Clinical Information

Immunoglobulin A (IgA) makes up about 10% to 15% of all serum immunoglobulin. Most serum IgA is in its monomeric form, but about 10% to 15% is its dimer form. Secretory IgA is synthesized mainly by plasma cells in the gastrointestinal and bronchial mucous membranes and lactating breast ductules. Secretory IgA can be found in tears, saliva, sweat, milk, colostrum, and gastrointestinal and bronchial secretions. Secretory IgA is composed of two monomers connected by a secretory molecule. This secretory molecule protects the IgA polymer from proteolytic enzymatic degradation. IgA can initiate complement activation through the alternative pathway. Although the specific role of serum IgA is unclear, it may be important for virus neutralization. Secretory IgA plays a major role in protecting the respiratory and gastrointestinal tracts from infections.

IgA does not cross the placenta and levels of serum IgA are very low in infants. Adult level concentrations are not seen until 12 years of age. About one in every 700 Caucasians is genetically deficient in IgA and can develop anti-IgA antibodies. These individuals are at risk of having a severe anaphylactic reaction when plasma or other blood products are transfused. Inherited IgA deficiency is also seen in ataxia telangiectasia and other immunodeficiency disorders. Individuals with absent IgA are more likely to develop rheumatic disorders and lymphoma. Secondary IgA deficiency is seen with non-IgA multiple myeloma or macroglobulinemia with nephrotic syndrome.

Elevated IgA levels are associated with polyclonal and monoclonal increases. Chronic liver disease, chronic infections - especially in the respiratory or GI tracts, neoplasia of lower GI tract, inflammatory bowel disease, and autoimmune diseases like rheumatoid arthritis can result in polyclonal increases. Monoclonal increases can be seen with IgA multiple myeloma and some other lymphomas.