W9TL2 - ABO Blood Group

Question 1

Distribution of ABO Blood Groups in Australia and the Antigens they Possess

Answer 1

A - 39%, A antigen
B - 11.5%, B antigen
AB - 3.5%, A and B antigen
O - 46%, H antigen

Question 2

ABO Antigens

Answer 2

Not fully developed at birth
Carbohydrate (CHO) in nature
Formed from a common precursor substance
- type 1 and type 2
- chain of specific sugars
- type 2 is found only on RBC surface
H antigen is formed from common precursor substance
A and B antigens are formed from H antigen

Question 3

ABO Antigen Production

Answer 3

H, A, and B antigens are produced by the addition of a single CHO residue to the precursor substance
- “immunodominant” sugar/residue
- defines the antigen
Performed by enzymes called glycosyltransferases
Glycosyltransferases are encoded by different genes
- H, A, and B genes encode specific glycosyltransferases
- O gene is an amorph gene

Question 4

ABO Antigen Structure

Answer 4

H antigen
- FUT1 (H) gene encodes for α-2-L-fucosyltransferase
- adds L-fucose to terminal D-galactose of type 2 precursor substance
A antigen
- A gene encodes for α-3-N acetylgalactosaminyltransferase
- adds N-acetyl-D-galactosamine to terminal D-galactose of H antigen
B Antigen
- gene encodes for α-3-D-galactosyltransferase
- adds D-galactose to terminal D-galactose of H antigen

Question 5

ABO Genetics

Answer 5

ABO gene is on chromosome 9
7 exons
Exons 6 and 7 encode the respective glycosyltransferase
Inheritance is autosomal co-dominant
- presence of one allele = antigen expression
- individuals have two alleles, both are expressed

Question 6

ABO Antibodies

Answer 6

“Naturally occurring”
- produced without prior exposure to antigen on RBC
- bacteria of the gut have the same antigenic structure as the ABO antigens
Usually IgM, but can also be IgG
Bind complement
React optimally at RT
Not detected until 3-6 months of age
Clinically very important
- cause intravascular haemolysis => death
- cause haemolytic disease of the newborn

Question 7

Universal Donors and Recpients

Answer 7

Group O individuals are universal donors
- can donate pRBCs to people of any ABO blood group
Group AB individuals are universal recipients
- can receive pRBCs of any ABO blood group

Question 8

Universal Compatibility Between Blood Product

Answer 8

Universal donor
- pRBCs: group O (doesn’t have A or B antigen)
- plasma: group AB (doesn’t contain anti-A or anti-B)
Universal recipient
- pRBCs: group AB (they express both A and B antigens)
- plasma - group O (already contains anti-A and anti-B)

Question 9

ABO Subgroups

Answer 9

Arise from mutations in the glycosyltransferase genes
Relevant glycosyltransferase has diminished activity
Decreased antigen expression on RBC surface
Both Group A and Group B
Rare but important to identify