Autoimmune Disorders

An autoimmune disorder is a malfunction of the body's immune system, causing the body to attack its own tissues.

Normally, the immune system can distinguish what is self from what is not self (or foreign (see Section 16, Chapter 183)) and reacts against foreign substances called antigens. Antigens may be contained within or on bacteria, viruses, other microorganisms, or cancer cells. Or antigens may exist on their own--for example, as pollen or food molecules. Sometimes the immune system malfunctions, interpreting the body's own tissues as foreign and producing abnormal 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. Different cells or tissues are targeted in different autoimmune disorders.

See the table Some Autoimmune Disorders.

Causes

Autoimmune reactions can be triggered in several ways:

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 attack.
A normal body substance is altered, for example, by a virus, a drug, sunlight, or radiation. The altered substance may 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.
The cells that control antibody production--for example, B lymphocytes (a type of white blood cell)--may malfunction and produce abnormal antibodies that attack some of the body's cells.

Heredity may be involved in some autoimmune disorders. Susceptibility, rather than the disorder itself, may be inherited. In susceptible people, a trigger, such as a viral infection or tissue damage, may cause the disorder to develop. Hormonal factors may also be involved, because many autoimmune disorders are more common among women.

Symptoms and Diagnosis

Autoimmune disorders commonly cause a fever. However, 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 may detect an autoimmune disorder. For example, the erythrocyte sedimentation rate (ESR) is often increased, because proteins, produced in response to inflammation, interfere with the ability of red blood cells (erythrocytes) to remain suspended in blood. Typically, the number of red blood cells is decreased, resulting in anemia. Blood tests can also detect different antibodies, some of which typically occur in people who have an autoimmune disorder. Examples of these antibodies are antinuclear antibodies (which attack the nuclei of cells) and rheumatoid factor.

Treatment

Treatment involves control of the autoimmune reaction by suppressing the immune system. However, many of the drugs used to control the autoimmune reaction interfere with the body's ability to fight disease, especially infections. Treatment to relieve symptoms may also be needed.

Drugs that suppress the immune system (immunosuppressants), such as azathioprine, chlorambucil, cyclophosphamide, cyclosporine, or methotrexate, are often given, usually by mouth and often for a long time (see Section 16, Chapter 187). 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 infection and of certain 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 Section 5, Chapter 67). When possible, corticosteroids are used for a short time--when the disorder begins or when symptoms worsen. However, corticosteroids must sometimes be used indefinitely.

Etanercept and infliximab 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 inflammatory bowel disease, but they may be harmful if used to treat certain other autoimmune disorders, such as multiple sclerosis.

Plasmapheresis is used to treat a few autoimmune disorders. Blood is withdrawn and filtered to remove the abnormal antibodies. Then the filtered blood is returned to the person.

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.