These antibodies are produced by the immune system in response to a trigger called an antigen. These foreign substances include things like bacteria and viruses. In rheumatoid arthritis, for reasons unknown, the body's immune system malfunctions and begins producing antibodies against its own tissues. This causes the body's immune system to attack its own joints , causing inflammation, swelling, and pain. Chronic inflammation of the synovial membrane lining the joint causes destruction of cartilage and bone within the joint.
Young children can have a form called juvenile rheumatoid arthritis.
Joint pain, swelling, and stiffness, which is especially severe and prolonged in the morning, are the most common symptoms of rheumatoid arthritis. The problems may migrate from one joint to another. When one joint is involved, the corresponding joint on the other side will usually become involved too. Usually many joints throughout the body are affected at the same time. Rheumatoid arthritis can cause deformities such as misshapen fingers, bunions , hammertoe , and knock-knees.