in PBC and EBO. However, of particular interest was the second category of reactivity, which was characterized by deposition of reaction products around the biliary lumen, including microvilli and adjacent subluminal ectoplasm and secretory substances in the biliary lumen. This staining pattern was frequent in PBC livers, only occasionally evident in EBO livers, and not found in normal livers. These data further define and highlight the unique subcellular distribution of PDC-E2 around the biliary lumen in PBC livers and suggest that this abnormality is related to the pathogenesis of bile duct lesions.

Granulomatous cholangitis in chronic hepatitis C : A new diagnostic problem in liver pathology

A case of chronic hepatitis C at the pre‐clrrhotic stage complicated with hepatocellular carcinoma is reported. The patient, a 64 year old female, showed elevated levels of serum alkaline phosphatase and immunoglobulin M. Anti‐mitochondrial antibodies were negative by indirect immuno‐fluorescence. Western blotting using beef heart mitochondria and recombinant polypeptides coding for mitochondrial antigens revealed that the patients serum was positive only for the E2‐subunit of the branched chain ketoacid dehydro‐genase complex. In the non‐neoplastic liver, chronic non‐suppurative cholangitis surrounded by epitheliold granuloma, resembling the granulomatous destructive cholangltis of primary biliary cirrhosis, was found. The damaged bile ducts were immunohistochemically minimally positive or ambiguous for HLA‐DR, and their expression of the E2‐subunit of the pyruvate dehydrogenase complex E2 (PDC‐E2) was diffuse or granular, and not typical of primary biliary cirrhosis. There was no bile duct loss, and orcein‐positive copper binding granules reflecting chronic cholestasis were negative in periportal hepatocytes. The overall features in this case were consistent with primary biliary cirrhosis presenting an infrequent profile of antimitochondrial antibodies and atypical expression of HLA‐DR and PDC‐E2 on biliary epithelial cells, with late superimposition on chronic hepatitis C. However, It is also possible that this is a case of chronic hepatitis C with hepatitis‐associated bile duct damage accompanied by granulomatous reaction. Either way, this case raises new diagnostic issues in the differential diagnosis of chronic liver diseases presented with granulomatous cholangitis.

Pathogenesis of Bile Duct Lesions in Primary Biliary Cirrhosis: Role of Autophagy Followed by Cellular Senescence

Abstract Primary biliary cirrhosis (PBC), an organ-specific autoimmune disease, is histologically characterized by chronic non-suppurative destructive cholangitis in small bile ducts, eventually followed by extensive bile duct loss and biliary cirrhosis. A high prevalence of serum antimitochondrial autoantibodies (AMAs) is also a feature of PBC. The autoimmune-mediated pathogenesis of bile duct lesions has been studied, but the mechanism has not been fully clarified. We have revealed for the first time that autophagy, deregulated autophagy, and cellular senescence are involved in bile duct lesions in PBC. Accumulation of microtubule-associated protein light chain 3β (LC3)-positive autophagic vesicles and aggregation of p62, a marker of deregulated autophagy, are observed in damaged small bile ducts in PBC, whereas such findings are not seen in small bile ducts in control livers. Interestingly, granular expression of the mitochondrial antigen PDC-E2 is co-localized with LC3, suggesting autophagy of mitochondria. In our hypothesis, deregulated autophagy may contribute to the abnormal expression of mitochondrial antigens and may be involved in the autoimmune pathogenesis of bile duct lesions in PBC. Furthermore, deregulated autophagy may precede the process of biliary epithelial senescence in PBC. Biliary epithelial cells in damaged bile ducts show characteristics of cellular senescence and may modulate the microenvironment around the bile ducts by expressing various chemokines and cytokines called senescence-associated secretory phenotypes, and contribute to the pathogenesis in PBC.