A condition in which the body’s immune system identifies the body’s own tissues as “foreign” rather than self. The purpose of the body’s immune system is to fight off infections, such as those caused by viruses and bacteria. Some degree of autoimmunity exists in everybody and usually does no harm. It may be useful, in fact, for destroying cancer cells and recognizing and removing old blood cells and damaged tissues. Yet in a small percentage of people the immune system wages an all-out war on certain proteins and tissues in the body, causing autoimmune diseases. Scientists have isolated more than 80 specific autoimmune diseases, including such common or well-known diseases as rheumatoid arthritis, Graves disease, Hashimoto thyroiditis, multiple sclerosis, systemic lupus erythematosus, Addison disease, and Type 1 diabetes.

Rheumatoid arthritis is a disease in which the immune system launches an attack on collagen (a fibrous protein) in the joints. White blood cells pour into the synovial membrane that lines these joints, causing pain, redness, and swelling.

In Graves disease, the immune system produces antibodies against certain proteins on the surface of the cells of the thyroid gland, a gland that regulates many processes throughout the body. These antibodies stimulate the thyroid gland to produce too much of its hormones, producing such symptoms as nervousness, heart palpitations, weight loss, sweating, and intolerance to heat.

Hashimoto thyroiditis is a disorder in which the immune system gradually destroys the thyroid gland, causing it to secrete less and less of its hormones. This destruction causes a slowing down of various body functions, producing fatigue, lethargy, poor concentration, thinning hair, depression, constipation, feeling cold, tingling in the extremities, and weight gain.

Multiple sclerosis results when the immune system destroys segments of myelin, the substance that sheathes and insulates nerve pathways in the brain and spinal cord and is necessary for efficient conduction of nerve impulses. Destruction of myelin can affect the body in many ways, causing a wide variety of symptoms, such as numbness, muscle weakness, unsteady movement, slurred speech, and blurry vision.

In systemic lupus erythematosus, the immune system forms antibodies against the nuclei of cells, DNA, RNA, and other material, causing inflammation of the connective tissue in one or more parts of the body. It may damage the skin, joints, and internal organs.

Addison disease occurs when the immune system gradually destroys the adrenal cortex, the outer layer of the adrenal glands that produce corticosteroid hormones. As a result, production of hormone decreases, causing loss of appetite, weight loss, weakness, and anemia.

Type 1 diabetes develops when the immune system recognizes and attacks proteins on the surface of the beta cells, the cells of the pancreas that secrete insulin. White blood cells flood into the pancreatic islets (cell clusters that include the beta cells) and cause an inflammation known as insulitis. Once enough beta cells have been destroyed, the symptoms of diabetes begin to appear.

While everyone has some autoimmunity, not everyone develops autoimmune diseases. Scientists believe that certain people are genetically susceptible to developing autoimmune diseases, but that environmental factors play a role in causing or “triggering” these diseases. They have identified a number of potential triggers for autoimmune diseases, including certain drugs, environmental pollutants, and viruses.

Researchers have identified two basic types of autoimmune disease: organ-specific and non-organ-specific. Organ-specific autoimmune diseases are those that attack specific types of tissues in specific organs, such as the thyroid gland, the adrenal glands, and the pancreas. Type 1 diabetes is one example of an organ-specific autoimmune disease. Non-organ-specific autoimmune diseases target more general types of tissues, such as connective tissue. The best known of the non-organ-specific autoimmune diseases are rheumatoid arthritis and systemic lupus erythematosus.

These two distinct clusters of autoimmune diseases tend to run together within individuals and within families. For example, some 15% to 20% of people with Type 1 diabetes have at least the early manifestations of autoimmune thyroid disease (Graves disease or Hashimoto thyroiditis). Their first-degree relatives (parents, siblings, and children) are at increased risk of developing these disorders as well. People with Type 1 diabetes also have a slightly elevated risk for developing Addison disease.

An estimated 40% of families in which one member has Type 1 diabetes has another member with at least the early indications of autoimmune disease.

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