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Topic 5 - Blood Transfusion
ABO Blood System
ABO describes the surface antigens located on RBCs, and these vary depending on the individual.
They produce specific glycotransferases, which add sugars to the basic precursor substance (H
substance) and combined with the lipids on the membrane, and this controls the synthesis of enzymes responsible for the addition of carbohydrate residues.
Chromosome 9 encodes for the ABO antigens, in autosomal dominant inheritance.
Alleles A and B are co-dominant, whilst O is recessive to both.
Blood Group A - The individual has anti-B antibodies in his blood.
Blood Group B - The individual has anti-A antibodies in his blood.
Blood Group O - The individual has anti-A and anti-B antibodies in his blood.
2x Different A-antigens (A1 + A2) have been described. The A1 gene makes 80% of the antigens (1 million), whilst the A2 gene makes 20% of the antigens (200,000).
There is a great variation in blood groups, and these can be derived from their historical lineage, if there was no migration then everyone would have the same blood group.
The Bombay Phenotype appears to be an exception as it is characterised by being incapable of producing
H-substance. So, antibodies to H-substance as well as A and B antigens are produced, resulting in them only being able to be transfused with blood from other Bombay phenotype individuals.
Universal Donor and Recipient
Universal Donor - Blood Group O (Excluding Bombay), Rh-.
A precaution must be taken however as small amount of Group O individuals have a very potent amount of anti-A and anti-B antibodies in their blood and this could generate an immune response in the recipient.
Universal Recipient - Blood Group AB, Rh+.
The recipient have no anti-A or anti-B antibodies in their blood.
Rh Blood Group System
In addition to the ABO system there is another 2x genes which encode antigens on the surface on RBCs.
These include 5x main antigens (C,c,D,E,e) but make up 49 in total.
RHD gene - This encodes proteins with the D antigen (and variants)
RHCE gene - This encodes the RhCE protein with the C,E,c and antigens (and variants).
The D antigen is inherited as one gene (RHD) and is dominant. It is inherited on the short arm of ch1, with 2x alleles in which Rh+ is dominant (D is present) and Rh- is recessive (D but others are present).
If both an individual's parents are Rh-, then that individual has to be Rh-.
The ABO and Rhesus genes are not linked and are inherited independently.
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