The ABO blood group system is based on antigens found on red blood cells, discovered by Karl Landsteiner in 1900. There are four blood types: A, B, AB, and O. A person’s blood type is determined by the presence of antigens. ABO antigen differences matter in blood transfusions, as the immune system generates antibodies against antigens not expressed by the recipient’s red blood cells. Therefore, a recipient must receive a blood transfusion with a compatible blood type to avoid an immune response.
An antigen is a protein found on the surface of red blood cells. This antigen is part of the ABO blood group system, which is the most important blood group system considered when someone receives a blood transfusion. The ABO blood group system was discovered in 1900 by Austrian scientist Karl Landsteiner, who later received a Nobel Prize for his work.
Landsteiner’s discovery was the existence of three blood groups, classified according to the presence of antigens which he described as A, B and O. In 1902 another research group discovered the existence of a fourth type, called AB, with blood cells reds expressing both the A and B antigens. A third group determined in 1910 that the ABO blood type was an inherited trait.
A person with red blood cells expressing A antigen on their surface is said to have type A blood. Someone who has B antigen has B blood, while someone with A and B antigen has B blood. type AB. People with type O blood express neither A nor B antigen.
Within the A antigen there are about twenty different subtypes. Most of these subtypes are extremely rare. More than 99% of people have A1 or A2; subtype A1 is the most common and is present in about 80% of people. Subtypes A1 and A2 are so similar that they need not be distinguished for transfusion purposes. Some of the other A subtypes are quite different from complications during blood typing, but these subtypes are so rare that such problems occur very rarely.
For the most part, ABO antigen differences only matter in situations where an individual requires a blood transfusion. Before someone receives a blood transfusion, the medical personnel performing the transfusion must know the recipient’s blood type. This is because the immune system generates antibodies against ABO antigens that are not expressed by red blood cells.
In the case of someone with type A blood, for example, that person’s red blood cells express the A antigen. That person’s immune system generates antibodies to the B antigen early in life, usually in the first year or so. two. The end result is that if someone with type A blood receives a blood transfusion from someone with type B blood, antibodies from the recipient’s immune system will destroy the transfused red blood cells.
Therefore, a recipient of a transfusion with type A blood must receive either a type A or type O blood transfusion. This is because these are the only blood types that do not elicit an immune response. Similarly, type A blood can only be donated to someone with type A or AB blood, due to the presence of antidotes to type A antigen in people with type B or type O blood.
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