Immunohistochemical Characterization of Macrophages and Myofibroblasts in α-Naphthylisothiocyanate (ANIT)-Induced Bile Duct Injury and Subsequent Fibrogenesis in Rats

To investigate pathogenesis of post-bile duct (BD) injury fibrosis, interlobular BD epithelial injury was induced in male F344 rats by a single IP injection of alpha-naphthylisothiocyanate (75 mg/kg body weight) and rats were observed for 12 days. On days 1 to 2, cholangiocytes were injured and desquamated. On days 3 to 5, the affected BD began to regenerate, showing positive staining for CK19 and vimentin. On days 5 to 9, fibrotic areas gradually developed around regenerating BD in Glisson's sheath. These consisted of cells positive for vimentin, desmin, and alpha-SMA; vimentin-and desmin-positive cells were increased in early stage (days 1-3), whereas alpha-SMA-positive cells appeared in mid (days 4-7) and late stages (days 8-12), although there were cells coexpressing these cytoskeletons. On day 12, BD regeneration almost completed, with reduced fibrosis. Macrophages positive for ED2 (CD163) increased transiently in early stage, whereas those reacting to ED1 (CD68), OX6 (MHC II), and SRA-E5 (CD204) showed a consistent increase throughout the experiment. Interestingly, OX6-positive cells were limited to Glisson's sheath, whereas SRA-E5-positive cells were seen exclusively along sinusoids of hepatic lobules. MCP-1 mRNA increased significantly in early stage. This study shows that macrophages exhibiting different immunophenotypes and distributions participate in post-BD injury fibrosis associated with myofibroblasts expressing various mesenchymal cytoskeletons.