Architectural organization of filiform papillae in normal and black hairy tongue epithelium - Dissection of differentiation pathways in a complex human epithelium according to their patterns of keratin expression

Background: An inadequate understanding of the complex morphologic characte ristics of human fili-form papillae has hampered the histopathological char acterization of disorders affecting tongue keratinization. To better define the 3-dimensional cyto-architecture of tongue epithelium, we performed det ailed immunohistochemical analyses of normal and black hairy tongue tissues using a panel of antikeratin antibodies. Observations: The dome-shaped base of the human filiform papilla (primary p apilla) is surmounted by 3 to 8 elongated structures (secondary papillae). These secondary papillae are composed of a central column of epithelial cel ls expressing hair-type keratins and an outer rim of cells expressing skin- type keratins. The epithelium over-lying the primary papillae and between t he individual primary papillae express esophageal-type keratins, In black h airy tongue disease, there is a marked retention of secondary papillary cel ls expressing hair-type keratins. Conclusions: Using a panel of antikeratin probes, we define the precise top ographical localization of cell populations undergoing ? distinct different iation programs in dorsal tongue epithelium. Comparative analyses of black hairy tongue specimens indicate that defective desquamation of the cells in the central column of filiform papillae results in the formation of highly elongated, cornified spines or "hairs"-the hallmark of this disease.