The immune system is the body's defense against foreign substances,
such as bacteria or viruses, that may be harmful. An autoimmune disease is an
abnormal condition that occurs when a person's immune system attacks its own
tissues as though they were foreign substances.
Normally, when a foreign substance enters the
body, the immune system creates special cells to attack and destroy the foreign
substance. These cells include antibodies and white blood cells
In a person with an autoimmune disease, the immune
system recognizes some of the person's own tissues as foreign substances. The
body makes antibodies and other cells that attack and destroy these tissues.
This process often leads to inflammation and eventually, if it continues,
scarring and destruction of the organs that are made up of those
Why the body attacks its own cells is not known. Autoimmune
diseases include lupus, rheumatoid arthritis, scleroderma, and Sjögren's
syndrome. Certain types of diabetes and thyroid disease are related to
autoimmune reactions. People who have autoimmune diseases are at an increased
risk for infections.