ABO group blood system



The ABO blood group system denotes the presence of one, both, or neither of the A and B antigens on erythrocytes.


The ABO blood group is the most important of the 38 different blood type, or group, classification systems currently recognized.


A mismatch of the ABO group in blood transfusion can cause a potentially fatal adverse reaction after a transfusion, or an unwanted immune response to an organ transplant.


Anti-A and anti-B antibodies are usually IgM antibodies, produced in the first years of life by sensitization to environmental substances such as food, bacteria, and viruses.


ABO blood group antigens present on red blood cells, while IgM antibodies present in the serum.


Group A blood agglutinates with group B, but never with its own type. 


Group B blood agglutinates with group A. 


The red blood cells are inert to the agglutinins which are present in the same serum.


African American: 47% O-positive, 24% A-positive, and 18% B-positive. Latin American: 53% O-positive, 29% A-positive, and 9% B-positive. Asian: 39% O-positive, 27% A-positive, and 25% B-positive. Caucasian: 37% O-positive, 33% A-positive, and 9% B-positive.



ABO epitopes were conferred by sugars, to be specific, N-acetylgalactosamine for the A-type and galactose for the B-type.



The human erythrocyte glycoproteins contain polylactosamine chains that contains ABH substances attached and represent the majority of the antigens.


ABO blood groups are carbohydrate moieties found on the surface of red blood cells. 


Carbohydrate moieties are attached to the H antigen, which constitutes a protein backbone. 


The three variant alleles A, B, and O located on the ABO gene of chromosomes 9q34.


The three variant alleles A, B, and O determine blood type by coding for three glycosyltransferases with distinct substrate specificities. 


Glycosyltransferases trigger the transfer of sugar moieties from activated donor molecules to specific acceptor molecules like the H antigen. 


The A and B alleles differ in eight nucleotides which result in four amino acid substitutions and altered enzyme specificity for the substrate. 


The A glycosyltransferase binds N-acetylgalactosamine and the B glycosyltransferase binds D-galactose. 


The O allele transcribes a nonfunctional glucosyltransferase, leaving the H antigen unmodified.


Carbohydrate chains that determine the ABO blood group.


The O-type antigen does not have a binding site.


A and B are codominant, giving the AB phenotype.


Blood groups are inherited from both parents. 


The ABO blood type is controlled by a single gene, the ABO gene.


The ABO gene is located on the long arm of the ninth chromosome (9q34).


The ABO gene encodes a glycosyltransferase enzyme that modifies the carbohydrate content of the red blood cell antigens. 


The  three types of alleles inferred from classical genetics: i, IA, and IB: isoagglutinogen (antigen).


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 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). 


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.


Occasionally, the blood types of children are not consistent with expectations.


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.


Only 4% of the US population has the AB blood group. 


Some A2 individuals produce antibodies against the A1 antigen. 


Complications can sometimes arise in rare cases when typing the blood.


With DNA sequencing, 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.


Therer are 18 rare alleles, which generally have a weaker glycosylation activity. 


Patients  with weak alleles of A can sometimes express anti-A antibodies, though usually not clinically significant.


Cis AB is a rare variant, in which A and B genes are transmitted together from a single parent.


A,B, O and AB blood groups distribution varies across the world populations.


Food and environmental antigens have epitopes similar enough to A and B glycoprotein antigens, and antibodies can be created against these environmental antigens in the first years of life.


Rarely, environmental antigens can


cross-react with ABO-incompatible red blood cells that it comes in contact with during blood transfusion later in life. 


Anti-A antibodies may originate from immune response towards influenza virus, eliciting a cross-reaction. 


Anti-B antibodies may originate from antibodies produced against Gram-negative bacteria.


Red blood cell surfaces have carbohydrate molecules that serve cell membrane integrity, cell adhesion, transportation of molecules, and act as receptors for extracellular ligands and enzymes.


ABO antigens are also found on epithelial cells with same functions.


The ABO antigens  are expressed on the von Willebrand factor (vWF) glycoprotein.


Type O blood predisposes to bleeding.


30% of the total genetic variation observed in plasma vWF is explained by the effect of the ABO blood group.


Group O blood type individuals normally have significantly lower plasma levels of vWF, and Factor VIII, than do non-O individuals.


In patients with blood group O vWF is degraded more rapidly.


The  gene for ADAMTS13 a vWF-cleaving protease maps to human chromosome 9 band q34.2, the same locus as ABO blood type. 


Higher levels of vWF are more common amongst people who have had ischemic stroke for the first time.


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.


O blood group have an increased risk of infection with cholera, and those O-group individuals who are infected have more severe infections. 


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.


IgM type antibodies do not cross the placenta. 


O-type mothers have IgG ABO antibodies produced and the baby can potentially develop ABO hemolytic disease of the newborn.


The  ABO alleles and their encoded glycosyltransferases have been described in several oncologic conditions, demonstrated that a loss of these enzymes was correlated to malignant bladder and oral epithelia.


In most carcinomas, including oral carcinoma, there is decreased expression of the A and B antigens.


Genome study (GWAS) has identified variants in the ABO locus associated with susceptibility to pancreatic cancer.


Converting  types A, B, and AB blood into type O has been done by using glycosidase enzymes from specific bacteria to strip the blood group antigens from red blood cells: still experimental.

Type A associated with a higher risk of Covid-19.

Type O has a higher risk of infection I, Colorado, Noreau, virus, and Helicobacter pylori.





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