ABO blood group system Nada Mohamed Ahmed, MD, MT (ASCP)i.

ABO blood group system

Nada Mohamed Ahmed ,MD, MT (ASCP)i

Objectives

• discovered by Karl Landsteiner; locus on chr 9

• most important blood group for

the selection and transfusion of blood

• widely expressed tissues & body fluids

including red cells, platelets & endothelial cells

• three antigens: A, B, H

• two major antibodies: anti-A and anti-B

• four phenotypes: A, B, AB, O

Characteristics ABO BLOOD GROUP SYSTEM

• Individual’s will form Individual’s will form immuneimmune

antibodies to ABO blood antibodies to ABO blood group antigens group antigens

they do not possess.they do not possess.

The body produce antibody to The body produce antibody to Antigen who lake it.Antigen who lake it.

• Blood group genetics are concerned with the way in which the different blood groups are inherited, that is passed on from parents to children.

• Blood group antigens are actually sugars attached to the red blood cell.

• The type of sugar added determines the blood group.

• A and B genes do not directly produce antigens produce an enzyme called transferase attaches a sugar molecule to the chemical structure of the antigen sugar molecule responsible for specificity

• O antigen no transferase no antigen produced

• A and B antigens on surface of RBC protrude from outermost layer of cell membrane

Formation of A ,B& H Antigen

• The ABO genes do not code for the production of ABO antigens, BUT rather produce specific glycosyl transferases

• ABO produces a specific glycosyl transferases that add sugars to a basic precursor substance on the RBCs

H gene products is an enzyme that produce H substance

The O gene is a silent allele

It does not alter the structure of H substance.

• Each gene codes for the production of a specific transferase enzyme, , and enable us to convert the basic precursor substance to the particular blood group substance.

• the H gene (HH/Hh) encodes for an enzyme, which converts the precursor substance in red cells in to H substance (H antigen).

• A and B genes encode specific transferase enzymes which convert H substance in to A and B red cell antigens.

• Some H substance remains unconverted.

Gene Enzyme

H L- fucosyltransferase

A 3 N-acetyl- D- galactosaminyl transferase

B 3-D- galactosyl transferase

O None

ABO BLOOD GROUP SYSTEM

ABO BLOOD GROUP SYSTEM

ABO BLOOD GROUP SYSTEM

• O gene encodes for an inactive enzyme, which results in no conversion of the substance in-group O red cells.

• This indicates group O individual contains the greatest concentration of H antigen.

• Persons who do not inherit H gene are unable to produce H substance

• This rare group is referred to as Oh (Bombay group).

• present on the surface of red cells as well as tissue and endothelial cells in the body

• found in soluble form in plasma & other body secretions in people known as secretors

• inherited in simple Mendelian fashion from an individual’s parents

• 3 possible genes that can be inherited: A, B, O

• A and B genes produce a detectable product

• O gene does not produce a detectable product

ABO Antigens

• GROUP A– Express A antigen on RBC surface– Genotypes AA or AO– Have naturally occurring, clinically

significant, predominantly IgM (with a small amount of IgG) antibodies against type B (anti-B)

– Subgroups• A1 (80%)• A2 (20%)• Significance: some with A2 have antibodies

against the A1 subgroup (anti-A1)

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– Express B Ag on RBC surface

– Genotypes BB or BO

– Have naturally occurring clinically significant, predominantly IgM (with a small amount of IgG) antibodies against type A cells

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GROUP B

• GROUP O– Have neither A nor B antigens on their

RBC– Genotype OO (“universal donors”)– Have naturally occurring,– clinically significant, very high titer, anti-

A, anti-B and anti-A,B antibodies– Group O cells have the most H antigen

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• GROUP AB– Express A and B

Ag on RBC surface

– Genotypes A1B or A2B

– have no ABO antibodies (“universal recipients”)

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ABO BLOOD GROUP SYSTEM

H Antigen

• required to produce either A or B antigens

• possible genetic combinations: HH, Hh, or hh

• HH or Hh (+) produce H Ag 99.99% of population.

• hh does not produce H Ag Bombay phenotype (Oh)

• anti-H antibodies rare – found only in individuals with Bombay phenotype

H Antigen• Seen on RBC of ABO-Universal

distributed

• BOMBAY (Oh)PHENOTYPE– Patients lack the H gene and

therefore cannot make H antigen, A or B antigen on their red cells

– Have very strong anti-A, anti-B, and anti-H and can only receive cells from a Bombay donor

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ABO System

Phenotype Antigen Natural antibody

Genotype

A A only Anti-B AA or AO

B B only Anti-A BB or BO

AB A and B None AB

O None Anti-A,

Anti-B

OO

Example of determining offspring blood types from known or suspected genotypes:

Genotype parent #1 (AO)

A O

Genotype parent A AA AO

#2 (AB) B AB BO

Phenotypes of possible offsprings: A, AB, B

Frequencies of ABO Blood Groups:

Blood GroupFrequency

O 45%

A 41%

B 10%

AB 4%

ABO Subtypes:

1. A variants (A1, A2)

• A1 most common (80%) & most antigenic

• A1 and A2 differentiated using antisera specific for A1 Ag (anti-A1 lectin) prepared from seed known as Dolichos biflorus (+) reaction with A1 but not A2

• Anti-A reacts with both A1 & A2 but more strongly with A2

ABO Subtypes:

2. Weak A and weak B phenotypes

3. Null phenotypes:

(a) Bombay (Oh)

• No A, B or H Ag on red cells & secretions

• With anti-A, anti-B & anti-H in their sera

(b) para-Bombay

• Absent or only trace A,B & H Ag’s detected on normal expression in secretions & body fluids

• Natural antibodies antigenic stimulus is environmental exposure occurs from birth

• Newborns without ABO antibodies of their own; begin to produce Ab with detectable titer at 6 months of age

• Other characteristics of ABO antibodies:

1. IgM

2. Reacts at room temp. after an immediate spin

ABO Antibodies

• Refer to the presence or absence of water- soluble ABH antigen substances in body fluids (saliva, semen, urine, sweat, tears, etc).

• Secretors possess the water soluble (glycoprotein) form of antigen, which appears in most body fluids.

• The production of A, B & H antigens in saliva is controlled by a secretor gene.

• The relevant gene is called Se, and its allele which amorphic is se.

• Pre-transfusion Testing• Prenatal Testing• Presurgical Testing• Paternity Determination• Transplant Matching• Donor Testing