Osteoclasts and a small population of peripheral blood cells share common surface antigens.

Several methods have been tried to identify mononuclear osteoclast precursors. We used a panel of 13 osteoclast-recognizing monoclonal antibodies (mabs) for the identification of osteoclast precursor cells from the bone, bone marrow, and peripheral blood of egg laying hens. Almost all mabs stained some mononuclear cells in the bone. Seven mabs recognized few mononuclear cells in the bone marrow and five mabs gave the positive immunofluorescence reaction in the white blood cell fraction. Possible immediate osteoclast precursor cells differing from osteoclasts in their densities were identified in the bone. Three mabs (K38, K52, and K70) stained the same amount of mononuclear cells (2.6-3.4%) enriched in Percoll density centrifugation. Of the monoclonal antibodies that recognized few cells in blood, K41 stained only osteoclasts. K47 and K52 also recognized some mononuclear cells in the bone marrow. Other monoclonal antibodies K51 and K70 were more unspecific, since they stained cells derived from other tissues. Blood cells detected with these different monoclonal antibodies were negative for tartrate-resistant acid phosphatase (TRAP). On the basis of our results, we suggest that there is in the blood a specific TRAP-negative cell population, which is a good candidate for osteoclast precursor.