Morphometric and immunohistochemical characterization of human liver regeneration.

Regeneration in human liver is characterized in part by the formation of ductular structures, so-called ductular hepatocytes in massive hepatic necrosis and bile ductules in mechanical biliary obstruction. In an attempt to characterize the liver regenerative process, we performed image analysis and immunohistochemical staining of the ductular structures in these well defined human liver disorders, 13 cases of massive hepatic necrosis and 9 cases of mechanical biliary obstruction. The proliferation index was determined and the expression of several antigens was localized by immunohistochemical staining using antibodies to alpha-fetoprotein, alpha-1-antitrypsin, albumin, and cytokeratin 19. The ductular structures in adult human liver were compared with the developing ductal plates in 11 fetal livers, ranging in age from 9 to 36 weeks of gestation. Image analysis demonstrated that the mean total area, mean nuclear area, and mean cell size of ductular hepatocytes were significantly larger than those of bile ductules (p < 0.05). The proliferation index of ductular hepatocytes and bile ductules was significantly higher than that of hepatocytes of normal livers (p < 0.02). Bile ducts, bile ductules in mechanical biliary obstruction, ductular hepatocytes in massive hepatic necrosis, and the ductal plate cells in fetal liver showed strong staining for cytokeratin 19, which characterizes intermediate filaments associated with bile duct epithelial cells. Albumin, a liver-specific protein, and alpha-1-antitrypsin, a protease inhibitor, were strongly expressed in ductal plate cells of fetal liver, hepatocytes, and ductular hepatocytes, whereas bile duct cells and bile ductules were negative for albumin. In summary, ductular hepatocytes demonstrate morphometric and immunophenotypic features of both hepatocytes and biliary epithelial cells, whereas bile ductules share characteristics primarily with fetal ductal plates and mature bile ducts. These findings suggest that ductular hepatocytes in massive hepatic necrosis may serve as bipotential progenitor cells, and bile ductules in mechanical biliary obstruction are related to ductal plates of fetal liver.