S U M M A R YThe localization and biosynthesis of perlecan, a basement membrane-type heparan sulfate proteoglycan, were studied in developing tooth germs by using murine molars in neonatal and postnatal stages and primary cultured cells of the enamel organ and dental papilla to demonstrate the role of perlecan in normal odontogenesis. Perlecan was immunolocalized mainly in the intercellular spaces of the enamel organ as well as in the dental papilla/pulp or in the dental follicle. By in situ hybridization, mRNA signals for perlecan core protein were intensely demonstrated in the cytoplasm of stellate reticulum cells and in dental papilla/pulp cells, including odontoblasts and fibroblastic cells in the dental follicle. Furthermore, the in vitro biosyntheses of perlecan core protein by the enamel organ and dental papilla/pulp cells were confirmed by immunofluorescence, immunoprecipitation, and reverse transcriptase-polymerase chain reaction. The results indicate that perlecan is synthesized by the dental epithelial cells and is accumulated in their intercellular spaces to form the characteristic stellate reticulum, whose function is still unknown.

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Lymphoepithelial lesions (LELs, or epi-myoepithelial islands) in lymphoepithelial sialadenitis (LESA, or benign lymphoepithelial lesion) of the salivary gland are known to be mainly composed of duct epithelial cells. However, other constituent cells are poorly characterized. Formalin-fixed paraffin sections obtained from six surgical specimens of LESA were examined using immunohistochemistry for cytoskeletal proteins, inflammatory cells, vascular endothelial cells, and extracellular matrix (ECM) molecules as well as by in situ hybridization for ECM molecules. In addition to keratin-immunopositive (+) duct-like epithelial cells, there were CD31/CD34+ vascular endothelial cells-which were either scattered in a singular fashion, in formed sheets, or in tubular structures-, CD20+ B lymphocytes, CD45RO+ T lymphocytes, and CD68 macrophages in the LELs. ECM molecules, such as heparan sulfate proteoglycan and tenascin, were immunolocalized in hyaline materials in the LELs. Their mRNAs were demonstrated mainly in endothelial cells and, to a lesser extent, in lympho-monocytic cells around hyaline materials, but were not as evident in epithelial constituent cells of LELs. The results indicate that endothelial cells as well as inflammatory cells are important constituents of the LELs, and the hyaline ECM cores mainly result from the intra-LEL angiogenesis by endothelial cells with the assistance of inflammatory cells. This intra-LEL vasculature seems to support regeneration and proliferation of salivary epithelial remnant cells.