Cytokeratins are a subfamily of intermediate filaments and characterized by remarkable biochemical diversity. Cytokeratins are represented in epithelial tissues by at least 20 different polypeptides, molecular weight between 40 kDa and 68 kDa. The individual cytokeratin polypeptides are designated 1 to 20 and divided into the type I (acidic cytokeratins 9-20) and type II (basic to neutral cytokeratins 1-8) families.Cytokeratin 18 belongs to type I family (acidic cytokeratins).