antigen

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Related to cancer antigen 125: Cancer antigen 15-3, Cancer antigen 19-9

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 ?
A meta-analysis of serum cancer antigen 125 array for diagnosis of ovarian cancer in Chinese.
5 IU/L for Human Chorionic Gonadotrpin (HCG), 35 U/mL for Cancer Antigen 125 (CA125), 37 U/mL for CA 19-9, 7 U/mL for alpha-fetoprotein (AFP) and 214 U/L for lactate dehydrogenase (LDH).
Ovarian cancer growth-related and cancer antigen 125 (CA-125)-related parameters from the published literature were used to "prime the model," thereby establishing the "baseline parameters" for the earliest detection time or the smallest tumor diameter or volume that could be detected by current CA-125 ELISA assays.
The Risk of Ovarian Malignancy Algorithm (ROMA) stratifies women at high or low risk for epithelial ovarian cancer based on menopausal status and preoperative serum levels of human epididymis protein 4 (HE4) and cancer antigen 125 (CA 125).
MIAMI -- A test for circulating lysophosphatidic acid dramatically improves detection of early-stage ovarian cancer, compared with current screening methods dependent on cancer antigen 125, Yan Xu, Ph.
San Antonio -- Elevated cancer antigen 125 levels measured after surgery but before chemotherapy are an independent prognostic indicator of recurrence and worse survival in women with high-risk, early-stage epithelial ovarian cancer, according to results of a Gynecologic Oncology Group study.
The Risk of Ovarian Malignancy Algorithm (ROMA) stratifies women as being at high or low risk for epithelial ovarian cancer based on menopausal status and preoperative serum levels of two biomarkers: human epididymis protein 4 (HE4) and cancer antigen 125 (CA 125).
Occasionally, we see a patient with a family history of ovarian cancer who requests a test for cancer antigen 125.
After this initial study, we had some biomarker candidates that, in conjunction with cancer antigen 125 (CA125), [2] appeared to provide a modest improvement over CA125 alone for the detection of early-stage ovarian cancer.
Soluble epidermal growth factor receptor (sEGFR) [corrected] and cancer antigen 125 (CA125) as screening and diagnostic tests for epithelial ovarian cancer.