It is well established that during apoptosis, keratin filaments are altered and remarkably stable keratin fragments are generated. During apoptosis, activation of caspases leads to proteolysis of numerous cellular proteins, including structural components of epithelial cells. K18 (also referred to in the literature as CK18) along with Keratin 8 are the major components of intermediate filaments in simple epithelial cells, and the only keratin pair in normal hepatocytes. K18 is often used to identify differentiated isolated hepatocytes. During apoptosis, K8/K18 fragments are dramatically reorganized and K18 is cleaved by caspases at multiple sequence sites. Cleavage of K18 is an early event occurring during apoptosis. The M30 antibody recognizes a neo-epitope exposed after caspase cleavage of K18 after the aspartic acid residue 396. Cleavage at this position occurs early during apoptosis by caspase 9 and during the execution phase by caspase 3 and caspase 7.
K18 is highly abundant in the liver, and apoptosis with caspase activation and K18 cleavage has been implicated in a variety of liver diseases. Development of the M30 antibody into an ELISA represented the first opportunity to measure a specific apoptosis product in the blood.
The M30 Apoptosense® ELISA measures the levels of soluble ccK18 fragments containing the K18Asp396 neo-epitope. After induction of apoptosis in epithelial tissues, ccK18 increases are observed in the blood. Caspase-cleaved K18 fragments are remarkably stable in human serum, further adding to convenience and the easy to use method of this ELISA.
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