Illustration comparing a normal immune system to the effects of autoimmune disease. At top, in a normal immune system, antigens invade (red) and antibodies (black Y) form to remove the antigens. The antibodies (black Y) then remain and protect within the immune system. The sequence at the bottom shows an abnormal immune response of the body against substances and tissues normally present in the body, known as autoimmune disease. The immune system forms antibodies (black Y) to selfantigens (purple). The antibodies attack the selfantigens resulting in inflammation and tissue damage. This disease may be restricted to certain organs or involve a particular tissue in different places.