Information AboutAntigen |
| CATEGORIES ABOUT ANTIGEN | |
| immune system | |
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TYPES OF ANTIGENS
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 Cell s can become activated. 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 s. Cytokines are substances that can activate Cytotoxic T Lymphocytes (CTL), antibody-secreting B Cells , Macrophages and other cells. 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 Molecule s. If activated cytotoxic CD8+ T Cells recognize them, the T cells begin to secrete different Toxin s 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. There is an exception to the exogenous/endogenous antigen paradigm, called Cross-presentation . 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 are those antigens that are presented by the MHC I molecules on the surface of Tumor Cell s. 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''' 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'''. Cytotoxic T Lymphocytes that recognized 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 . EXTERNAL LINKS
National Library of Medicine/Medline (National Insititute of Health) website http://www.nlm.nih.gov/medlineplus/ency/article/002224.htm |
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