Arthritis means inflammation of the joints. Rheumatoid arthritis(RA) is an autoimmune disease. The white cells and antibody proteins in your blood that usually fight infections enter your joints and cause inflammation. This causes heat, swelling and excess fluid to be produced. Eventually, this may lead to thinning of the cartilage that covers the ends of your bones and may cause the bone to be worn away. RA may also cause inflammation of the sheaths around your tendons. Rarely, the condition can affect other parts of your body, eg your lungs.
Attribution: BUPA