Chapter 5 ABO and H Blood Group Systems and Secretor Status

Question 1

What is Landsteiner’s rule?

Answer 1

Healthy individuals possess ABO antibodies to the ABO blood group antigens absent from their RBCs.

Question 2

What are ABO antigens made of?

Answer 2

Glycolipid (attached to ceramide) or glycoprotein.

Intrinsic to RBC membrane.

Question 3

What cells or location in body can ABO antigens be found?

Answer 3

RBCs, lymphocytes, platelets, most epithelial cells and organs.

Soluble form MAY be found in body fluids (except CSF) - attached to carrier protein.

Question 4

When are ABO antigens detectable in a human?

Answer 4

5-6 weeks in utero

Question 5

How is a newborns antigens compare to an adult?

Answer 5

Newborns RBCs have fewer numbers and partially developed antigens. (~25-50% the # of an adult).

Question 6

When does full expression of ABO antigens occur in a child?

Answer 6

2-4 years of age, then remains constant through a healthy life.

Question 7

What genes influence the occurrence and location of ABO antigens?

Answer 7

ABO, H, Se,
Hence:
1. Presence or absence of the ABH antigens on the RBC membrane is controlled by the H gene.
2. Presence or absence of ABH antigens in secretions is influenced by the Se gene.

Question 8

What does the ABO and H antigen genes do?

Answer 8

Produce specific glycosyltransferases, enzymes that catalyze the transfer of a chemical group from one molecule to another –> glycosyl group (in this case).

Question 9

What is the H gene called?

Answer 9

FUT1

Question 10

How common is the H gene?

Answer 10

99.99% have H (either as HH or Hh) on Chromosome 19.

Question 11

What is the Se gene called and what are its alleles?

Answer 11

FUT2
Se and se alleles (se is an amorph)

Question 12

How common is the Se gene?

Answer 12

80% of people have the Se Se or Se se genotype on Chromosome 19.

Question 13

What chromosome are the ABO genes on?

Answer 13

ABO genes –> A, B, and O alleles (O is an amorph) on Chromosome 9.

Question 14

What kind of sugar chain is the precursor structure for A, B and H antigens?

Answer 14

Oligosaccharide chain.

Question 15

What does the H gene do?

Answer 15

1. The H gene codes for a glucosyltransferase enzyme that transfers the immunodominant sugar, L-fucose, to the terminal sugar of the oligosaccharide chain (Type 2).
2. The H antigen is the foundation for the A and/or B antigens a person has.

Question 16

What gene codes for the transferase that adds N-acetylgalactosamine to the terminal sugar of the H antigen?

Answer 16

A gene
Gene Product:
N-acetylgalactosaminyltransferase

(Draw a diagram of the A antigen).

Question 17

What immunodominant sugar does the B gene attach to the terminal sugar of the H antigen?

Answer 17

D-galactose

Question 18

Does the O gene have a transferase?

Answer 18

The “O” gene lacks a transferase therefore it cannot convert any H antigen.

Question 19

What blood group has the most H antigens and which one has the least?

Answer 19

Group O –> most
Group A1B –> Least

O>A2>B>A2B>A1>A1B

Question 20

How does the amount of antigen sites vary between A1, A2 and B gene expression?

Answer 20

Group A1 gene has the highest concentration of transferase.

Antigen sites per cell (million):
A1 - 0.8 to 1.2 million
B gene – 0.6 to 0.8 million
A2 ~ 0.25 million

Question 21

What AB type may be able to produce an H antibody?

Answer 21

A1B may have converted enough H antigen to either A or B that they may be able to produce an H antibody.

Question 22

What percentage of people out of the A and AB types are A1 versus A2?

Answer 22

80% of A or AB individuals are A1.
20% are A2 and A2B

Question 23

What antibody does A2 individual produce?

Answer 23

A2 Phenotype - produce anti-A1.
But only a small % of those people:
1-8% of A2 and ~35% of A2B will.

Question 24

How does A1 and A2 both react to anti-A reagent?

Answer 24

Strongly (3+ or 4+)

Question 25

How do you distinguish between A1 and A2 red cells?

Answer 25

Lectin Dolichos biflorus is used (anti-A1).

Agglutinates with A1 but not with A2.

Question 26

What is the purpose to use lectin Dolichos biflorus?

Answer 26

Its not needed for transfusion purposes but to solve typing discrepancies.

Question 27

What other rare subgroups are there for A antigen?

Answer 27

Aint, A3, Ax, Am, Aend, Ael, and Abantu
(subscripts after the A).

Question 28

When may a rare subgroup of A be suspected?

Answer 28

Rare subgroup of A may be present if:
1. Weak or non agglutination with commercial anti-A and anti-A,B occurs.
2. Anti-A1 is present.
3. Anti-H causes strong agglutination.

Question 29

Why is it important to identify subgroups?

Answer 29

If a weak subgroup is missed in a donor, the incorrect blood group could be given to a patient.

Example: If a A subgroup is classified as group O; the group O recipient receives the unit and has a transfusion reaction (i.e. their anti-A reacts with the donor cells).

Question 30

What is the theory of why we have ABO antibodies?

Answer 30

It is believed we have ABO antigens from exposure to A and B like antigens in the environment (e.g., normal bacterial flora, pollen, etc.).

Question 31

What antibodies are present in a baby before 3-6 months of age?

Answer 31

Maternal antibodies.

Question 32

Is reverse typing done on babies prior to 3-6 months?

Answer 32

No, as the antibodies would be maternal.

Question 33

How do titers of our ABO antibodies vary with age?

Answer 33

Titers reach maximum levels by 5 to 10 years of age and decrease as an individual ages.

Question 34

What type of antibody is anti-A and anti-B?

Answer 34

Predominantly IgM.

Binds to complement.
Reacts optimally during immediate spin in cross-matching.

Question 35

What antibody type is Anti-AB in group O individuals? What is the implication of this?

Answer 35

Usually IgG.
Therefore can cross the placenta and cause HDFN*.

*Note: Common but not severe. Often place baby under light to help with bilirubin levels.

Question 36

Who is the universal donor and the universal recipient for RBC transfusions?

Answer 36

Group O: universal donor
Group AB: universal recipient

Question 37

What is the sequence preference for RBC transfusions? plasma transfusions?

Answer 37

Preference is ABO-identical unit, followed by ABO-compatible unit in RBC transfusions.

ABO identical unit is preferred or compatible for plasma transfusions.

See Slide 29 and study that for clarity. You must know that!

Question 38

What can happen to the patient with an incompatible RBC transfusion?

Answer 38

Acute hemolytic transfusion reaction.

Question 39

What type of blood is required for whole blood transfusions?

Answer 39

ABO identical unit.

Whole blood transfusions done in the US but not Cda.

Question 40

What are the universal donor and recipient for plasma transfusions?

Answer 40

Donor unit antibodies must be compatible with recipient’s RBCs.
Group AB: universal donor.
Group O: universal recipient.

Question 41

What is the bombay phenotype?

Answer 41

RBCs lack the H antigen –> hh.

The h gene is an amorph and results in little or no production of L-fucosyltransferase.

Question 42

What antibodies does a person with the bombay phenotype carry?

Answer 42

Patients’ serum contains anti-A, anti-B and also anti-H.

Anti-H will agglutinate strongly with O red cells.

Question 43

What blood type can a bombay phenotype receive from a donor?

Answer 43

For a transfusion, a bombay type must receive blood from another bombay type, i.e. only autologous units or rare donor files can be used.

Question 44

What percentage of the populations are secretors?

Answer 44

80% of the population
SeSe (homozygous)
Sese (heterozygous)
20% are nonsecretors (sese)