The development of blood transfusion, a potentially life-saving technique, was hampered by a serious problem: many times the patient would suffer an often fatal "transfusion reaction," apparently to the donated blood itself. The cause of such reactions was unknown.
In the late 1800s, several researchers noted that when blood cells from one animal or person were mixed with cells from another, agglutination occurred--the cells stuck together in clumps. An Austrian physician named Karl Landsteiner showed what caused this clumping in 1900. Mixing different samples of human red blood cells and human sera (blood without the cells), Landsteiner observed that one mixture would clump, while another different mixture would not. He determined that the different reactions were caused by differing antigens in the red blood cells reacting to antibodies in the sera. In 1901, Landsteiner published a paper describing a method of categorizing human blood into three groups, or types: A, B, and C (later called O). In 1902, two of Landsteiner's assistants, Alfred von Decastello and Adriano Sturli, found a fourth blood type, AB. Depending on the antibodies and antigens present in each type of blood, serum from one type can cause clumping in another type. By identifying the blood type of both donor and recipient in a potential transfusion, it was now possible to avoid mixing bloods that would precipitate agglutination. Landsteiner's discovery paved the way to safe blood transfusion, and the physician (now an American citizen) received the Nobel Prize in medicine or physiology for his work in 1930.
Landsteiner and his associates, Alexander S. Wiener (1907-1976) and Philip Levine (1900-), discovered another important blood group, the Rh system, or Rhesus factor, in 1940. People with the Rh factor present in their blood are termed Rh positive; people without it are Rh negative. An Rh negative person exposed to Rh positive blood forms antibodies against the Rh factor. Once this has occurred, any future transfusion of Rh positive blood can cause a severe, possibly fatal, transfusion reaction. A fetus carried by an Rh-negative woman who has developed Rh antibodies (perhaps by previously carrying an Rh-positive baby) can have its red blood cells attacked by these antibodies, a condition called erythroblastosis fetalis, which may result in brain damage or death. The Landsteiner group's identification of the Rh factor made it possible to avoid Rh-incompatible transfusions and to diagnose and thus correct fetal Rh incompatibilities via a blood transfusion in the womb.
In 1910, Emil von Dungern and Ludwik Hirszfeld (1884-1954) demonstrated that blood groups are inherited, a concept confirmed by B. A. Bernstein in 1924. This, coupled with the discovery of many more blood groups--Landsteiner and his group found M, N, and P in 1927, for example--stimulated interest in the use of blood types in studying heredity. Soon, blood typing was being used in court cases to establish or disprove paternity. In the mid-twentieth century, American immunochemist William C. Boyd (1903-) pioneered the study of blood types as distributed throughout the human race, tracing the evolution and migration of the species and demonstrating that there is no genetically "pure" race, as all blood types are present in all human populations.
The most common blood types in the United States are O+ (O Rh-positive), found in 38 percent of the population, and A+, found in 34 percent of people. In an emergency, anyone can receive type O red blood cells. For this reason, people with type O blood are often called "universal donors."
Today an estimated 14 million units of blood are donated by about 8 million donors each year. These units are transfused into as many as 4 million patients annually, according to the American Association of Blood Banks. Among those who benefit from blood transfusions are accident victims, patients undergoing surgery, and people receiving treatment for diseases such as cancer and sickle cell disease.
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