L.2 ABO Blood Group System #2 Flashcards
Who discovered the ABO blood group system?
Landsteiner
Landsteiner discovered the ABO blood group system by mixing the red cells and serum of his staff.
What did Landsteiner demonstrate with his early experiments?
The serum of some people agglutinated the red cells of others
This led to the identification of three types: A, B, and C.
What was C later renamed to?
O
C was renamed O for the German word ‘Ohne’, meaning ‘without’.
Who discovered the fourth blood group AB?
Von Decastello and Sturli
AB was discovered a year later in 1902.
In what year did Landsteiner receive the Nobel Prize?
1930
He received the Nobel Prize in physiology and medicine for his work.
What is the ABO blood group antigens encoded by?
ABO locus
The ABO locus has three alternative (allelic) forms—A, B, and O.
How many possible genotypes can arise from the ABO blood group inheritance?
Six possible genotypes
This occurs as a child receives one allele from each parent.
How many possible blood types (phenotypes) can arise from the ABO blood group system?
Four possible blood types
The four blood types are A, B, AB, and O.
On which chromosome is the ABO locus located?
Chromosome 9
The ABO locus encodes specific glycosyltransferases.
What must be present for A/B antigen synthesis to occur?
H antigen
The H antigen is synthesized by specific enzymes encoded by the H locus and Se locus.
What encodes the enzyme that synthesizes the H antigen in RBCs?
H locus (FUT1)
The enzyme is crucial for A/B antigen synthesis.
What encodes the enzyme that synthesizes the H antigen in saliva?
Se locus (FUT2)
This enzyme is present in other bodily secretions.
How do the A and B alleles differ from each other?
By seven nucleotide substitutions
Four of these substitutions translate into different amino acids.
What determines the A or B specificity of glycosyltransferase?
Residues at positions 266 and 268
These positions influence the specificity of the enzyme.
What causes the O allele to differ from the A allele?
Deletion of guanine at position 261
This deletion results in a frameshift and a non-functional protein.
What type of gene is the O gene classified as?
Recessive or silent
A recessive gene is expressed only when inherited from both parents.
What does codominant mean in the context of blood group antigens?
Equal expression of two different alleles
Blood group antigens A and B are codominant.
What does dominant mean in genetics?
Gene that is expressed over another gene
For example, the A antigen gene is expressed over the O gene.
What are amorphic genes?
Genes that do not express a detectable product
The O gene is an example of an amorphic gene.
What are the ABO antibodies?
Anti-A and anti-B are naturally occurring antibodies present in the sera of individuals who lack the corresponding antigen.
These antibodies are IgM in nature.
How are ABO antibodies produced?
Their production is stimulated when the immune system encounters the ‘missing’ ABO blood group antigens in foods or in micro-organisms.
This occurs at an early age due to sugars similar to ABO antigens found in nature.
Why are ABO antibodies clinically significant?
They are naturally occurring, highly reactive, and can cause acute haemolytic transfusion reactions.
This is particularly dangerous in transfusions with non-group O RBCs.
What happens if a blood group O recipient is transfused with non-group O RBCs?
The anti-A and anti-B in the recipient’s serum binds to corresponding antigens on transfused RBCs, causing rapid intravascular hemolysis.
This can trigger severe complications such as disseminated intravascular coagulation, shock, acute renal failure, and death.
What does Landsteiner’s rule state?
Healthy individuals possess ABO antibodies to the ABO blood group antigens absent from their RBCs.
