Figure 4.

Macrophage and regulatory hormones and factors. Arrow represents “stimulatory modification;” the gray triangle means “enlarged display.” Macrophages play a part in the anabolic response to intermittent PTH therapy via osteoblasts which can secrete factors (IL-6, etc.) that promote the differentiation and recruitment of macrophages; Worthy to be mentioned the work of CSF-1 and Ca²⁺ on macrophages; Macrophage-derived BMP-2 has effect on BMSCs, osteoblasts and macrophages via BMP-R to accelerate the osteogenic differentiation so as to make bone metabolism balance; Estrogen regulates bone homeostasis mainly through osteoblasts and osteoclasts. Estrogen mainly affects the activity of macrophages by interfering with the macrophage-mediated osteoclast formation process.