Different lineages of chemically induced hepatocellular carcinoma in rats defined by monoclonal antibodies

Different lineages of hepatocellular carcinoma (HCC) were identified by the application of selected monoclonal antibodies to the study of the sequential histopathological changes which occurred during two regimens of chemical carcinogenesis in the rat. One regimen, that of Solt-Farber, caused prominent oval cell proliferation and large multiple neoplastic nodules, and the other regimen, continuous administration of diethylnitrosamine, produced minimal oval cell proliferation and a few small nodules. However, both regimens produce HCC in most exposed rats. Three monoclonal antibodies to liver cells, OV-6, H-4, and T-6, were selected on the basis of different tissue staining. OV-6 stains the cytoskeleton of bile duct cells, oval cells, and HCC but not that of hepatocytes. H-4 stains the cytoplasm of hepatocytes but of not hepatomas. T-6 stains the cytoskeleton of HCC only. In the Solt-Farber model, the monoclonal antibodies identified groups of hepatocytes within the persistent neoplastic nodules which had acquired the OV-6 epitope and had lost the H-4 epitope. HCC derived from this regimen had the same staining pattern, suggesting that the OV-6 positive H-4 negative hepatocytes were the precursors of the HCC. The presence within the nodules of oval cells, atypical duct structures, cells intermediate between duct cells and hepatocytes, and nodular hepatocytes all containing the OV-6 epitope raises the possibility that any of these cell types could serve as the precursor of the OV-6 positive hepatocytes that arose within the nodule. In the continuous diethylnitrosamine regimen a different staining pattern was seen. T-6 positive hepatocytes first appeared in periportal areas by the 5th week. These cells increased in numbers during the later weeks and with rare exceptions neither acquired the OV-6 epitope nor completely lost the H-4 epitope. Most HCC derived by the continuous diethylnitrosamine regimen were T-6 positive and OV-6 negative, suggesting a direct lineage from the periportal T-6 positive hepatocytes. These findings indicate that the lineage and phenotype of chemically induced HCC may vary with the carcinogenic regimen used and that HCC which arise in nodules may originate from cell types other than typical nodular cells.