Karl Landsteiner, (born June 14, 1868, Vienna, Austrian Empire [Austria]—died June 26, 1943, New York, N.Y., U.S.), Austrian American immunologist and pathologist who received the 1930 Nobel Prize for Physiology or Medicine for his discovery of the major blood groups and the development of the ABO system of blood typing that has made blood transfusion a routine medical practice.
Landsteiner made numerous contributions to both pathological anatomy, histology and immunology, all of which showed, not only his meticulous care in observation and description, but also his biological understanding. But his name will no doubt always be honoured for his discovery in 1901 of, and outstanding work on, the blood groups, for which he was given the Nobel Prize for Physiology or Medicine in 1930.
After receiving his M.D. in 1891 from the University of Vienna, Landsteiner studied organic chemistry with many notable scientists in Europe, including the German chemist Emil Fischer. In 1897 he returned to the University of Vienna, where he pursued his interest in the emerging field of immunology and in 1901 published his discovery of the human ABO blood group system. At that time, although it was known that the mixing of blood from two individuals could result in clumping, or agglutination, of red blood cells, the underlying mechanism of this phenomenon was not understood. Landsteiner discovered the cause of agglutination to be an immunological reaction that occurs when antibodies are produced by the host against donated blood cells. This immune response is elicited because blood from different individuals may vary with respect to certain antigens located on the surface of red blood cells. Landsteiner identified three such antigens, which he labeled A, B, and C (later changed to O). A fourth blood type, later named AB, was identified the following year. He found that if a person with one blood type—A, for example—receives blood from an individual of a different blood type, such as B, the host’s immune system will not recognize the B antigens on the donor blood cells and thus will consider them to be foreign and dangerous, as it would regard an infectious microorganism. To defend the body from this perceived threat, the host’s immune system will produce antibodies against the B antigens, and agglutination will occur as the antibodies bind to the B antigens. Landsteiner’s work made it possible to determine blood type and thus paved the way for blood transfusions to be carried out safely.