FLOW-CYTOMETRY ANALYSIS OF GINGIVAL AND PERIODONTAL-LIGAMENT CELLS

Gingival and periodontal ligament (PDL) fibroblasts are the major cell ular components of periodontal soft connective tissues, but the precis e differences between these cells are not yet known. In the present st udy, we have therefore examined the phenotypic and functional features of the cells obtained from gingival and PDL biopsy samples. Spindle-s haped cells characteristic of fibroblasts were the main cell type obse rved in vitro, although epithelial cells were also present in primary gingival cell cultures. Flow cytometry was used to measure the size an d granularity of the cultured cells, and showed that the gingival fibr oblasts were smaller and less granular compared with the PDL cells. Th e expression of certain key extracellular matrix (ECM) proteins, fibro nectin, collagen type I, and tenascin was measured by flow cytometry. Analysis of the fluorescence profiles of these cultures showed that th e majority of cells expressed fibronectin and that the average fluores cence intensity of this antigen in the PDL cells was higher than that in the gingival fibroblasts. Moreover, the fibronectin-positive PDL ce lls apparently comprised two subpopulations which expressed fibronecti n at different levels, suggesting that the cells in the PDL cultures w ere functionally heterogeneous. The level of collagen type I was also found to be upregulated in the PDL compared with the gingival cells an d, as with fibronectin, was expressed at two different levels by subse ts of the PDL cells. In contrast, tenascin was expressed at very simil ar levels by both the gingival fibroblasts and PDL cells. In addition, measurement of alkaline phosphatase, a marker enzyme for mineralized tissue-forming cells, showed that the PDL cells had higher activity th an the gingival fibroblasts and that the alkaline phosphatase activity in the PDL cells was far more markedly up-regulated by dexamethasone. Our findings demonstrate that, despite their similar spindle-shaped a ppearance, fibroblasts derived from gingival and PDL tissues appear to display distinct functional activities which are likely to play a vit al part in the maintenance of tissue integrity and regenerative proces ses.