RESUMO
Osteopontin is a cytokine essential for initiation of Th1 immune reaction. We established transgenic mice expressing osteopontin in hepatocyte, in which liver necrosis with lymphocyte infiltration developed gradually from 12 weeks of age with up-regulated osteopontin levels in the circulation, suggesting that extrahepatic manifestations might also occur as a result of excessive Th1 immune reaction. We examined histological and immunohistochemical features of various organs in these mice. Splenomegaly and enlargement of lymph nodes around the liver and intestine became apparent with marked infiltration of small lymphocytes in the transgenic mice later than 24 weeks of age. Immunostaining revealed that lymphocytes in the spleen and lymph nodes were positive for either CD3 or CD20, suggesting that the infiltrating lymphocytes were both B and T cells. Similar lymphocyte infiltration was found in the lung, kidney and submandibular gland. Alveolar septa became hypertrophic with lymphocyte infiltration, and the lung showed the appearance of interstitial pneumonia. These lesions are similar to extrahepatic manifestations in chronic hepatitis C patients, suggesting that augmented Th1 immune reaction to hepatitis C virus (HCV) proteins or the proteins with molecular mimicry of HCV may be a contributing factor for the formation of the pathological state not only in the liver but also in various organs under chronic infection of hepatitis C virus.
RESUMO
Osteopontin, a crucial factor for Th1 immune response, is expressed in stellate cells and macrophages activated in injured liver. To clarify the role of osteopontin in inflammatory changes in the liver, we attempted to establish transgenic mice expressing osteopontin in hepatocytes. Mouse osteopontin cDNA, cloned from concanavalin-A-stimulated spleen cells in C57BL/6 mice, was constructed into the vector containing serum amyloid-P component promoter. This construction was microinjected into fertilized eggs of C57BL/6 mice, and 4 lines of the transgenic mice were obtained. Western blotting and immunohistochemistry revealed that osteopontin was expressed in hepatocytes, but not in non-parenchymal cells, in the transgenic mice. The mean osteopontin concentrations in the liver and plasma in the mice were 13 and 2.6 times higher than those in negative littermates. Antinuclear antibody was positive in the plasma in 50% of the transgenic mice. In the transgenic mice later than 12 weeks of age, mononuclear cell infiltration in the liver developed, and these cells were positive for CD8 and HLA-DR. Plasma ALT activity was increased with focal necrosis in hepatic lobules in the transgenic mice later than 24 weeks of age. The transgenic mice expressing osteopontin in hepatocytes may be useful as a model of autoimmune hepatitis.
