Formation of multinucleated giant cells derived from rat peritoneal macrophages

Evidence has accumulated that cells of the mononuclear phagocytic system are capable of bone resorption in vitro1-7). Furthermore, it has been suggested that macrophages and multinucleated giant cells (MGC) in vivo are involved in the resorptive process of bone tissue in bone fragment implantation8). The MGC in vitro also have bone resorption ability9). Therefore, the formation of MGC is thought to be important in resorption of bone tissue. Recently, it has been reported that MGC could be formed in vitro from macrophages in a culture medium supplemented with lymphokines10-12) and with human serum9). These agents are considered to induce cell-fusion of macrophages. We have previously confirmed formation of MGC from rat peritoneal macrophages in Ham's medium supplemented with 5% fetal calf serum. However, it is of interest to determine whether MGC are formed in culture conditions without fetal calf serum. Accordingly, we investigated the formation of MGC derived from rat peritoneal macro-