A COMBINATION OF OSTEOCLAST DIFFERENTIATION FACTOR AND MACROPHAGE-COLONY-STIMULATING FACTOR IS SUFFICIENT FOR BOTH HUMAN AND MOUSE OSTEOCLAST FORMATION IN-VITRO

Both human and murine osteoclasts can be derived in vitro from hematop oietic cells or monocytes that are cocultured with osteoblasts or marr ow-derived stromal cells. The osteoclastogenic stimulus provided by mu rine osteoblasts and marrow-derived stromal cells is now known to be m ediated by osteoclast differentiation factor (ODF), a membrane-bound t umor necrosis factor-related ligand. This study demonstrates that mous e spleen cells and monocytes form osteoclasts when cultured in the pre sence of macrophage-colony stimulating factor (M-CSF) and a soluble fo rm of murine ODF (sODF). Numerous multinucleated osteoclasts expressin g tartrate resistant acid phosphatase (TRAP) and calcitonin receptor ( CTR) formed within 7 days of culture and engaged in extensive lacunar bone resorption. Osteoclast number and bone resorption area was depend ent on sODF concentration. Long-term cultured human monocytes also for med bone resorbing osteoclasts in response to co-stimulation by sODF a nd M-CSF, although this required more than 11 days in culture. This hu man osteoclast differentiation was strongly inhibited by granulocyte-m acrophage colony stimulating factor. This study further characterises murine osteoclast differentiation caused by sODF and M-CSF co-stimulat ion in vitro, and shows that the same co-stimulation causes human oste oclast differentiation to occur. We propose that this methodology can be employed to investigate the direct effects of cytokines and other f actors on human osteoclast differentiation.