(redirected from Protective Antigen)
Also found in: Dictionary, Thesaurus, Medical, Acronyms.


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.
..... Click the link for more information.


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 ?
Vaccination against anthrax with attenuated recombinant strains of Bacillus anthracis that produce protective antigen.
For the production of whole killed bacterial endosymbionts or the native purified protective antigens of endosymbionts in vitro culture of the organisms is essential.
The neutrophi-activating protein (HP-NAP) of Helicobacter pylori is a protective antigen and a major virulence factor.
anthracis protective antigen antibodies (anti-PA) (Centers for Disease Control and Prevention, Atlanta, GA, USA).
Contracts and grants revenue for 2012 is primarily attributable to revenues from our contracts with BARDA for large-scale manufacturing of BioThrax and for development of PreviThrax(TM) (Recombinant Protective Antigen Anthrax Vaccine, Purified).
Glide Technologies, a company focused on solid dose formulations of therapeutics and vaccines and non-invasive diagnostics, has extended a subcontract with Pfenex, a clinical-stage biotechnology company, for solid dose formulation of its recombinant protective antigen (rPA)-based anthrax vaccine, Px563L-mrPA, it was reported yesterday.
US-based, Paragon Bioservices, contract research and manufacturing firm has won a contract from Pfenex for the current Good Manufacturing Practice (cGMP) manufacturing of its Recombinant Protective Antigen (rPA) based anthrax vaccine.
It is the same technology VaxGen is using to develop its recombinant Protective Antigen anthrax vaccine, rPA102, under contract from the National Institute of Allergy and Infectious Diseases (NIAID).
It releases the three components of its toxin--known as lethal factor, edema factor, and protective antigen (PA)--which assemble on cell surfaces.
Department of Health and Human Services (HHS) has exercised a contract option to further advance the development of PreviThrax(TM) (Recombinant Protective Antigen Anthrax Vaccine, Purified), the company's novel rPA anthrax vaccine candidate.
Raxibacumab injection is a monoclonal antibody targeting the protective antigen (PA) component of the lethal toxin of Bacillus anthracis and is being developed for the treatment of inhalational anthrax.
The company said that the claims of the allowed patent cover a human monoclonal antibody specifically recognizing the cell binding protein known as protective antigen of Bacillus anthracis, the bacteria causing anthrax.