antigen

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antigen:

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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Antigen

A substance that initiates and mediates the formation of the corresponding immune body, termed antibody. Antigens can also react with formed antibodies. Antigen-antibody reactions serve as host defenses against microorganisms and other foreign bodies, or are used in laboratory tests for detecting the presence of either antigen or antibody. See Antibody, Antigen-antibody reaction

A protein immunogen (any substance capable of inducing an immune response) is usually composed of a large number of antigenic determinants. Thus, immunizing an animal with a protein results in the formation of a number of antibody molecules with different specificities. The antigenicity of a protein is determined by its sequence of amino acids as well as by its conformation. Antigens may be introduced into an animal by ingestion, inhalation, sometimes by contact with skin, or more regularly by injection into the bloodstream, skin, peritoneum, or other body part.

With a few exceptions, such as the autoantigens and the isoantigens of the blood groups, antigens produce antibody only in species other than the ones from which they are derived. All complete proteins are antigenic, as are many bacterial and other polysaccharides, some nucleic acids, and some lipids. Antigenicity may be modified or abolished by chemical treatments, including degradation or enzymatic digestion; it may be notably increased by the incorporation of antigen into oils or other adjuvants. See Isoantigen

Bacteria, viruses, protozoans, and other microorganisms are important sources of antigens. These may be proteins or polysaccharides derived from the outer surfaces of the cell (capsular antigens), from the cell interior (the somatic or O antigens), or from the flagella (the flagellar or H antigens). Other antigens either are excreted by the cell or are released into the medium during cell death and disruption; these include many enzymes and toxins, of which diphtheria, tetanus, and botulinus toxins are important examples. The presence of antibody to one of these constituent antigens in human or animal sera is presumptive evidence of past or present contact with specific microorganisms, and this finds application in clinical diagnosis and epidemiological surveys. See Botulism, Diphtheria, Toxin

Microbial antigens prepared to induce protective antibodies are termed vaccines. They may consist of either attenuated living or killed whole cells, or extracts of these. Since whole microorganisms are complex structures, vaccines may contain 10 or more distinct antigens, of which generally not more than one or two engender a protective antibody. Examples of these are smallpox vaccine, a living attenuated virus; typhoid vaccine, killed bacterial cells; and diphtheria toxoid, detoxified culture fluid. Several independent vaccines may be mixed to give a combined vaccine, and thus reduce the number of injections necessary for immunization, but such mixing can result in a lesser response to each component of the mixture. See Vaccination

Allergens are antigens that induce allergic states in humans or animals. Examples are preparations from poison ivy, cottonseed, or horse dander, or simple chemicals such as formaldehyde or picryl chloride. See Hypersensitivity, Immunology

antigen

[′an·tə·jən]
(immunology)
A substance which reacts with the products of specific humoral or cellular immunity, even those induced by related heterologous immunogens.

antigen

a substance that stimulates the production of antibodies
References in periodicals archive ?
Superiority of tissue polypeptide antigen to carcinoembryonic antigen and carbohydrate antigenic determinant 19-9.
A direct assay for carcinoembryonic antigen in serum and its diagnostic value in metastatic breast cancer.
3 and carcinoembryonic antigen in metastatic breast cancer compared by computer simulation of marker data.
Studies on the control of gene expression of the carcinoembryonic antigen family in human tissue.
Browse the full report Carcinoembryonic Antigen (CEA) Market - Growth, Share, Opportunities, Competitive Analysis, and Forecast, 2016 2023 at http://www.
High levels of carcinoembryonic antigens are typically found in the blood of persons with cancer of the large intestine.
Serum biomarkers including chromogranin A, carcinoembryonic antigen, and parathyroid hormone-related protein might be helpful for diagnosis (2).
Thus, novel insights into carcinoembryonic antigen cell adhesion molecule 1 (CEACAM1) may lead to promising strategies in melanoma treatment.
The immunohistochemical studies revealed tumor cell positivity for cytokeratin 19, carcinoembryonic antigen (partial positive), villin, caudal-related homeodomain transcription-2, and Ki67 50%, but studies were negative for TTF-1, cytokeratin 7, cytokeratin 20, and NapsinA.
Other tests look for carcinoembryonic antigens and phosphohexose isomerase (an enzyme implicated in metastasis).