Osteopontin is involved in the formation of epithelioid granuloma and bile duct injury in primary biliary cirrhosis.

Recently, it was shown that osteopontin (OPN) is involved as a chemoattractant cytokine in the recruitment of macrophages and T lymphocytes in the granulomas of diverse etiologies and also plays an important role in the production of autoantibodies and development of autoimmune diseases. Primary biliary cirrhosis (PBC) is characterized by immune-mediated bile duct damage with frequent epithelioid granulomas. In this study, the expression of OPN was immunohistochemically examined in 25 PBC and 52 control livers. Epithelioid cells within granuloma in PBC expressed OPN variably. These cells were also positive for CD68, suggesting their histiocyte/macrophage lineage. In addition, strong expression of OPN was seen in the cytoplasm of mononuclear cells infiltrating around granulomas and also damaged bile ducts in PBC. The number of such positive mononuclear cells and the ratio of OPN-positive cells/total infiltrating cells in portal tracts were higher in PBC than in controls. The majority of these OPN-positive cells were found to be IgG- or IgM-producing plasma cells. These suggest that in PBC, OPN is an important immune molecule in portal tracts, and contributes to the recruitment of mononuclear cells into epithelioid granuloma and also participates in bile duct injury via B-cell differentiation and plasma cell expansion.