Ductal plate in hepatoblasts in human fetal livers: I. ductal plate-like structures with cytokeratins 7 and 19 are occasionally seen within human fetal hepatoblasts.

The author has studied the organogenesis of human intrahepatic bile duct in fetal livers. The developmental studies of the liver have focused mainly on the development of intrahepatic bile ducts including the ductal plate (DP). The DP is a single or double layered structures composed of small cuboidal cells and located in the interface between the hepatoblasts and portal mesenchyme. Herein, the author discovered the DP within the parenchymal hepatocytes. The DP-like structures within the hepatoblasts were found in 17 human fetal livers out of the 32 human fetal livers. The gestational ages of the 17 fetal livers were as follows: 7, 8, 9, 10 (n=2), 11, 12, 13, 14 (n=2), 15, 16, 17, 18, 19, 21, and 23 weeks. The presence of intraparenchymal DP-like structures were mainly found in the fetus of early gestational ages. Morphologically, the DP-like structures within the hepatoblasts were composed of small cuboidal epithelial cells with normal chromatin patterns. The cytoplasm was scant and relatively basophilic. The nuclei were small and round, and had no nucleoli. These cells formed the DP-like structures. The DP-like structures frequently formed cords, tubules, and duplicating patterns. These DP-like structures were scattered and the remaining hepatoblasts are normal hepatoblasts. The density of these DP-structures was low (one or two per 5 low power fields), but varied from case to case and area to area in the same case. The overall appearances were very similar to the true DP. Comparative observations of HE and CK immunostaining were performed. The DP-like structures within the hepatoblasts were positive for biliary-type CK7 and CK19. They were also positive for CK8 and CK18 that are expressed in both hepatocyte and biliary lineages. The true DP was positive for biliary-type CK7 and CK19. They were also positive for CK8 and CK18. Thus, the intraparenchymal DP-like structures were the same as the true DP located in the interface. Thus, the author discovered the intraparenchymal DP in the human fetal livers. This discovery should be confirmed by other researchers. If it is true, many studies of the functions of these intraparenchymal DPs are need.