ABO Blood Group System[Harmening Ch. 5 & 7]

Speaker

Professor A Pourazar

History

Carl Landsteiner:1. Discovered the ABO Blood Group System in 19012. He and five co-workers began mixing each others

red blood cells and serum together and inadvertently performed the first forward and reverse ABO groupings.

3. Landsteiners Rule: If an antigen is present on a patients red blood cells the corresponding antibody will NOT be present in the patients plasma, under ‘normal conditions’.

ABO Blood Group System

• The ABO Blood Group System was the first to be identified and is the most significant for transfusion practice. AABB Technical Manual

• It is the ONLY system that the reciprocal (antithetical) antibodies are consistently and predictably present in the sera of people who have had no exposure to human red cells. AABB Technical Manual

Major ABO Blood Groups

ABO Group

Antigen Present

Antigen Missing

Antibody Present

A A B Anti-B

B B A Anti-A

O None A and B Anti-A,B

AB A and B None None

Forward GroupingDefinition: Determination of ABO antigens found on

patient red blood cells using reagent antisera.

Patient Red Cells Tested With:

Patient Anti-A Anti-B Interpretation

1 0 0 O

2 4+ 0 A

3 0 4+ B

4 4+ 4+ AB

Reverse GroupingDefinition: Determination of ABO antibodies found in

patient serum using reagent red blood cells.

Patient Serum Tested With:

Patient A1 Cells B Cells Interpretation

1 4+ 4+ O

2 0 4+ A

3 4+ 0 B

4 0 0 AB

Reaction of Cells Tested With:

Reaction of Serum Tested

Against: ABO Group

% USWhitePop.

% US BlackPop.Anti-A Anti-B A Cells B Cells

1. 0 0 + + O 45 49

2. + 0 0 + A 40 27

3. 0 + + 0 B 11 20

4. + + 0 0 AB 4 4

ABO Antibodies• Generally IgM class antibodies

– I need you to recall the characteristics of IgM antibodies, because now they apply to the ABO blood group system antibodies.

• ABO Antibody Development: Hypothesis– Immune response following exposure to

environmental antigens (such as bacterial cell walls) similar to A and B antigens during infancy results in production of ABO antibodies. Remember, babies have a tendency to put EVERYTHING into their mouths…

ABO Antibodies• For Group A and Group B persons the

predominant antibody class is IgM• For Group O people the dominant antibody class

is IgG (with some IgM)• React best at room temperature (22-24oC) or

below in vitro.• Activates complement to completion at 37oC

– Can cause acute hemolytic transfusion reactions• RBC Immune form: Predominantly IgG

Which ABO blood group presents a higher risk for Hemolytic Disease of

the Newborn? Why?

• Group O - because the dominant immunoglobulin class is IgG, which crosses the placenta.

• Group A and B can but only the immune form. Which means that only after exposure to foreign ABO antigens will the mother make immune anti-A or anti-B that is predominantly IgG.

ABO AntibodiesTime of appearance:

• Generally present within first 4-6 months of life– Do we perform a reverse grouping on newborns

(<4-6 months of age) and cord blood?– If there are anti-A or anti-B antibodies in newborn

serum where did they most likely originate? What source?

• ABO antibody titers with age:– Reach adult level at 5-10 years of age– Level off through adult life– Begin to decrease in later years: >65 years of age

ABO AntibodiesGroup O Phenotype

• Anti-A,B Antibody– Inseparable anti-A and anti-B antibody. If we add

A cells to anti-A,B serum all of the antibody activity is removed, not just anti-A!!

• RBC immune Anti-A,B– When exposed to Group A or B antigens (or both)

Group O persons will have an immune response that results in the production of separate immune anti-A and/or anti-B antibodies. This could be seen in a fetomaternal bleed of a Group O mom with a Group A baby. (Hemolytic Disease of the Newborn)

ABO Antibodies Group B or O phenotype

• Have both anti-A and Anti-A1 antibodies

Anti-A• Reacts with both A1 and A2 red blood cell antigens

Anti-A1• Reacts only with A1 antigens on red blood cells• A2 and A2B phenotypes can make anti-A1

antibodies. What is clinical significance? Thermal range is up to 25oC - not usually clinically significant. Can cause an ABO discrepancy.

ABO Antibodies

• Is there a reagent anti-A1 antisera?• NO!!

• But there is Dolichos biflorus, a plant lectin that has anti-A1 activity when diluted properly.

• This is not an antibody, but a chemical that acts like an antibody in that it specifically agglutinates A1 red blood cells.

ABO Genetics

• Genes at three separate loci control the OCCURRENCE and LOCATION of A and B antigens

1. Hh genes – H and h alleles– H allele codes for a fucosyltransferase

enzyme that adds a fucose on Type 2 chains (primarily) to form the H antigen onto which A and B antigens are built on red blood cells.

– h allele is a silent allele (amorph)

ABO Genetics2. Se genes – Se and se alleles

– Se allele codes for a fucosyltransferase enzyme that adds fuscos onto Type 1 chains (primarily) in secretory glands. Controls expression of H antigens in secretions (i.e. saliva, body fluids, etc.)

– se allele is an amorph3. ABO genes – A, B and O alleles

– A and B alleles code for glycosyltransferase enzymes that add a sugar onto H antigens to produce A and B antigens

– O allele does not code a functional enzyme

• A, B and H antigens are built on oligosaccharide chains of 4 types. The most common forms are Type 1 and Type 2.

Type 1: #1 carbon of Gal is attached to the #3 carbon of GlcNAc.

Type 2: #1 carbon of Gal is attached to the #4 carbon of GlcNAc.

Dad = A/Oand

Mom = B/O

Mom

B O

DadA A/B A/O

O B/O O/O

This represents a method to determine possible genotypes and phenotypes. For future reference, if you happen to be asked a question concerning possible ABO genotypes and/or phenotypes of offspring, now you could do it!!

Genes at three separate loci control the Occurrence and Location

of ABO antigens1. OCCURRENCE

a) The presence or absence of the ABH antigens is controlled by the H and ABO genes.

2. LOCATION a) The presence or absence of the ABH antigens

on the red blood cell membrane is controlled by the H gene

b) The presence or absence of the ABH antigens in secretions is indirectly controlled by the Se genes.

ABO Antigen Genetics

1. Hh gene – H and h alleles (h is an amorph)

2. Se gene – Se and sealleles (se is an amorph)

3. ABO genes– A, B and Oalleles

1. Controls presence of H, A, and B antigens on both RBCs and in Secretions

2. Controls presence of H antigen in the secretions

3. Inherit 1 gene from each parent that codes for an enzyme that adds a sugar to the H antigen

H gene acts on a Precursor substance(PS)*by adding Fucose

H Antigen

*PS = oligosaccharide chain attached to either glycosphingo-lipid, Type 2 chain (on RBC) or glycoprotein, Type 1 chain (in secretions)

The H gene codes for an enzyme (fucosylytranferase) that adds a Fucose to the terminal sugar of a Precursor

Substance (PS*). The biochemical structure below constitutes the H Antigen. (h gene is an amorph.)

H antigen is the foundation upon which A and B antigens are

built. A and B genes code for enzymes that add an

immunodominant sugar to theH antigen.

Formation of theA Antigen

The A gene codes for an enzyme that

adds GalNAc (N-Acetyl-D

galactosamine) to the terminal

sugar of theH Antigen. This biochemical structure

constitutes the A antigen.

Formation of theB Antigen

B gene codes for an enzyme that adds

D-Galactoseto the terminal sugar

of the H Antigen.

This biochemical structure constitutes the B Antigen.

The H antigen is found on the rbc when you have the Hh or HH genotypes but NOTwith the hh genotype.

The A antigen is found on the rbc when you have the Hh, HH, and A/A, A/O or A/B genotypes.

The B antigen is found on the rbc when you have the Hh, HH, and B/B, B/O or A/B genotypes.

Amount of H Antigen According to Blood Group

• Blood Group O people have red blood cells rich in H antigen. Why?

Neither the A or B genes have converted the H antigens to A or B antigens - just a whole bunch of H!

Greatest Amount of H

LeastAmount of HO > A2 > B > A2B > A1 > A1B

Bombay (Oh) Phenotype• Homozygous inheritance of the h gene (hh) results

in the inability to form the H antigen and subsequently the A or B antigens.

• This is referred as the Bombay or Oh phenotype due to the location of its discovery.

• This phenotype has no H, A or B antigens on the red blood cell membrane, only an abundant amount of precursor substance.

• They also have anti-H, anti-A and Anti-B. What blood type can we safely transfuse?

ABO Antigens in Secretions• Secretions:

– Body fluids including plasma, saliva, synovial fluid, etc.

• Blood Group Substance: Soluble antigen– Soluble antigen found in the secretions not

bound to a membrane such as a rbc or epithelial cell.

Soluble blood group substances (A, B and H) can be found in the secretions. This is

controlled by the H and Se genes.

FORMATION OF ABO ANTIGENS IN SECRETIONSSECRETIONS

Se/se H/H A/OPS1 PS2 H Ag A, H Ag

genes genes genes

From left to right is the gene interactions necessary for the production of ABH antigens in secretions. Must have Se gene (78% of population) for ABO Ag’s to be in secretions.

FORMATION OF ABO ANTIGENS IN SECRETIONSSECRETIONS

Se/se H/H O/OPS1 PS2 H Ag H Ag

genes genes genes

Inheritance of the O/O genotype results in the presence of only H antigen in the secretions.

LACK OF ABO ANTIGENS IN SECRETIONSSECRETIONS

Se/se h/h A/OPS1 PS2 PS2 PS2

genes genes genes

Two mechanisms exist that account for a LACK of ABO antigens in secretions:

Either se/se or h/h genotypes.

LACK OF ABO ANTIGENS IN SECRETIONSSECRETIONS

se/se H/h A/OPS1 PS1 PS1 PS1

genes genes genes

Two mechanisms exist that account for a LACK of ABO antigens in secretions:

Either se/se or h/h genotypes.

Relationship of ABO Blood Group with Le, I and P

• As we continue to study the Other Blood Groups we will learn that there is a genetic and biochemical relationship between the ABO blood group and the Lewis, I and P systems.

• The following table gives us a taste of that relationship. Don’t worry about it now, just know that it exists.

ABO Subgroups• ABO Phenotypes that differ in the amount of

antigen carried on red cell and saliva, for secretors: There are fewer Ag sites!

• Subgroups are the results of less effective glycosyltransferase enzymes – just not as good at attaching the immunodominant sugar to the H antigen.

• Subgroups of A are more common than Subgroups of B.

ABO Subgroups

• 80% of all Group A’s are A1 and about 19% are A2.– A1’s have 4-6 times the # of antigen sites on the

RBC surface than A2’s.– Both react strongly with reagent Anti-A but…– Only A1 cells are agglutinated with Dolichos

biflorus plant lectin and not A2 cells. • The remainder of the Subgroups of A have

even weaker expression of A antigen.

ABO Subgroups

• You will be responsible for knowing the reaction patterns of the A1, A2, A3 and Axsubgroups of A. The table on the next slide if a very good reference.

• Knowing these reactions will help you resolve weak reaction strengths and ABO discrepancies.

Subgroups of B

• The same explanation of Subgroups of A applies to Subgroups of B.

• Subgroups of B are less common than Subgroups of A and thus encountered less often.

• You will be responsible for knowing the reaction patterns of the B, B3 and Bxsubgroups of B.