[Cytokeratins, markers of epithelial cell differentiation: expression in normal epithelia]

Intermediate filaments, the most stable of cytoskeleton components, are extremely diverse and usually correlate with the histological subtype since in nearly all cell types a single type of intermediate filament (IF) is found. The cytokeratins, which are specific of epithelia, are the largest and most diverse class of intermediate filaments. Twenty different cytokeratin polypeptides have been identified in humans and separated on the basis of isoelectrical pH and apparent molecular weight using two-dimensional electrophoresis. These data have been used to establish a cytokeratin catalogue which currently serves as a reference [43, 48]. The number of cytokeratin polypeptides expressed ranges from 2 to 5 for each epithelial cell and from 2 to 10 for each epithelium and even of each cell layer within a given epithelium. A broad spectrum of anticytokeratin antibodies with subgroup or single polypeptide specificity is currently available. The distribution of cytokeratins in normal epithelia is reviewed herein and commercially available anti-cytokeratin antibodies are listed.