Rheumatoid arthritis belongs to a group of diseases called autoimmune disorders , in which the body produces antibodies against its own tissues. A person with rheumatoid arthritis produces antibodies against his or her own tissue, for no apparent reason.
Antibodies are protein molecules that the body uses to fight infection.
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.