antigen

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Related to antigenic: antigenic determinant, Antigenic drift

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 ?
Further studies are needed to determine whether additional antigenic clusters of H3 IAVs are present in migratory waterfowl.
If a virus eludes antibodies, all five antigenic sites would have to mask themselves by mutating.
The epidemic was notable because of the initial difficulty in establishing its cause as an influenza A virus because of its considerable antigenic difference from previous influenza A viruses.
This process, termed antigenic drift, results from the high mutation rate of the viral genome and the continuous selection of mutants with improved replication characteristics in the immune human host population.
It interacts with a regulatory site on MHC class II molecules just outside the antigenic peptide-binding site to loosen bound antigenic peptide.
The ability of these spirochetes to undergo antigenic variation is well documented (25).
In cases where an antigenic peptide has been identified to be an important target of a cellular immune response, this patent covers our use of HSPs as an adjuvant and delivery vehicle for that antigen," said Garo H.
He subsequently showed in detail how fragments of the Ii protein regulate charging of MHC class II with antigenic peptides for presentation to the immune system.
In the absence of virus isolation, the diagnosis of infections with ONNV is difficult because of the close antigenic relationship of this virus with other alphaviruses, especially CHIKV.
Eric von Hofe, Vice President, Technology Development at Antigen Express, who presented this report, said: "This technology is revolutionary in the sense that we bioengineer cancer cells to present their antigenic epitopes directly to T helper lymphocytes.
Vaccine-induced antibodies to heterologous influenza A H1N1 viruses: effects of aging and "original antigenic sin.
made from Vystar's patented Vytex(TM) NRL, which has less than 2 micrograms/dm2, virtually undetectable levels, of the antigenic proteins that can cause an allergic response, while retaining and improving upon all the desirable qualities of latex.