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. 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. eMedicineHealth Medical Reference
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