Chapter 5 ABO and H Blood Group Systems and Secretor Status Flashcards
What is Landsteiner’s rule?
Healthy individuals possess ABO antibodies to the ABO blood group antigens absent from their RBCs.
What are ABO antigens made of?
Glycolipid (attached to ceramide) or glycoprotein.
Intrinsic to RBC membrane.
What cells or location in body can ABO antigens be found?
RBCs, lymphocytes, platelets, most epithelial cells and organs.
Soluble form MAY be found in body fluids (except CSF) - attached to carrier protein.
When are ABO antigens detectable in a human?
5-6 weeks in utero
How is a newborns antigens compare to an adult?
Newborns RBCs have fewer numbers and partially developed antigens. (~25-50% the # of an adult).
When does full expression of ABO antigens occur in a child?
2-4 years of age, then remains constant through a healthy life.
What genes influence the occurrence and location of ABO antigens?
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.
What does the ABO and H antigen genes do?
Produce specific glycosyltransferases, enzymes that catalyze the transfer of a chemical group from one molecule to another –> glycosyl group (in this case).
What is the H gene called?
FUT1
How common is the H gene?
99.99% have H (either as HH or Hh) on Chromosome 19.
What is the Se gene called and what are its alleles?
FUT2
Se and se alleles (se is an amorph)
How common is the Se gene?
80% of people have the Se Se or Se se genotype on Chromosome 19.
What chromosome are the ABO genes on?
ABO genes –> A, B, and O alleles (O is an amorph) on Chromosome 9.
What kind of sugar chain is the precursor structure for A, B and H antigens?
Oligosaccharide chain.
What does the H gene do?
- 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).
- The H antigen is the foundation for the A and/or B antigens a person has.
What gene codes for the transferase that adds N-acetylgalactosamine to the terminal sugar of the H antigen?
A gene
Gene Product:
N-acetylgalactosaminyltransferase
(Draw a diagram of the A antigen).
What immunodominant sugar does the B gene attach to the terminal sugar of the H antigen?
D-galactose
Does the O gene have a transferase?
The “O” gene lacks a transferase therefore it cannot convert any H antigen.
What blood group has the most H antigens and which one has the least?
Group O –> most
Group A1B –> Least
O>A2>B>A2B>A1>A1B
How does the amount of antigen sites vary between A1, A2 and B gene expression?
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
What AB type may be able to produce an H antibody?
A1B may have converted enough H antigen to either A or B that they may be able to produce an H antibody.
What percentage of people out of the A and AB types are A1 versus A2?
80% of A or AB individuals are A1.
20% are A2 and A2B
What antibody does A2 individual produce?
A2 Phenotype - produce anti-A1.
But only a small % of those people:
1-8% of A2 and ~35% of A2B will.
How does A1 and A2 both react to anti-A reagent?
Strongly (3+ or 4+)
How do you distinguish between A1 and A2 red cells?
Lectin Dolichos biflorus is used (anti-A1).
Agglutinates with A1 but not with A2.
What is the purpose to use lectin Dolichos biflorus?
Its not needed for transfusion purposes but to solve typing discrepancies.
What other rare subgroups are there for A antigen?
Aint, A3, Ax, Am, Aend, Ael, and Abantu
(subscripts after the A).
When may a rare subgroup of A be suspected?
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.
Why is it important to identify subgroups?
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).
What is the theory of why we have ABO antibodies?
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.).
What antibodies are present in a baby before 3-6 months of age?
Maternal antibodies.
Is reverse typing done on babies prior to 3-6 months?
No, as the antibodies would be maternal.
How do titers of our ABO antibodies vary with age?
Titers reach maximum levels by 5 to 10 years of age and decrease as an individual ages.
What type of antibody is anti-A and anti-B?
Predominantly IgM.
Binds to complement.
Reacts optimally during immediate spin in cross-matching.
What antibody type is Anti-AB in group O individuals? What is the implication of this?
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.
Who is the universal donor and the universal recipient for RBC transfusions?
Group O: universal donor
Group AB: universal recipient
What is the sequence preference for RBC transfusions? plasma transfusions?
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!
What can happen to the patient with an incompatible RBC transfusion?
Acute hemolytic transfusion reaction.
What type of blood is required for whole blood transfusions?
ABO identical unit.
Whole blood transfusions done in the US but not Cda.
What are the universal donor and recipient for plasma transfusions?
Donor unit antibodies must be compatible with recipient’s RBCs.
Group AB: universal donor.
Group O: universal recipient.
What is the bombay phenotype?
RBCs lack the H antigen –> hh.
The h gene is an amorph and results in little or no production of L-fucosyltransferase.
What antibodies does a person with the bombay phenotype carry?
Patients’ serum contains anti-A, anti-B and also anti-H.
Anti-H will agglutinate strongly with O red cells.
What blood type can a bombay phenotype receive from a donor?
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.
What percentage of the populations are secretors?
80% of the population
SeSe (homozygous)
Sese (heterozygous)
20% are nonsecretors (sese)
