ABO system Flashcards
What is the most common blood group in Ireland
O+
What is the least common blood group in ireland
AB-
Who was the ABO blood group system first described by and when?
Karl Landsteiner in 1901
Why is the ABO system the most clinically important blood group system in transfusion
- Nature of the ABO antibodies -> they are mainly IgM and cause intravascular haemolysis of incompatible red cells via complement activation.
- ABO incompatibility accounts for a significant number of fatal haemolytic transfusion reactions.
Reasons for severe haemolytic transfusion rxns (4)
- Mislabelling of blood sample -> patient sample A being labelled with patient B details for blood grouping
- Mislabelling donated blood packs -> blood packs are labelled with the name and other identifiers of patient receiving the blood
- Transfusing the wrong patient
- Serological errors -> patient or donor blood misgrouped in the lab
Where are the three common alleles (A, B and O) located
At the ABO locus on chromosome 9
What is located on chromosome 19
The H and h alleles
What are the foundation blocks for the building of the ABO blood group antigens
Oligosaccharide chains
Where are these oligosaccharide chains found
Red blood cells have the oligosaccharide chains attached to the membrane
What does the H gene code for
The transferase enzyme that adds fucose to the precursor oligosaccharide chains on the red cell membranes
What does the H antigen act as
The precursor material on which A and B antigens are built
What do the A and B genes encode
A transferase enzyme
What does the transferase enzyme encoded by the A and B genes do
It acts upon the H precursor antigen material to produce the A and B antigen
What is the O gene known as and why
It is known as an amorph (is silent). This is beacuse the O gene does not encode a functional enzyme and therefore does not produce a detectable antigen
What do the red cells of a group O person have
An abundant amount of H antigen but no A or B antigens
What is the full name of the enzyme that the A gene codes for
Alpha 1,3-Nacetyl-galactosaminyltransferase
How is the A antigen produced
The enzyme alpha 1,3-Nacetylgalactosaimyltransferase uses the H antigen as a substrate and catalyses the addition of the sugar N-acetyl galactosamine to the terminal galactose of the oligosaccharide chain to produce the A antigen
The A enzyme can only produce the A antigen if a H antigen is already present
What is the full name of the enzyme that the B gene codes for
Alpha 1,3-galactosyltransferase
How is the B antigen produced
The enzyme 1,3-galactosyltransferase uses the H antigen as a substrate and catalyses the addition of the sugar D-galactose to the terminal galactose of the oligosaccharide chain to produce the B antigen
What is the Bombay blood group
- A rare case where individuals are homozygous for the h allele (lack the H gene) and cannot form the H antigen,the precursor for the A and B antigens
- Bombay red cells type as blood group O
- The serum of a Bombay individual contains Anti H, Anti A and Anti B and will react if transfused with blood that contains the A, B or H antigens
- Bombay blood frozen for emergency requirements
What are ABO antibodies thought to be stimulated by?
Bacteria, viruses and other environmental antigens. (Bacteria and viruses known to contain structures that are chemcally similar to human A and B antigens and can stimulate the production of Anti A and Anti B in individuals who lack these)
What type of antibody are most ABO antibodies
IgM antibodies, however some individuals also have some IgG (at low levels)
How long after birth can ABO antibodies be demonstrated
3-6 months after birth
What temp do ABO antibodies best react at? (mainly IgM antibodies)
4-22 degrees C
