Why is blood classified into groups?

For centuries beliefs persisted that some people, according to race or linage, had superior blood. Members of the same families and races had the same blood type, it was said, but for reasons not explained some blood was purer.

When transfusions were first tried seriously in the seventeenth century, some succeeded, but others failed inexplicably, killing so many patients that in France, Italy and England the practice was banned. In 1990, Austrian pathologist Karl Landsteiner found the key to the doctors’ dilemma. He mixed blood taken from several different people, and discovered that some blood types were compatible and others were not.

His research led to a theory that all blood would divide into four groups – A, B, AB and O. In general, transfusion works safely only within each group (except that all groups are compatible with O, and AB is compatible with everything). ever since, blood has been broadly grouped in this way.

Marker proteins on the surface or fed blood cells distinguish each group. These markers, know as antigens, equip cells to provoke an immune responses to such threats as disease-carrying bacteria. In group A, red blood cells carry antigen A and the plasma has a protein called antibody b. Group B blood has antigen B and antibody a. Group AB has both antigens but no antibody. Group O has neither of the antigens but both antibodies.

World War I confirmed Landsteiner’s ideas, and brought an end to theories about the superiority of some blood types. In 1915, during the Gallipoli and Macedonian campaigns, British and French doctors used Adamites, Sensegalese and Indians as blood donors to save the lives of wounded British and French soldiers. Provided the transfusions came from compatible blood types, they were successful. Where the donor came from really didn’t matter at all.

Some forty years later, Landsteiner, who was awarded a Nobel Prize for his life-saving research, discovered the rhesus (Rh) factor in the blood, a system he first identified in rhesus monkeys. About 85 percent of people are Rh positive. They have blood containing D antigen, one of the body’s safeguards against disease. About 15 percent are RH-negative; their blood lacks this factor. Both of these rhesus factors are inherited traits and use traits and usually make little difference to a person’s life. The rhesus factor is extremely important in pregnancy. A pregnant woman who is Rh-negative may have a baby who is Rh-negative and Rh-positive may have a baby who is Rh-positive. As a reaction she may form antibodies against the baby’s blood. When the baby is born, the mother is given special antibodies. This ensures that, if she has subsequent pregnancies of Rh-positive children, her blood does not give them haemolytic disease, which wold destroy their red blood cells.

In addition to his work on blood groups, Landsteiner discovered that the blood of all humans – like our fingerprints – is unique. That is why genetic figner-printing, a technique in modern criminal investigation, may positively identify a suspect from the slightest trace of blood. There is always body wonders.

blood types

blood types

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