山本 和秀

Anti-idiotype antibodies (Ab2) play an important role in the homeostasis of immune responses and are related to the development and the disease activity of certain autoimmune diseases. The asialoglycoprotein receptor (ASGPR) is considered one of the target antigens in the pathogenesis of autoimmune chronic active hepatitis (AIH). We previously developed a mouse monoclonal antibody (clone 8D7) which recognizes rat and human ASGPR. In this study, to help investigate the anti-ASGPR antibody-anti-idiotype antibody network in patients with AIH, we developed a syngeneic mouse monoclonal Ab2 to the 8D7 anti-ASGPR antibody (Ab1). One clone, designated as 3C8, tested positive for specific reactivity to 8D7-Ab1 and did not bind to other irrelevant immunoglobulins. By competitive inhibition assays, the binding of 8D7-Ab1 to liver membrane extracts, i.e., the crude antigen preparation, was inhibited by 3C8-Ab2 in a dose-dependent manner, and the binding of 8D7-Ab1 to 3C8-Ab2 was inhibited by the liver membrane extracts. In the immunohistochemical analysis, 3C8-Ab2 blocked the specific staining of sinusoidal margins of rat hepatocytes by 8D7-Ab1. These results suggest that 3C8 anti-idiotype antibody recognizes the specific idiotypic determinants within the antigen-binding site of 8D7-Ab1.

In autoimmune chronic active hepatitis (AIH) and primary biliary cirrhosis (PBC), various autoantibodies including anti-asialoglycoprotein receptor (ASGPR) antibodies have been found in patients' sera. We have previously developed a mouse monoclonal antibody against rat and human ASGPR. In this study, we developed a capture enzyme-linked immunosorbent assay (ELISA) for detection of anti-ASGPR antibodies using this monoclonal antibody and investigated the occurrence of anti-ASGPR antibodies in the sera of patients with various liver diseases. Serum samples were obtained from 123 patients with various liver diseases, including 21 patients with AIH and 40 patients with PBC. In this capture ELISA, the target antigen in the crude rat liver membrane extracts was captured on the ELISA wells by the ASGPR-specific mouse monoclonal antibody. Thus, the cumbersome process of antigen purification was rendered unnecessary. Using this capture ELISA, we detected the anti-ASGPR antibody in 67% of the patients with AIH, in 100% of the patients with PBC, and in 57% of the patients with acute hepatitis type A. However, the anti-ASGPR antibody was rarely detected in patients with other liver diseases such as primary sclerosing cholangitis and obstructive jaundice. Our findings suggest that this capture ELISA would be useful for the detection of anti-ASGPR antibodies in autoimmune liver diseases.

To characterize primary sclerosing cholangitis (PSC) in Japanese patients and its association with inflammatory bowel disease (IBD), 155 reported cases of PSC, including 6 cases of our own, were reviewed. The prevalence of IBD was less in Japanese PSC patients than in Western patients (23% versus 62-100%). Japanese PSC patients with IBD were younger (mean age, 33.1 versus 51.8 years) and were more often women (51% versus 36%) than those without IBD. Seventy-four percent of PSC patients with IBD had extensive colonic lesions, and 89% of those developed IBD simultaneously, with or prior to PSC. There were 3 cases of neutrophilic cholangitis among the PSC patients with IBD but none in those without IBD. Based on these observations, we speculate that there may be subtypes of PSC which differ pathophysiologically.

Phalloidin, a toxin from the plant Amanita phalloides, irreversibly polymerizes actin filaments and causes cholestasis. Three-dimensional structural changes induced by phalloidin in the bile canaliculi and the intra-acinar localization of these changes were studied in the rat liver by scanning and transmission electron microscopy. After 3 days of treatment, canalicular changes appeared mainly in zones 2 and 3 of Rappaport's acinus, but after 7 days of treatment changes occurred in bile canaliculi of the whole acinus. The changes in the bile canaliculi included tortuosity, saccular dilatation, loss of microvilli, bleb formation and elongation of canalicular side branches. Some side branches extended near to Disse's space, leaving only a thin cytoplasmic rim between the canalicular lumen and Disse's space. Kupffer cells were occasionally situated near such extended bile canaliculi and protruded their processes into the hepatic cord. These results suggest that bile canaliculi in zone 3 are more susceptible to phalloidin toxicity than those in zone 1 and that biliary constituents may leak from such altered bile canaliculi.

The three-dimensional arrangement of ductular structures formed by oval cells in rats fed 2-acetylaminofluorene (2-AAF) was studied by scanning electron microscopy (SEM) of biliary tract casts and light microscopy of sections of liver injected with india ink via the biliary tract. Both resin and india ink were well injected up to bile ductules, and the findings of each method correlated with each other. By the second week after 2-AAF administration, a few oval cells appeared in the periportal areas forming ductular structures which connected with the portal bile ducts. At the 4th week, increased ductular structures occupied two thirds of the lobule and formed networks communicating with each other, and with the portal bile ducts. At the 8th week, such ductular structures were compressed around hyperplastic nodules and appeared like a basket in biliary casts examined by SEM. Although a histochemical study of gamma-glutamyl transpeptidase revealed activity both on the luminal side of the ductular structures and hepatocytes in hyperplastic nodules, no transition was observed between these two cell populations. These results suggest that oval cells have characteristics more similar to those of biliary epithelia than of hepatocytes, and have no relation to the development of hyperplastic nodules.