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5
THE BLOOD BANKERS
If you have ever been a blood donor, or ever needed a transfusion, then you will know your blood
group. You will know whether you belong to Group A, B, O or even AB. The reason for testing is
to avoid a possibly fatal reaction if you were to be transfused with unmatched blood. You cannot
tell, just by looking, what blood group a person belongs to. Unlike hair and eye colour or the shape
of heads, blood groups are an invisible signal of genetic difference which can be discovered only
by carrying out a specific test.
Though the first blood transfusions were performed in Italy in 1628, so many people died that
the procedure was banned. As a desperate measure to save women who were haemorrhaging after
childbirth, there was a revival of transfusion in the mid-nineteenth century. Though some patients
had no problems accepting a transfusion, a great many patients died from their reaction to the
transfused blood. What caused the reaction was a mystery.
The puzzle was eventually solved in 1900 by the Austrian physiologist Karl Landsteiner. After
experimenting with mixing the blood of his laboratory dogs and observing their cross-reactions, he
began his work on humans. He mixed the blood of several different individuals together and
noticed that sometimes when he did this the red blood cells stuck together in a clump. This did not
happen every time, but only with certain combinations of individuals. If this red-cell clumping was
occurring in transfused patients, the blood would virtually solidify, which would explain the fatal
reaction. It also explained why some patients tolerated a transfusion and showed no signs at all of a
reaction.
Landsteiner interpreted the results of his mixing experiments by suggesting that people
belonged to one of the three blood groups, A, B or O. Two years later a fourth group, AB, was
discovered. This also explained the erratic pattern of transfusion complications. Giving a group A
patient a transfusion of blood from a group A donor was fine; tranfuse a group A patient with blood
from a group B donor and there would be trouble. But so long as the donor and patient blood
groups were the same there was no problem.
It took a few years to discover the chemical basis for the different types of blood. The blood
groups are the result of a simple genetic difference that occurs on the surface of red blood cells, the
cells that carry oxygen and give blood its colour. On the outside of each red blood cell sits a
molecule that can occur in two very slightly different forms, A or B. People in group A have,
unsurprisingly, version A on the surface of their red cells while in group B, this is replaced by
version B. In the rare AB group the cells have both A and B versions on their outer surface. People
in group O have neither A nor B versions of the molecule. Their red cells are, in a sense, bald.