Siga wot this Wikipedia the language links are at the top of the page across from the article title. Two views, one rotated 90 degrees with respect to the other, of the amino acid chains comprising secretory IgA1.

Coordinates of each backbone carbon atom were derived PDB entry 3CHN. Two views, one rotated 90 degrees with respect to the other, of the amino acid chains comprising secretory IgA2. Coordinates of each backbone carbon atom were derived PDB entry 3cm9. The amount of IgA produced in association with mucosal membranes is greater than all other types of antibody combined. IgA exists in two isotypes, IgA1 and IgA2.

They are both heavily glycosylated proteins. IgA1 is the predominant IgA subclass found in serum. Most lymphoid tissues have a predominance of IgA1-producing cells. In IgA2, the heavy and light chains are not linked with disulfide, but with non-covalent bonds. Both IgA1 and IgA2 have been found in external secretions like colostrum, maternal milk, tears and saliva, where IgA2 is more prominent than in the blood.

Polysaccharide antigens tend to induce more IgA2 than protein antigens. Both IgA1 and IgA2 can be in membrane-bound form. Clearance of IgA is mediated at least in part by asialoglycoprotein receptors, which recognizes galactose-terminating IgA N-glycans. Decreased or absent IgA due to an inherited inability to produce IgA is termed selective IgA deficiency and can produce a clinically significant immunodeficiency.