The Effect of Interleukin-1β, Tumour Necrosis Factor a and Particle Phagocytosis on Monocyte-Osteoclast Differentiation

Interleukin-1 (IL-1) and tumour necrosis factor (TNF) are inflammatory cytokines which are known to influence osteoclastic bone resorption. To determine the effect of these cytokines on inflammatory macrophage-osteoclast differentiation, we added IL-1ß and TNFα to long term co-cultures of mouse monocytes and osteoblastic cells. IL-1ß (10 & 100 pg/ml) stimulated osteoclast formation as measured by expression of TRAP and the extent of lacunar bone resorption whereas TNFα (10 & 100 ng/ml) inhibited macrophage-osteoclast differentiation and bone resorption. Particle phagocytosis (which is known to stimulate the release of these cytokines) did not influence the extent of osteoclast formation. IL-1ß stimulation of osteoclast formation may in part account for the increase in bone resorption associated with this inflammatory cytokine; TNFα inhibition of osteoclast formation may be due to interruption of the interaction between osteoblasts and osteoclast precursors.