IgA is found as a Monomer in serum but a dimer in secretions and is the dominant class of Antibody found in secretions. These two subclasses differ in susceptibility to bacterial Proteases. IgA has several functions including the inhibition of microbial adherance to mucosal cells and the intestinal protection of neonates as it is present in breast milk. IgA also activates Complement through the alternative pathway.
Being the most abundant immunoglobulin in the human body, IgA plays a major role in mucusal immunity, tolerance development and protection against infection. Notably, the respiratory and gastrointestinal (GI) tracts provide the major intimate interface between the human body and the environment and, IgA is the major immunoglobulin in these areas. "IgA deficiency has been found to co-exist with autoimmune diseases, allergies and malignancies. The mutations leading to IgA deficiency have not been identified but, in some cases of IgA dificiency, it has been suggested that the pathogenesis involves a failure in switched memory B cells that can lead to this cohort experiencing an increased incidence of recurrent bacterial infections or autoimmune diseases".
- ↑ Sinqh K, Chanq C, Gershwin M.E. (2013) IgA deficiency and autoimmunity. Autoimmun Rev. 1568-9972 (13), 00180-8.