Immunoglobulin A

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Schematic representation of immunoglobulin A as a dimer: H-chain (1), L-chain (2), J-chain (3) and secretion piece (4).

Immunoglobulin A ( IgA ) is an antibody that is mainly found in the external body fluids (for example urogenital mucus, milk, or intestinal fluids) and there forms an important defense barrier against pathogens. In the blood serum it forms about 15% of all immunoglobulins. It is synthesized by plasma cells located under the epithelium . IgA can occur as a monomer (ie only one molecule) or as a dimer (two molecules, connected at the long ends of the antibody Ypsilon ). The dimers are the so-called secretory IgA ( sIgA ).

Some people are unable to produce IgA. This disease is known as selective immunoglobulin A deficiency .


There are two subclasses, IgA 1 and IgA 2 . These differ in the molecular mass of the H chain (IgA 1 : 56  kDa , IgA 2 : 52 kDa, but the total molecular mass for both is 160 kDa) and in the concentration in the serum (IgA 1 : 3 mg / ml, IgA 2 : 0.5 mg / ml).

SIgA consists of two IgA molecules, a so-called J chain and a polypeptide with a molecular mass of 70 kDa, the so-called secretory component or secretion piece (SC chain). The SC chain is required for transport on mucous membranes and as protection against digestive enzymes. This polymerisation only takes place in the mucous membranes as it is necessary for transport through the epithelial cells .


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