Liver tumors distinguished by immunofluorescence microscopy with antibodies to proteins of intermediate-sized filaments

Antibodies against constitutive proteins of different types of intermediate-sized filaments were used in immunofluorescence microscopy on frozen sections of normal rat liver and various rat liver tumors induced by treatment with nitrosamines. Antibodies to tonofilament prekeratin stained bile duct epithelia and hepatocytes of normal liver and hepatocellular carcinoma cells and ductal cells of cholangiofibromas. These cells were not significantly stained by antibodies to vimentin. By contrast, antibodies to vimentin stained mesenchymal cells of normal liver and cells of early and advanced angiosarcomas and of undifferentiated spindle cell sarcoma. These mesenchymal tumor cells were not stained with antibodies to prekeratin. The presence of intermediate-sized filaments in these tumors, often in large whorl-like aggregates, was also demonstrated by electron microscopy. The results show that immunofluorescence microscopy with antibodies to cytoskeletal proteins is a powerful tool for the classification and differential diagnosis of mesenchymal and epithelial liver tumors. We propose that staining with antibodies to proteins of different types of intermediate filaments can be used to improve the identification of tumors of other organs, including metastases, as well as non-neoplastic proliferative lesions.