A NEW EPITHELIAL-CELL TYPE IN THE HUMAN CORNEA

Purpose. To study the expression of intermediate filaments in the huma n cornea. Methods. Light and electron microscopic and immunohistochemi cal studies were performed on 20 corneas from subjects of various ages . Results. A hitherto unrecognized epithelial cell population emerged from the immunohistochemical studies. Epithelial cells were invariably present in the superior cornea, whereas the nasal, temporal, and infe rior segments almost lacked these cells. They were situated at the tra nsition between peripheral cornea and limbus, and occurred as small gr oups in the basal epithelium. On electron microscopy, they were recogn ized by their marginated nuclear chromatin, large nucleoli, prominent bundles of intermediate filaments, and numerous hemidesmosomes and des mosomes. Immunohistochemistry on frozen sections revealed a unique int ermediate filament make-up: ie, strong co-expression of vimentin and c ytokeratin 19; other intermediate filaments, including cytokeratins 3, 4, 6, 7, 8, 10, 13, and 18 were negative. Finally, the cells lacked u ltrastructural and immunohistochemical features of melanocytes, neuroe ndocrine cells, Langerhans' cells, and leukocytes. Conclusions. A new epithelial cell type in the human cornea is described with characteris tic morphologic and immunohistochemical features. According to their p articular segmental distribution, restricted localization at the junct ion between cornea and limbus, and expression of an ''early'' intermed iate filament profile, it is tempting to speculate that they represent stem cells of the human cornea. Further studies are aimed to characte rize their phenotype and function more extensively.