[Cells in the normal human periodontal ligament. An ultrastructural, histo-enzymological and immunocytochemical study on in vitro cultures].

Four cellular cultures from explants of human periodontal ligament were studied. In these cultures, cells were fusiform or stellate with a high percentage (5 to 10%) of round mitotic cells. The scanning electron microscope confirmed the simultaneous presence of flat cells in interphase and cells in prophase with microvilli and long filipodes and of round mitotic cells with microvilli and blebs. Histoenzymology disclosed in these cells high activities in oxidative enzymes and leucine aminopeptidase. Furthermore some cells showed an alkaline phosphatase activity. Immunocytochemistry detected in most of these cells intermediate vimentin filaments and the presence of type I and III collagen irregularly distributed among these cells. In transmission electron microscopy the elongated cells presented a clear nucleus, numerous endocytosic vesicles, ribosomes and longitudinal filaments. Variations were noted, especially in the quantity and quality of cell secretions, the fibroblasts secreting either the two type I and III collagen or only type I. The rare cells assuming alkaline phosphatase activity were atypical in possibly being provided with osteogenic potential.