Bone-resorbing cytokines enhance release of macrophage colony-stimulating activity by the osteoblastic cell MC3T3-E1.

It has been observed that bone resorption in response to interleukin 1 (IL 1) or tumor necrosis factor (TNF) is accompanied by an increase in osteoclast number. Because the osteoclast is of hemopoietic lineage, recruitment could be regulated by colony-stimulating factors, one of which may be macrophage colony-stimulating factor (M-CSF). In this study, we show that the constitutive release of M-CSF activity by the osteoblastic cell MC3T3-E1 is enhanced by the presence of recombinant IL 1 alpha, recombinant TNF alpha, or by the concurrent presence of purified transforming growth factor beta (TGF beta) and epidermal growth factor (EGF). Increased release of CSF by the osteoblast in response to these agents may provide a signal for the growth and maturation of osteoclast precursors leading to subsequent bone resorption.