REACTIVE BILIARY EPITHELIUM - THE PRODUCT OF A PLURIPOTENTIAL STEM-CELL COMPARTMENT

Liver parenchymal cells (hepatocytes) have a low rare of turnover, but can nevertheless mount a rapid and efficient regenerative response. H owever, in some cases of extreme hepatotoxicity hepatocyte proliferati on is restricted or even abolished, and instead biliary epithelial cel ls, commonly referred to as ductular oval cells, migrate into the peri portal and midzonal parenchyma. Initially these cells behave as authen tic biliary epithelium with expression of the biliary cytokeratin inte rmediate filaments, but then show hepatocytic traits such as alpha fet oprotein and albumin synthesis. Thereafter these biliary ducts rapidly vanish to be replaced by either small hepatocytes or intestinal-type cells. The proliferation and differentiation of oval cells is probably strongly influenced by paracrine signalling from liver stellate cells . Oval cells appear to be the progeny of facultative pluripotential st em cells which have the lineage potential of uncommitted gastrointesti nal stem cells; these stem cells are Likely to be located in the chola ngioles and small interlobular bile ducts. Oval cells thus constitute an important reserve compartment for hepatocytes when hepatocyte regen eration is compromised. Copyright (C) 1996 by W.B. Saunders Company