Change of cytokeratin organization during development of Mallory bodies as revealed by a monoclonal antibody

A monoclonal murine antibody (K(M) 54-5) was produced against Mallory body (MB) material isolated from liver tissue of griseofulvin treated mice. The antigen was identified by positive immunofluorescence microscopy of MBs and by the immunoblotting technique on polypeptides separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis. In immunoblotting experiments, antibody K(M) 54-5 reacted with cytokeratins A (human no. 8) and D (human no. 18) of murine, bovine, and human hepatocytes as well as with cytokeratin A (no. 8) and its degradation products present in isolated murine MB. In immunofluorescence microscopy the antibody did not react with cytokeratin filaments of normal liver but showed a positive reaction with MBs after a certain stage in MB development had been reached. In a dot blot assay, using individual cytokeratin polypeptides isolated from murine liver and purified by ion exchange chromatography in pH 8 buffer containing 8 M urea, the antibody reacted with the individual polypeptides A (no. 8) and D (no. 18) but not with the heterotypic tetramer (A₂D₂) reconstituted from these polypeptides in 4 M urea. These findings confirm the cytokeratin nature of MB filaments. In addition, they show that the pathologic process of MB formation involves changes in cytokeratin organization and conformation, resulting in the accessibility of a specific antigenic determinant which is inaccessible ('masked') in the heterotypic tetramer subunit and in the cytokeratin filaments of normal cells. Hence this study presents an example of a pathological change of cytokeratin filaments and illustrates the value of monoclonal antibodies in the detection of such changes.