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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 ?
Only the extremely rare combination of HBsAg and HBsAb together, without HBcAb, which occurred in 12 of the 39 774 specimens (a frequency of 0.
HIV-infected patients who are HBsAg negative on screening, but are at high risk of acquiring HBV infection, should be tested for the presence of hepatitis B core IgG antibody (HBcIgG) and if negative, should be offered vaccination against HBV.
HBsAg carriers, particularly those with detectable serum HBV DNA, have the highest risk of reactivation, but episodes can occur in patients with resolved infection (HBsAg negative, anti-HBc positive) when treated with highly aggressive immunosuppression (9).
Compounds 1-3,9,11,12 inhibited the secretion of both HBsAg and HBeAg, with [IC.
In addition to examining seroprevalence of HEV in Malawi, this study has several other notable features: 1) samples from 6 epidemiologic studies conducted by the same research team among adult men and women in urban and rural Malawi during 1989-2008 were included, representing diverse populations and time periods; 2) analyses of viral hepatitides seroprevalence included both HIV-negative and HIV-positive persons (the prevalence of HIV remains high in southern Africa); and 3) these samples were also tested for total antibodies (IgG and IgM) against HAV and HCV and for the presence of HBsAg, leading to a comprehensive seroprevalence profile of all viral hepatitides in these populations.
In cases of acute viral hepatitis, testing with HBV DNA in serum may be a helpful adjunct in the diagnosis of acute HBV infection, since HBV DNA can be detected approximately 21 days before HBsAg appears in the serum.
The ARCHITECT system offers 12 assays for hepatitis A, B and C outside the US: HBsAg, HBsAg Confirmatory, HBsAg Quantitative, HBeAg, Anti-HBe, HAVAb IgG, HAVAb IgM, Anti-HBc, Anti-HBc IgM, Anti-HBs, Anti-HCV and HCV Ag.
Subjects positive for serum R249Smutation by HBsAg status [n/total (%)].
Yeast HBsAg standards at different concentrations were purchased from the National Center for Clinical Laboratory Science.
Mothers of negative HBsAg status, provide the Universal dose of Hepatitis B vaccine within 12 hours of birth or before hospital discharge.
We carried out simultaneous assay of HBsAg and HBeAg with Eu(III)-BHHCT-and Tb(lll)-BPTA-coated nanoparticles as follows.
She was known to have been a chronic HBsAg carrier for 6 years and had never received any antiviral treatment.