Leanne Dooley
Learning Objectives
By the end of this section, you will be able to:
- Describe the two basic physiological consequences of transfusion of incompatible blood
- Compare and contrast ABO and Rh blood groups
- Identify which blood groups may be safely transfused into patients with different ABO types
- Discuss the pathophysiology of hemolytic disease of the newborn
Blood transfusions in humans were risky procedures until the discovery of the major human blood groups by Karl Landsteiner, an Austrian biologist and physician, in 1900. Until that point, physicians did not understand why rapid death often followed blood transfusions. They assumed that all human blood was the same. Landsteiner discovered that the plasma of some individuals caused the red blood cells of some other individuals to clump together (agglutinate), and he surmised that fatal transfusion reaction occurred when the type of donor blood infused into the patient was incompatible with the patient’s own blood. Blood groups are determined by the presence or absence of specific marker molecules on the plasma membranes of erythrocytes. With the discovery of these inherited markers, it became possible for the first time to match patient-donor blood types and prevent severe hemolytic transfusion reactions and deaths.
Antigens, Antibodies and Transfusion Reactions
Antigens are substances that the body does not recognise as belonging to the “self” and that therefore trigger a defensive response from the leukocytes of the immune system. (Seek more content for additional information on immunity.) Here, we will focus on the role of antibody-mediated (humoral) immunity in blood transfusion reactions. With RBCs in particular, you may see the antigens referred to as isoantigens or agglutinogens (surface antigens) and the antibodies referred to as isoantibodies or agglutinins. In this chapter, we will use the more common terms antigens and antibodies.
Antigens are generally large proteins, but may include other classes of organic molecules, including carbohydrates, lipids, and nucleic acids. Following an infusion of incompatible blood, erythrocytes with foreign antigens appear in the bloodstream and trigger an immune response. Proteins called antibodies (immunoglobulins), which are produced by certain B lymphocytes called plasma cells, attach to the antigens on the plasma membranes of the infused erythrocytes. Large antibodies, called IgM antibodies, can cause direct destruction of incompatible RBC via activation of group of plasma proteins called complement. This type of RBC destruction is called intravascular haemolysis and the reaction is referred to as an acute haemolytic transfusion reaction, which can be fatal after infusion of as little as 10mL of incompatible RBC. Smaller antibodies, called IgG antibodies, bind to the incompatible RBC and mark them for destruction by macrophages in the spleen. This type of RBC destruction is called extravascular haemolysis and the reaction is ca