What secrets do our blood types hide? AB is the rarest, what else should we know?

From the history of blood groups and blood transfusions

Since ancient times, people have believed in the supernatural properties of animal and human blood. It has been part of various religious rituals and ceremonies.

Human blood was considered the most valuable sacrifice to the gods. They observed that the loss of large amounts of blood in humans and animals seriously endangered their lives.

The most famous blood lady is Countess Elizabeth Bathory. Legends tell how she bathed in vats of virgin blood to preserve her youth and beauty.

She probably believed in the rejuvenating effect of hormone-filled blood, which may indeed have had that effect.

Ironically, the first blood transfusions were performed long before people had any idea that blood types existed. Therefore, these procedures were high-risk and usually resulted in death. But there have been some miraculous cures.

The origins of blood transfusions begin with the discovery of the bloodstream. We owe its discovery in 1616 to the Englishman William Harvey.

In France, in 1667, during the reign of King Louis XIV, the first blood transfusion was performed using lamb's blood. The patient miraculously survived.

It wasn't until 150 years later that people dared to give human blood from a donor. This was in 1818. The obstetrician James Blundell saved the lives of mothers who at that time often died after a difficult birth, precisely from bleeding from postpartum injuries.

Finally, we come to the watershed period when the greatest discovery of transfusiology was made.

In 1901, the Viennese physician Karl Landsteiner discovered the phenomenon of agglutination, the ability of red blood cells to aggregate in other human serum. Landsteiner proposed the idea of three blood groups.

For this achievement he was awarded the Nobel Prize in Medicine in 1930.

Eventually, the Czech psychiatrist Jan Janský expanded the knowledge of blood groups by adding a fourth blood group. At that time, the groups were simply referred to as I to IV.

Today's names A, B, 0 and AB were introduced after 1930.

In addition to this basic division of blood groups, however, we know that there are other subgroups. The second most famous blood group was discovered again by Landsteiner and Wiener. In 1941, they discovered the existence of the Rh system.

Nowadays, we can dilute blood, store it, separate the individual cells from it and its components such as proteins, coagulation factors, antibodies, etc.

Human blood is thus becoming an even more valuable commodity, ready to treat and heal thousands of patients after severe injuries, operations, burns, cancer patients, haemophiliacs, people with severe autoimmune reactions. Blood products are also used in medical cosmetics.

How do the different AB0 blood groups differ?

Blood groups are certain characteristics of red blood cells. The essence of their existence is based on the principle of two components, namely antigen and antibody.

An antigen is a solid particle found on the surface of a cell. It can be, for example, a carbohydrate, a lipid, a protein, etc. It is an integral part of the cell membrane.

An antibody is found in the serum. It is actually an immunoglobulin that recognizes antigens and launches an attack against foreign ones.

The antigen on the surface of red blood cells is called agglutinogen. The antibody against it is agglutinin. When agglutinin meets agglutinogen, it triggers a reaction called agglutination, or clumping of red blood cells. It was this phenomenon that was the basis for the discovery of blood groups.

There are four basic blood groups in the AB0 system, namely 0 (zero), A, B and AB.

Specific sugars (carbohydrates) are found on the surface of red blood cells. The presence of N-acetylgalactosamine is the antigen for blood group A. The presence of the carbohydrate D-galactose is in turn the antigen that makes up blood group B.

Both carbohydrate antigens are linked to the cell membrane by a so-called H-antigen. If this H-antigen is empty, i.e. there is no carbohydrate on it, the resulting blood group is zero.

It is the natural ability of the body's immune system to produce antibodies against antigens. This is also the case for antigens present on red blood cells.

People who have blood type A have anti-B agglutinins present in their serum. People with blood type B have anti-A antibodies.

Individuals with blood type zero do not have antigens but have antibodies of both types, i.e. anti-A and anti-B. These people are universal blood donors but can only accept blood of their blood type, i.e. blood type zero.

Finally, people with blood type AB have both antigens present on their red blood cells but no antibodies. They are universal recipients but can only donate blood to a person who has blood type AB.

For example, in transfusions, only the basic four blood groups AB0 are not considered. Matching in the Rh system is also important. In transplants, the matching criteria are even stricter. In addition to blood groups, matching in other immune characteristics and molecules is also important.

Donated blood that does not match the recipient's blood group is called AB0 incompatible or Rh incompatible. Transfusion of such blood can be fatal. An immune reaction triggered by antibodies causes haemolysis, i.e. the breakdown of red blood cells.

Inheritance of blood groups

Blood groups are characteristics of red blood cells and therefore, like hair or eye colour, are inherited from parents to their offspring.

The inheritance of blood groups is provided by genes that carry the genetic information about all our characteristics.

Blood groups are inherited according to Mendel's rules of inheritance. The resulting blood group of a child is created by crossing the genotypes of the parents.

We will briefly explain this crossbreeding using the example of two parents. One of them will have blood type A and the other blood type 0.

The phenotype of blood group A can have two types of alleles (in which the gene is stored). Either it consists of two alleles AA or A0. The result is the same - blood group A. Blood group zero can have only one genotype, namely allele 00.

If we cross AA with 00, 100% of the time we get the genotype A0. All the children of these parents will have blood type A.

If we cross genotype A0 and 00, 50% of the time we will get genotype A0 and the other 50% will get genotype 00. If we cross genotype A0 and 00, 50% of the time we will get genotype A0. The child of these parents has half the chance of being born with blood type A or blood type 0.

Knowledge of the inheritance of blood groups is particularly important in forensic medicine and in paternity disputes.

Blood type is written in our genetic information and does not change from birth. In exceptional situations it can change temporarily. This is for example after an exchange transfusion in a newborn or after a bone marrow transplant.

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Geographical differences in the prevalence of blood groups

Just as the distribution of people with different skin colors varies, humanity also varies in the prevalence of blood types.

Other blood groups

In modern times, we know several dozen blood groups of humans.

The International Society for Blood Transfusion lists up to 33 blood group systems. These blood groups consist of more than 300 antigens present on red blood cells.

We will mention a few of the most well-known and important blood groups:

Rhesus system

The Rhesus system is the second most important blood group system after the ABO system. The Rh system consists of 50 antigens, but only five of them are important. It is named after the Macacus rhesus monkey, in which this blood system was first described.

The so-called Rh factor may or may not be present on the cell membrane of human red blood cells. The Rh factor is actually antigen D, which is immunogenic, i.e. capable of inducing the production of antibodies.

If a person has this antigen D on their red blood cells, they are Rh positive. If they do not have it, they are Rh negative.

Rh-negative people, when they come into contact with Rh-positive blood, begin to make antibodies against this antigen. This D-antigen is identified as foreign to the body and is not recognised by the immune system.

The antibodies begin to fight against these red blood cells and destroy them. This is how a hemolytic reaction occurs when Rh positive blood is transfused into an Rh negative individual.

The person with Rh positive blood does not make antibodies against the D-antigen because the immune system recognizes this antigen and knows that it is inherent in the body.

The immune antibodies to the D-antigen are similar to IgG antibodies and can therefore cross the placenta. This is why there is sometimes a problem when an Rh negative mother gives birth to an Rh positive baby (if the father is Rh positive and the baby has inherited the D-antigen).

There may be no complications during pregnancy, but the blood of the mother and baby may meet at birth. At that point, the mother's body starts to make antibodies against the D-antigen.

The antibodies are present in the body for a long time. In a second pregnancy with an Rh-positive baby, these antibodies cross the placenta and destroy the baby's red blood cells. This causes hemolysis, or breakdown.

Currently, there is an effective prevention against haemolytic disease in newborns. Pregnant Rh negative mothers who have given birth to an Rh positive baby are given anti-D immunoglobulin either before delivery or as postpartum prophylaxis.

H-antigen

H-antigen is found on all red blood cells regardless of blood group in the AB0 system. It is a precursor for AB0 blood group antigens.

However, there are people with a very rare Bombay phenotype. These people do not have the H-antigen present on the cell membrane of their red blood cells. If they do not have the H-antigen, they do not have the antigen for blood group A or B.

It would appear that such people do not have a blood group. Even if they do not have antigens, they still produce antibodies to the H-antigen, and therefore antibodies to antigens A and B. If they do not have antigens, they can make antibodies to antigens A and B. Therefore, they can only receive blood from a donor who has blood group 0.

The MNS antigen system

The blood group system MNS was discovered by the famous pair of scientists Landsteiner and Levine in 1927. Antibodies against antigens are of the IgG type and are called anti-M and anti-N.

These antibodies can cause rare transfusion reactions when compatible in other systems (AB0 and Rh).

Association of some diseases with AB0 blood group

There are some known associations between an increased incidence of certain diseases and blood groups in the AB0 system. For example, people with blood group zero have a lower risk of pancreatic cancer, thromboembolic disease and are also more protected against fatal malaria.

A link between blood groups and SARS-CoV-2 infection and the course of COVID-19 is also currently being considered.

From observations to date, researchers have found that individuals with blood type 0 have a lower risk of infection, as well as a lower risk of severe disease and the need for artificial lung ventilation.

Blood groups B and AB had the highest risk of artificial lung ventilation.

Conversely, individuals with blood group 0 had a higher risk of infection with Vibrio cholerae, the bacterium that causes fatal cholera. Individuals with blood group AB are most protected against this disease.