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Chapter 107. Transfusion Biology and Therapy (Part 1)

Harrison's Internal Medicine Chapter 107. Transfusion Biology and Therapy Blood Group Antigens and Antibodies The study of red blood cell (RBC) antigens and antibodies forms the foundation of transfusion medicine. Serologic studies initially characterized these antigens, but now the molecular composition and structure of many are known. Antigens, either carbohydrate or protein, are assigned to a blood group system based on the structure and similarity of the determinant epitopes. Other cellular blood elements and plasma proteins are also antigenic and can result in alloimmunization, the production of antibodies directed against the blood group antigens of another individual. These antibodies are. | Chapter 107. Transfusion Biology and Therapy Part 1 Harrison s Internal Medicine Chapter 107. Transfusion Biology and Therapy Blood Group Antigens and Antibodies The study of red blood cell RBC antigens and antibodies forms the foundation of transfusion medicine. Serologic studies initially characterized these antigens but now the molecular composition and structure of many are known. Antigens either carbohydrate or protein are assigned to a blood group system based on the structure and similarity of the determinant epitopes. Other cellular blood elements and plasma proteins are also antigenic and can result in alloimmunization the production of antibodies directed against the blood group antigens of another individual. These antibodies are called alloantibodies. Antibodies directed against RBC antigens may result from natural exposure particularly to carbohydrates that mimic some blood group antigens. Those antibodies that occur via natural stimuli are usually produced by a T cellindependent response thus generating no memory and are IgM isotype. Autoantibodies antibodies against autologous blood group antigens arise spontaneously or as the result of infectious sequelae e.g. from Mycoplasma pneumoniae and are also often IgM. These antibodies are often clinically insignificant due to their low affinity for antigen at body temperature. However IgM antibodies can activate the complement cascade and result in hemolysis. Antibodies that result from allogeneic exposure such as transfusion or pregnancy are usually IgG. IgG antibodies commonly bind to antigen at warmer temperatures and may hemolyze RBCs. Unlike IgM antibodies IgG antibodies can cross the placenta and bind fetal erythrocytes bearing the corresponding antigen resulting in hemolytic disease of the newborn or hydrops fetalis. Alloimmunization to leukocytes platelets and plasma proteins may also result in transfusion complications such as fevers and urticaria but generally does not cause hemolysis. Assay for .