Abstract

Osteoclasts differentiate from cells that share some phenotypes with mature macrophages and monocytes, but early precursors for osteoclasts still remain obscure. To characterize osteoclast precursors, using monoclonal anti-c-Fms and anti-c-Kit antibodies, bone marrow cells were separated and the frequency of clonogenic progenitors were measured. Osteoclast precursors in the bone marrow mainly expressed c-Kit and diminished in frequency when they expressed c-Fms. In contrast to bone marrow, the precursors in the peritoneal cavity were enriched with a population of c-Fms+. Injection of these antibodies into mice demonstrated that peritoneal osteoclast precursors were sensitive to anti-c-Fms but not to anti-c-Kit antibodies, whereas those in bone marrow only declined in the presence of both antibodies. Meanwhile, c-Fms as opposed to c-Kit played an essential role in the generation of osteoclasts in cultures. We also compared osteoclast precursors with colony forming cells (CFU-M) by a macrophage colony stimulating factor. CFU-M in bone marrow decreased when anti-c-Kit antibody was administered and no CFU-M was detected in peritoneum. In this study, we show differences between proliferative potential osteoclast precursors maintained in bone marrow and peritoneum and between CFU-M and osteoclast precursors.