Immunoglobulin A (IgA) is the major immunoglobulin class in body secretions that protects against infections of the mucous membranes lining the mouth, airways, and digestive tract. Its serum concentration is approximately 0.2 g/l and biological survival (T1/2 in plasma) 6 days. Plasma IgA is predominantly monomeric (160 kDa) and of the IgA1 subclass, and is mostly produced in the bone marrow. Over half of IgA produced by the intestinal lamina propria plasmocytes is in oligomeric form and 35 % of it is IgA2.,Immunoglobulin A