Role of cytokines, acute-phase proteins, and chemokines in the progression of rheumatoid arthritis.

Rheumatoid arthritis (RA) has no firm etiologic basis. It progresses as an autoimmune disease and evolves into a chronic inflammatory joint disease complicated by recurrent episodes of systemic acute-phase reactions, which sometimes result in amyloidosis. Cytokines play a pivotol role in inflammation and the immune response. Proinflammatory cytokines such as interleukin-1, tumor necrosis factor alpha (TNF-alpha), and interleukin-6 are present at high levels in arthritic joints, and their blood concentration correlates with the severity of the RA. Some of the activities of the proinflammatory cytokines, such as stimulation of leukocyte infiltration and release of their proteolytic enzymes, may be mediated by acute phase proteins (APPs), such as C-reactive protein and serum amyloid A, and by chemokines such as interleukin-8. Cytokines, chemokines, and APPs reciprocally regulate each others' expression and activities, constituting a communication network between fibroblasts, macrophages, lymphocytes, and hepatocytes. Activation of the network results in inflammation and the progressive destruction of joints and systemic symptoms characteristic of RA.