How it began
Karl Landsteiner, an Austrian pathologist and immunologist, worked in Vienna at the Hygiene Institute and then at the Institute of Pathological Anatomy. In 1900 he noted in a footnote that serum from healthy humans clumped the red cells of other humans. By late 1901 he had provided the experimental evidence and explained that people have different types of red blood cells.
Before it existed
Before blood groups were known, blood transfusions were fraught with danger. In 1899 and 1900 another researcher had described the clumping of red cells by serum from patients with pneumonia and other diseases and concluded that it reflected a disease process. Landsteiner at first could not tell whether clumping was a sign of disease or a result of individual differences.
How it works
Landsteiner mixed red cells and serum from different people and saw that clumping, called agglutination, occurred in a predictable pattern. He found that the reaction is caused by an interaction between the blood cells and the serum, which contains antibodies. From this he identified three groups, A, B and O. Group A blood, for example, carries the A antigen on red cells and anti-B antibodies in the plasma.
How it spread
In 1902 Alfred von Decastello, a colleague of Landsteiner, and his student Adriano Sturli found the fourth group, AB, which completed the ABO system as it is known today. Landsteiner later moved to the Rockefeller Institute for Medical Research in New York, where he and colleagues described the M, N and P systems in 1927 and the Rh system in 1940.
What lasted
The discovery led to safe blood transfusions between people with compatible blood groups and laid the foundation for modern transfusion medicine and hematology. Landsteiner received the 1930 Nobel Prize in Physiology or Medicine "for his discovery of human blood groups."
