This reduction was noted early in the disease trajectory, showed specificity to cell types, and was particular to PSC as well as Abcb4 −/− BECs and the extrahepatic bile ducts of Abcb4 −/− mice; it was not encountered in other hepatic conditions such as PBC, nonalcoholic steatohepatitis, drug-induced liver injury, or viral hepatitis. Here, ABCB4 is linked to animal viral hepatitis.