TNFSF11 and rheumatoid arthritis: At the same time, immune cells such as Th17 cells and B cells and synovial fibroblasts in the synovium activate OC by secreting pro-inflammatory TNF-α, IL-17 and other cytokines and signaling molecules such as RANKL, and activated OC releases catalases and acid enzymes, which are the main causes of increased bone resorption leading to bone erosion in RA patients (9).