DE NOVA EXPRESSION OF NONHEPATOCELLULAR CYTOKERATINS IN MALLORY BODY FORMATION

Mallory bodies (MBs) are eosinophilic cytoplasmic inclusions observed predominantly in alcoholic liver disease. Although linked to disease a ctivity, their pathogenesis is still unclear. Since intermediate filam ents (cytokeratins) are major components of MBs, their cytokeratin pol ypeptide composition was analysed with monospecific antibodies for cyt okeratins 7, 8, 14, 18, 19, and 20 by immunohistology. MBs were identi fied by light microscopy and ubiquitin immunostaining. All MBs were po sitive for cytokeratins 8 and 18. A significant percentage of the MBs was strongly positive for cytokeratins 19 and/or 20, which are not det ectable in hepatocytes of normal liver and, in the case of cytokeratin 20, in hepatocytes of diseases devoid of MBs. MBs were essentially ne gative for cytokeratins 7 and 14. De novo expression of cytokeratins 1 9 and 20 was independent of the aetiology, occurring in all MB-associa ted diseases analysed, and seemed to precede MB formation, since in so me hepatocytes a cytoskeletal-type staining pattern for these cytokera tins was present. In hepatocellular carcinomas cytokeratins 19 and 20 were frequently detected, but their cellular distribution was less clo sely associated with MBs. The ectopic expression of cytokeratins 19 an d 20 appears to be related to MB formation and may take part in the de rangement of the intermediate filaments during MB formation.