An immunohistological study of cytokeratin 20 in human and mammalian oral epithelium

Cytokeratin (CK) 20 is a low molecular-weight intermediate filament reporte dly expressed only by benign and malignant gastrointestinal epithelium, uro thelium and Merkel cells. The main aims here were to map its expression in normal oral mucosa of humans and other mammals, and to determine whether it was expressed by abnormal human oral epithelium. Salivary and odontogenic epithelium were also analysed. An immunoperoxidase method was used on wax-e mbedded and cryostat sections. In addition, double-labelling experiments we re undertaken to determine the association between CK 20 expression and tha t of CK 8/18 or S100 protein. Normal human oral mucosa from four sites, tog ether with abdominal skin, was studied in autopsy samples from 32 individua ls. CK 20-positive, basally situated, round or angular cells, consistent wi th Merkel cells, were recorded in 24/32 (75.0%) samples of mandibular gingi va, 25/32 (78.1%) samples of hard palate, 7/32 (21.9%) samples of buccal mu cosa, 0/32 samples of lateral border of tongue, and 2/32 (6.3%) samples of abdominal skin. Double-labelling showed that all CK 20-positive Merkel cell s also expressed CK 8/18 and S100. The only other cells to express CK 20 we re human taste buds. There was no expression by dysplastic or invasive oral epithelium from biopsy samples. Colonic mucosa showed luminal-cell positiv ity in man, marmoset, ferret, rabbit and guinea-pig, but oral mucosa was un iversally negative in non-human species. It is concluded that in oral mucos a CK 20 is a specific marker of Merkel cells and taste buds, that Merkel ce lls are more frequently present in keratinized than non-keratinized oral mu cosa, that CK 20-positive Merkel cells are also S100-positive, that there m ay be interspecies variations in CK 20 polypeptide composition and that, by contrast to urothelium, CK 20 has no value in the diagnosis of oral epithe lial dysplasia. (C) 2000 Elsevier Science Ltd. All rights reserved.