Human osteoclast-specific antigens are expressed by osteoclasts in a wide range of non-human species.

A series of monoclonal antibodies have been developed which react specifically with human osteoclasts in human fetal bone and a range of neoplastic and non-neoplastic bone lesions. We have examined whether such antibodies retain reactivity and specificity with osteoclasts isolated from the bone of newborn non-human mammals and embryonic chickens. Of seven osteoclast-specific monoclonal antibodies, three retain their reactivity with rabbit and two with guinea-pig; none react with mouse or rat osteoclasts; two antibodies detect avian osteoclasts. The extensive retention of some osteoclast antigens during phylogeny suggests that they might represent functionally important molecules in the regulation of osteoclast activity. Moreover, the existence of antibodies capable of defining multi- and mononuclear osteoclasts, from species where osteoclast function is well characterized, suggests possible experimental routes towards the isolation, and hence study of purified populations of osteoclasts and their precursors.