Spindle-shaped cells derived from giant-cell tumor of bone support differentiation of blood monocytes to osteoclast-like cells

Spindle-shaped cells were established from four giant-cell tumors of bone. When human blood monocytes were co-cultured with these cells, multinucleate d giant-cell formation of monocytes was induced. Intriguingly, even when a filter (pore size: 0.45 mu m) was interposed between monocytes and the spin dle-shaped cells, polykaryocytes also appeared. These multinucleated giant cells were positive for tartrate-resistant acid phosphatase, expressed calc itonin receptor, and showed bone-resorption activity, characteristics of os teoclast-like cells. These findings indicate that soluble factors secreted from these cells play an important role in osteoclast-like cell formation f rom blood monocytes. These data additionally suggest that these cells suppo rt osteoclast-like cell formation in giant-cell tumors of bone. The cells a lso expressed mannose receptor, fibronectin, receptor activator of nuclear factor kappa B, and several cytokine mRNAs, including interleukin-6, recept or activator of nuclear factor kappa B ligand/osteoclast differentiation fa ctor/osteoprotegerin ligand, and macrophage colony-stimulating factor. Howe ver, all of these molecules except receptor activator of nuclear factor kap pa B ligand mRNA could also be detected in control HeLa and CV-1 cells. Alt hough the soluble receptor activator of nuclear factor kappa B ligand has n ot been found under physiological conditions, it is possible that it is cle aved by cellular proteases and the truncated receptor activator of nuclear factor kappa B is released from cells. Identification of the soluble factor s capable of inducing osteoclast formation from blood monocytes is a pressi ng problem to be solved.