blood groups

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blood groups,

differentiation of blood by type, classified according to immunological (antigenic) properties, which are determined by specific substances on the surface of red blood cells. Blood groups are genetically determined and each is characterized by the presence of a specific complex carbohydratecarbohydrate,
any member of a large class of chemical compounds that includes sugars, starches, cellulose, and related compounds. These compounds are produced naturally by green plants from carbon dioxide and water (see photosynthesis).
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. About 200 different blood group substances have been identified and placed within 19 known blood group systems. The most commonly encountered blood group system is the ABO, or LandsteinerLandsteiner, Karl
, 1868–1943, American medical research worker, b. Vienna, M.D. Univ. of Vienna, 1891. In 1922 he came to the United States to join the staff of the Rockefeller Institute (now Rockefeller Univ.). He later became a U.S. citizen.
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, system. Individuals may contain the A, B, or both A and B antigenic substances, or else lack these substances (type O). In the ABO system an individual who lacks one or more of these antigens will spontaneously develop the corresponding antibodiesantibody,
protein produced by the immune system (see immunity) in response to the presence in the body of antigens: foreign proteins or polysaccharides such as bacteria, bacterial toxins, viruses, or other cells or proteins.
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 (agglutinins) shortly after birth. Thus a person with A type blood will naturally produce anti-B agglutinins, a person with B blood will produce anti-A agglutinins, and a person with O blood will produce anti-A and anti-B agglutinins; but a person with AB blood will not produce any agglutinins in this blood group system. Since these agglutinins are always present in the blood, in blood transfusionblood transfusion,
transfer of blood from one person to another, or from one animal to another of the same species. Transfusions are performed to replace a substantial loss of blood and as supportive treatment in certain diseases and blood disorders.
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 the donor blood must be compatible with the recipient's blood, i.e., the donor's blood must not contain antigen corresponding to the recipient's antibody. Other blood group systems, such as the MNSs, Lewis, Lutheran, and P systems, are not as important in transfusion because they act like true antigen-antibody systems, i.e., antibodies do not appear in blood plasma until the individual has been immunized by exposure to the other blood group antigens as in previous transfusions. In general, blood group substances are weak antigens, and antibody formation after transfusion occurs less than 3% of the time. Immunization can occur by pregnancy as well as by transfusion. Thus, in the Rh factorRh factor,
protein substance present in the red blood cells of most people, capable of inducing intense antigenic reactions. The Rh, or rhesus, factor was discovered in 1940 by K. Landsteiner and A. S.
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 blood group system, an Rh-negative mother carrying an Rh-positive fetus produces anti-Rh antibodies against fetal red blood cells that cross the placenta. Since blood type is a genetic trait that is easy to test and the blood type of an individual is related to his or her parent's blood types by the laws of Mendelism (see under Mendel, GregorMendel, Gregor Johann
, 1822–84, Austrian monk noted for his experimental work on heredity. He entered the Augustinian monastery in Brno in 1843, taught at a local secondary school, and carried out independent scientific investigations on garden peas and other plants until
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), blood group typing is used legally to establish paternity. Anthropologists use the frequency of occurrence of various blood groups as tools to study racial or tribal origins.

Blood groups

Genetically determined markers on the surface of cellular blood elements (red and white blood cells, platelets). In medicine, the matching of ABO and Rh groups of recipients and donors before blood transfusion is of paramount importance; other blood groups also can be implicated in incompatibility. Markers on white cells (histocompatibility antigens) are shared by a number of body tissue cells; these markers are important to the survival of transplanted organs and bone marrow. In law, the recognition of identity between bloodstains found at the scene of a crime and those on clothing of a suspect has resulted in many convictions, and blood typing has served to resolve paternity disputes. From an anthropologic standpoint, some blood groups are unique to specific populations and can be a reflection of tribal origin or migration patterns. Blood groups are also valuable markers in gene linkage analysis, and their study has contributed enormously to the mapping of the human genome.


Human blood can be classified into different groups based on the reactions of red blood cells with blood group antibodies (Table 1). Naturally acquired antibodies, such as anti-A and anti-B antibodies, are normally found in serum from persons whose red blood cells lack the corresponding antigen. It is thought that they are stimulated by antigens present in the environment, and are acquired by infants within months of birth. Because anti-A and anti-B antibodies can cause rapid, life-threatening destruction of incompatible red blood cells, blood for transfusion is always selected to be compatible with the plasma of the recipient. See Antibody, Antigen

ABO blood group system
Blood group RBC antigens Possible genotypes Plasma antibody
A A A/A or A/O anti-B
B B B/B or B/O anti-A
O O/O Anti-A and anti-B
AB A and B A/B

Most blood group antibodies, including Rh antibodies, are immune in origin and do not appear in serum or plasma unless the host is exposed directly to foreign red blood cell antigens. The most common stimulating event is blood transfusion or pregnancy. Because of the large number of different blood group antigens, it is impossible, when selecting blood for transfusion, to avoid transfusing antigens that the recipient lacks. However, these foreign antigens may or may not be immunogenic. A single-unit transfusion of Rh D-positive to an Rh D-negative recipient causes production of anti-D in about 85% of cases. Consequently, in addition to matching for ABO types, Rh D-negative blood is almost always given to Rh D-negative recipients. In pregnancy, fetal red blood cells cross the placenta and enter the maternal circulation, particularly at delivery. The fetal red blood cells may carry paternally derived antigens that are foreign to the mother and stimulate antibody production. These antibodies may affect subsequent pregnancies by destroying the fetal red blood cells and causing a disease known as erythroblastosis fetalis.

Antigens, genes, and blood group systems

Approximately 700 distinct blood group antigens have been identified on human red blood cells. Biochemical analysis has revealed that most antigen structures are either protein or lipid in nature; in some instances, blood group specificity is determined by the presence of attached carbohydrate moieties. The human A and B antigens, for example, can be either glycoprotein or glyco-lipid, with the same attached carbohydrate structure. With few exceptions, blood group antigens are an integral part of the cell membrane.

A number of different concepts have been put forth to explain the genetics of the human blood groups. The presence of a gene in the host is normally reflected by the presence of the corresponding antigen on the red blood cells. Usually, a single locus determines antigen expression, and there are two or more forms of a gene or alleles (for example, a and b) that can occupy a locus. Each individual inherits one allele from each parent. For a given blood group, when the same allele (for example, allele a) is inherited from both parents, the offspring is homozygous for a and only the antigen structure defined by a will be present on the red blood cells. When different alleles are inherited (that is, a and b), the individual is heterozygous for a (and b), and both a and b antigens will be found on the red blood cells. In some blood group systems, several loci govern the expression of multiple blood group antigens within that system. These loci are usually closely linked, located adjacent to each other on the chromosome. Such complex loci may contain multiple alleles and are referred to as haplotypes.

Some 200 antigens have been assigned to 25 different blood group systems. Eight such systems are shown in the Table 2. For a system to be established, the genes involved must be distinct from other blood group system genes, and either they must be polymorphic (that is, two or more alleles, each with an appreciable frequency in a population) or the chromosome location must be known. Antigens that do not meet the criteria for assignment to a specific blood group system have been placed into collections, based primarily on biochemical data or phenotypic association, or into a series of either high- or low-frequency antigens.

Human blood group systems
System ISBT* System Antigens Chromosome
name symbol number in system location Gene products
ABO ABO 001 4 9q34.1-q34.2 A = α-N-acetylgalactosaminyl transferase B = α-galactosyl transferase
MNS MNS 002 43 4q28-q31 GYPA = glycophorin A; 43-kDa single-pass glycoprotein
GYPB = glycophorin B; 25-kDa single-pass glycoprotein
Rh RH 004 45 1p36.13-p34 RHD and RHCE, 30–32-kDa multipass polypeptides
Lutheran LU 005 18 19q13.2 78- and 85-kDa single-pass glycoproteins
Kell KEL 006 23 7q33 93-KDa single-pass glycoprotein
Duffy FY 008 6 1q22-q23 38.5-kDa multipass glycoprotein
Diego DI 010 18 17q12-q21 95–105-kDa multipass glycoprotein
Xg XG 012 1 Xp22.32 22–29-kDa single-pass glycoprotein
*International Society of Blood Transfusion. Chromosome locations of genes/loci are identified by the arm (p = short; q = long), followed by the region, then by the band within the region, in both cases numbered from the centromere; ter = end.

ABO was the first human blood group system to be described. Three major alleles at the ABO locus on chromosome 9 govern the expression of A and B antigens. Gene A encodes for a protein (α-N-acetylgalactosaminyl transferase) that attaches a blood group–specific carbohydrate (α-N-acetyl- d -galactosamine) and confers blood group A activity to a preformed carbohydrate structure called H antigen. Gene B encodes for an α-galactosyl transferase that attaches α- d -galactose and confers blood group B activity to H antigen. In both instances, some H remains unchanged. The O gene has no detectable product; H antigen remains unchanged and is strongly expressed on red blood cells. These three genes account for the inheritance of four common phenotypes: A, B, AB, and O. A and O blood types are the most common, and AB the least common. The A and B genes are codominant; that is, when the gene is present the antigen can be detected. The O gene is considered an amorph since its product cannot be detected. When either A or B antigens are present on red blood cells, the corresponding antibody or antibodies should not be present in the serum or plasma. In adults, when A or B or both are absent from the red blood cells, the corresponding naturally acquired antibody is present in the serum. This reciprocal relationship between antigens on the red blood cells and antibodies in the serum is known as Landsteiner's law. Other ABO phenotypes do exist, but these are quite rare. Further, the A blood type can be subdivided, based on strength of antigen expression, with A1 red blood cells having the most A antigen.

Currently 45 antigens are assigned to the Rh blood group system, although D is the most important. Red blood cells that carry D are called Rh-positive; red blood cells lacking D are called Rh-negative. Other important Rh antigens are C, c, E, and e. Rh antigen expression is controlled by two adjacent homologous structural genes on chromosome 1 that are inherited as a pair or haplotype. The RhD gene encodes D antigen and is absent on both chromosomes of most Rh-negative subjects. The RhCE gene encodes CE protein. Nucleotide substitutions account for amino acid differences at two positions on the CE protein, and result in the Cc and Ee polymorphisms.

Biological role

The function of blood group antigens has been increasingly apparent. Single-pass proteins such as the LU and XG proteins are thought to serve as adhesion molecules that interact with integrins on the surface of white blood cells. Multipass proteins such as band 3, which carries the DI system antigens, are involved in the transportation of ions through the red blood cell membrane bilipid layer. Some blood group antigens are essential to the integrity of the red blood cell membrane, for their absence results in abnormal surface shape; for example, absence of KEL protein leads to the formation of acanthocytes, and absence of RH protein results in stomatocytosis and hemolytic anemia. Many membrane structures serve as receptors for bacteria and other microorganisms. For example, the FY or Duffy protein is the receptor on red blood cells for invasion by Plasmodium vivax, the cause of benign tertian malaria. Particularly significant is the fact that Fy(a-b-) phenotype is virtually nonexistent among Caucasians but has an incidence of around 70% among African-Americans. Presumably, the Fy(a-b-) phenotype evolved as a selective advantage in areas where P. vivax is endemic. Similarly, the S-s-U-red blood cell phenotype in the MNS blood group system affords protection against P. falciparum, or malignant tertian malaria. Yet other blood group antigens can be altered in disease states; A, B, and H antigens are sometimes weakened in leukemia or may be modified by bacterial enzymes in patients with septicemia. See Blood, Immunology

Blood Groups


the division of individuals of the same biological species (for example, humans, monkeys, or horses) by blood characteristics according to structural differences in erythrocytic proteins (glycoproteins), which are determined by different types of biosynthesis.

Three blood groups were first discovered in human beings by the Austrian physician K. Landsteiner in 1900 and a fourth was soon identified. A theory of the main blood groups was formulated in 1907 by the Czech scientist J. Jansky, who designated the groups by numerals. In 1928 the Health Commission of the League of Nations accepted a letter nomenclature of blood groups, now used throughout the world (the ABO system). The A and B factors (antigens, or agglutinogens) contained in erythrocytes and the ɑ and β factors (antibodies, or agglutinins) found in blood plasma determine the classification of a given blood group. In man, the erythrocytes in one of the groups do not contain the A and B agglutinogens, while the ɑ and β agglutinins are found in the serum. This group is called type I, or Oɑβ. In persons with type II blood the erythrocytes contain the A agglutinogen and the plasma the β agglutinin; the letter designation is Aβ. Erythrocytes of blood group III contain the B agglutinogen and the plasma the ɑ agglutinin; the letter designation is B ɑ . Group IV, whose erythrocytes contain the A and B agglutinogens but whose plasma has no agglutinins, is designated ABO. A and B group antigens are also present in leukocytes, thrombocytes, spermatozoa, normal and tumorous tissues, saliva, gastric juice, bile, and amniotic fluid.

When the same kind of agglutinogens and agglutinins (for example A + ɑ , B + β) interact, the erythrocytes adhere to one another (hemagglutination) and then undergo hemolysis. This interaction causes group incompatibility; it can occur only when blood of a different group is transfused.

New isoantigenic characteristics were discovered as research proceeded on the isoantigenic and isoserologic phenomena that determine the division of human beings by blood groups. The Aβ group, it was found, could be subdivided into A, (88 percent of the people belong to this group), wherein the erythrocytes have a marked ability to be agglutinated by serum containing the a agglutinin, and A2 (12 percent), wherein the erythrocytes are agglutinated only if highly active sera are used. Other subgroups have been found as well (A3, A4, A5, Am, A0, Ax, Az, Ag), but they are extremely rare (one per 1,000 persons). The B antigen is highly uniform. The serum of some persons sometimes contains additional isoagglutinins; for example, persons with type A1 or A, B blood may in some cases have the a2 agglutinin, which reacts with A2 and O erythrocytes. Human blood contains other antigens that are combined into the MNP and other systems on the basis of genetic and immunologic characteristics. Next to the ABO system, the Rh system is clinically the most important; somewhat less so are the Kell (K factor) and other systems. In Kell-negative subjects antibodies to the K factor are formed after the first blood transfusion.

The blood group is already evident during the fetal period in man, and it remains unchanged throughout life. In man (and animals) the blood group is determined by hereditary factors (allelic genes). One factor (A or B) is transmitted to a child from the father and one from the mother; each of the two factors present in the parents may be transmitted with equal probability (Mendelian inheritance). Thus, a child born to parents with the first blood group (OO and 00) will also have the first blood group. Parents with the AO (group II) and BO (group III) factors may have a child with any of the four blood groups.

Erythrocytic antigens of the ABO system are determined by the action of a single group of allelic genes. The Rh factor antigen system is transmitted by three different groups of genes (Cc, Dd, Ee). If the dominant C, D, and E genes are present, the corresponding erythrocytic antigens are synthesized in Rh-positive persons. If an individual inherits two recessive genes (for example, dd) he is Rh-negative for the corresponding antigen. With an Rh-positive father who has a double set of dominant genes (DD) and an Rh-negative mother (dd), the fetus will invariably be Rh-positive (Dd) and its blood will be incompatible with the erythrocytic antigens in its mother’s blood. With an Rh-positive father who has one dominant and one recessive gene (Dd) and an Rh-negative mother (dd), the fetus may be either Rh-positive (DD) or Rh-negative (dd). In repeated births of D-Rh-positive children to a d-Rh-negative mother, the mother may become immune against the Rh factor and her antibodies may cause hemolytic disease of the newborn. Rh incompatibility of two persons may be caused by differences in any one of three factors (C, D, E), as well as in two or in all three. All three factors are always inherited together (linked genes). Thus, the individual inherits three factors from each of both parents, but some of them may be dominant while others are recessive. In a small percentage of cases, hemolytic disease of the newborn may occur when the parental blood is incompatible with respect to the erythrocytic antigens of the ABO system (specifically, when the mother has the first blood group and the father the second).

A number of erythrocytic antigen systems in man (for example, P, MN, Kell, and Lewis) are caused by the existence of several groups of allelic genes. The patterns of inheritance in all of these systems are roughly the same as in the ABO. The erythrocytic antigens of one system are inherited independently of the erythrocytic antigens of the other systems. Human erythrocytes may have a set of antigens of many systems or of only a few of them. Fraternal twins in man (as well as the young of multiparous animals) may have different combinations of parental blood group factors.

The patterns of inheritance of blood groups are used in forensic medicine to determine questions of disputed paternity or maternity or to resolve cases of the substitution of children.

Study of the prevalence of various erythrocytic antigens in a given people or ethnographic group may provide clues to the group’s origin and historical contacts with other peoples.

The blood of all blood groups is qualitatively of equal value, but group differences must be taken into account in blood transfusions and in tissue and organ transplants. Blood group compatibility between donor and recipient is a prerequisite for successful transplantation.

The blood group is determined by mixing standard sera on a slide with the blood under study; the latter will belong to the group whose serum was not agglutinated. If all four drops are agglutinated, the blood tested belongs to type AB (IV). Any person can be transfused with blood of his own group or of type O (I). Type O (I) blood may be transfused to recipients of all groups, since type O (I) has no antigens-agglutinogens; the recipient’s agglutinins do not combine with anything and the agglutination reaction does not occur. Type O (I) donors are called “universal” donors. Persons with type AB (IV) blood can be transfused with the blood of any group. Since AB (O) recipients do not have agglutinins, no reaction with any agglutinogen, even with that of a foreign group, occurs. Blood of the same group is ideally compatible for the recipient because persons with types A1 or A1B, which contain the highly active a2 agglutinin, may have a severe reaction to transfusion of blood of groups A2 or O (I). Transfusion of type O (I) blood may produce severe complications if a large quantity of blood with a high titer of ɑβ antibodies in the donor’s blood is transfused; agglutinins of the transfused type O (I) may agglutinate the recipient’s erythrocytes, in which there are corresponding agglutinogens.

The antigenic-serologic substances characterizing the specificity of group biochemical division in human blood have also been found to some extent in a number of animals. However, natural antibodies to blood group antigens are found irregularly and in low titers in animals. Certain erythrocytic antigens are found, therefore, by using sera taken from immunized animals of the same or other species.

The blood groups of swine, cattle, horses, and sheep have been studied in greatest detail. The blood groups of chickens, dogs, cats, rabbits, and certain other species have also been investigated. There are a large number of antigens and antigenic blood group systems in animals. At least 12 systems of erythrocytic antigens and more than 100 of their constituent factors have been described for cattle. The variety of combinations of antigens creates hundreds of varieties of blood groups in animals of a single species. The variety of blood groups decreases after prolonged selection within a single breed. The frequency of occurrence of various erythrocytic antigens is one of the characteristics of a breed. Blood group determination is used in animal husbandry for line breeding, determination of parentage, establishment of breed structure, analysis of genealogical and stud lines, and breed verification for import and export. However, animal blood, regardless of the group to which it belongs, is absolutely incompatible with human blood.


Rukovodstvo po primeneniiu krovi i krovozamenitelei. Edited by A. N. Filatov. Leningrad, 1965.
Kosiakov, P. N. Immunologiia izoantigenov i izoantitel. Moscow, 1965.
Tikhonov, V. N. Geneticheskie sistemy grupp krovi zhivotnykh. Novosibirsk, 1966.
Efroimson, V. P. Vvedenie v meditsinskuiu genetiku, 2nd ed. Moscow, 1968.
Prokop, O., and G. Uhlenbruck. Lehrbuch der menschlichen Blul-und Serumgruppen, 2nd ed. Leipzig, 1966. (Bibliography.)
Race, R. R., and R. Sanger. Blood Groups in Man, 4th ed. Oxford [1962].


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