| 单词 | immunoglobulin | |||||||||||||||||||||
| 释义 | immunoglobulinim·mu·no·glob·u·linI0051700 (ĭm′yə-nō-glŏb′yə-lĭn, ĭ-myo͞o′-)immunoglobulin(ˌɪmjʊnəʊˈɡlɒbjʊlɪn)im•mu•no•glob•u•lin(ˌɪm yə noʊˈglɒb yə lɪn, ɪˌmyu-)n. im·mu·no·glob·u·lin(ĭm′yə-nō-glŏb′yə-lĭn, ĭ-myo͞o′nō-glŏb′yə-lĭn)
immunoglobulinimmunoglobulin:see antibodyantibody,protein produced by the immune system (see immunity) in response to the presence in the body of antigens: foreign proteins or polysaccharides such as bacteria, bacterial toxins, viruses, or other cells or proteins. ..... Click the link for more information. ; 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. ; immunologyimmunology, branch of medicine that studies the response of organisms to foreign substances, e.g., viruses, bacteria, and bacterial toxins (see immunity). Immunologists study the tissues and organs of the immune system (bone marrow, spleen, tonsils, thymus, lymphatic system), ..... Click the link for more information. . ImmunoglobulinAny of the glycoproteins in the blood serum that are induced in response to invasion by foreign antigens and that protect the host by eradicating pathogens. Antibodies belong to this group of proteins. An antigen is any substance capable of inducing an immune response. Intact antigens are able to specifically interact with the induced immunoglobulins. Normally, the immune system operates in a state known as self-tolerance, and does not attack the host's own tissues, but occasionally the immune system targets host-specific antigens, resulting in autoimmune disease. See Autoimmunity Immunoglobulins are composed of two identical heavy (H) and two identical light (L) polypeptide chains. Each H and L chain has an amino-terminal variable (V) region and a carboxyl-terminal constant (C) region. Although V regions from different antibodies exhibit considerable sequence variation, there is a large degree of sequence similarity among C regions of different antibodies. In the living animal, antibodies first bind to antigen at the antigen combining site and then, ideally, eliminate it as a threat to the host. Immunoglobulins are heterogeneous with respect to charge, size, antigenicity, and function. There are three categories of antigenic determinants present on immunoglobulins: isotypes are found in all individuals, allotypes are found in some individuals, and idiotypes are associated with the amino-terminal variable region. Isotypic determinants are located on the carboxyl-terminal constant region and are used to group immunoglobulin H and L chains into isotypes or classes. In total, there are five human H-chain classes. IgM contains mu (μ) H chains, IgG contains gamma (γ) H chains, IgA contains alpha (α) H chains, IgD contains delta (δ) H chains, and IgE contains epsilon (ε) H chains. IgG has four subclasses, IgG1, IgG2, IgG3, and IgG4, while IgA has two subclasses, IgA1 and IgA2. There are two L-chain isotypes named kappa (κ) and lambda (λ). Kappa and lambda chains may be associated with H chains of any isotype, and a complete description of an immunoglobulin molecule requires identification of both H and L chains. IgG is the most abundant immunoglobulin class in the serum. IgG isotypes are associated with complement fixation, opsonization (that is, rendering more susceptible to phagocytosis), fixation to macrophages, and membrane transport. Of the two IgA subclasses, IgA1 is the predominant subclass of IgA in human serum. IgA1 is the dominant subclass in all external secretions, including milk, saliva, tears, and bronchial fluids. The percentage of subclass IgA2 is higher in these fluids than in serum. IgM is the first immunoglobulin to appear during the primary immune response. IgD and IgE are present in minute amounts in normal human serum. No function has been clearly attributed to IgD. IgE is active against parasites and acts as a mediator of immediate hypersensitivity. See Anaphylaxis, Antibody, Antigen, Antigen-antibody reaction, Hypersensitivity, Immunology, Protein immunoglobulin[¦im·yə·nō′glä·byə·lən]Immunoglobulinimmunoglobulin[im″u-no-glob´u-lin]Two types of IgA have been identified. They are serum IgA and secretory IgA (sIgA). In sIgA two IgA molecules are linked by a polypeptide called the secretory piece and by a chain" >J chain. Secretory IgA is present in nonvascular fluids, such as saliva, bile, synovial fluid, and intestinal and respiratory tract secretions. Both IgA types are known to have antiviral properties; their production is stimulated by oral vaccines and aerosol immunizations. IgD is found in trace quantities in the serum (about 3 mg/dl). It serves as a lymphocyte" >B lymphocyte surface receptor. IgE is called the reaginic antibody and is generally present in increased levels in persons with allergy. Its normal mean serum concentration is 0.03 mg/dl. When IgE attaches itself to cells within the body, such as those of the mucous membrane or skin, the cells become sensitized to allergens, causing them to release histamine and histamine-like substances when they come in contact with the allergen. Such allergic reactions as hives, hay fever, asthma, and anaphylactic shock are manifestations of IgE-mediated reactions. IgG is the most abundant of the five classes of immunoglobulins. Its normal mean serum concentration is 1240 mg/dl. It is the major antibody in the secondary humoral response of immunity, serves to activate the complement system, and is frequently involved in opsonization. IgG is the only immunoglobulin that can cross the placental barrier. IgM is principally concerned with the primary antibody response, appearing soon after initial invasion by an antigen and capable of destroying the antigen when it is first introduced. Its normal mean serum concentration is 120 mg/dl. Like IgG, IgM activates the complement system and together these two classes of immunoglobulins serve as specific antitoxins against the toxins of diphtheria, tetanus, botulism, and anthrax microorganisms, and snake venoms.  im·mu·no·glob·u·lin (Ig),(im'yū-nō-glob'yū-lin),When split by papain, IgG yields three pieces: the Fc piece, consisting of the C-terminal portion of the H chains, with no antibody activity but capable of fixing complement, and crystallizable; and two identical Fab pieces, carrying the antigen-binding sites and each consisting of an L chain bound to the remainder of an H chain. Antibodies are immunoglobulins, and all immunoglobulins probably function as antibodies. However, immunoglobulin refers not only to the usual antibodies, but also to a great number of pathologic proteins classified as myeloma proteins, which appear in multiple myeloma along with Bence Jones proteins, myeloma globulins, and immunoglobulin fragments. From the amino acid sequences of Bence Jones proteins, it is known that all L chains are divided into a region of variable sequence (VL) and one of constant sequence (CL), each comprising about half the length of the L chain. The constant regions of all human L chains of the same type (κ or λ) are identical except for a single amino acid substitution, under genetic controls. H chains are similarly divided, although the VH region, although similar in length to the VL region, is only one third or one fourth the length of the CH region. Binding sites are a combination of VL and VH protein regions. The large number of possible combinations of L and H chains make up the "libraries" of antibodies of each individual. immunoglobulin(ĭm′yə-nō-glŏb′yə-lĭn, ĭ-myo͞o′-)immunoglobulinA highly-specific molecule of the immune system, produced by mature B cells in response to an antigen Structure 2 identical light-L, 2 identical heavy–H chains; the L and H chains have constant and variable regions, the variable regions are critical for antigen recognition and binding; immunoglobulin production requires prior rearrangement of the variable, diversity and joining gene segments, that form part of a potential repertoire of 1010-1012 antibodies that may be encoded in response to a molecule's surface binding site or epitope Types Idiotype–evoked by a particular epitope; isotype–Ig subtype–IgG, IgA, IgM, IgD, IgE that all normal persons have; allotype–a subtype shared by population groups–eg, with racial differences. See Hinge, Polyclonal immunoglobulin, Protein electrophoresis, Sporidin-G™ Bovine immunoglobulin. immunoglobulina protein (such as gamma globulin) made in B-CELLS that possesses ANTIBODY activity and is made up of four POLYPEPTIDE CHAINS, two identical light (L) chains and two identical heavy (H) chains joined by DISULPHIDE BRIDGES to form a Y-shaped macromolecule. The H chains are connected by two or more disulphide bridges at the hinge region of the Y. One 1 chain runs beside each of the two limbs of the Y, attached by a disulphide bridge. There are five main classes of human immunoglobins, differentiated principally by their heavy chains:
Each heavy and light chain consists of a CONSTANT REGION (C region or domain) of amino acids that is virtually the same in all antibodies of that class, and a VARIABLE REGION (V region or domain) containing a sequence of amino acids that makes the antibody specific to a particular ANTIGEN. Only a few of these amino acids actually contact the antigen and this contact region is called the complementarity determining region (CDR). For the genetics of immunoglobulin production see C-GENE, D-GENE, J-GENE and V-GENE. Immunoglobulin (Ig)im·mu·no·glob·u·lin(im'yū-nō-glob'yū-lin)immunoglobulin
Synonyms for immunoglobulin
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