HEM 2133

Immunohaematology IImmunohaematology I

Lesson 2: ABO Blood Group

System

Introduction

Major blood group system ABO system

4 major types A, B, AB or O

Discovered by Karl Landsteiner around 1900

Took samples of blood from himself and 5 of Took samples of blood from himself and 5 of

his colleagues

Mixing of each others serum with saline

suspension of RBCs from the other

Noticed agglutination in some mixtures but

not in others

Classify into A, B and O group named

according to the antigen present on the red

cells

Group AB was discovered by Landsteiners Group AB was discovered by Landsteiners

pupils von Decastello and Sturli (1902)

Some Terms Commonly Used in Genetics

Allele two or more genes responsible for the

same characteristic occupying the same

position on the chromosomes

Homozygous a person who has inherited Homozygous a person who has inherited

same allelic genes from both parents e.g.

having both blue eyed colour genes

Heterozygous a person who has inherited

different allelic genes for a trait e.g. having a

blue and brown-eye colour genes

Dominant gene certain alleles are stronger

than other alleles. A dominant gene expresses

itself in both homozygous and heterozygous

states

Recessive gene the recessive genes are

expressed only when their dominant allele is expressed only when their dominant allele is

absent e.g. only in the homozygous state.

Co-dominant genes in a co-dominant gene,

various alleles for the same character are

equally dominant, e.g. alleles for a particular

blood group system

Genotype the genetic make up of an

individual or a cellindividual or a cell

Phenotype it is the observable

characteristics of an individual or a cell

ABO Blood Group Antigens

ABO grouping is based on the presence or

absence of two blood group antigens

designated A and B

These antigens are found on the cell These antigens are found on the cell

membranes of red blood cells, platelets and

leukocytes

The blood group antigens are products of

inherited allelic genes

Each individual inherits one blood group allele

from each parent the A, B or O allele

Homozygous alleles are the same for any

given trait on both chromosomes (e.g. AA)given trait on both chromosomes (e.g. AA)

Heterozygous alleles for a given trait are

different on each chromosome (e.g. AB or AO)

A and B inherited as autosomal dominant

A and B are codominant

Anytime an individual inherits an A or B gene

it will be expressed.

The O gene signifies lack of A or B antigens The O gene signifies lack of A or B antigens

It is not expressed unless this gene is inherited

from both parents (OO)

Therefore the O gene is recessive.

Individuals are grouped according to the

antigens present on their blood cells

A person who is group A has A antigen

A person who is group B has B antigenA person who is group B has B antigen

A person who is group AB has A and B

antigens

A person who is group O has neither A nor B

antigen

Inheritance Pattern

Some basic rules of ABO inheritance are as follows:

1.A/A parent can only pass along A gene

2.A/O parent can pass along either A or O gene 2.A/O parent can pass along either A or O gene

3.B/B parent can only pass along B gene

4.B/O parent can pass along either B or O gene

5.O/O parent can only pass along O gene

6.AB parent can pass along either A or B gene

ABO Phenotypes and Genotypes

1. Group A phenotype = A/A or A/O genotype

2. Group B phenotype = B/B or B/O genotype

3. Group O phenotype = O/O genotype

4. Group AB phenotype = A/B genotype 4. Group AB phenotype = A/B genotype

Inheritance of ABO group

Genes Antigens Phenotype Genotype

A A A AA/AO

B B B BB/BOB B B BB/BO

AB AB AB AB

O - O OO

H H H HH/Hh

h - Oh (Bombay) hh

ABO genes

The blood type/group is established by

specific genes inherited from both the parents

(one gene from mother, one gene from father)

These genes determine which ABO antigens These genes determine which ABO antigens

will be present on the red cells

A and B genes chromosome 9

Family studies to determine genotypes of A

or B people

H gene

H gene chromosome 19

The expression of the A and B genes depend

on the action of H gene

Most individuals homozygous (HH) Most individuals homozygous (HH)

Phenotype h extremely rare

O gene

The O gene a silent allele (amorph) codes

for a protein that is not functional (inactive

transferase)

H substance structure unchanged H substance structure unchanged

Large amounts of H substance on group O

persons cells

Blood Group Antigens and

Antibodies

ABO system is the only system in which the

reciprocal antibodies are consistently and

predictably present in the sera of normal

people whose RBCs lack the corresponding people whose RBCs lack the corresponding

antigen

Based on Landsteiners Law, normal

individuals who lack an A or B antigen on their

red cells will have antibody in their serum

directed against the missing antigen

Blood group Antigen on RBC

membrane

Antibody in the

serum

A A Anti-B

B B Anti-AB B Anti-A

AB A and B Nil

O Nil Anti-A and Anti-B

Blood Group Antibodies

The discovery of the A and B antigens was

accompanied by the discovery of the

corresponding ABO blood group antibodies in

human bloodhuman blood

Blood group antibodies are named according

to the antigen with which they react

Anti-A reacts with A antigen

Anti-B reacts with B antigen

The blood group O was so named because the

red blood cells have neither A nor B antigenred blood cells have neither A nor B antigen

Therefore, there is no anti-O antibody

ABO blood group antibodies occur naturally in

serum and are of immunoglobulin M (IgM)

class

If an antigen is missing from an individuals If an antigen is missing from an individuals

cells, the antibody specific for the missing

antigen will be present

Blood group Antigen on RBC

membrane

Antibody in the

serum

A A Anti-B

B B Anti-AB B Anti-A

AB A and B Nil

O Nil Anti-A and Anti-B

ABO Antibodies

Anti-A and anti-B predominantly IgM

Naturally occurring

React best at low temperatures

Can react at body temperature Can react at body temperature

Complement activity intravascular hemolysis

Small quantities IgG molecules

IgG can be produced if stimulated by red

cells transfusion, pregnancy

Blood Group Antigens and

Antibodies

The ABO grouping procedures are

agglutination tests

A and B antigens on patient or donor red

blood cells are detected by reacting the cells blood cells are detected by reacting the cells

with known (commercial) antibodies in a

procedure called forward grouping or direct

grouping

Testing patient blood for the presence of the

blood group antibodies is called reverse

grouping, confirmatory grouping or indirect

groupinggrouping

It is performed by reacting serum or plasma

with (commercial) red blood cells whose A

and B antigens are known

Although the blood group antigens are

present on red blood cells of newborns, the

blood group antibodies are not well

developed at birthdeveloped at birth

The ABO antibodies may not be easily

detectable until the age of about 6 months

For this reason, only forward grouping is

reliable in newborns and young infants

Importance of ABO Grouping

ABO grouping who?

Blood donors

Transfusion blood recipients

Transplant candidates and donors Transplant candidates and donors

Prenatal patients

Newborns

Paternity testing

Forensic investigation

Genetic studies

Importance of ABO Grouping

The ABO group must be determined before procedures such as blood transfusion can be performed

An individual should be transfused with blood An individual should be transfused with blood of the same ABO blood group

Because of the presence of the naturally occurring antibodies to A and B antigens, severe transfusion reactions can occur if blood is not matched properly

The rule to follow in transfusing blood is to

avoid giving the patient an antigen he does

not already have

In an emergency, O blood can be used In an emergency, O blood can be used

because it contains neither A nor B antigen

For this reason, people of blood group O are

called universal donors

Principle of ABO Slide Grouping

Detects A or B antigens on red blood cells by combining the patients blood cells with a known antiserum on a slide and observe for agglutination

If the antigen present on the cells corresponds If the antigen present on the cells corresponds to the antibody in the antiserum, the antibody will bind to the antigen and cause clumping of the cells, or agglutination

If the antigen is not present on the cells, no agglutination will be observed

Performing ABO Slide Grouping

Performed using commercial typing slides or

microscopic slides

One drop of commercial anti-A serum is added

to one labeled slideto one labeled slide

One drop of anti-B serum is added to a

separate labeled slide

A drop of well-mixed capillary or venous blood

is placed adjacent to each drop of antiserum

Reagents for ABO Typing

The anti-A is mixed with the drop of blood

using a disposable applicator stick, stirrer or

spreader

The procedure is repeated with the anti-B and The procedure is repeated with the anti-B and

the other drop of blood using a clean stirrer

The slides are then rocked gently for 2

minutes and observed for agglutination using

good lighting

Agglutination, a positive reaction, will appear

as a clumping together of the red blood cells

Absence of agglutination is a negative reaction

The reactions with each antiserum should be The reactions with each antiserum should be

recorded as positive (+) or negative (0)

Interpretation of Slide Grouping

Results

If only the A antigen is present on the red

blood cells, the blood cells will agglutinate

with anti-A but not with anti-B

If only B antigen is present, the blood cells will If only B antigen is present, the blood cells will

agglutinate with anti-B but not with anti-A

Group O blood cells will not agglutinate with

either anti-A or anti-B

Group AB blood will agglutinate with both

anti-A and anti-B

Blood Group Reactions of cells with

Anti-A Anti-B

A + 0

B 0 +

AB + +

O 0 0