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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


A substance which reacts with the products of specific humoral or cellular immunity, even those induced by related heterologous immunogens.


a substance that stimulates the production of antibodies
References in periodicals archive ?
Independent variation in nature of the hemagglutinin and neuraminidase antigens of influenza virus: distinctiveness of the hemagglutinin antigen of Hong Kong-68 virus.
capsulatum antigen, and acute and convalescent sera tests for antibodies to H.
Thery speculates that the first dendritic cells to encounter an infectious microbe produce exosomes bearing microbial antigens as messages to other dendritic cells, sparking a chain reaction that amplifies and perhaps speeds the overall immune response.
The effect of pre-treatment with beta-glucuronidase, hyaluronidase, and antigen on anaphylactic sensitivity of guinea-pigs, rats and mice.
In-depth discussion of key opportunities and risks for novel vaccine antigen delivery technologies
Family 4, like family 2, is directed to cancer antigens, specifically other immunogenic portions of MUC1.
We observed that several metal ions enhanced antigen-mediated mast cell activation (Figures 3 and 5), which resulted in the release of mediators in amounts exceeding the maximum amount observed with antigen alone.
Studies in mice indicate that the presence of multiple antigens (32) does not appear to interfere with immune responses.
Only those skin tests that can quantify the patient's sensitivity to each antigen can provide the information necessary to formulate an optimal treatment program.
Hoping to create individualized vaccines without requiring that the tumor have a known antigen, Kufe's team in 1997 fused whole cancer cells with dendritic cells.
It can play the role of antigen in experimental animal models of MS and may well play this role in the human disease.
First, Select VLPs have a specific size and assembly process different from other VLPs which enables the expression of much larger vaccine antigens than can be expressed on other types of VLPs and also offers the prospect for distinctive antigen processing.