Cytokeratin 18, also known as keratin 18, is a type I intermediate filament protein with a molecular weight of approximately 48 kD. Cytokeratin 18 is a heterotetramer composed of two type I and two type II keratins. Cytokeratin 18 associates with cytokeratin 8 and is widely expressed in simple epithelial tissues in the adult where it is found in the cytoplasm, nucleus, and nucleolus. Cytokeratin 18 is associated with the cytoskeleton and mutations in this protein have been associated with liver disease after environmental insult. Cytokeratin 18 can be modified by glycosylation, phosphorylation (Ser34 and Ser53), acetylation (Ser2) and proteolytic cleavage at amino acids 238 and 397 by caspase family members. The cytokeratin 18 protein interacts with a number of proteins including caspase 3, 14-3-3 gamma, 14-3-3 zeta, 14-3-3 sigma 14-3-3 beta, 14-3-3 eta, keratin 5, keratin 8, TNF receptor II, plakophilin 2, EGF receptor, and usherin, among others. The DA-7 monoclonal antibody recognizes human cytokeratin 18 and is useful for Western blotting. This antibody has also been reported to be useful for immunoprecipitation, immunohistochemistry (paraffin sections), immunocytochemistry, and ELISA.