LPS administration increases CD11b+ c-Fms+ CD14+ cell population that possesses osteoclast differentiation potential in mice

Osteoclasts are multinucleated giant cells that originate from a monocyte/macrophage lineage, and are involved in the inflammatory bone destruction accompanied by periodontitis. Recent studies have shown that osteoclast precursors reside not only in the bone marrow, but also in the peripheral blood and spleen, though the precise characteristics of each precursor have not been analyzed. We hypothesized that the number of osteoclast precursors in those tissues may increase under pathological conditions and contribute to osteoclast formation in vivo in a mouse model. To test this hypothesis, we attempted to identify cell populations that possess osteoclast differentiation potential in the bone marrow, spleen, and blood by analyzing macrophage/monocyte-related cell surface markers such as CD11b, CD14, and colony-stimulating factor-1 receptor (c-Fms). In the bone marrow, the CD11b− cell population, but not the CD11b+ cell population, differentiated into osteoclasts in the presence of receptor activator of nuclear factor-κB ligand and macrophage colony-stimulating factor. On the other hand, in the spleen and blood, CD11b+ cells differentiated into osteoclasts. Interestingly, lipopolysaccharide (LPS) administration to the mice dramatically increased the proportion of CD11b+ c-Fms+ CD14+ cells, which differentiated into osteoclasts, in the bone marrow and spleen. These results suggest that LPS administration increases the proportion of a distinct cell population expressing CD11b+, c-Fms+, and CD14+ in the bone marrow and spleen. Thus, these cell populations are considered to contribute to the increase in osteoclast number during inflammatory bone destruction such as periodontitis.