Cytokeratins

Definition
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Dominant cytoskeletal proteins of epithelial cells, which represent the most important part of the cytoskeleton. Cytokeratins (= alpha-keratins; see below keratins) are cytoplasmically localized and belong to the group of intermediate filaments. They can also be expressed in non.epithelial tumors, e.g. leiomyosarcoma, epithelioid angiosarcoma, epithelioid fibrosarcoma. Possible co-expression with other intermediary filaments (e.g. vimentin). Cytokeratins have, among other things, a high diagnostic importance (see CK7, CCK10, CK20 and others) in determining the histogenesis of tumours.

General information
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More than 20 different cytokeratins (CK/ZK) are known. They are classified according to their chemical properties into acidic (TYPE A) or neutral-basic cytokeratins (TYPE B) or according to their molecular weight into high and low molecular cytokeratins. There are a number of antibodies with specificity for individual cytokeratins, several cytokeratins or cytokeratin groups. In the cytoskeleton, a type A-ZK forms a complex with a type B-ZK, so that epithelia always express at least 2 cytokeratins. Antibodies such as KL-1 or MNF-116 are suitable as markers for pancytokeratin, but also the mixture of two antibodies against acidic and basic cytokeratins AE1/AE3.

Histology
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Antibodies against individual cytokeratins help to clarify the histogenesis of a tumour (epithelial origin) in the case of a positive immunohistological reaction. Also the lack of detection of cytokeratins in tumors (e.g. in malignant melanoma or in melanocytic nevi) and sometimes also the staining pattern can indicate a certain histogenesis (e.g. punctiform pattern in Merkel cell carcinoma). An expression of cytokeratins is also present in certain sarcomas and has a high diagnostic value in connection with conventional histology and further immune staining. Melanoma metastases can show aberrant cytokeratin formation in about 10% of cases. This finding can also occur in smooth muscle tumours, rhabdomyosarcomas, schwannomas and in anaplastic large cell lymphomas.