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 ?
Furthermore, given the similarities between anti-helminth and anti-allergen responses [46], comparative studies (schistosome antigens versus allergens) would provide the spectrum of antigen recognition and inform on possible cross-reactivity.
Coexpression of PD-1, 2B4, CD160 and KLRG1 on exhausted HCV-specific CD8+ T cells is linked to antigen recognition and T cell differentiation.
This lack of antibody response in a large proportion of patients has been attributed mainly to two factors: (i) the possible formation and circulation of specific immune complexes that are not detected by regular ELISA performed with whole serum and (ii) the person-to-person variation of antigen recognition. A number of methods have been used for detection and quantification of IC in various chronic diseases [36].
Useful as a study guide as well as a text, this version has completely updated information on innate immunity, antigen capture and presentation in lymphocytes, antigen recognition in the adaptive immune system, cell-mediated immune response, effector mechanisms of cell-mediates immunity, humoral immune responses, effector mechanisms of humoral immunity, immunologic tolerance and autoimmunity, immune responses against tumors and transplants, hypersensitivity diseases and congenital and acquired immunodeficiencies.
When the pANCA pattern is observed in UC patients and treated with DNase I, in 70 percent there is ablation of antigen recognition, and in 30 percent there is conversion to a homogeneous pattern.
Using monoclonal antibodies, the researchers measured T cell concentrations of surface receptors for a protein crucial in antigen recognition processes.
(2) Immunogenicity: The majority of the antigen recognition region used in a genetically modified T cell is derived from mouse mAb [47], of which the foreign potential immunogenicity may lead to severe anaphylaxis [48-50] (Figure 1(f)).
The tools included TCRdist, which researchers used to calculate the similarity and differences of key features of T cell receptors, such as amino acid sequences in important regions for antigen recognition. TCRdist allowed the scientists to identify T cell receptors that recognized the same epitope.
Further chapters focus on specific details of avian immune system: its development, structure, innate immune responses and antigen recognition. Chapters on avian diseases--immunosuppressive, autoimmune, tumors--follow.
These discrepancies might be caused by differences in antigen recognition depending on the mode of antigen presentation, e.g., adsorbed to a plastic surface or free in solution.
analyzed aspects of antigen recognition by T and B cells that are relevant for epitope prediction and provided a systematic and inclusive review of available tools, paying particular attention to their foundations.