On the origin of the osteoclast: the cell surface phenotype of rodent osteoclasts

The origin and development of the osteoclast is not well defined; although it is derived from a bone marrow stem cell, it is not proven whether the osteoclast progenitor comes from the multipotential hemopoietic stem cell or comprises an entirely separate cell lineage. We have studied the cell lineage relationship of osteoclasts isolated from newborn rodent bone to other bone marrow cell types, in particular the monocyte-macrophage cell line, by the use of cell surface phenotyping. In studies in mouse and rat we failed to detect the expression of markers characteristic of mononuclear phagocytes or other bone marrow cell types, including the hemopoietic tissue restricted common leucocyte antigen (T200). Our findings cast further doubt on the view that osteoclasts arise by fusion of mononuclear phagocytes in a similar fashion to the formation of multinucleate inflammatory giant cells.