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The water-accessible surface area of an IgG antibody. Immunoglobulin G (IgG) is a type of antibody. Representing approximately 75% of serum antibodies in humans, IgG is the most common type of antibody found in blood circulation. [1] IgG molecules are created and released by plasma B cells. Each IgG antibody has two paratopes.
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 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. This also occurs when C1q binds directly to the surface of the pathogen.
Antibody (or immunoglobulin) structure is made up of two heavy-chains and two light-chains.These chains are held together by disulfide bonds.The arrangement or processes that put together different parts of this antibody molecule play important role in antibody diversity and production of different subclasses or classes of antibodies.
In IgG, IgA and IgD antibody isotypes, the Fc region is composed of two identical protein fragments, derived from the second and third constant domains of the antibody's two heavy chains; IgM and IgE Fc regions contain three heavy chain constant domains (C H domains 2–4) in each polypeptide chain. [1] [2] The Fc regions of IgGs bear a highly ...
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]
The C1q domain is a conserved protein domain. C1q is a subunit of the C1 enzyme complex that activates the serum complement system.C1q comprises 6 A, 6 B and 6 C chains.These share the same topology, each possessing a small, globular N-terminal domain, a collagen-like Gly/Pro-rich central region, and a conserved C-terminal region, the C1q domain. [2]
IgG3 is an efficient activator of pro-inflammatory responses by triggering the classical complement pathway. [10] It has the shortest half-life compared to the other IgG subclasses [11] and is frequently present together with IgG1 in response to protein antigens after viral infections. [12]