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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 ?
Successful treatment with paclitaxel/carboplatin chemotherapy in advanced adenocarcinoma of the urinary tract producing carcinoembryonic antigen, carbohydrate antigen 19-9 and carbohydrate antigen 125.
001 (f) Abbreviations: BPD, benign pulmonary diseases; CEA, carcinoembryonic antigen; CYFRA 21-1, cytokeratin 19 fragment; NPD, no specific pulmonary diseases; smokers, smokers without specific pulmonary diseases.
Induction of type 1 cytokines during neem leaf glycoprotein assisted carcinoembryonic antigen vaccination is associated with nitric oxide production.
Pulmonary carcinoembryonic antigen (CEA) production in patients with end-stage lung diseases submitted to lung transplantation.
A blood test called Carcinoembryonic antigen (CEA) is often used to find out if the tumour is back or find how well it has responded to treatment.
29, alpha-fetoprotein [AFP], and carcinoembryonic antigen [CEA]) for their diagnostic efficacy in breast cancer patients.
In such cases, a second transvaginal ultrasound study was done and tumor markers were measured, including CA 125, CA 19-9, carcinoembryonic antigen, alpha-fetoprotein, and lactate dehydrogenase fraction.
These include prostate specific antigen (PSA), associated with prostate cancer, and carcinoembryonic antigen (CEA) which is found in 90 per cent of colon cancers and 40 per cent of breast cancers.
Contract awarded for Line Route 2 Model carcinoembryonic packing district refurbishment
Patients with colorectal cancer are usually monitored by quantifying carcinoembryonic antigen (CEA) in serum in order to detect relapse earlier.
In addition to targeting the carcinoembryonic antigen (CEA or CEACAM5) expressed by many human cancers, TF2 has been engineered to recognize a small peptide that carries radioactivity.
The serum levels of carcinoembryonic antigen and carbohydrate antigen 19-9 were within the normal reference range.