Arthritis can attack joints such as the knee

Autoimmune diseases occur when the immune system mistakes its own tissues as foreign and mounts an inappropriate attack on the body. Overblown inflammation is a common thread in these chronic conditions. Examples include multiple sclerosis, type 1 diabetes, Crohn's disease, lupus, and rheumatoid arthritis.

In the case of autoimmune diseases, overproduction of cytokines and chemokines leads to inflammation of a body tissue. For example, too many cytokines in the joints can lead to rheumatoid arthritis. This condition worsens when chemokines summon more and more destructive immune system components — cells such as macrophages, neutrophils, and T cells — to the joint, amplifying the inflammatory response.

Multiple sclerosis, the most common nerve disease in young adults, is a chronic inflammatory disorder of the nervous system that is believed to be due to a misguided autoimmune attack on myelin, a protective coating on nerve cells. In multiple sclerosis, myelin is slowly eroded by the body's immune system, leading to problems with muscle coordination (because muscles require the action of nerves) and vision. As the disease progresses, for some reason inflammation decreases, but lasting damage has already been done to body tissues. Researchers suspect that the autoimmune trigger in multiple sclerosis may be infection by a virus or other microorganism, but this has not been proven beyond doubt.