The practice of blood transfusions was already in vogue in old Europe in the 17th century. The first results, however, were disappointing, given that the transfusion very often proved to be a truly lethal poison for the patient. For this reason, before the end of the 1600s this practice was banned by France and England.
Doctors had to wait until the beginning of the twentieth century to understand the real reason for this alternation of successes and failures.
In 1901 the studies of the Austrian Karl Landsteiner led him to discover blood groups. This discovery, which earned him the Nobel Prize for Medicine and Physiology in 1930, revolutionized the widespread belief of those times according to which blood was an identical tissue in all individuals.
In particular, Landsteiner identified the presence of four different blood groups, which he called A, B, AB and 0. The reason for this differentiation was discovered later when the existence of the so-called erythrocyte antigens was noticed.
What is a blood type?
When the organism is attacked by a pathogen (virus, bacteria, etc.), it triggers a defense mechanism that attacks and neutralizes these antigens thanks to the presence of plasma proteins called antibodies.
On the surface of red blood cells two different antigens can be distinguished: antigen A and antigen B. Similarly, anti-A antibodies and anti-B antibodies can exist in plasma. Both neutralize and kill red blood cells carrying the corresponding antigen.
Each blood group is therefore characterized by the presence of specific antigens and corresponding antibodies:
Group A contains A antigens and anti-B antibodies
group B contains B antigens and anti-A antibodies
group AB contains A antigens, B antigens and none of the corresponding plasma antibodies
group 0 lacks antigens but contains both anti-A and anti-B antibodies
the subject carrying the AB blood group is the luckiest since, being devoid of specific antibodies, he can receive blood from both type A, B, AB and 0 donors (universal recipient)
the opposite is true for those with type 0 blood who can only receive similar blood (universal donor)
the individual of group A can instead receive blood from groups A and 0; while type B blood is only compatible with groups B and groups 0
If these combinations are not respected, the antibodies present in the plasma (agglutinins) attack the red blood cells of the transfused blood, neutralizing them (agglutination reaction) and forming small clots which block the blood vessels causing very serious damage to the organism.
The blood group to which one belongs is inherited from the parents and is immutable from birth to death. The frequency of these groups varies based on the ethnicity of the population: in England around 40% of individuals are group A and only 10% are group B; in India group A is present in 27% of cases and group B in 50%. The AB blood group is the rarest in Europe.