Red cell antigens as functional molecules and obstacles to transfusion.

Blood group antigens (BGAs) can act as functional molecules but also can evoke autoantibodies and alloantibodies, causing autoimmune hemolytic anemia, hemolytic disease of the newborn and hemolytic transfusion reactions. In Section I, Dr. Marilyn Telen discusses physiologic and pathologic functions of RBC BGA-bearing molecules. She reviews some associations of BGAs with RBC membrane integrity and hemolytic anemia; association of BGAs with enzymatic and transport functions; and adhesion molecules expressed by RBCs, especially with reference to their pathophysiological role in sickle cell disease. In Section II, Dr. Lawrence Petz discusses the problems of providing blood for patients who have RBC autoantibodies. He provides an algorithm for excluding the presence of "hidden" alloantibodies, when all units appear to be incompatible due to the autoantibody. He emphasizes that clinicians should be aware of these approaches and not accept "the least incompatible unit." In Section III, Dr. George Garratty describes two processes, in development, that produce RBCs that result in RBCs that can be described as "universal" donor or "stealth" RBCs. The first process involves changing group A, B, or AB RBCs into group O RBCs by removing the immunospecific sugars responsible for A and B specificity by using specific enzymes. The second process involves covering all BGAs on the RBC surface using polyethylene glycol (PEG). Results of in vitro and in vivo studies on these modified RBCs are discussed.