Recombinant CD200 inhibits osteoclast formation.

<p>(A) Adherent peripheral blood mononuclear cells (PBMCs) were cultured with M-CSF for 48 hr, RANKL was added on day 3 of culture and medium was changed every 3 days. rCD200 was added at the beginning of the culture and every 3 days. After 21 days of culture, osteoclast formation was determined by the use of tartrate-resistant acid phosphatase (TRAP) assay. Data are mean±SD area of osteoclasts from 3 independent experiments. (B) rCD200 inhibits bone resorption activity. PBMCs were plated on bone slices in wells of 96-well plates and stimulated as described. After 21 days of culture, resorbtion pitt number and area were count under a light microscope (arrows). **, P<0.01 compared with none; *, P<0.05 compared with M+R alone.