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 ?
To harvest the antigen 10 ml of sterile normal saline was added to each flask, flasks were rocked after the additon of sterile glass beeds to get the even suspension, suspension was collected in a separate flask and was treated with absoulte alcohal at 2: 1 by volume and allowed to stand for 36 hours for complete precipitation.
The most commonly recognized of these are the ABO blood groups, and Rh antigens (which are signified by the "positive" or "negative" that comes after A, B or O on your blood type).
In this study, we determined that when the A antigen cutoff was 13.5 SFCs per 2.5 x 10[sup]5 PBMCs, the diagnostic value was optimal; at this cutoff, Youden index reached a maximum of 0.71, and the sensitivity and specificity were 84.10% and 86.50%, respectively.
The two antigen B sub-units EgAgB8/1 and EgAgB8/2 showed a sensitivity of 66.7% and 80% and specificity of 71.3% and 73.3%, respectively.
HLA-DQB1 epitopes: epitope 2002 is shared exclusively by the beta chains of the DQ4 antigen and defined by leucine (L) in position 56.
A screening trial of Helicobacter pylori-specific antigen test in saliva to identify an oral infection.
This paper describes the development of latex beads coated with purified recombinant versions of these antigens and demonstrates the usefulness of these antigen-coated latex beads in the serological diagnosis of canine brucellosis.
Dual CAR T cells showed weak cytokine production against target cells expressing only one tumor-associated antigen in lab assays, similar to first-generation CAR T cells bearing the CD3 activation domain only, but demonstrated enhanced cytokine production upon encountering natural or engineered tumor cells expressing both antigens, equivalent to second-generation CAR T cells with dual, but unseparated signaling.
Antigen Express and its collaborators have conducted phase one and two trials and are aiming to move into the third phase of studies.
Sadegh-Nasseri says the team's new lab test takes a fraction of the time involved in current methods, which rely on sequencing, or identifying every single peptide in the antigen's make-up, one after another.
It is known that conformational alterations of proteins result in increasing the numbers of exosed epitopes and this was attempted with the cyst antigens. Six of the T.
Combining the 11 RA-specific antigen clones into a panel produced 100% specificity and 37% sensitivity for diagnosis.