An autoimmune disorder is a malfunction of the body's immune system that causes the body to attack its own tissues.
What triggers an autoimmune disorder is not known.
Symptoms vary depending on which disorder develops and which part of the body is affected.
Several blood tests are often used to check for an autoimmune disorder.
Treatment depends on the type of autoimmune disorder and often involves drugs that suppress the activity of the immune system.
(See also Overview of Allergic Reactions.)
The immune system must first recognize foreign or dangerous substances before it can defend the body against them. Such substances include bacteria, viruses, parasites (such as worms), certain cancer cells, and even transplanted organs and tissues. These substances have molecules that the immune system can identify and that can stimulate a response by the immune system. These molecules are called antigens. Antigens 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.
When certain white blood cells (B cells and T cells) encounter an antigen, they learn how to attack it and thus defend the body from the potentially dangerous antigen. B cells produce antibodies, which are one of the body's main immune defenses against antigens. Antibodies tightly bind to a specific antigen and tag it for attack or directly neutralize it. The body produces thousands of different antibodies. Each antibody is specific to a particular antigen. Cells of the immune system remember the specific antigen so that they can attack it even more efficiently the next time they encounter it.
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. Having autoantibodies in the blood does not mean that a person has an autoimmune disorder.
There are many autoimmune disorders. Some of the more common autoimmune disorders include Graves disease, rheumatoid arthritis, Hashimoto thyroiditis, type 1 diabetes mellitus, 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.
Causes of Autoimmune Disorders
Autoimmune reactions can be triggered in several ways:
A normal body substance is altered, for example, by a virus, a drug, sunlight, or radiation. The altered substance may then appear foreign to the immune system. For example, a virus can infect and thus alter cells in the body. The virus-infected cells stimulate the immune system to attack.
A foreign substance that resembles a natural body substance may enter the body. The immune system may inadvertently target the similar body substance as well as the foreign substance. For example, the bacteria that cause strep throat have an antigen that is similar to an antigen in human heart cells. Rarely, the immune system attacks a person's heart after strep throat (this reaction is part of rheumatic fever).
The cells that control antibody production—for example, B cells (a type of white blood cell)—may malfunction and produce abnormal antibodies that attack some of the body's cells.
T cells, another type of white cell that are involved in the immune response, may also malfunction and damage the body's cells.
A substance in the body that is normally confined to a specific area (and thus is hidden from the immune system) is released into the bloodstream. For example, a blow to the eye can cause the fluid in the eyeball to be released into the bloodstream. The fluid stimulates the immune system to identify the eye as foreign and attack it.
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 of Autoimmune Disorders
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.
Diagnosis of Autoimmune Disorders
Blood tests
Doctors suspect an autoimmune disorder based on a person's symptoms. To help confirm the diagnosis, doctors do several laboratory tests.
Blood tests that indicate the presence of inflammation may suggest an autoimmune disorder. Such tests include the following:
The erythrocyte sedimentation rate (ESR): This test measures how quickly red blood cells (erythrocytes) settle to the bottom of a test tube containing blood. When inflammation is present, the ESR is often increased because proteins that are produced in response to inflammation interfere with the ability of red blood cells to remain suspended in blood.
Complete blood count (CBC): This test includes determining the number of red blood cells in blood. This number is frequently 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 also 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
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.
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Prognosis for Autoimmune Disorders
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.
Treatment of Autoimmune Disorders
Drugs that suppress the immune system, including corticosteroids
For some autoimmune disorders, plasma exchange and intravenous immune globulin
Drug treatment
Drugs that suppress the immune system
Often, corticosteroids
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.
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 drugs specifically target white blood cells. White blood cells help defend the body against infection but also participate in autoimmune reactions. These drugs include the following:
blocks the activation of one kind of white blood cell (T cell) and is used in rheumatoid arthritis.
, 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
Other drugs that target white blood cells are being developed.
Plasma exchange and intravenous immune globulin
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 and given by vein) is used to treat a few autoimmune disorders. How it works is unknown.
