Immunohistochemical studies of keratin in human bronchus and lung tumors

Lung tumors of various types, fixed in 4% formaldehyde-1% glutaraldehyde, were stained for keratin proteins. The results were compared with previous ultrastructural evidence of intermediate filament bundles (IFBs), presumed to be keratin. Electron and light microscopic methods were largely complimentary and the results were in agreement in 79% of cases. Light microscopy was superior for demonstrating keratinizing foci containing numerous well-developed IFBs, whereas electron microscopy was superior when keratin filaments were sparsely distributed in cells throughout a tumor. Fetal and adult bronchial specimens were also studied. Normal adult bronchus, fixed in aldehydes, was unreactive but keratin was observed in similarly fixed bronchi that showed epidermoid metaplasia and/or intraepithelial carcinoma. Keratin was demonstrated in normal adult bronchi fixed in ethanol. Keratin was not observed in fetal lung until the 14th week of gestation, when it appeared in basal cells and a few columnar cells of the larger bronchi. Thereafter, keratin progressively appeared in the more distal branches. As specimens from gestations of less than 14 weeks were fixed in aldehydes, the apparent lack of immunoreactivity may have been artifactual. Nevertheless, keratin was demonstrable in aldehyde-fixed fetal bronchi at 16 and 23 weeks' gestation.