Osteoclast precursors in bone marrow and peritoneal cavity.

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.