Production of interleukin-6 by human osteoclast-like cells from giant cell tumor of bone

Giant cell tumor (GCT) is a bone neoplasm which is characterized by the presence of large numbers of multinucleated osteoclast-like giant cells. Although GCT can be considered a benign lesion, it exhibits high local aggressiveness often associated with osteolytic properties. In this study, we used five different GCT primary cell cultures to evaluate whether osteoclast-like cells from GCT are able to produce interleukin-6 (IL-6), a cytokine strictly involved in the induction of osteoclast-mediated bone resorption. IL-6 assessment with ELISA revealed that osteoclast-like GCT cells produce low levels of this cytokine, which can be greatly increased after treatment with both lipopolysaccharide (LPS) or interleukin-1 beta (IL-1 beta). These data were confirmed by molecular analysis which revealed that GCT cells synthesize IL-6 mRNA and that the levels of IL-6 transcripts are greatly increased after treatment with both LPS and IL-1 beta. Moreover, by using a biologic assay with the 7TD1, a IL-6 dependent cell Line, we also determined that IL-6 synthesized by GCT cells is biologically active. This study supports the hypothesis that IL-6 locally released by GCT osteoclast-like cells may be involved in the induction of the osteolysis which is strictly associated with the biologic aggressiveness of GCT cells.