A blood type (also called a blood group) is a classification ofblood based on the presence or absence of inherited antigenicsubstances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrates, glycoproteins, orglycolipids, depending on the blood group system. Some of these antigens are also present on the surface of other types of cells of various tissues. Several of these red blood cell surface antigens can stem from one allele (or very closely linked genes) and collectively form a blood group system.[1] Blood types are inheritedand represent contributions from both parents. A total of 30 human blood group systems are now recognized by the International Society of Blood Transfusion (ISBT).[2]
Many pregnant women carry a fetus with a different blood type from their own, and the mother can form antibodies against fetal RBCs. Sometimes these maternal antibodies are IgG, a small immunoglobulin, which can cross the placenta and causehemolysis of fetal RBCs, which in turn can lead to hemolytic disease of the newborn, an illness of low fetal blood counts that ranges from mild to severe.[3]
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[edit]Blood group systems
A complete blood type would describe a full set of 30 substances on the surface of RBCs, and an individual's blood type is one of the many possible combinations of blood-group antigens.[2] Across the 30 blood groups, over 600 different blood-group antigens have been found,[4] but many of these are very rare, some being found mainly in certain ethnic groups.
Almost always, an individual has the same blood group for life, but very rarely an individual's blood type changes through addition or suppression of an antigen in infection, malignancy, or autoimmune disease.[5][6][7][8] An example of this rare phenomenon is the case ofDemi-Lee Brennan, an Australian citizen, whose blood group changed after a liver transplant.[9][10] Another more common cause in blood-type change is a bone marrow transplant. Bone-marrow transplants are performed for many leukemias and lymphomas, among other diseases. If a person receives bone marrow from someone who is a different ABO type (e.g., a type A patient receives a type O bone marrow), the patient's blood type will eventually convert to the donor's type.
Some blood types are associated with inheritance of other diseases; for example, the Kell antigen is sometimes associated with McLeod syndrome.[11] Certain blood types may affect susceptibility to infections, an example being the resistance to specific malaria species seen in individuals lacking the Duffy antigen.[12] The Duffy antigen, presumably as a result of natural selection, is less common in ethnic groups from areas with a high incidence of malaria.[13]
[edit]ABO blood group system
Main article: ABO blood group system
The ABO system is the most important blood-group system in human-blood transfusion. The associated anti-A and anti-B antibodies are usuallyImmunoglobulin M, abbreviated IgM, antibodies. ABO IgM antibodies are produced in the first years of life by sensitization to environmental substances such as food, bacteria, and viruses. The O in ABO is often called 0 (zero, or null) in other languages.[14]
| Phenotype | Genotype |
|---|---|
| A | AA or AO |
| B | BB or BO |
| AB | AB |
| O |
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