The intraarticular and systemic expression of proinflammatory cytokines—particularly tumor necrosis factor α (TNFα), interleukin 1 (IL-1) and IL-6, which are produced primarily by synovial macrophages and synoviocytes—plays a crucial role in the pathogenesis of RA, in that these cytokines can contribute to the increased number of the fibroblast-like synoviocytes. The gene discussed is TNF; the disease is rheumatoid arthritis.