In previous biochemical analyses,
keratin 5 (Mr 58,000) has been detected in most
mesotheliomas with epithelial component but not in pulmonary
adenocarcinomas (Blobel et al., Am J Pathol 121: 235-247, 1985). In the present study, we have characterized a
monoclonal antibody, AE14, as being selectively specific for
keratin 5 (apart from the reactivity with certain hair
proteins) as shown by immunoblotting of gel-electrophoretically separated
proteins from various tissues. Immunohistochemical screening of a variety of normal human tissues, using immunoperoxidase microscopy on cryostat sections, revealed the binding of this antibody to the basal, immature cells of stratified squamous epithelia, to basal cells of pseudostratified epithelia, to some myoepithelial cells, thymic reticulum cells, certain pancreatic duct cells, as well as a variable subpopulation of mesothelial cells of the pleura and the peritoneum. In 12/13 epithelial and biphasic
mesotheliomas of the pleura, heterogeneous but extended staining with antibody AE14 was seen whereas 21 pulmonary
adenocarcinomas were negative or, in six of these cases, showed staining of only a few cells. Among
carcinomas from other sites, colonic
adenocarcinomas and
renal cell carcinomas were negative whereas limited staining was found in some pancreatic
adenocarcinomas. It is suggested that antibody AE14 may be useful, as a defined
polypeptide-specific
reagent, in the histologic distinction between
mesotheliomas and most
adenocarcinomas. Furthermore, the expression patterns of
keratin 5 as detected by antibody AE14 in various normal and malignant epithelial tissues are discussed, particularly their relation to processes of squamous
metaplasia and their indication of phenotypic
tumor heterogeneity.