The biological roles of the third component of complement in osteoclast formation

We previously reported that 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25-(OH)2D3] tissue-specifically stimulated the production of the third component of complement (C3) in bone in vitro and in vivo. In the present study, we examined the possible roles of C3 in bone using bone marrow cultures with antibodies against C3 and C3 receptors (Mac 1, 8C12, and 7G6) and the purified mouse C3 protein. The C3 protein produced preferentially by stromal cells in response to 1 alpha,25-(OH)2D3 was distributed in macrophage-like mononuclear cells and small cells with few nuclei. Adding anti-C3 antibody together with 1 alpha,25-(OH)2D3 to bone marrow cultures greatly inhibited not only the appearance of tartrate-resistant acid phosphatase (TRAP)-positive mononuclear and multinucleated cells, but also the growth of macrophage-like mononuclear cells and stromal cells. The inhibitory effect of anti-C3 antibody on osteoclast-like cell formation was most prominent when it was added between days 2-4 of the 6-day culture period,...