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07-SEPTEMBER-2008 03:17:44 - Antigen Redirected from Antigens Image:Split-arrows.svg It has been suggested that this article be split into articles entitled Antigen and Immunogen. Discuss An antigen from antibody-generating or immunogencitation needed is a substance that prompts the generation of antibodies and can cause an immune response.1 The word originated from the notion that they can stimulate antibody generation. We now know that the immune system does not consist of only antibodies. The modern definition encompasses all substances that can be recognized by the adaptive immune system. Immunogens, strictly, are those substances that elicit a response from the immune system, while antigens, strictly, are defined as a substance that binds to specific antibodies. Not all antigens produce an immunogenic response, but all immunogens are antigens Immunobiology, Janeway and Travers, 1994. Antigens are usually proteins or polysaccharides. This includes parts coats, capsules, cell walls, flagella, fimbrae, and toxins of bacteria, viruses, and other microorganisms. Lipids and nucleic acids are antigenic only when combined with proteins and polysaccharides. Non-microbial exogenous non-self antigens can include pollen, egg white, and proteins from transplanted tissues and organs or on the surface of transfused blood cells. Tolerogen - A substance that invokes a specific immune non-responsiveness due to its molecular form. If its molecular form is changed, a tolerogen can become an immunogen. Allergen - An allergen is a substance that causes the allergic reaction. The detrimental reaction may result after exposure via ingestion, inhalation, injection, or contact with skin. Cells present their antigens to the immune system via a histocompatibility molecule. Depending on the antigen presented and the type of the histocompatibility molecule, several types of immune cells can become activated. Contents 1 Origin of antigens 1.1 Exogenous antigens 1.2 Endogenous antigens 1.3 Autoantigens 2 Tumor antigens 3 Nativity 4 See also 5 References 6 External links Origin of antigens Antigens can be classified in order of their origins. Exogenous antigens Exogenous antigens are antigens that have entered the body from the outside, for example by inhalation, ingestion, or injection. By endocytosis or phagocytosis, these antigens are taken into the antigen-presenting cells APCs and processed into fragments. APCs then present the fragments to T helper cells CD4+ by the use of class II histocompatibility molecules on their surface. Some T cells are specific for the peptide:MHC complex. They become activated and start to secrete cytokines. Cytokines are substances that can activate cytotoxic T lymphocytes CTL, antibody-secreting B cells, macrophages, and other particles. Endogenous antigens Endogenous antigens are antigens that have been generated within the cell, as a result of normal cell metabolism, or because of viral or intracellular bacterial infection. The fragments are then presented on the cell surface in the complex with MHC class I molecules. If activated cytotoxic CD8+ T cells recognize them, the T cells begin to secrete various toxins that cause the lysis or apoptosis of the infected cell. In order to keep the cytotoxic cells from killing cells just for presenting self-proteins, self-reactive T cells are deleted from the repertoire as a result of tolerance also known as negative selection. They include xenogenic heterologous, autologous and idiotypic or allogenic homologous antigens. Autoantigens An autoantigen is usually a normal protein or complex of proteins and sometimes DNA or RNA that is recognized by the immune system of patients suffering from a specific autoimmune disease. These antigens should, under normal conditions, not be the target of the immune system, but, due to mainly genetic and environmental factors, the normal immunological tolerance for such an antigen has been lost in these patients. Tumor antigens Tumor antigens or Neoantigens are those antigens that are presented by MHC I or MHC II molecules on the surface of tumor cells. These antigens can sometimes be presented by tumor cells and never by the normal ones. In this case, they are called tumor-specific antigens TSAs and, in general, result from a tumor-specific mutation. More common are antigens that are presented by tumor cells and normal cells, and they are called tumor-associated antigens TAAs. Cytotoxic T lymphocytes that recognize these antigens may be able to destroy the tumor cells before they proliferate or metastasize. Tumor antigens can also be on the surface of the tumor in the form of, for example, a mutated receptor, in which case they will be recognized by B cells. Nativity A native antigen is an antigen which isn't yet processed by an APC to smaller parts. T cells cannot bind native antigens, but require that they are processed by APCs, while B cells can be activated by native ones. See also Epitope Linear epitope Conformational epitope Original antigenic sin Polyclonal B cell response References ^ Antigen - Definitions from Dictionary.com. dictionary.reference.com. Retrieved on 2008-04-28. External links Antigen Retrieval Protocol Immunology National Library of Medicine/Medline National Insititute of Health website v d e Immune system / Immunology Systems Adaptive immune system vs. Innate immune system · Humoral immune system vs. Cellular immune system · Complement system Anaphylatoxins · Intrinsic immune system Antibodies and antigens Antibody Monoclonal antibodies, Polyclonal antibodies, Autoantibody · Allotype · Isotype · Idiotype · Antigen Superantigen · Polyclonal B cell response Immune cells/White blood cells Lymphoid: T cell · B cell · NK cell Myeloid: Mast cell · Basophil · Eosinophil · Macrophage Phagocytes: Neutrophil · Macrophage/Reticuloendothelial system Professional APCs: Dendritic cell · Macrophage · B cell Immunity vs. tolerance Immunity · Autoimmunity · Allergy · Tolerance Central · Immunodeficiency Immunogenetics Somatic hypermutation · VDJ recombination · Immunoglobulin class switching · MHC/HLA Substances Cytokines · Opsonin · Cytolysin Other Inflammation · Epitope Linear epitope and Conformational epitope · Hapten · Cross-reactivity · Diagnostic immunology · Immune complex Retrieved from http://en..org/wiki/Antigen Categories: Immune systemHidden categories: articles to be split from August 2008 | All articles with statements | Articles with statements since March 2008 Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages Afrikaans БългарÑ?ки Català Česky Dansk Deutsch Ελληνικά Español Euskara Français í•œêµì–´ Bahasa Indonesia Italiano עברית Lietuvių Nederlands 日本語 ‪Norsk bokmÃ¥l‬ Polski Português Română РуÑ?Ñ?кий Simple English SlovenÄ?ina SlovenÅ¡Ä?ina СрпÑ?ки / Srpski Srpskohrvatski / СрпÑ?кохрватÑ?ки Suomi Svenska Tiếng Việt УкраїнÑ?ька ä¸æ–‡ This page was last modified on 22 August 2008, at 21:11
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