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Rhesus factor - Assurance during pregnancy and blood transfusion

Two rhesus macaques (Macaca mulatta) at the animal husbandry at the German Primate Center. Photo: Anton Säckl
Two rhesus macaques (Macaca mulatta) at the animal husbandry at the German Primate Center. The rhesus factor of human blood was discovered through experiments with such animals. Photo: Anton Säckl

The name indicates that this characteristic of the human blood originates from the findings of animal experiments with monkeys: Rhesus factor derives from the rhesus monkey (Macaca mulatta). These monkeys also have the factor, and the name is due to the use of red blood cells from the blood of rhesus monkeys to obtain the first test serum. Serum is the watery substance that is separated from the clotted blood. Around 1940, the Austrian Karl Landsteiner and his colleague Alexander Wiener wanted to find out why, the most important human blood group system "AB0", which had previously been discovered, sometimes had shock effects and in some cases fatal consequences after blood transfusions. They wanted to find out why the immune systems of some people had allergic reactions after a transfusion.

For this, they took blood from rhesus monkeys, which are very similar to humans and with that, they "vaccinated" guinea pigs. The rodents produced a defensive substance against the foreign substance in their blood. From the guinea-pig's blood, the researchers once again gained serum, which they added to a hundred human blood samples, each from a different donor. The results: About 85 of the samples clumped, 15 remained unaffected. The rhesus factor was discovered and became the second most important blood group system for humans.

The rhesus factor can be harmful (even fatal) to humans in two different situations: in blood transfusions and in pregnancies. Surface proteins on the envelope of the red blood cells (erythrocytes) which some humans possess and others do not, are responsible for the rhesus factor: positive ("Rh +") with the proteins, negative ( "Rh-") without. About 15 percent of all Europeans do not have this factor in their blood. The surface proteins ensure that the blood of rhesus-positive humans is seen as foreign bodies during a blood transfer from the immune system of the rhesus-negative human in order to form antibodies against it. A renewed blood transfusion can lead to a life-threatening reaction of the immune system of the recipient.

In this video the two most important blood group systems, AB0 and rhesus factor, are explained in detail.

A similar constellation known as rhesus incompatibility can occur in women with multiple pregnancies: it occurs when a rhesus-negative woman is pregnant with a rhesus-positive child with the corresponding father. The rhesus-negative organism of the female forms antibodies against the Rhesus-positive erythrocytes during the first pregnancy and during the next pregnancy hemolysis occurs in the child. Hemolysis, is referred to by doctors as the dissolution of red blood cells, which, among other things, lead to the lack of oxygen supply to the fetus. This can have fatal consequences for the child and in many cases it causes serious health problems. According to the physician Reinhard Roos, statistically such a constellation occurs in approximately every tenth pregnancy, the danger of such a pregnancy concerns a high number of pregnant women.

The routine testing of blood groups, which has been possible since the discovery of the rhesus factor, saved many babies in the womb and also recipients of blood transfusions from severe dangers during major surgery. Without the use of rhesus monkeys in basic research, this would not have been possible. Like numerous other researchers who were dependent on animal experiments, Karl Landsteiner received the Nobel Prize in Medicine for his life-saving results.