Autoimmunity
In an autoimmune disease, a certain tissue in the body is attacked by its own defender cells. These cells start to destroy other cells, treating them like invading germs rather than part of the body. This immune response triggers inflammation. In rheumatoid arthritis, the layers of cells lining the joints are affected. This causes stiffness, swelling and pain. Doctors don't yet know what causes this or other autoimmune diseases.
