Stimulation of bone resorption in vitro by a non-prostanoid factor released by human monocytes in culture

Cultured human monocytes produce a non-prostanoid factor which stimulates bone resorption in vitro. Production of the factor is not dependent on prostaglandin synthesis, but stimulation of resorption by the factor does involve prostaglandin production by bone. Salmon calcitonin inhibits the stimulatory activity by up to 80%. Production of the factor is not increased by the presence of lymphocytes in the monocyte cultures. Partial purification of the bone-resorbing activity by Ultrogel ACA 54 chromatography shows that it has an apparent molecular weight between 12 000 and 20 000. We suggest that the resorptive activity is due to an interleukin 1-like factor rather than an osteoclast activating factor.