An autoimmune disorder is a malfunction of the body's immune system that causes the body to attack its own tissues.
The immune system defends the body against what it perceives to be foreign or dangerous substances (see Recognition). Such substances include parasites (such as worms), certain cancer cells, and even transplanted organs and tissues. Substances that can stimulate a response by the immune system are called antigens. Antigens are molecules that may be contained within cells or on the surface of cells (such as bacteria or cancer cells) or be part of a virus. Some antigens, such as pollen or food molecules, exist on their own.
Cells in a person's own tissues also have antigens. But normally, the immune system reacts only to antigens from foreign or dangerous substances, not to antigens from a person's own tissues. However, the immune system sometimes malfunctions, interpreting the body's own tissues as foreign and producing antibodies (called autoantibodies) or immune cells that target and attack particular cells or tissues of the body. This response is called an autoimmune reaction. It results in inflammation and tissue damage. Such effects may constitute an autoimmune disorder, but many people produce such small amounts of autoantibodies that an autoimmune disorder does not occur.
There are many autoimmune disorders. Some of the more common autoimmune disorders include Graves disease, rheumatoid arthritis, Hashimoto thyroiditis, type I diabetes, systemic lupus erythematosus (lupus), and vasculitis. Additional disorders that are believed to be autoimmune include Addison disease, polymyositis, Sjögren syndrome, progressive systemic sclerosis, many cases of glomerulonephritis (inflammation of the kidneys), and some cases of infertility.
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Autoimmune reactions can be triggered in several ways:
Why something triggers an autoimmune reaction or disorder in one person (and not another) is usually unknown. However, heredity is sometimes involved. Some people have genes that make them slightly more likely to develop an autoimmune disorder. This slightly increased susceptibility to an autoimmune disorder, rather than the disorder itself, is inherited. In susceptible people, a trigger, such as a viral infection or tissue damage, may cause the disorder to develop.
Many autoimmune disorders are more common among women.
Symptoms vary depending on the disorder and the part of the body affected. Some autoimmune disorders affect certain types of tissue throughout the body—for example, blood vessels, cartilage, or skin. Other autoimmune disorders affect a particular organ. Virtually any organ, including the kidneys, lungs, heart, and brain, can be affected. The resulting inflammation and tissue damage can cause pain, deformed joints, weakness, jaundice, itching, difficulty breathing, accumulation of fluid (edema), delirium, and even death.
Blood tests that indicate the presence of inflammation may suggest an autoimmune disorder. For example, the erythrocyte sedimentation rate (ESR) is often increased because proteins that are produced in response to inflammation interfere with the ability of red blood cells (erythrocytes) to remain suspended in blood. Frequently, the number of red blood cells is decreased (anemia) because fewer red blood cells are produced when inflammation is present.
Because inflammation has many causes (many of which are not autoimmune), doctors often do blood tests to detect different antibodies that can occur in people who have particular autoimmune disorders. Examples of these antibodies are antinuclear antibodies, which are typically present in systemic lupus erythematosus, and rheumatoid factor or anti-cyclic citrullinated peptide (anti-CCP) antibodies, which are typically present in rheumatoid arthritis. But even these antibodies sometimes occur in people who do not have an autoimmune disorder, so doctors usually use a combination of test results and the person's symptoms to decide whether an autoimmune disorder is present.
Treatment may involve control of the autoimmune reaction by suppressing the immune system. However, many of the drugs used to control the autoimmune reaction also interfere with the body's ability to fight disease, especially infections.
Drugs that suppress the immune system (immunosuppressants), such as azathioprine, chlorambucil, cyclophosphamide, cyclosporine, mycophenolate, and methotrexate, are often given, usually by mouth and often for a long time (see Drugs Used to Prevent Transplant Rejection). However, these drugs suppress not only the autoimmune reaction but also the body's ability to defend itself against foreign substances, including microorganisms that cause infection and cancer cells. Consequently, the risk of certain infections and cancers increases.
Often, corticosteroids, such as prednisone, are given, usually by mouth. These drugs relieve inflammation as well as suppress the immune system. Corticosteroids given for a long time have many side effects (see Sidebar 3: Corticosteroids: Uses and Side Effects). When possible, corticosteroids are used for a short time—when the disorder begins or when symptoms worsen. However, corticosteroids must sometimes be used indefinitely.
Certain autoimmune disorders (such as multiple sclerosis and thyroid disorders) are also treated with drugs other than immunosuppressants and corticosteroids. Treatment to relieve symptoms may also be needed.
Etanercept, infliximab, and adalimumab block the action of tumor necrosis factor (TNF), a substance that can cause inflammation in the body. These drugs are very effective in treating rheumatoid arthritis and some other autoimmune disorders, but they may be harmful if used to treat certain other autoimmune disorders, such as multiple sclerosis. These drugs can also increase the risk of infection and certain skin cancers.
Certain new drugs specifically target white blood cells. White blood cells help defend the body against infection but also participate in autoimmune reactions. Abatacept blocks the activation of one kind of white blood cell (T cell) and is used in rheumatoid arthritis. Rituximab, first used against certain white blood cell cancers, works by depleting certain white blood cells (B cells) from the body. It is effective in some autoimmune disorders, such as rheumatoid arthritis and certain disorders that cause inflammation of blood vessels (vasculitis), including granulomatosis with polyangiitis (Wegener granulomatosis). Rituximab is under study in a variety of other autoimmune disorders. Other drugs that target white blood cells are being developed.
Plasma exchange is used to treat a few autoimmune disorders. Blood is withdrawn and filtered to remove abnormal proteins such as autoantibodies. Then the filtered blood is returned to the person.
Intravenous immune globulin (a purified solution of antibodies obtained from volunteer donors) is used to treat a few autoimmune disorders. How it works is unknown.
Some autoimmune disorders resolve as inexplicably as they began. However, most autoimmune disorders are chronic. Drugs are often required throughout life to control symptoms. The prognosis varies depending on the disorder.
Last full review/revision May 2014 by Peter J. Delves, PhD