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Immunosuppression is a reduction of the activation or efficacy of the immune system. Some portions of the immune system itself have immunosuppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse reaction to treatment of other conditions. In general, deliberately induced immunosuppression is performed to prevent the body from rejecting an organ transplant, treating graft-versus-host disease after a bone marrow transplant, or for the treatment of auto-immune diseases such as systemic lupus erythematosus, rheumatoid arthritis or Crohn's disease. This is typically done using medications, but may involve surgery (spleen removal), plasmapharesis, or radiation. A person who is undergoing immunosuppression, or whose immune system is weak for other reasons (for example, chemotherapy or HIV), is said to be ''immunocompromised''. An immunosuppressant is any agent that weakens the immune system, including immunosuppressive drugs and some environmental toxins. ==Deliberately induced== Administration of immunosuppressive medications or immunosuppressants is the main method of deliberately induced immunosuppression. In optimal circumstances, immunosuppressive drugs are targeted only at any hyperactive component of the immune system, and in ideal circumstances would not cause any significant immunodeficiency. However, in essence, all immunosuppressive drugs have the potential to cause immunodeficiency. Immunodeficiency can cause increased susceptibility to opportunistic infections and decreased cancer immunosurveillance. The term ''immunotoxin'' is also sometimes used (incorrectly) to label undesirable immunosuppressants, such as various pollutants. Immunosuppressants may be prescribed when a normal immune response is undesirable, such as in autoimmune diseases. Cortisone was the first immunosuppressant identified, but its wide ranging side-effects limited its use. The more specific azathioprine was identified in 1959, but it was the discovery of cyclosporine in 1970 that allowed significant expansion of kidney transplantation to less well-matched donor-recipient pairs as well as broad application to liver transplantation, lung transplantation, pancreas transplantation, and heart transplantation. After an organ transplantation, the body will nearly always reject the new organ(s) due to differences in human leukocyte antigen haplotypes between the donor and recipient. As a result, the immune system detects the new tissue as "foreign", and attempts to remove it by attacking it with recipient white blood cells, resulting in the death of the donated tissue. Immunosuppressants are given as an attempt to prevent this rejection; the side-effect is that the body becomes more vulnerable to infections and malignancy, as in advanced HIV infection. Throughout its history, radiation therapy has been used to decrease the strength of the immune system. Dr. Joseph Murray of Harvard Medical School and chief plastic surgeon at Children's Hospital Boston from 1972-1985 was awarded the Nobel Prize in Physiology or Medicine in 1990 for his work on immunosuppression. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「immunosuppression」の詳細全文を読む スポンサード リンク
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