Blood Types: Differents Systems, Relationship Between Antigens/Antibodies And Transfusion's Principles
First of all, let's go through some definitions: An antigen is a molecule capable of initiating an immune reaction, it can be carbohydrates, proteins, glycolipids or any other type of molecules.
An antibody is an immune molecule produced by a specific type of cells called plasmocytes and used by the immune system to neutralize pathogens such as bacteria and viruses.Its variable portion binds to the antigen (agglutination) and initiates the immune response.That being said it's crucial to know that every cell in the body exposes different antigens but immune cells recognize these antigens as self-antigens and no immune response is initiated, this phenomenon is called immune tolerance.In the opposite side, through complex events immune cells are able to recognize antigens of invasive organisms and sometimes memorize it for a possible reinfection, scientists rely on this memorization to create vaccines.
There are several blood types and each blood type is the result of two major antigen systems found in the surface of red blood cells, The ABO system, and The Rhesus system.These two systems are capable of initiating a strong immune response, unlike other systems.
Blood typing was discovered by an Austrian scientist called Karl Landsteiner at the beginning of the 20 the century and he earned a Nobel Prize for his work.
The ABO system
This is the major system considering blood typing, it has 2 different types of antigens: Antigen A and Antigen B and if there is no antigen present then the blood type is O.Therefore four different types of phenotypes can be seen, A, B, AB, and O.
The ABO system doesn't involve only red blood cells, in fact, it's abundant in the majority of human tissues.
In the serum, there are several natural antibodies produced against the non-existent antigens of ABO.Their production is stimulated at an early age of life when the immune system encounters the "missing" ABO blood group antigens in foods or other microorganisms.For example, blood type A people have naturally antibodies anti-B, the following table shows the different antibodies found in each blood type.
If a blood type A person with anti-B antibodies receives blood type B then what will happen? The natural antibodies in his serum bind to the antigens B of the transfused blood and the activation of complement which are different types of proteins with a destructive function of external organisms take place.
The result is an acute destruction of red blood cells(Acute hemolytic reaction) a very dangerous and lethal accident.
In 1924 Bernstein constructed the Three allele model where ABO blood system antigens are encoded by one genetic locus, the ABO locus, which has three alternative forms or alleles A, B, and O.We inherit one allele of our father and one from our mother thus 6 different genotypes can be seen:
AA and AO for blood type A, BB, and BO for blood type B, AB for blood type AB and OO for blood type O.
Rhesus system
In 1940 K. Landsteiner and A.S. Wiener discovered the Rhesus system and their discovery was the most important event in the science of human blood groups since the description of the ABO blood groups.
The Rhesus is the second most important blood group system, it has about 50 antigens discovered so far making him the largest of all 29 blood group systems.Five main antigens D, C, c, E, and e are able to provoke a powerful immune response where antigen D is the most significant one of them all.
+ and - are used to say if the antigen D is present or absent, this means if a person has a blood type A- then he lacks the antigen D.
A blood type A- a person who receives type A- blood doesn't necessarily develop an acute hemolytic accident, instead, he develops antibodies anti-D type IgM.A second exposure can be very dangerous because a secondary immune response produces specific IgG antibodies that have the potential to induce a more powerful immune response and complement activation than IgM type antibodies.
The other blood type systems such as Kell system, Lewis system, MNS systems are generally overlooked in transfusions because they induce a weak immune response with almost no adverse effects at all but they can be considered if that person in transfused several times
Principles of transfusion
When someone donates blood, a special machine separates its different compounds for future uses, thus blood products can be red blood cells, white cells, plasma, platelets or clotting factors.For the purpose of the subject, we're gonna discuss the transfusion of plasma and red blood cells.
[Image credit: Original]
Two systems are respected in red blood cells' transfusion, ABO, and Rhesus systems.For the Rhesus system, its pretty simple because D-positive blood types can be transfused only to D-positive blood types and D-negative blood types can be transfused to both D-positive and D-negative blood types.
For the ABO system because of the natural abundant antibodies, things are slightly more complex.On one hand, blood type O is the universal donor because there are no antigens in the surface of red blood cells capable of interacting with antibodies and it accepts only blood type O, I call it Mother Teresa of the blood types.
On the other hand blood type, AB is the universal receiver because its serum doesn't contain any antibodies and it can only be transfused to AB blood type making it the greedy one of blood types.
A blood type can receive only from A or O and B blood type can only receive from B or O (see the red blood cells compatibility chart in red).
For the plasma transfusion, it's the exact opposite, AB becomes the universal donor and O becomes the universal receiver ( see the plasma compatibility chart in yellow)
Image credit: Wikimedia 1/2
Blood is the cheapest yet the most precious gift you can donate.Humans are the only source of transfusable blood, millions of people die each year due to a lack of blood.If you are not a donor yet, it's time to know your blood type, become one and spread a good message to others.Your blood will save lives and give hope to your brothers and sisters.Give it to those who give life.
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