Cholangiocyte biology and pathobiology

Cholangiocytes are the epithelial cells that line the intrahepatic and extrahepatic biliary tree. The biliary system is a complex network of tubules coated by epithelial cells, or cholangiocytes, which starts from the canals of Hering in the liver lobules, continues outside the liver, and terminates into the ampulla of Vater. The extra- and intrahepatic branches of the biliary tree originate from different embryological areas, explaining their morphological and biological properties. A fundamental function of epithelial cells, including cholangiocytes, is to selectively control the diffusion of ions and molecules through the epithelial barrier. Biliary epithelial cells are usually quiescent, following a liver insult, cholangiocytes activate and/or proliferate as a part of the so-called "hepatic reparative complex". Proliferation of cholangiocytes is fundamental for the maintenance of the normal homeostasis of the biliary tree, and in response to liver damage. A major role in epithelial innate immunity in cholangiocytes is played by toll-like receptors, and by nuclear receptors.