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The first correct description of the antigen-antibody reaction was given by Richard J. Goldberg at the University of Wisconsin in 1952. [1] [2] It came to be known as "Goldberg's theory" (of antigen-antibody reaction). [3] There are several types of antibodies and antigens, and each antibody is capable of binding only to a specific antigen.
An immune complex, sometimes called an antigen-antibody complex or antigen-bound antibody, is a molecule formed from the binding of multiple antigens to antibodies. [1] The bound antigen and antibody act as a unitary object, effectively an antigen of its own with a specific epitope. After an antigen-antibody reaction, the immune complexes can ...
The classical complement pathway can be initiated by the binding of antigen-antibody complexes to the C1q protein. The globular regions of C1q recognize and bind to the Fc region of antibody isotypes IgG or IgM. [2] These globular regions of C1q can also bind to bacterial and viral surface proteins, apoptotic cells, and acute phase proteins. [5]
An antibody is made up of two heavy chains and two light chains. The unique variable region allows an antibody to recognize its matching antigen. [73] A B cell identifies pathogens when antibodies on its surface bind to a specific foreign antigen. [74] This antigen/antibody complex is taken up by the B cell and processed by proteolysis into ...
The classical pathway is triggered by activation of the C1-complex. The C1-complex is composed of 1 molecule of C1q, 2 molecules of C1r and 2 molecules of C1s, or C1qr 2 s 2. This occurs when C1q binds to IgM or IgG complexed with antigens. A single pentameric IgM can initiate the pathway, while several, ideally six, IgGs are needed.
A single antibody molecule has two antigen receptors and therefore contains twelve CDRs total. There are three CDR loops per variable domain in antibodies. Sixty CDRs can be found on a pentameric IgM molecule, which is composed of five antibodies and has increased avidity as a result of the collective affinity of all antigen-binding sites combined.
Activation of the C1 complex initiates the classical complement pathway. This occurs when C1q binds to antigen-antibody complexes. The antibodies IgM or certain subclasses of IgG complexed with antigens are able to initiate the complement system: a single pentameric IgM can initiate the pathway, while several monomeric IgG molecules are needed. [3]
The complex is believed to be unstable until it binds properdin, a serum protein. The addition of properdin forms the complex C3bBbP, a stable compound which can bind an additional C3b to form alternative pathway C5-convertase. The C5-convertase of the alternative pathway consists of (C3b) 2 BbP (sometimes referred to as C3b 2 Bb).