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Encyclopedia > Antigen

An antigen or immunogen is a molecule that stimulates an immune response. The word originated from the notion that they can stimulate antibody generation. We now know that the immune system does not only consist of antibodies. The modern definition encompasses all substances that can be recognized by the adaptive immune system. Image File history File links Question_book-3. ... A scanning electron microscope image of a single neutrophil (yellow), engulfing anthrax bacteria (orange). ... Wikipedia does not yet have an article with this exact name. ... The immune system is the collection of organs and tissues involved in the adaptive defense of a body against foreign biological material. ...


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. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Polysaccharides (sometimes called glycans) are relatively complex carbohydrates. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... This article is about biological infectious particles. ... A cluster of Escherichia coli bacteria magnified 10,000 times. ... Some common lipids. ... Look up nucleic acid in Wiktionary, the free dictionary. ...

  • Tolerogen - An antigen 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. Geometry of the water molecule Molecules have fixed equilibrium geometries--bond lengths and angles--that are dictated by the laws of quantum mechanics. ... Pancreatitus can be caused by an Allergic Reaction to a food. ... The major histocompatibility complex (MHC) is a large genomic region or gene family found in most vertebrates containing many genes with important immune system roles. ... White Blood Cells is also the name of a White Stripes album. ...

Contents

Origin of antigens

Antigens can be classified in order of their origins and also people with diabetes.


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. Endocytosis (IPA: ) is a process whereby cells absorb material (molecules such as proteins) from the outside by engulfing it with their cell membrane. ... Steps of a macrophage ingesting a pathogen: a. ... An antigen-presenting cell (APC) is a cell that displays foreign antigen complexed with MHC on its surface. ... T cells are a subset of lymphocytes that play a large role in the immune response. ... CD4 (cluster of differentiation 4) is a molecule that is expressed on the surface of T helper cells (as well as regulatory T cells and dendritic cells). ... Protein images comparing the MHC I (1hsa) and MHC II (1dlh) molecules. ... Cytokines are a group of proteins and peptides that are used in organisms as signaling compounds. ... A cytotoxic (or TC) T cell is a T cell (a type of white blood cell) which has on its surface antigen receptors that can bind to fragments of antigens displayed by the Class I MHC molecules of virus infected somatic cells and tumor cells. ... B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response). ... Macrophages (Greek: big eaters) are cells found in tissues that are responsible for phagocytosis of pathogens, dead cells and cellular debris. ...


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 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 tolerance (also known as negative selection which occurs in the thymus). Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ... An infection is the detrimental colonization of a host organism by a foreign species. ... MHC class I molecules are cell surface proteins found on most cells of the body. ... A cytotoxic T cell (also known as TC, CTL or killer T cell) belongs to a sub-group of T lymphocytes (a type of white blood cell) which are capable of inducing the death of infected somatic or tumor cells; they kill cells that are infected with viruses (or other... For other uses, see Toxin (disambiguation). ... This article is about the biological definition of the word Lysis. ... A section of mouse liver showing an apoptotic cell indicated by an arrow Apoptosis (pronounced apo tō sis) is a process of suicide by a cell in a multicellular organism. ... It has been suggested that toleration be merged into this article or section. ... In biology, negative selection is artificial selection in which negative, rather than positive traits of a species are selected. ... Thymus, see Thyme. ...


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. Autoantigen is an endogenous antigen that stimulates the production of autoantibodies, as in an autoimmune reaction. ... Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. ... This article or section is in need of attention from an expert on the subject. ...


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 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. MHC class I molecules are cell surface proteins found on most cells of the body. ... The major histocompatibility complex (MHC) is a large genomic region or gene family found in most vertebrates. ... See the article about cancer for the main article about malignant tumors. ... A cytotoxic (or TC) T cell is a T cell (a type of white blood cell) which has on its surface antigen receptors that can bind to fragments of antigens displayed by the Class I MHC molecules of virus infected somatic cells and tumor cells. ... Metastasis (Greek: change of the state) is the spread of cancer from its primary site to other places in the body. ...


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. B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response). ...


See also

An epitope is the part of a macromolecule that is recognized by the immune system, specifically by antibodies, B cells, or cytotoxic T cells. ... Original antigenic sin (first described in 1960 by Thomas Francis, Jr. ...

External links


  Results from FactBites:
 
Antigen Receptors (846 words)
Both B cells and T cells have surface receptors for antigen.
The tertiary structure of antibodies brings the 3 hypervariable regions of both the L and the H chains together.
The antigen receptor on most T cells is made up of two transmembrane polypeptides designated alpha and beta (thus forming a heterodimer).
Antigen - Wikipedia, the free encyclopedia (636 words)
Exogenous antigens are antigens that have entered the body from the outside, for example by inhalation, ingestion, or injection.
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.
Tumor antigens are those antigens that are presented by the MHC I molecules on the surface of tumor cells.
  More results at FactBites »

 
 

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