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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 ?
Caption: Figure 4: AAM[phi]s appear with constant soluble antigen treatment.
P1: peptide 1; P2: peptide 2; P3: peptide 3, MIX: P1 + P2 + P3; G1: Group 1 (patients with clinical cutaneous leishmaniosis and parasites isolated); G2: Group 2 (patients with clinical cutaneous leishmaniosis and serological diagnosis positive); SA: soluble antigen.
The findings about the protective immunity exerted by soluble antigens against blackleg leave no doubt about the importance of these antigens in the pathogenesis of this condition.
The stimulation of inflammatory and Th1 cytokines leads to the proposal of Dectin-1 targeting of soluble antigens by appropriate ligands to stimulate cellular immunity.
The aim of this work is the study of the humoral immune response in these animals using crude soluble antigens (CAP) from 8 different isolates of Venezuelan patients, looking for the best antigen for diagnostic purposes.
Production of soluble antigens for ELISA assay and immunoblotting was carried out as described by Castro et al.
The method was successful in detecting the strikingly increased concentrations of soluble antigens characteristic of A.
Hochrein et al., "CpG-DNA aided cross-presentation of soluble antigens by dendritic cells," European Journal of Immunology, vol.
Previously, we demonstrated that histamine is able to increase the presentation of soluble antigens via MHC class I [16].
Hence, the effect of temperature on the kinetics of immunoglobulin production should be further investigated using purified soluble antigens, adjuvant combinations, and fish kept at a wider range of temperatures, such as those found during late summer.
meningitidis isolates were identified, either from culture or by soluble antigens identification.
In addition to Leishmania soluble antigens, we have chosen to use Leishmania excreted/secreted antigens as previous reports have shown that such proteins, released by the parasite in the phagolysosomal compartment, may constitute interesting targets for the host cellular Th1 and cytotoxic immune responses and have been shown to be strongly immunogenic and protective in mice and dogs [12-17].