Post on 06-Nov-2015
description
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