Suppression of osteoclast-like cell formation by periodontal ligament cells

Abstract

When human peripheral blood lymphocytes (PBL) were cocultured separately with periodontal ligament (PDL) cells, osteoblasts (OB), and gingival (GIN) cells using a membrane filter (millicell), the formation of osteoclast (OC)-like cells was clearly suppressed in PBL cocultured with PDL cells, but was enhanced in PBL cocultured with OB and GIN cells. This suppression and enhancement of OC-like cell formation was found in all of the 50% coculture fluids. When PBL were cocultured with PDL or GIN cells for 4, 6, and 8 days, a smaller number of PBL (when cocultured with PDL cells) and a larger number of PBL (when cocultured with GIN cells) were observed. It was also confirmed that the nonadherent type of PBL was suppressed by coculture with PDL cells, while both the nonadherent and adherent types of PBL were increased by coculture with GIN cells. When PBL cocultured with PDL cells for 4 days were analyzed by flow cytometry, an increase of Mac-1-positive cells was not observed, although an increase of Mac-1-positive cells was clearly shown in PBL cocultured with OB. Although the DNA-synthesizing activity of PBL was clearly observed after treatment with macrophage-colony stimulating factor (M-CSF) or granulocyte macrophage-colony stimulating factor (GM-CSF), this activity was clearly suppressed by the addition of a 50% coculture fluid of PBL/PDL cells. Moreover, the number of OC-like cells shown in PBL treated with M-CSF or GM-CSF was clearly suppressed by the addition of a 50% coculture fluid of PBL/PDL cells. These results indicate that PDL cells may produce some suppressing factors of OC precursor cells, and this function of PDL cells may act to protect alveolar bone from bone resorption caused by the bite force.