Blood groups

In 1901, the Austrian pathologist and later Nobel Prize winner Karl Landsteiner noticed, whilst conducting experiments with blood, that the blood of different people agglutinates when it is mixed together. This agglutination is due to the fact that each individual has quite specific blood group characteristics, which are not all compatible with one another. 

When red blood cells of one blood group are mixed with the blood plasma of the other blood group, he discovered that agglutination took place. He concluded that there must be antibodies in the blood plasma that react with the antigens of foreign red blood cells, but not with the surface properties of their own blood cells (“Landsteiner’s law”).

Landsteiner discovered that red blood cells can have different surface properties, which can be recognised as foreign by the body. He found two different antigens, which he called A and B. As the antigens A and B can be present individually, together or not at all, he inferred the existence of four blood groups: A, B, AB and C, which was later called O.

People with the blood group A have the antigen A and antibodies against the blood group B, whilst people with the blood group B have the antigen B and antibodies against the blood group A. People with the blood group AB have antigens for A and B, but no antibodies, as they react to the antigens. The blood group O, on the other hand, has neither antigen A nor antigen B, but antibodies against A and B are produced.

On the basis of this discovery, the first successful blood transfusion was carried out in 1907.

The rhesus factor plays an important role in blood transfusion. Rhesus-negative blood can be transferred to a rhesus-positive patient unscathed, but not vice versa. If rhesus-positive blood is transferred to a rhesus-negative patient, antibodies can form against the red blood cells of the donor blood, which can lead to major problems during subsequent further blood transfusions. This must particularly be avoided in transfusions for girls and women of childbearing age and for children.

The rhesus factor can have particularly serious consequences during pregnancy: if a rhesus-negative woman is pregnant with a rhesus-positive child, rhesus-positive blood may enter the mother’s bloodstream during the birth. Then antibodies form in the blood of the rhesus-negative woman against the antigen D. 

This carries the risk that the D antibodies will get into the child’s bloodstream during a second pregnancy with a rhesus-positive child and destroy the child’s vital red blood cells. 

These consequences can be prevented if D antibodies are administered to the rhesus-negative mother during the pregnancy and directly after the birth of a rhesus-positive child. These intercept the child’s rhesus factors and thus prevent the mother’s production of antibodies against the child’s rhesus factors.