TNFSF11 and rheumatoid arthritis: In fact, RA is defined as an inflammatory and autoimmune disease characterized by accumulation of leukocyte inflammatory infiltrate in the synovial membrane, as well as mediators such as PGE2, TNF-α, IL-1β, IL-6, IL-12, IL-17, IL-18, IL-33, granulocyte macrophage colony-stimulating factor (GM-CSF), Monocyte Colony-Stimulating Factor (M-CSF), RANKL, MMPs, and NO, all being found in the synovial fluid [20–24], and leading to synovitis and joint architecture destruction.