immunoglobulin A (IgA), one of the most prevalent of the five classes of antibodies produced by the body. It is found in all secretions of the body and is the major antibody in the tears, saliva, and mucous membranes lining the intestines and bronchi. IgA combines with a protein in the mucosa and defends body surfaces by seeking out foreign microorganisms and triggering an antigen-antibody reaction. The normal concentration of IgA in serum is 50 to 250 mg/dL. Compare immunoglobulin D, immunoglobulin E, immunoglobulin G, immunoglobulin M. See also IgA deficiency.
