IL6 and rheumatoid arthritis: We found that treatment of OA synovial fibroblasts (OASF cells) and RA synovial fibroblasts (RASF cells) with RANKL significantly enhanced the production of proinflammatory cytokines (IL-1β and IL-6) and increased the secretion of catabolic factor MMP-13, while TNF-α and matrix metalloproteinase-1 (MMP-1) did not significantly increase in protein levels.