The dento-epithelial junction: Cell adhesion by type I hemidesmosomes in the absence of a true basal lamina

Background: The junctional epithelium (JE) is a unique structure that makes contact with both a non-renewable hard tooth surface and with a basement membrane (BM) facing the connective tissue. Ultrastructurally, this attachment occurs through hemidesmosomes (HD) and a basal lamina-like extracellular matrix which, on the tooth side, is termed the internal basal lamina. In this study we investigated the expression of basal cell markers in the tooth-facing (TF) cells of JE. Methods: Samples of healthy marginal gingiva were removed by careful dissection. The expression of laminin-5 was used to indicate TF cell preservation in double immunofluorescence labeling and confocal laser scanning microscopy. Results: The results show that integrin alpha (6)beta (4) and laminin-5 colocalize unequivocally in the TF cells. The results also show the specific expression of the basal cytokeratin 14 and the a, integrin subunit in the TF cells. All 3 major hemidesmosomal components BP180, BP230, and HD1 antigen are likewise present. On the other hand, type IV collagen, laminin-1/10, type VII collagen, and the BM proteoglycan perlecan are all absent from the dento-epithelial junction. Conclusions: The results indicate that the epithelium-tooth interface is a unique structure wherein epithelial cells adhere by means of bona fide hemidesmosomes to an epithelium-derived extracellular matrix lacking most of the common BM components. Moreover, TF cells differ from connective tissue facing (CTF) cells, not only by their cell surface molecules and their production of extracellular matrix, but also by their cytoskeletal architecture.