IgA deficiency: implications for transfusion.

Anaphylactic transfusion reactions are acute, potentially life-threatening events with generalized signs and symptoms. Usually IgE mediated they may also result from antigen -antibody reaction involving non-IgE antibodies which fix complement and generate anaphylatoxins. The best documented reactions of the latter type result from presence of anti IgA antibodies in IgA deficient patients who receive transfusion of blood/components containing donor plasma. Anti IgA usually belongs to the immunoglobulin class IgG, less commonly IgM and rarely IgE. Anti IgA of the IgE type has been detected in patients with hypogammaglobulinaemia and not selective IgA deficiency who had developed anaphylactic reaction to blood products. IgA is the predominant immunoglobulin in various human external secretions, but it also constitutes 10 to 15 per cent of the total concentration of serum immunoglobulins. It exists in two subclasses, IgA1 and IgA2. The IgA2 subclass has two allotypes designated as IgA2m (1) and IgA2m (2). Secretary IgA prevents entry of pathogens across mucosal surfaces. From immunological point of view, individuals with serum IgA levels <5 mg/dl are considered IgA deficient and are potentially at risk for recurrent respiratory and gastrointestinal tract infections. However, the spectrum of clinical symptoms of IgA deficiency is wide; majority of those affected are asymptomatic, while others suffer form recurrent respiratory and gastrointestinal infections and have increased propensity to develop malabsorption, allergic and autoimmune disorders.