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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

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


A substance which reacts with the products of specific humoral or cellular immunity, even those induced by related heterologous immunogens.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


a substance that stimulates the production of antibodies
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Talbot, "A naturally occurring C-terminal truncated isoform of the latent nuclear antigen of Kaposi's sarcoma-associated herpesvirus does not associate with viral episomal DNA," Journal of General Virology, vol.
The immunohistochemical expression of proliferating cell nuclear antigen (PCNA/cyclin) in malignant and benign epithelial ovarian neoplasms and correlation with prognosis.
Influence of the Epstein-barr virus nuclear antigen EBNA-2 on the growth phenotype of virus-transformed B cells.
Abbreviations: H & E, hematoxylin and eosin; DNA, deoxyribonucleic acid; TNF-[alpha], tumor necrosis factor-alpha; PCNA, proliferating cell nuclear antigen; AST, aspartate transaminase; ALT, alanine transaminase; ALP, alkaline phosphatase; ELISA, enzyme-linked immunoassay; IL-6, interleukin-6; GCMS, gas chromatography and mass spectrometry analyses
The virus expresses nuclear antigen only when it becomes latent, and following that, the patient will be EBNA positive for the rest of his or her life, Dr.
Proliferating Cell Nuclear Antigen (PCNA) staining was used to detect mitotically active cells through immunocytochemistry.
KSHV encodes for a major immunoreactive latency-associated nuclear antigen (LANA-1), analogous to the Epstein-Barr virus latency-associated nuclear antigens.
Another important point is that proliferating cell nuclear antigen (PCNA), or any other marker of uterine cell proliferation, may give erroneous results if measured after 3 days of continuous treatment with an estrogen, as described by Markey et al.
Proliferating cell nuclear antigen (PCNA), or cyclin, is a protein produced during the late G1 and S phases of the cell cycle (3, 4).
Harms reported on 30 patients with infiltrating breast cancers of 0.8-6.0 cm who underwent laser photocoagulation therapy The women subsequently had a lumpectomy or mastectomy permitting pathologic correlation between MRI indications of ablation success and cell death as determined by tissue staining with hematoxylin and eosin and proliferating cell nuclear antigen.
Anti-dsDNA, anti-double stranded DNA; Anti-ENA, anti-extractable nuclear antigen; ANCA, anti-neutrophil cytoplasmic antibody; ESR, erythrocyte sedimentation rate; Gamma-GT, gamma-glutaryl transferase; LDH, lactate dehydrogenase; SGOT, serum glutamic oxaloacetic transminase; SGPT serum glutamic pyruvic transminase.
Characteristics of a soluble nuclear antigen precipitating with sera of patients with systemic lupus erythematosus.

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