MEMBRANE ANTIGEN EXPRESSION OF SYNGENETICALLY BUT HETEROTOPICALLY TRANSPLANTED HEPATOCYTES IN RATS

The expression of membrane antigens on rat hepatocytes transplanted sy ngeneically and heterotopically was analyzed immunohistochemically usi ng monoclonal antibodies against rat hepatocytes. Isolated adult and f etal hepatocytes were able to survive in the spleen, salivary gland, t hymus, or subcapsular region of the kidney for various periods after t ransplantation. Fairly clear expression of HAM2, 4, and 8 antigens was observed on hepatocytes transplanted into syngeneic spleen, suggestin g that the cells might be functionally equivalent to hepatocytes in si tu. HAM4 antigen was localized specifically on the newly formed bile-c analicular faces of hepatocytes. The expression of HAM2 (MHC class 1) 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 l ymphoid tissue. HAM8 antigen, which is localized on gap junctions betw een neighboring hepatocytes in rat liver, was also recognized between transplanted hepatocytes. In salivary glands where hepatocytes were tr ansplanted, bile-canaliculus-like structures were observed not only be tween neighboring hepatocytes but also between hepatocytes and salivar y acinar cells, suggesting good interaction between the two different epithelial cell types. Hepatocytes transplanted into thymus appeared v iable, but most showed fatty degeneration. Some healthy hepatocytes su rvived in the interlobular connective tissue and the thymic cortical t issue. 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 ge station. These results suggest that transplanted hepatocytes can grow in any syngeneic tissues, and that a common feature on such hepatocyte s is a rich reticulin fiber network, visualized by silver staining. To judge the state of transplanted hepatocytes, monoclonal antibodies ag ainst rat hepatocyte surface antigens might therefore be a useful tool .