Immunocytochemical analysis of the human osteoclast: phenotypic relationship to other marrow-derived cells.

The immunocytochemistry of the osteoclast, which is known to be derived from a circulating mononuclear precursor cell of bone marrow origin, is controversial. In this study, we have determined the antigenic phenotype of human osteoclasts in fetal and adult (Paget's disease, giant cell tumour of bone) specimens using a large number of monoclonal antibodies which react with granulocytes and mononuclear phagocytes. We have identified antibodies which reacted with human osteoclasts including CD13, CD15 and several groups of anti-macrophage antibodies. All the antibodies which reacted with osteoclasts are also known to react with monocytes or macrophages. Other marrow elements such as granulocytes, megakaryocytes and platelets were also commonly stained. Expression of myeloid and platelet antigens on osteoclasts shows that they are phenotypically related to these cells and is in keeping with the origin of osteoclast precursors from the pluripotential haemopoietic stem cell. Only a proportion of osteoclasts in fetal bone preparations were stained by CD15 antibodies, suggesting that subsets or different populations of osteoclasts, which can be identified by monoclonal antibodies, may be present in bone.