EXPRESSION OF MAC-2 ANTIGEN IN THE PREOSTEOCLAST AND OSTEOCLAST IDENTIFIED IN THE OP OP MOUSE INJECTED WITH MACROPHAGE-COLONY-STIMULATING FACTOR/

Osteoclast deficiency in op/op mice is cured by a single injection of 5 mu g recombinant human macrophage colony-stimulating factor (rhM-CSF ). In this study, we found that mouse osteoclasts are positive for Mac -2 antigen, but not for F4/80, MOMA-2, Mac-1, or BM8 antigen. By using F4/80 and MOMA-2 monoclonal antibodies, we confirmed the absence of m ature macrophages in the femora of op/op mice and found that multiple injections of rhM-CSF are required for the recruitment of macrophages in the bones. After a single rhM-CSF injection, we found Mac-2 positiv e mononuclear cells in the femora of op/op mice. The time course of th e appearance of Mac-2-positive cells was very similar to that of tartr ate-resistant acid phosphatase (TRAP)-positive cells. In bone sections prepared from the mutant mice that received rhM-CSF 3 days earlier, 9 1% of the TRAP-positive mononuclear cells were also positive for Mac-2 antigen. These results demonstrate the expression of Mac-2 antigen in preosteoclasts. The antigen was detected on the plasma membrane of pr eosteoclasts, as well as in their cytoplasm and nucleus, and in the ex tracellular matrix in the space between the cells and bone. Since Mac- 2 is a galactose-specific lectin, a potential role of the lectin in ce ll-cell and cell-matrix adhesion during osteoclast differentiation is suggested.