TNFSF13B and rheumatoid arthritis: Studies have found that the level of the B‐cell‐activating factor cloning to the tumor necrosis factor family (BAFF) in serum and synovial fluid of RA patients is usually increased, which is associated with the severity of the disease, while BAFF mainly activates noncanonical NF‐κB pathway to facilitates survival and maturation of B cells.198, 199