Figure 3. Synovial fluid induces osteoclast formation from human peripheral monocytes in the presence of M-CSF. The synovial fluids were de-salted by dialysis, lyophilized, and concentrated up to the original concentration (around 100-fold). Then, the reconstituted samples were applied to the osteoclast formation assay by PBMC, and to the pit-formation assay, in the presence of M-CSF (100 ng/mL). **P < 0.01, ***P < 0.005 compared with control groups. #P < 0.05, ##P < 0.01, and ###P <0.005, as indicated by the brackets. Experiments were repeated 3 times with similar results. Arrows point to osteoclasts. Original magnification, 40x for TRAP staining (bar = 200 µm), and 100x for pit-formation assay (bar = 500 µm).