immunosuppressive drug

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immunosuppressive drug,

any of a variety of substances used to prevent production of antibodiesantibody,
protein produced by the immune system (see immunity) in response to the presence in the body of antigens: foreign proteins or polysaccharides such as bacteria, bacterial toxins, viruses, or other cells or proteins.
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. They are commonly used to prevent rejection by a recipient's body of an organ transplanted from a donor. A transplant is rejected when the recipient's immune system acts against it; current methods aim at suppressing the activity of the lymphocytes, the cells that form antibodies (see immunityimmunity,
ability of an organism to resist disease by identifying and destroying foreign substances or organisms. Although all animals have some immune capabilities, little is known about nonmammalian immunity.
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; transplantationtransplantation, medical,
surgical procedure by which a tissue or organ is removed and replaced by a corresponding part, usually from another part of the body or from another individual.
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). The steroidssteroids,
class of lipids having a particular molecular ring structure called the cyclopentanoperhydro-phenanthrene ring system. Steroids differ from one another in the structure of various side chains and additional rings. Steroids are common in both plants and animals.
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, such as cortisonecortisone
, steroid hormone whose main physiological effect is on carbohydrate metabolism. It is synthesized from cholesterol in the outer layer, or cortex, of the adrenal gland under the stimulation of adrenocorticotropic hormone (ACTH).
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, which suppress the antibody-forming lymphocyte cells, have been used to prolong human organ transplants. Steroids may also prevent antigens from entering cells and thereby prevent local allergic inflammation reactions. In another immunosuppressive method, human lymphocytes are injected into horses, stimulating the animals to produce antilymphocyte serum. The serum, administered to humans with transplanted organs, in some way inactivates lymphocyte cells. The procedure will not work effectively for more than a few injections of serum. Another group of immunosuppressive drugs act by interfering with the synthesis of nucleic acidsnucleic acid,
any of a group of organic substances found in the chromosomes of living cells and viruses that play a central role in the storage and replication of hereditary information and in the expression of this information through protein synthesis.
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 and are especially effective against proliferating cells such as stimulated lymphocytes. Some of these are analogs of purines and pyrimidines, substances that are nucleic acid subunits; the purine analog azothioprine has been used to suppress rejection of transplanted human kidneys. Most substances that inhibit nucleic acid synthesis, such as nitrogen mustardnitrogen mustard,
any of various poisonous compounds originally developed for military use (see poison gas). Like mustard gas and lewisite, it is a vesicant (blistering agent).
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, cyclophosphamide (CytoxanCytoxan
, trade name for the drug cyclophosphamide, used to inhibit growth of tumors and rapidly proliferating cells. It is used in the treatment of leukemia, Hodgkin's disease, and lymphosarcoma and other solid tumors.
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), chloramphenicolchloramphenicol
, antibiotic effective against a wide range of gram-negative and gram-positive bacteria (see Gram's stain). It was originally isolated from a species of Streptomyces bacteria.
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, actinomycinactinomycin
, any one of a group of antibiotics produced by bacteria of the genus Streptomyces. Actinomycin was the first antibiotic reported to be able to halt cancer; however, it is not widely used to treat cancers because it is highly toxic to humans, interfering with
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, and colchicinecolchicine
, alkaloid extracted from plants of the genus Colchicum and especially from the corms of the autumn crocus, Colchicum autumnale (see meadow saffron).
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, are not widely used clinically because they are too toxic. Many of the drugs that suppress the function of the immunological system are also used clinically to check growth of cancerous tissue, which is composed of rapidly dividing cells. The drugs currently used to suppress antibody formation also leave an individual susceptible to infection.