Interleukin-3 and Granulocyte-Macrophage Colony-stimulating Factor Inhibits Tumor Necrosis Factor (TNF)- -induced Osteoclast Differentiation by Down-regulation of Expression of TNF Receptors 1 and 2*

Osteoclasts, the multinucleated cells that resorb bone, differentiate from hemopoietic precursors of monocyte/ macrophage lineage, which also give rise to macrophages or dendritic cells. In this study we investigated the mechanism by which interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GMCSF) inhibit tumor necrosis factor (TNF)-induced osteoclast differentiation in mouse osteoclast precursors. We show here that both IL-3 and GM-CSF potently inhibits TNF-induced osteoclast differentiation by direct action on osteoclast precursors. The inhibitory effect of IL-3 and GM-CSF on osteoclast differentiation was completely neutralized by anti-IL-3 and anti-GMCSF antibodies, respectively. In addition, the inhibitory effect of IL-3 and GM-CSF on TNF-induced osteoclast differentiation was irreversible. In osteoclast precursors, IL-3 and GM-CSF inhibited c-Fms expression posttranscriptionally. Interestingly, IL-3 and GM-CSF downregulated both mRNA and surface expression of TNF receptor 1 (TNFR1) and TNFR2. Furthermore, cells in the presence of IL-3 and GM-CSF showed high expression of macrophage antigen CD11b, and low expression of dendritic cells antigen CD11c and prolong exposure of osteoclast precursors to GM-CSF increased the CD11c expression compare with IL-3. In summary, we provide the first evidence that IL-3 and GM-CSF block TNFinduced osteoclast differentiation by down-regulation of mRNA and surface expression of TNFR1 and TNFR2.