In most populations, nearly 80 percent of people are secretors. It is believed that the presence of water-soluble antigens in the tissues, particularly in the gastrointestinal tract, is of some selective advantage; attempts to correlate secretion with disease have shown that duodenal ulcers (especially in persons with blood type O) and possibly also rheumatic fever and polio are more common in nonsecretors than in secretors.
The secretor system consists of a pair of alleles, designatedSe (dominant) and se, in genotypesSeSe and Sese (secretors), and sese (nonsecretors); it is thus a good example of a simple Mendelian genetic system (seeheredity). The secretor system is intimately associated with the Lewis system biochemically and genetically. Antigens present in both the secretor system and the Lewis system are encoded by a gene known as FUT2 (fucosyltransferase 2).
For more information on human blood antigens, seeblood group.
This article was most recently revised and updated by Kara Rogers.
ABO blood group system, the classification of human blood based on the inherited properties of red blood cells (erythrocytes) as determined by the presence or absence of the antigens A and B, which are carried on the surface of the red cells. Persons may thus have type A, type B, type O, or type AB blood. The A, B, and O blood groups were first identified by Austrian immunologist Karl Landsteiner in 1901. Seeblood group.
Blood containing red cells with type A antigen on their surface has in its serum (fluid) antibodies against type B red cells. If, in transfusion, type B blood is injected into persons with type A blood, the red cells in the injected blood will be destroyed by the antibodies in the recipient’s blood. In the same way, type A red cells will be destroyed by anti-A antibodies in type B blood. Type O blood can be injected into persons with type A, B, or O blood unless there is incompatibility with respect to some other blood group system also present. Persons with type AB blood can receive type A, B, or O blood.
*Not if the patient's serum contains anti-A1 (antibody to common type A red cell in subgroup A patients).
**Not if the patient is a female less than 45 years old (childbearing possible), unless life-threatening hemorrhage is present and transfusion of Rh-positive blood is lifesaving.
***Not if the patient's serum contains anti-D (antibody to positive red cells), except under unusual medical circumstances.
ABO
A
A* or O
A or AB
ABO
B
B or O
B or AB
ABO
O
O only
O, A, B, or AB
ABO
AB
AB*, A*, B, or O
AB
Rh
positive
positive or negative
positive or negative
Rh
negative
negative or positive**, ***
negative or positive**
How humans inherit A, B, and O blood typesOverview of the ABO blood group system and heredity in humans.
Blood group O is the most common blood type throughout the world, particularly among peoples of South and Central America. Type B is prevalent in Asia, especially in northern India. Type A also is common all over the world; the highest frequency is among Australian Aboriginal peoples, the Blackfoot Indians of Montana, and the Sami people of northern Scandinavia.
The ABO antigens are developed well before birth and remain throughout life. Children acquire ABO antibodies passively from their mother before birth, but by three months of age infants are making their own; it is believed that the stimulus for such antibody formation is from contact with ABO-like antigenic substances in nature. ABO incompatibility, in which the antigens of a mother and her fetus are different enough to cause an immune reaction, occurs in a small number of pregnancies. Rarely, ABO incompatibility may give rise to erythroblastosis fetalis (hemolytic disease of the newborn), a type of anemia in which the red blood cells of the fetus are destroyed by the maternal immune system. This situation occurs most often when a mother is type O and her fetus is either type A or type B.
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