TNF and Arthritis: Arthritis, an inflammation of the joints, is a chronic disease that results from dysregulation of proinflammatory cytokines (e.g., tumor necrosis factor and interleukin-1β) and proinflammatory enzymes that mediate the production of prostaglandins (e.g., cyclooxygenase-2) and leukotrienes (e.g., lipoxygenase), together with the expression of adhesion molecules and matrix metalloproteinase, and hyperproliferation of synovial fibroblasts.