ABO blood group system
The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes. In human blood transfusions it is the most important of the 35 different blood type (or group) classification systems currently recognized. A very rare (in modern medicine) mismatch in this, or any other serotype, can cause a serious, potentially fatal, adverse reaction after a transfusion, or a contra-indicated immune response to an organ transplant. The associated anti-A and anti-B antibodies are usually IgM antibodies, which are produced in the first years of life by sensitization to environmental substances, such as food, bacteria, and viruses. ABO blood types are also present in some other animals, for example rodents and apes, such as chimpanzees, bonobos, and gorillas.
- 1 History of discoveries of the blood types
- 2 Alteration of ABO antigens for transfusion
- 3 Genetics
- 4 Clinical relevance
- 5 Pseudoscience
- 6 Data tables
- 7 See also
- 8 References
- 9 Further reading
- 10 External links
History of discoveries of the blood types
The ABO blood group system is widely credited to have been discovered by the Austrian scientist Karl Landsteiner, who identified the O, A, and B blood types in 1900. Landsteiner originally described the O blood type as type "C", and in parts of Europe it is rendered as "0" (zero), signifying the lack of A or B antigen. Landsteiner was awarded the Nobel Prize in Physiology or Medicine in 1930 for his work. Alfred von Decastello and Adriano Sturli discovered the fourth type, AB, in 1902.
It was subsequently found that the Czech serologist Jan Janský had independently pioneered the classification of human blood into four groups in 1907, but Landsteiner's independent discovery had been accepted by the scientific world while Janský remained then in relative obscurity. However, in 1921 an American medical commission acknowledged Janský's classification. Jan Janský is nowadays credited with the first classification of blood into the four types (I, II, III, IV).
Janský's classification remains in use today. In Russia and states of the former USSR, blood types O, A, B, and AB are respectively designated I, II, III, and IV. The designation A and B with reference to blood groups was proposed by Ludwik Hirszfeld.
In America, W.L. Moss published his own (very similar) work in 1910.
Ludwik Hirszfeld and E. von Dungern discovered the heritability of ABO blood groups in 1910–11. Felix Bernstein demonstrated the correct blood group inheritance pattern of multiple alleles at one locus in 1924. Watkins and Morgan, in England, discovered that the ABO epitopes were conferred by sugars, to be specific, N-acetylgalactosamine for the A-type and galactose for the B-type. After much published literature claiming that the ABH substances were all attached to glycosphingolipids, Finne et al. (1978) found that the human erythrocyte glycoproteins contain polylactosamine chains that contains ABH substances attached and represent the majority of the antigens. The main glycoproteins carrying the ABH antigens were identified to be the Band 3 and Band 4.5 proteins and glycophorin. Later, Yamamoto's group showed the precise glycosyl transferase set that confers the A, B and O epitopes.
Alteration of ABO antigens for transfusion
In April 2007, an international team of researchers announced in the journal Nature Biotechnology an inexpensive and efficient way to convert types A, B, and AB blood into type O. This is done by using glycosidase enzymes from specific bacteria to strip the blood group antigens from red blood cells. The removal of A and B antigens still does not address the problem of the Rh blood group antigen on the blood cells of Rh positive individuals, and so blood from Rh negative donors must be used. Patient trials will be conducted before the method can be relied on in live situations.
Blood groups are inherited from both parents. The ABO blood type is controlled by a single gene (the ABO gene) with three types of alleles inferred from classical genetics: i, IA, and IB. The I designation stands for isoagglutinogen, another term for antigen. The gene encodes a glycosyltransferase—that is, an enzyme that modifies the carbohydrate content of the red blood cell antigens. The gene is located on the long arm of the ninth chromosome (9q34).
The IA allele gives type A, IB gives type B, and i gives type O. As both IA and IB are dominant over i, only ii people have type O blood. Individuals with IAIA or IAi have type A blood, and individuals with IBIB or IBi have type B. IAIB people have both phenotypes, because A and B express a special dominance relationship: codominance, which means that type A and B parents can have an AB child. A couple with type A and type B can also have a type O child if they are both heterozygous (IBi,IAi) The cis-AB phenotype has a single enzyme that creates both A and B antigens. The resulting red blood cells do not usually express A or B antigen at the same level that would be expected on common group A1 or B red blood cells, which can help solve the problem of an apparently genetically impossible blood group.
|Blood group inheritance|
|Genotype||ii (OO)||IAi (AO)||IAIA (AA)||IBi (BO)||IBIB (BB)||IAIB (AB)|
OO OO OO OO
|O or A
AO OO AO OO
AO AO AO AO
|O or B
BO OO BO OO
BO BO BO BO
|A or B
AO BO AO BO
|A||IAi (AO)||O or A
AO AO OO OO
|O or A
AA AO AO OO
AA AA AO AO
|O, A, B or AB
AB AO BO OO
|B or AB
AB AB BO BO
|A, B or AB
AA AB AO BO
AO AO AO AO
AA AO AA AO
AA AA AA AA
|A or AB
AB AO AB AO
AB AB AB AB
|A or AB
AA AB AA AB
|B||IBi (BO)||O or B
BO BO OO OO
|O, A, B or AB
AB BO AO OO
|A or AB
AB AB AO AO
|O or B
BB BO BO OO
BB BB BO BO
|A, B or AB
AB BB AO BO
BO BO BO BO
|B or AB
AB BO AB BO
AB AB AB AB
BB BO BB BO
BB BB BB BB
|B or AB
AB BB AB BB
|AB||IAIB (AB)||A or B
AO AO BO BO
|A, B or AB
AA AO AB BO
|A or AB
AA AA AB AB
|A, B or AB
AB AO BB BO
|B or AB
AB AB BB BB
|A, B, or AB
AA AB AB BB
The table above summarizes the various blood groups that children may inherit from their parents. Genotypes are shown in the second column and in small print for the offspring: AO and AA both test as type A; BO and BB test as type B. The four possibilities represent the combinations obtained when one allele is taken from each parent; each has a 25% chance, but some occur more than once.
|Blood group inheritance by phenotype only|
|O||O||O or A||O or B||A or B|
|A||O or A||O or A||O, A, B or AB||A, B or AB|
|B||O or B||O, A, B or AB||O or B||A, B or AB|
|AB||A or B||A, B or AB||A, B or AB||A, B or AB|
Historically, ABO blood tests were used in paternity testing, but in 1957 only 50% of American men falsely accused were able to use them as evidence against paternity. Occasionally, the blood types of children are not consistent with expectations—for example, a type O child can be born to an AB parent—due to rare situations, such as Bombay phenotype and cis AB.
The A blood type contains about 20 subgroups, of which A1 and A2 are the most common (over 99%). A1 makes up about 80% of all A-type blood, with A2 making up almost all of the rest. These two subgroups are not always interchangeable as far as transfusion is concerned, as some A2 individuals produce antibodies against the A1 antigen. Complications can sometimes arise in rare cases when typing the blood.
With the development of DNA sequencing, it has been possible to identify a much larger number of alleles at the ABO locus, each of which can be categorized as A, B, or O in terms of the reaction to transfusion, but which can be distinguished by variations in the DNA sequence. There are six common alleles in white individuals of the ABO gene that produce one's blood type:
|B101 (B1)||O01 (O1)
The same study also identified 18 rare alleles, which generally have a weaker glycosylation activity. People with weak alleles of A can sometimes express anti-A antibodies, though these are usually not clinically significant as they do not stably interact with the antigen at body temperature.
Cis AB is another rare variant, in which A and B genes are transmitted together from a single parent.
Distribution and evolutionary history
The distribution of the blood groups A, B, O and AB varies across the world according to the population. There are also variations in blood type distribution within human subpopulations.
In the UK, the distribution of blood type frequencies through the population still shows some correlation to the distribution of placenames and to the successive invasions and migrations including Norsemen, Danes, Saxons, Celts, and Normans who contributed the morphemes to the placenames and the genes to the population.
The two common O alleles, O01 and O02, share their first 261 nucleotides with the group A allele A01. However, unlike the group A allele, a guanosine base is subsequently deleted. A premature stop codon results from this frame-shift mutation. This variant is found worldwide, and likely predates human migration from Africa. The O01 allele is considered to predate the O02 allele.
Some evolutionary biologists theorize that the IA allele evolved first, followed by O (by the deletion of a single nucleotide, shifting the reading frame) and then IB. This chronology accounts for the percentage of people worldwide with each blood type. It is consistent with the accepted patterns of early population movements and varying prevalent blood types in different parts of the world: for instance, B is very common in populations of Asian descent, but rare in ones of Western and Northern European descent. Another theory states that there are four main lineages of the ABO gene and that mutations creating type O have occurred at least three times in humans. From oldest to youngest, these lineages comprise the following alleles: A101/A201/O09, B101, O02 and O01. The continued presence of the O alleles is hypothesized to be the result of balancing selection. Both theories contradict the previously held theory that type O blood evolved first.
It is possible that food and environmental antigens (bacterial, viral, or plant antigens) have epitopes similar enough to A and B glycoprotein antigens. The antibodies created against these environmental antigens in the first years of life can cross-react with ABO-incompatible red blood cells that it comes in contact with during blood transfusion later in life. Anti-A antibodies are hypothesized to originate from immune response towards influenza virus, whose epitopes are similar enough to the α-D-N-galactosamine on the A glycoprotein to be able to elicit a cross-reaction. Anti-B antibodies are hypothesized to originate from antibodies produced against Gram-negative bacteria, such as E. coli, cross-reacting with the α-D-galactose on the B glycoprotein.
However, it is more likely that the force driving evolution of allele diversity is simply negative frequency-dependent selection; cells with rare variants of membrane antigens are more easily distinguished by the immune system from pathogens carrying antigens from other hosts. Thus, individuals possessing rare types are better equipped to detect pathogens. The high within-population diversity observed in human populations would, then, be a consequence of natural selection on individuals.
The carbohydrate molecules on the surfaces of red blood cells have roles in cell membrane integrity, cell adhesion, membrane transportation of molecules, and acting as receptors for extracellular ligands, and enzymes. ABO antigens are found having similar roles on epithelial cells as well as red blood cells.
Bleeding and thrombosis (von Willebrand factor)
The ABO antigen is also expressed on the von Willebrand factor (vWF) glycoprotein, which participates in hemostasis (control of bleeding). In fact, having type O blood predisposes to bleeding, as 30% of the total genetic variation observed in plasma vWF is explained by the effect of the ABO blood group, and individuals with group O blood normally have significantly lower plasma levels of vWF (and Factor VIII) than do non-O individuals. In addition, vWF is degraded more rapidly due to the higher prevalence of blood group O with the Cys1584 variant of vWF (an amino acid polymorphism in VWF): the gene for ADAMTS13 (vWF-cleaving protease) maps to the ninth chromosome (9q34), the same locus as ABO blood type. Higher levels of vWF are more common amongst people who have had ischemic stroke (from blood clotting) for the first time. The results of this study found that the occurrence was not affected by ADAMTS13 polymorphism, and the only significant genetic factor was the person's blood group.
Compared to O group individuals, non-O group (A, AB, and B) individuals have a 14% reduced risk of squamous cell carcinoma and 4% reduced risk of basal cell carcinoma. Conversely, type O blood is associated with a reduced risk of pancreatic cancer. The B antigen links with increased risk of ovarian cancer. Gastric cancer has reported to be more common in blood group A and least in group O.
According to Glass, Holmgren, et al., those in the O blood group have an increased risk of infection with cholera, and those O-group individuals who are infected have more severe infections. The mechanisms behind this association with cholera are unclear in the literature.
ABO hemolytic disease of the newborn
ABO blood group incompatibilities between the mother and child does not usually cause hemolytic disease of the newborn (HDN) because antibodies to the ABO blood groups are usually of the IgM type, which do not cross the placenta. However, in an O-type mother, IgG ABO antibodies are produced and the baby can potentially develop ABO hemolytic disease of the newborn.
In human cells, the ABO alleles and their encoded glycosyltransferases have been described in several oncologic conditions. Using anti-GTA/GTB monoclonal antibodies, it was demonstrated that a loss of these enzymes was correlated to malignant bladder and oral epithelia. Furthermore, the expression of ABO blood group antigens in normal human tissues is dependent the type of differentiation of the epithelium. In most human carcinomas, including oral carcinoma, a significant event as part of the underlying mechanism is decreased expression of the A and B antigens. Several studies have observed that a relative down-regulation of GTA and GTB occurs in oral carcinomas in association with tumor development. More recently, a genome wide association study (GWAS) has identified variants in the ABO locus associated with susceptibility to pancreatic cancer.
A multi-locus genetic risk score study based on a combination of 27 loci, including the ABO gene, identified individuals at increased risk for both incident and recurrent coronary artery disease events, as well as an enhanced clinical benefit from statin therapy. The study was based on a community cohort study (the Malmo Diet and Cancer study) and four additional randomized controlled trials of primary prevention cohorts (JUPITER and ASCOT) and secondary prevention cohorts (CARE and PROVE IT-TIMI 22).
Other popular but unsupported ideas include the use of a blood type diet, claims that group A causes severe hangovers, group O is associated with perfect teeth, and those with blood group A2 have the highest IQs. Scientific evidence in support of these concepts is nonexistent.
|ABO allele frequencies in Korean, Japanese and German populations.|
|aKorean versus Japanese, p<0.001. bKorean versus Japanese, p<0.01.
cKorean versus German, p<0.001. dKorean versus German, p<0.01.
eKorean versus German, p<0.05 (Fisher's exact probability test).
1Fukumori et al., 1996. 2Nishimukai et al., 1996.
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