TNF and rheumatoid arthritis: Rheumatoid arthritis (RA) is characterized by synovitis, interaction of lymphocytes, macrophages, and synovial cells, the production of matrix metalloproteinases and cytokines such as tumor necrosis factor (TNF), interleukin-1 (IL-1), and interleukin-6 (IL-6), leading to excessive erosion of articular cartilage and marginal bone, and defective bone repair [2–6].