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Immunoglobulin M (IgM) is the largest of several isotypes of antibodies (also known as immunoglobulin) that are produced by vertebrates. IgM is the first antibody to appear in the response to initial exposure to an antigen ; [ 1 ] [ 2 ] causing it to also be called an acute phase antibody.
The J chain is a glycoprotein of molecular weight 15 kDa. Its secondary structure remains undetermined but is believed to adopt either a single β-barrel or two-domain folded structure with standard immunoglobulin domains. [10] The J chain's primary structure is unusually acidic having a high content of negatively charged amino acids. [11]
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.
Each antibody binds to a specific antigen in a highly specific interaction analogous to a lock and key.. An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that cause disease.
The pentameric structure of IgM antibodies makes them efficient at binding antigens with repetitive epitopes (e.g. bacterial capsule, viral capsid) and activation of complement cascade. As IgM antibodies are expressed early in a B cell response, they are rarely highly mutated and have broad antigen reactivity thus providing an early response to ...
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.
Each heavy chain has two regions: a constant region (which is the same for all immunoglobulins of the same class but differs between classes).. Heavy chains γ, α and δ have a constant region composed of three tandem (in a line next to each other) immunoglobulin domains but also have a hinge region for added flexibility.
[2] [16] Among the many functions of C1q, C1q triggers clearance of immune complexes and apoptotic cells by activating the classical pathway and binding directly onto phagocytes. [ 1 ] [ 17 ] Consequently, systemic lupus erythematosus from insufficient amounts of C1q is characterized by the accumulation of autoantibodies and apoptotic cells. [ 4 ]