Most serum IgA is monomer, and about 10% ~ 15% is dimer, but a few polymers are also found.
The distribution of IgA functional regions is very similar to IgG, and the biggest difference between the two subclasses (IgA 1 and IgA2) is in the hinge region.
IgA2 lacks disulfide bond region between H-L chains and is easy to dissociate.
In terms of content, stability and half-life, serotype IgA is inferior to IgG, but higher than other IgG.
IgA can bind antigen, but it can't activate the classical pathway of complement, so it can't exert many biological effects like IgG, so it has always been mistaken that serotype IgA is of little significance. Recent studies have found that there is a considerable proportion of IgA in circulating immune complex antibodies, so it is considered that serotype IgA can remove a large number of antigens in a non-inflammatory form, which is very beneficial to maintain the stability of the internal environment of the body.
Secretory IgA(sIgA) is a dimer with sedimentation coefficient of 1 1S and molecular weight of 400kD. Each sIgA molecule contains a J chain and a secretory tablet. α-chain, L-chain and J-chain are all produced by plasma cells, while secretory tablets are synthesized by epithelial cells. J chain connects two IgA monomers through the penultimate disulfide bond; The structure of SIgA combined with secretory tablets is more compact, which helps sIgA to maintain antibody activity on the surface of mucosa and exudate. The high concentration of IgA in exocrine fluid is mainly synthesized locally, especially in gut-associated lymphoid tissue (GALT).
Secretory IgA has stable performance and high local concentration, which can inhibit pathogens and harmful antigens from adhering to mucosa and preventing them from entering the body. At the same time, because it regulates phagocytosis and dissolution, it also constitutes the first defense mechanism of mucosa. Secretory IgA in breast milk provides a local immune barrier for infants from 4 to 6 months after birth; Therefore, secretory IgA is often called local antibody.
According to network information