Two of the antigens found on the surface of red blood cells are called antigen A and antigen B.
What Are Blood Types?
The ABO group system for blood typing is based on which of these antigens you have on your red blood cells. You inherit the particular combination of blood group antigens you have from your parents. How this occurs is not clear yet. The other blood typing system commonly used is the Rhesus system, also called Rh system, named after the Rhesus monkey in which it was first discovered.
The most common blood group in the Australian population is O positive, with about 40 per cent of people having this blood type. On the other hand, only about 1 per cent of Australians are AB negative — the least common type. One difference between the Rhesus system and the ABO group system is that Rh negative people don't usually possess antibodies against RhD unless they have been previously exposed to it , whereas in the ABO group system if the antigen is absent from the red blood cell, the antibody against it is present in the plasma.
Testing to see if you are Rh positive or Rh negative is routinely done during pregnancy, and for blood donors and for people receiving a blood transfusion. When there is a risk of this happening threatened miscarriage, termination, chorionic villus sampling CVS , abdominal trauma, at delivery , an injection called anti-D can be given to the mother to help prevent these antibodies against Rh positive blood being produced.
It is vital that any blood you receive from a donor is compatible with your own blood. If it is not, you can get very sick or even die. If you need blood, ideally it will come from a donor who is the same ABO and Rh type as you. In general, people who are Rh negative should only be given Rh negative blood as it contains no RhD antigens.
If they are given Rh positive blood which does carry the RhD antigen , their immune system will see it as foreign non-self and start producing antibodies against the RhD antigen. A sample of your blood is tested separately against 2 laboratory solutions — one that contains antibodies against the A antigen anti-A and one that contains antibodies against the B antigen anti-B.
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The way your blood reacts to the antibodies shows which antigens your blood contains. For example, if you have the A antigen on your red blood cells you are blood group A , when the solution containing anti-A antibodies is added, your blood cells will react by clumping together agglutinating. And the large-scale application started during the First World War when citric acid was developed as blood clot prevention.
Blood groups are inherited from both parents. The I designation stands for isoagglutinogen , another term for antigen. The gene is located on the long arm of the ninth chromosome 9q I A I B 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.
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 A 1 or B red blood cells, which can help solve the problem of an apparently genetically impossible blood group. The table above summarizes the various blood groups that children may inherit from their parents.
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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.
Introductory Chapter: Blood Groups - From Past to the Future
There are six common alleles in white individuals of the ABO gene that produce one's blood type:  . 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.
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 nucleotides with the group A allele A 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 there are four main lineages of the ABO gene and that mutations creating type O have occurred at least three times in humans. The continued presence of the O alleles is hypothesized to be the result of balancing selection. 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-B antibodies are hypothesized to originate from antibodies produced against Gram-negative bacteria , such as E. 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.
HIV can be neutralized in in vitro experiments using antibodies against blood group antigens specifically expressed on the HIV-producing cell lines.
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. The ABO antigen is also expressed on the von Willebrand factor vWF glycoprotein ,  which participates in hemostasis control of bleeding. Higher levels of vWF are more common amongst people who have had ischemic stroke from blood clotting for the first time.
According to Glass, Holmgren, et al. The mechanisms behind this association with cholera are unclear in the literature. 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. In human cells, the ABO alleles and their encoded glycosyltransferases have been described in several oncologic conditions.
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. 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.
In April , 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. 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.
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The sort of blood is named "enzyme converted to O" ECO blood. Patient trials will be conducted before the method can be relied on in live situations. Another approach to the blood antigen problem is the manufacture of artificial blood , which could act as a substitute in emergencies. During the s, connecting blood groups to personality types became popular in Japan and other areas of the world. 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. From Wikipedia, the free encyclopedia. For other uses, see ABO disambiguation.
The term human blood group systems is defined by International Society of Blood Transfusion as systems in the human species where cell-surface antigens —in particular, those on blood cells—are "controlled at a single gene locus or by two or more very closely linked homologous genes with little or no observable recombination between them",  and include the common ABO and Rh Rhesus antigen systems, as well as many others; thirty-five major human systems are identified as of November In addition to the ABO and Rh systems, the antigens expressed on blood cell membrane surfaces include red blood cell antigens and 33 platelet antigens, as defined serologically.
Blood is composed of cells suspended in a liquid called plasma. Suspended in the plasma are three types of cells:. The most common type of grouping is the ABO blood group system. The varieties of glycoprotein and glycolipid coating on red blood cells divides blood into four groups:. Another antigen, the Rh factor , plays an important part in the grouping of blood. If this is present, the particular blood type is called Rh-positive. If it is absent, it is called Rh-negative. In addition to the ABO and Rh blood group systems, there are more than two hundred [ contradictory ] minor blood groups that can complicate blood transfusions.
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These are known as rare blood types. From Wikipedia, the free encyclopedia. For a less technical article on the common blood types, see Blood type. This article has multiple issues. Please help improve it or discuss these issues on the talk page. Learn how and when to remove these template messages. This article needs attention from an expert in Medicine. See the talk page for details. WikiProject Medicine may be able to help recruit an expert. February This article needs additional citations for verification.