Morphological characterization of small hepatocytes after bile duct ligation in chicken.

Small hepatocytes have hepatocyte-like characteristics and high proliferation activity. Most small hepatocyte studies report on in vitro rat or human hepatocytes. Only a few studies of small hepatocytes after bile duct ligation have been reported, and none of these have focused on these cells in birds. In this study, small hepatocytes appearing in bile duct ligation chicken liver were examined using the morphological method with histological, immunohistochemical, and ultrastructural studies. Nine Boris Brown hens (over 744-d old) were used. In all chickens, both the common hepatoenteric duct and hepatocystic duct were ligated, and the livers were examined 1, 4, 6, 9, and 13 weeks after bile duct ligation. Histologically, the small cells were half the size of normal liver cells, and mitotic figures were often observed. The nuclei showed two forms: large and small. Many small cells were negative for periodic acid-Schiff stain, but positive cells were rarely observed. The cells existed in colonies on the side of the sinusoid of the hepatic lamina. Immunohistochemically, the small cells with large nuclei were strongly positive for CD44, albumin and proliferation cell nuclear antigen, and the cells with small nuclei were weakly positive. In the CD44-positive cell colony, negative cells were often observed to have mature hepatocyte-like morphology. Moreover, many of the cells were PAN cytokeratin negative. Ultrastructurally, the small cells had more nuclei with rich heterochromatin, poor cytoplasmic organelles, and narrow cytoplasm with a high electron density than mature hepatocytes. Moreover, cells having a middle ultrastructural characteristic existed between the small cells and mature hepatocytes. The small hepatocellular colony of the chicken appeared as a regeneration-related change in the liver after bile duct ligation. The cell had high cell proliferation activity and morphological, immunohistochemical, and ultrastructural characteristics similar to those of the mammalian small hepatocyte, as well as a similar progenitor cell.