An autoimmune disease is any of a group of disorders caused by the body's production of antibodies which attack the body's own tissues. Examples of such an autoimmune diseases include rheumatoid arthritis, insulin-dependent diabetes mellitus, and systemic lupus erythematosus (SLE), an inflammation of the connective tissue occurring most often in young women. The occasional presence of so-called auto-antibodies in an individual does not necessarily indicate autoimmune disease. Treatment depends on the specific disease process, but often includes drugs such as cortisone which damp down the immune response.
The disease-producing processes in autoimmunity are called hypersensitivity reactions, of which there are several types. These reactions are similar to the reactions that occur in allergy except that in autoimmune disorders the hypersensitivity response is to the body itself rather than to an outside substance.
Causes of autoimmune diseases
The immune system is normally able to distinguish "self" from "nonself". Some lymphocytes (a type of white blood cell) are capable of reacting against self, but these lymphocytes are generally suppressed. Autoimmune disorders occur when there is some interruption of the normal control process, allowing lymphocytes to escape from suppression, or when there is an alteration in some body tissue so that it is no longer recognized as "self" and is consequently attacked.
The exact mechanisms causing these changes are not fully understood, but bacteria, viruses, and drugs may play a role in triggering an autoimmune process in someone who already has a genetic predisposition. It is theorized that the usual inflammatory response of tissues to these agents somehow provokes an abnormal sensitization response to the tissues involved.
Types of autoimmune diseases
Autoimmune processes can have various results – for example, slow destruction of a particular type of cell or tissue, stimulation of an organ into excessive growth, or interference in its function. Organs and tissues frequently affected by autoimmune processes include the endocrine glands (such as the thyroid, pancreas, and adrenal glands), components of the blood (such as the red blood cells), and the connective tissues, skin, muscle, and joints.
Specific autoimmune diseases are often classified into organ-specific and non-organ-specific types. In organ-specific disorders, the autoimmune process is directed mainly against one organ. Examples include Hashimoto's thyroiditis (thyroid gland), pernicious anemia (stomach), Addison's disease (adrenal glands), and insulin-dependent diabetes mellitus.
In non-organ-specific disorders, autoimmune activity is widely spread throughout the body. Examples are systemic lupus erythematosus, rheumatoid arthritis, and dermatomyositis. Some autoimmune diseases fall between the two types. Sometimes patients may experience several organ-specific or non-organ-specific disorders at the same time. However, there is little overlap between the two ends of the spectrum.
Treatment of autoimmune diseases
The first principle in treating any autoimmune disorder is to correct any major deficiencies. This may involve replacing, hormones, such as thyroxine or insulin, that are not being produced by a gland. Alternatively, it may involve replacing components of the blood by transfusion.
The second principle is to lessen the activity of the immune system but not to the extend of compromising the body's ability to defend against disease in general. The drugs most commonly used are corticosteroids. More severe cases can be treated with other more powerful immunosuppressant drugs such as cyclophosphamide, methotrexate, and azoathioprine, but all of these drugs can damage rapidly dividing tissues, such as the bone marrow, and so are used with caution. Drugs that act more specifically on the immune system (for example, by blocking a particular hypersensitivity reaction) are being developed.