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 ?
The pleomorphic, large, epithelioid, and spindle-shaped neoplastic cells of both specimens showed a diffuse cytoplasmic positivity for vimentin and membranous expression of leukocyte common antigen and UCHL-1 (Figure 6).
PAX5 and TdT are also commonly seen, while expression of leukocyte common antigen (CD45), CD34, and CD20 may show any pattern of expression from bright to negative (see Figure 3, c for a representative example).
The spindle cells were negative for melanin A, HMB-45, epithelial membrane antigen, pankeratin, muscle actin, CD 117, low-molecular-weight keratin, high-molecular-weight keratin, CD34, CD5, factor VIIIa, and CD45/leukocyte common antigen.
Boston University (Boston, MA) has patented methods for the creation and use of libraries of proteins which comprise polyclonal antibodies to a common antigen or group of antigens, receptor proteins with related variable regions, or other immune related proteins with variable regions.
A second evaluation is appropriate for persistent symptoms after a negative EIA toxin assay, but is not useful after a negative common antigen test.
For example, a person whose cells lack C antigen--a common antigen in the Rh blood-group system--may form anti-C.
The mediastinal tumor samples taken from our patient stained positively for vimentin, muscle-specific actin, and desmin and were negative for cytokeratin AE 1/3, cytokeratin 7, cytokeratin 20, epithelial membrane antigen (EMA), calretinin, S100 protein, melanoma antibody (HMB45), and leukocyte common antigen.
Thus, the study provided preliminary evidence of a specific response to the Psoraxine antigen, without the suppression of normal immunologic response to other common antigens.
Therefore the study provided preliminary evidence of a specific response to the Psoraxine(R) antigen, without the suppression of normal immunologic response to other common antigens.

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