Arthritis News – 1999

One of the cardinal features of RA is erosion of periarticular bone. Osteoclasts play a key role in bone resorption but the mechanisms by which osteoclasts are formed from progenitor cells is not fully understood. In this study, Kotake, etal (J Clin Invest 103:1345, 1999) observed that Interleukin 17 (IL-17), a newly discovered cytokine, could induce the formation of osteoclast-like cells in cocultures of mouse hemopoietic cells and primary osteoblasts. This IL-17 induced osteoclastogenesis was inhibited by indomethacin, a selective inhibitor of cyclooxygenas-2 (COX-2). The synovial fluids from rheumatoid arthritis patients were found to have significantly higher levels of IL-17 as compared to osteoarthritis patients. Furthermore, using immunostaining, IL-17-positive mononuclear cells were detected in the synovial tissues of RA patients and not in tissue from OA patients. These findings indicate that IL-17 may contribute to bone erosion and joint damage in RA and may therefore, be another target for inhibition.