A study of the effect of human monocytes on the mechanisms of bone resorption

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Recently it has been demonstrated by Mundy et al.(1977) that mononuclear phagocytes are present in alveolar bone which has been destroyed or on the resorbed surface of alveolar bone. Also, Heersche (1978)reported that osteoclastic bone resorption may occur by the action of fibroblast-like cells and monocyte-derived cells, too. On the other hand, it has been suggested by Kahn et al.(1975) and Ash et al.(1980) that macrophages are probably related ontogenetically to osteoclasts.Therefore, we examined the bone-resorbing activity of monocytes in vitro and effect of supernatants prepared from cultured peripheral blood leukocytes(PBL-sup) on this activity. Using ^<45>Ca-labeled synthetic hydroxyapatite(^<45>Ca-HA), the bone-resorbing activity of human monocytes was investigated, and the effects of PBL-sup from patients with periodontal disease(PPD) and from clinically hyalthy individuals on this monocyte activity were examined. And, the mechanism of bone-mineral destruction (^<45>Ca release … More from ^<45>Ca-HA) by human monocytes was investigated.The results were as follows: 1. Human monocytes apparently induced the release of^<45>Ca from^<45>Ca-HA, depending on culture time and cell concentration; and this activity was increased significantly more by addition of PBL-sup from PPD than from healthy patients. 2. The addition of PBL-sup (of PPD or healthy patients) led to increased nitro blue tetrazorium-reducting activity・and [^3H] Thymidine incorporation of the monocytes. 3. Monocytes adhering to HA were observed by lightmicroscopy and electronmicroscopy in 48 hr culture. 4. By addition of PHA-sup, monocytes-adhering activity to HA was enhanced significantly and the quantity of released ^<45>Ca from ^<45>Ca-H a by monicytes was increased. 5. By addition of cytochalasin B(1 g/ml-10 g/ml), the quantity of released^<45>Ca from^<45>Ca-HA was decreased dependently to the concentration. 6. Released ^<45>Ca in media from ^<45>Ca-HA was detected in 24 hr culture, but cell-intral ^<45>Ca was detected in 96 hr culture.These results suggest that bone-mineral destruction by monocytes is related to the concentration of citric acid in the micro-enviroment of the adherene site. Less