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glossary:antigens

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glossary:antigens [2007/09/08 09:19]
Pat O'Connor
glossary:antigens [2012/10/16 14:40] (current)
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 +substances which are capable, under appropriate conditions, of inducing a specific [[immune response]] and of reacting with the products of that response, that is, with specific [[antibodies]] or specifically sensitised t-[[lymphocytes]],​ or both. antigens may be soluble substances, such as toxins and foreign proteins, or particulates,​ such as [[bacteria]] and [[tissue cells]]; however, only the portion of the [[protein]] or polysaccharide molecule known as the antigenic determinant (epitopes) combines with antibody or a specific receptor on a lymphocyte. ​
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 +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 class i histocompatibility molecules. If activated cytotoxic CD8 t cells recognize them, the t cells begin to secrete different 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 central tolerance (also known as negative selection which occurs in the thymus). Only those CTL that do not react to self-peptides that are presented in the [[thymus]] in the context of mhc class i molecules are allowed to enter the bloodstream. ​
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 +there is an exception to the exogenous/​endogenous antigen paradigm, called cross-presentation. ​
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 +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. ​
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 +tumor antigens tumor antigens are those antigens that are presented by the mhc i molecules on the surface of tumor cells. These antigens can sometimes be presented only by tumor cells and never by the normal ones. In this case, they are called tumor-specific antigens (TSAs) and typically 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 recognized these antigens may be able to destroy the tumor cells before they proliferate or metastasize. ​
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 +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. ​
  
glossary/antigens.txt ยท Last modified: 2012/10/16 14:40 (external edit)