Rheumatoid arthritis is a disorder in which the body's own immune system starts to attack body tissues. The attack is not only directed at the joint but to many other parts of the body. In rheumatoid arthritis, most damage occurs to the joint lining and cartilage which eventually results in erosion of two opposing bones. Rheumatoid arthritis often affects joints in the fingers, wrists, knees and elbows. The disease is symmetrical (appears on both sides of the body) and can lead to severe deformity in a few years if not treated. Rheumatoid arthritis occurs mostly in people aged 20 and above. In children, the disorder can present with a skin rash, fever, pain, disability, and limitations in daily activities. Often, it is not clear why the rheumatoid arthritis occurred. With earlier diagnosis and aggressive treatment, many individuals can lead a decent quality of life. The drugs to treat rheumatoid arthritis range from corticosteroids to monoclonal antibodies given intravenously. The latest drugs like Remicade can significantly improve quality of life in the short term. In rare cases, surgery may be required to replace joints but there is no cure for the illness.[14]
This adaptive immune response is initiated in part by CD4+ T helper (Th) cells, specifically Th17 cells.[15] Th17 cells are present in higher quantities at the site of bone destruction in joints and produce inflammatory cytokines associated with inflammation, such as interleukin-17 (IL-17).[16]
Bone erosion is a central feature of rheumatoid arthritis. Bone continuously undergoes remodeling by actions of bone resorbing osteoclasts and bone forming osteoblasts. One of the main triggers of bone erosion in the joints in rheumatoid arthritis is inflammation of the synovium, caused in part by the production of pro-inflammatory cytokines and receptor activator of nuclear factor kappa B ligand (RANKL), a cell surface protein present in Th17 cells and osteoblasts.[16] Osteoclast activity can be directly induced by osteoblasts through the RANK/RANKL mechanism.[17]
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