The osteoclast is a hematopoietic cell derived from CFU-GM and branches from the
monocyte-macrophage lineage early during the differentiation process. The marrow
microenvironment appears critical for osteoclast formation due to production of RANK
ligand, a recently described osteoclast differentiation factor, by marrow stromal cells in
response to a variety of osteotropic factors. In addition, factors such as osteoprotegerin, a
newly described inhibitor of osteoclast formation, as well as secretory products produced by …