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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 ?
This family differs structurally, antigenically, and in the way it replicates from the Flaviviridae.
Cross-immune precipitation analyses have confirmed that viruses in the Nairovirus genus share antigenic determinants and are antigenically distinct from representative members of the family Bunyaviridae (15).
2) Unlike previous pandemics, pandemic influenza (H1N1) 2009, although not a new subtype of influenza virus, does represent a virus that is new to the human population both antigenically and biologically.
Preliminary evidence indicates that 10%-15% of type B and 10%-15% of type A H3N2 isolates don't match antigenically with the formulation of the current influenza vaccine.
HI antibodies were induced after MVA-H5sfMR vaccination that displayed considerable reactivity with the antigenically distinct H5N8 strain A/chicken/ Netherlands/EMC-3/2014 (Figure, panel A).
2013-2014 Influenza Strains and Use of Antiviral Medications This year's vaccine will protect against three viral strains most likely to cause the flu in the upcoming year: A/California/7/2009 (H1N1) pdm09-like virus; A(H3N2) virus antigenically like the cell-propagated prototype virus A/Victoria/361/2011; and B/Massachusetts/2/2012-like virus.
The novel H1N1 was antigenically different from earlier human H1N1 viruses; therefore the entire world population was susceptible to infection.
Since 2000, the two co-circulating lineages of influenza B viruses (B/Yamaguchi and B/Victoria) have become more antigenically distinct, raising the issue of whether adding a second B strain to the seasonal flu vaccine would have a positive public health benefit, Rakesh Pandey, Ph.
This RNase, or an antigenically similar protein, is also found in serum.
presented data on its novel bivalent VLP vaccine technology which creates VLP vaccines each bearing two antigenically distinct molecules.
No attempts were made to antigenically characterize the strain to confirm differences from the Caraparu virus.
The CDC advisory also noted that the oseltamivir-resistant viruses are antigenically similar to the influenza A (HlNl) strain that is included in the current flu vaccine and emphasized that vaccination should continue as the "primary method to prevent influenza.