Cytokeratin 19 is a member of type I acidic subfamily of intermediate filaments. It is expressed in various different human tissues except in liver. Keratin 19 is not expressed in hepatocytes, therefore, antibody to CK19 is useful in the identification of liver metastasis.BA17reacts with the MCF-7 cells, which are known to contain CK19. It shows no reaction with the cells lacking CK19 such as A431 and Hela. In combination with HBME1, CK19 is useful in differentiating thyroid carcinoma from benign thyroid follicles.