Immunoglobulin A (IgA) is majorly found in the mucosal secretions. IgA exists as two subclasses, IgA1 and IgA2. IgA is a dimer in animals, but a monomer in humans. IgA interacts with the Fc fragment of IgA receptor (FCAR) to elicit immune response against inhaled pathogens. Secretory IgA (S-IgA) produced by B1 lymphocytes triggers phagocytosis and leucocyte respiratory burst. S-IgA exists as a polymer and is crucial for primary defense. The high levels of IgA in human milk and colostrum may provide immune protection to infants. Deficiency of IgA leads to increased susceptibility to infections. High levels of IgA in kidney is present in IgA nephropathy and IgA myeloma. Autoantibodies of IgA is present in celiac disease.
