Expression of a hepatocyte membrane antigen during hepatocarcinogenesis and in the developing liver of the rat

Release of bile canalicular membrane antigen into blood in experimental extrahepatic cholestasis of the rat

The level of a bile canalicular membrane antigen in serum during extrahepatic cholestasis was serially analyzed using HAM.4, a monoclonal antibody against a bile canalicular membrane glycoprotein of normal rat hepatocytes. After bile duct ligation, the level of HAM.4 antigen in serum promptly increased within 1 hr, reached a maximum at 3 hr, and declined somewhat until 48 hr, where it plateaued. Elevated levels of HAM.4 antigen in serum preceded those of well-known biliary marker enzymes activities. Immunohistochemical studies showed that the expression of HAM.4 antigen in hepatocytes and bile duct cells was not altered appreciably after bile duct ligation even when HAM.4 antigen in serum reached a maximal level. The serum and hepatic HAM.4 antigen had a molecular weight of 110 kDa. These results suggest that HAM.4 antigen may be regarded as a potential marker of the early stage of cholestasis, with release occurring before apparent histological changes.

Membrane antigen expression of syngeneically but heterotopically transplanted hepatocytes in rats

The expression of membrane antigens on rat hepatocytes transplanted syngeneically and heterotopically was analyzed immunohistochemically using monoclonal antibodies against rat hepatocytes. Isolated adult and fetal hepatocytes were able to survive in the spleen, salivary gland, thymus, or subcapsular region of the kidney for various periods after transplantation. Fairly clear expression of HAM2, 4, and 8 antigens was observed on hepatocytes transplanted into syngeneic spleen, suggesting that the cells might be functionally equivalent to hepatocytes in situ. HAM4 antigen was localized specifically on the newly formed bile-canalicular faces of hepatocytes. The expression of HAM2 (MHC class I) antigen on the transplanted hepatocytes appeared much stronger on the side facing lymphoid tissues, than on the other faces, suggesting that some immunological reactions may take place between hepatocytes and lymphoid tissue. HAM8 antigen, which is localized on gap junctions between neighboring hepatocytes in rat liver, was also recognized between transplanted hepatocytes. In salivary glands where hepatocytes were transplanted, bile-canaliculus-like structures were observed not only between neighboring hepatocytes but also between hepatocytes and salivary acinar cells, suggesting good interaction between the two different epithelial cell types. Hepatocytes transplanted into thymus appeared viable, but most showed fatty degeneration. Some healthy hepatocytes survived in the interlobular connective tissue and the thymic cortical tissue. When fetal hepatocytes were transplanted heterotopically, they formed a mass consisting of hepatocytes and bile duct-like structures 7 wk after transplantation. The inoculated hepatocytes possessed HAM4 antigen, which was not recognized on fetal hepatocytes at day 14 of gestation.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical analysis of rat liver using a monoclonal antibody (HAM8) against gap junction

Four monoclonal antibodies were raised against crude gap junction fractions of rat liver to clarify the distribution of gap junctions during animal development and to analyze gap junction expression in vivo and the polarity of hepatocytes in vitro. Among the monoclonal antibodies obtained, HAM8 antibody recognized the 27-kDa rat liver gap junction protein connexin 32. This antibody recognized gap junctions at the contiguous faces of hepatocytes, and the antigen was also observed in exocrine pancreas and salivary gland but not in kidney, heart, esophagus, or thymus. HAM8 did not react with amphibian or fish liver, heart, esophagus, stomach, or intestine as assessed via the immunofluorescence method on frozen sections. A few hepatocytes and many hemopoietic cells were seen in rat fetal liver at 15 days of gestation. HAM8 antigen was expressed on some hepatocytes but not on any hemopoietic cells. As the fetus grew, the number of hepatocytes in the liver increased gradually, together with the amount of HAM8 antigen. The distribution of HAM8 antigen at 25 days after birth was similar to that in adult liver. When the expression of HAM8 antigen was examined in primary cultured hepatocytes using the immunofluorescence method, the antigen was observed clearly between the hepatocytes. However, most of the HAM8 antigen on the free surface of hepatocytes disappeared within 4 hr. HAM8 antigen was not expressed on AH-7974 rat hepatoma cells when they formed small islets in the rat peritoneal cavity or within the liver. When HAM8 IgG antibody was injected intravenously, the HAM8 signal was expressed in the liver.