Autoimmunity and Autoimmune Disorders
Autoimmune diseases are conditions in which a person's immune system attacks the body's own cells, causing tissue destruction. Autoimmune diseases are classified as either general, in which the autoimmune reaction takes place simultaneously in a number of tissues, or organ specific, in which the autoimmune reaction targets a single organ. Autoimmunity is accepted as the cause of a wide range of disorders, and is suspected to be responsible for many more. Among the most common diseases attributed to autoimmune disorders are rheumatoid arthritis, systemic lupus erythematosis (lupus), multiple sclerosis, myasthenia gravis, pernicious anemia, and scleroderma.
To further understand autoimmune disorders, it is helpful to understand the workings of the immune system. The purpose of the immune system is to defend the body against attack by infectious microbes (germs) and foreign objects. When the immune system attacks an invader, it is very specific—a particular immune system cell will only recognize and target one type of invader. To function properly, the immune system must not only develop this specialized knowledge of individual invaders, but it must also learn how to recognize and not destroy cells that belong to the body itself. Every cell carries protein markers on its surface that identifies it in one of two ways: what kind of cell it is (e.g., nerve cell, muscle cell, blood cell, etc.) and to whom that cell belongs. These markers are called major histocompatibility complexes (MHCs) . When functioning properly, cells of the immune system will not attack any other cell with markers identifying it as belonging to the body. Conversely, if the immune system cells do not recognize the cell as "self," they attach themselves to it and put out a signal that the body has been invaded, which in turn stimulates the production of substances such as antibodies that engulf and destroy the foreign particles. In case of autoimmune disorders, the immune system cannot distinguish between self cells and invader cells. As a result, the same destructive operation is carried out on the body's own cells that would normally be carried out on bacteria , viruses , and other such harmful entities.
The reason why the immune system become dysfunctional is not well understood. Most researchers agree that a combination of genetic, environmental, and hormonal factors play into autoimmunity. The fact that autoimmune diseases run in families suggests a genetic component. Recent studies have identified an antiphospholipid antibody (APL) that is believed to be a common thread among family members with autoimmune diseases. Among study participants, family members with elevated APL levels showed autoimmune disease, while those with other autoantibodies did not. Family members with elevated APL levels also manifested different forms of autoimmune disease, suggesting that APL may serve as a common trigger for different autoimmune diseases. Further study of the genetic patterns among unrelated family groups with APL suggests that a single genetic defect resulting in APL production may be responsible for several different autoimmune diseases. Current research focuses on finding an established APL inheritance pattern, as well as finding the autoimmune gene responsible for APL production.
A number of tests can help diagnose autoimmune diseases; however the principle tool used by physicians is antibody testing. Such tests involve measuring the level of antibodies found in the blood and determining if they react with specific antigens that would give rise to an autoimmune reaction. An elevated amount of antibodies indicates that a humoral immune reaction is occurring. Elevated antibody levels are also seen in common infections. These must be ruled out as the cause for the increased antibody levels. The antibodies can also be typed by class. There are five classes of antibodies and they can be separated in the laboratory. The class IgG is usually associated with autoimmune diseases. Unfortunately, IgG class antibodies are also the main class of antibody seen in normal immune responses. The most useful antibody tests involve introducing the patient's antibodies to samples of his or her own tissue—if antibodies bind to the tissue it is diagnostic for an autoimmune disorder. Antibodies from a person without an autoimmune disorder would not react to self tissue. The tissues used most frequently in this type of testing are thyroid, stomach, liver, and kidney.
Treatment of autoimmune diseases is specific to the disease, and usually concentrates on alleviating symptoms rather than correcting the underlying cause. For example, if a gland involved in an autoimmune reaction is not producing a hormone such as insulin, administration of that hormone is required. Administration of a hormone, however, will restore the function of the gland damaged by the autoimmune disease. The other aspect of treatment is controlling the inflammatory and proliferative nature of the immune response. This is generally accomplished with two types of drugs. Steroid compounds are used to control inflammation . There are many different steroids, each having side effects. The proliferative nature of the immune response is controlled with immunosuppressive drugs. These drugs work by inhibiting the replication of cells and, therefore, also suppress non-immune cells leading to side effects such as anemia. Prognosis depends upon the pathology of each autoimmune disease.
See also Antigens and antibodies; Antibody formation and kinetics; Antibody-antigen, biochemical and molecular reactions; Immune system; Immunity, cell mediated; Immunity, humoral regulation; Immunologic therapies; Immunosuppressant drugs; Major histocompatibility complex (MHC)
World of Microbiology and Immunology
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