Why does the blood group vary from person to person?
Even though the blood of all the human beings looks alike, in reality, it is not so. Our blood is mainly composed of red blood corpuscles, white blood corpuscles, platelets and plasma. It has been observed from microscopic investigations that molecules of antigens found on the surface of red blood corpuscles are different in different people. Antigen molecules are a kind of proteins that stimulate the production of antibodies. It is this difference in the antigen molecules that gives rise to different groups of blood.
In the year 1900 Dr Karl Landsteiner discovered two kinds of antigen- A and B type. He was awarded the Nobel Prize for medicine in 1930 for this discovery. Blood containing A type antigen was classified as A group, while that containing B type as B group. Subsequently, it was discovered that the blood of some people contains both A and B type antigens. This type was classified as AB group. The blood that contained neither A nor B type antigens was called O group. Thus the blood of all human beings has been divided into four groups. Studies made till now have revealed the existence of more than 200 groups of human blood.
However, as far as the transfusion of blood of nay patient is concerned, only the aforesaid four groups of blood are important. Before transfusing blood to any patient, it is essential to get his blood group tested. It is very essential to match the blood of the patient with that of the donor before transfusion. It has been found that the blood of even real brothers and sisters may not be of the same group. On the other hand, the blood of two individuals belonging to two different states may be of the same group.
If the wrong blood is transfused to patient, he can die, because antigens of different classes cannot combine with each other. However, blood plasma of one individual can be given to another because it is the same in every body.
Landsteiner and Alexander S. wiener discovered another important blood antigen in 1940. This additional factor is called the rhesus antigen or Rh factor.
Rhesus antibodies do not occur in naturally blood groups- both for
recipients and donors. AB groups are called the universal recipients whereas O is the universal donor.