Immunoglobulin A antigen reactions. Immunoglobulin A (Chapter 22)is the principal immunoglobulin in such human secretions as saliva, bile, and gastric juice. Class-specific anti-IgA occurs in patients who lack IgA; these persons may be clinically normal or may have such disorders as malabsorption syndrome, autoimmune disease, or recurrent sinus or pulmonary infection. Interestingly, only 40% develop anti-A antibodies. Limited specificity anti-IgA occurs in persons who have normal IgA levels but who become sensitized from exposure to human plasma proteins from blood transfusion or pregnancy. Anti-IgA antibodies produce reaction only in transfusions that include human plasma proteins and are considered to be a type of anaphylactic reaction. Symptoms consist of tachycardia, flush, headache, dyspnea, and sometimes chest pain. Typically there is no fever. Severe episodes may include hypotension. Again, these are nonspecific symptoms that could be produced by leukoagglutinins or hemolytic reactions. Tests to prove IgA incompatibility are available only in a few medical centers; therefore, the diagnosis is rarely confirmed. Substantially decreased IgA on serum IgA assay would be presumptive evidence of anti-IgA reaction of the class-specific type. IgA immunologic reactions can be prevented by eliminating donor plasma proteins through the use of washed cells or frozen cells.