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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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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

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


A substance which reacts with the products of specific humoral or cellular immunity, even those induced by related heterologous immunogens.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


a substance that stimulates the production of antibodies
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Jacoby based his supposition on two citations of Hellanicus in the scholia to Aristophanes' Frogs, for events occurring in the archonship of Antigenes (407/6 B.C.).(59) The validity of those two citations is uncertain.
Les antigenes sont des molecules a la surface de ces organismes etrangers permettant de les reconnaitre comme telles (on peut les imaginer comme une piece d'identite).
The etiology of hydroa vacciniforme is not known and its association with human leukocyte antigenes DRB1 locus has been demonstrated (4).
* Preciser la toxicite, dans l'environnement, des produits geniques, des produits de leur degradation et de leurs derives toxigenicite potentielle pour les predateures, les brouteurs, les parasites, les pathogenes, les competiteurs et les symbiotes connus ou potentiels; effets nuisibles possibles sur Ia sante humanine notamment risques d'exposition a des toxines, des agents irritants ou des antigenes.
Et parmi les defis a relever, notre pays doit maintenir une couverture vaccinale uniforme superieure ou egale a 95% a tous les niveaux et introduire de nouveaux antigenes et rappels.
En vue de consolider ces acquis, la semaine nationale de vaccination 2015 se fixe comme objectifs la sensibilisation des differents acteurs a l'importance de la vaccination en tant qu'intervention efficace pour ameliorer la sante de la population, la contribution a la concretisation de l'objectif d'assurer une couverture vaccinale de 95% par antigenes uniforme a tous les niveaux et la promotion du nouveau calendrier national de vaccination et la necessite de respecter les dates d'administrations de toutes les doses requises, ainsi que l'organisation d'actions de communication de proximite pour mettre l'accent sur la place privilegiee qu'occupe la vaccination en matiere de promotion de la sante de l'enfant.