The significance of bile ductular proliferation in the progression of various
hepatobiliary diseases remains unclear. Increased expression of MUC6
apomucin, a major
gastric mucin, has previously been noticed in proliferating bile ductules in chronic viral
hepatitis. The purpose of the present study was to characterize MUC6
apomucin and
mRNA expression in 35 histologically 'normal livers', 47 livers with chronic viral
hepatitis, 28 with
primary biliary cirrhosis, and seven with extrahepatic biliary obstruction. MUC6
protein was expressed focally in cytoplasm and/or on the
luminal surface of septal and interlobular bile ducts in normal and diseased livers. Bile ductules in normal livers rarely expressed MUC6
protein. The MUC6 expression intensified and spread in proliferating bile ductules and small bile ducts in chronic viral
hepatitis and to a lesser degree in other diseases. In the former, the extent and degree of MUC6 expression paralleled the degree of active necroinflammation. MUC6
mRNA expression resembled MUC6
protein expression in proliferating bile ductules and intralobular small biliary cells, suggesting increased transcription and synthesis of MUC6. In conclusion, proliferating bile ductular cells express MUC6
apomucin in diseased liver, especially in chronic viral
hepatitis with active necroinflammation. This secreted
mucin may act as a cytoprotective agent and represent a phenotype of reactive biliary epithelium in chronic viral
hepatitis.