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Blood Groups

Distinguished by particular cell membrane surface antigens (protein markers) on red blood cells (RBCs), there have been over 35 different blood groups identified thus far. Although these include groups such as MNSs, Duffy, Lewis and so on, the ABO and Rh blood groups play the most significant role in blood transfusions. The frequency and stability of these blood groups in human population not only enhances our knowledge of human migration but have also been found to play a vital role in many applications of medicine including blood transfusion, transplantation, disease, and other physiological processes.

Immune System and Blood Group Compatibility

A blood transfusion involves the transfer of blood from one individual to another to restore the RBC levels and their ability to carry sufficient oxygen throughout the body. Our blood is composed of plasma (liquid portion) and formed elements, which consist of RBCs, white blood cells, and platelets. On the surface of the RBCs are antigens (substances that induce an immune response), which when bound by specific antibodies (plasma protein markers) cause agglutination or cell clumping to occur. In addition, the interactions between antibodies and antigens may lead to the destruction of RBCs, called hemolysis.

On the whole, medicine has come a long way in understanding the importance of blood group compatibility and biological mechanisms associated with blood transfusions and graft rejection. Today, matching the blood groups to prevent destruction of the donor RBCs is a relatively easy and successful procedure. As efficient as this system may be, it quickly becomes challenging due to the large numbers of blood groups and antibodies. It becomes extremely difficult when matching the various antigens that are present on tissues and organs. As a result, even after matching ABO and Rh blood groups between donor and recipient, transfusion reactions and transplantation rejection may still occur.

Whether it is a microorganism, bacterial infection, or donor blood that enters our body, our immune system has the remarkable ability to distinguish self from nonself in fighting off foreign material. This provides an explanation for unsuccessful blood transfusions of the past, where the antibodies of a recipient would combine with blood antigens from the donor, causing the transfusion reaction. The first recorded blood transfusions took place in Italy in 1628; however, the procedure was quickly banned due to the large number of deaths. It was not until the mid-19th century that human blood transfusions were again being performed in an attempt to fight against severe hemorrhages that were killing many infants after birth. This led to Leonard Lalois, a physiologist, discovering that blood cells from different species would clump together when mixed.

ABO Blood Group

The ABO blood group system was discovered in 1900 to 1902 by Karl Landsteiner and his fellow students. According to the presence or absence of antigens on the surface of RBCs, four different blood groups were determined: type A, B, AB, or O.

In the ABO system, type A blood has the A surface antigen with the ability to produce B antibodies in its blood plasma against type B antigens, which makes it compatible with type A and O. Type B has the B antigen on its surface with the ability to produce A antibodies against type A antigens, making it compatible with type B and O. Furthermore, Type AB, known as the universal acceptor, has both A and B surface antigens and cannot produce A nor B antibodies against other ABO blood antigens. Last, type O blood, which is known as the universal donor, has neither A nor B surface antigens and has the ability to produce both A and B antibodies against type A and B antigens.

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