Download Blood group system

6th lesson
Medical students
Medical Biology
Blood group system
ABO system
ABO, the most important blood group system from the clinical blood
transfusion perspective, was discovered in 1900 by Landsteiner, the discovery that
first made blood transfusion feasible. At its basic level, there are two ABO antigens,
A and B, giving rise to four phenotypes, A, B, AB and O. In the O phenotype, neither
A nor B is produced . Group A people generally have anti-B in their plasma, group B
people have anti-A, group AB people have neither antibody, and group O people have
anti-A,B. These are predominantly agglutinating immunoglobulin (IgM) antibodies.
Anti-A,B will agglutinate group A or B cells. In transfusion medicine it is imperative
that donor red cells that are agglutinated by the patient’s plasma are not transfused.
"Natural" antibodies called isoagglutinins exist in an individual's serum, directed
against whichever of the A and B antigens is not present on that person's red cells.
The presence of ABO antigens and antibodies (isoagglutinins) in the four blood types
is summarized below:
The success of blood transfusions depends on ensuring the compatibility of the
blood types between donor and recipient. If the recipient has antibodies to the infused
red cells, these red cells will be rapidly destroyed, resulting in a potentially lethal
transfusion reaction. Type A blood given to a type B recipient, for instance, can
result in such a reaction, since the recipient's serum contains anti-A antibodies.
Structure of ABO antigens; "natural antibodies"
Why are there so-called "natural" antibodies to A and B blood group antigens?
A description of the nature and distribution of these antigens will help answer this
question. The blood group substances A and B represent two modified forms of a
"stem" carbohydrate present on red blood cells and other tissues. Their structures are
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shown below (where GLU is glucosamine, GAL is galactose or galactosamine, FUC
is fucose, and NAc represents an N acetyl group):
These same carbohydrates are also a common component of many foods we
eat and many microorganisms in our intestinal tract. The immune system is therefore
constantly exposed to these antigens, and responds by making an effective humoral
response. Since the immune system does not in general respond to antigens which are
a normal part of "self", a type B individual does not make antibodies to the B blood
group substance, although the response to the type A antigens is robust. The net result
is the production of antibodies, mostly of the IgM class, to whichever of these
substances is not present on an individual’s red blood cells. It is important to
remember that the A and B blood group substances are present not only on red blood
cells, but also in virtually every other tissue. They are therefore important
transplantation antigens and must be taken into account together with HLA tissuetyping, when organ transplantation is performed.
Genetics of ABO
The presence of A and B carbohydrates in our tissues is determined by three
alleles at a single genetic locus. One allele encodes an enzyme which produces the A
substance, another the B substance; and when both of these alleles are present in a
heterozygote both carbohydrates are made. The third allele, O, behaves essentially as
a "null" allele, producing neither A nor B substance. Only a single genotype can
produce the phenotype AB, namely the heterozygous state A/B. Likewise, type O
individuals must be homozygous O/O. However, type A or type B individuals can be
either homozygous or heterozygous, the O allele being effectively recessive since it
does not contribute either of the two antigens. The inheritance of the ABO blood
groups follows simple Mendelian rules. For instance, a homozygous type A mother
and a type AB father can yield only two kinds of offspring, type A (genotype A/A) or
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type AB (genotype A/B). A heterozygous type A and a heterozygous type B, on the
other hand , can yield four genotypes and four corresponding phenotypes.
The ABO gene is autosomal (the gene is not on either sex chromosomes). The
ABO gene locus is located on the chromosome 9. A and B blood groups are dominant
over the O blood group. A and B group genes are co-dominant. This meant that if a
person inherited one A group gene and one B group gene their red cells would possess
both the A and B blood group antigens. These alleles were termed A (which produced
the A antigen), B (which produced the B antigen) and O (which was "non functional"
and produced no A or B antigen).
Group A



Group AB
Group B
Approximately 10% of the
population is group B.
 No A antigens present.
 These individuals form
potent anti-A antibodies
which circulate in the blood
plasma at all times.

Approximately 40% of the
population is group A.
No B antigens present.
These individuals form
potent anti-B antibodies
which circulate in the
blood plasma at all times.
Approximately 5% of the
population is group AB.
 Both A and B antigens present.
 These individuals possess no
ABO antibodies.
 NOTE: This slide is in error as it
only illustrates presence of one
antigen not 2.

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Hemolysis


If an individual is transfused with an
incompatible blood group destruction of the red
blood cells will occur.
This may result in the death of the recipient.
Charts show the possible blood type results for offspring
Mother's type
Blood Type
O
A
B
AB
O
O
O, A
O, B
A, B
A
O, A
O, A
O, A, B, AB
A, B, AB
B
O, B
O, A, B, AB
O, B
A, B, AB
AB
A, B
A, B, AB
A, B, AB
A, B, AB
Fathers' type
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Rh system
Rh is the most complex of the human blood group systems, with 45 well
defined antigens. The most immunogenic and clinically important antigen of the Rh
system is D. The other main polymorphisms of the Rh system are C/c and E/e, two
pairs of allelic antigens. Before the 1970s, anti-D was the most common cause of
haemolytic disease of the newborn (HDN). Injection of D negative women with antiD immunoglobulin within 72 hours of giving birth to a D-positive baby prevents the
mothers from producing the anti-D that could damage their subsequent babies. This
prophylactic procedure has made HDN due to anti-D relatively rare.
The antigens of the Rh system are encoded by two genes, RHCE and RHD.
These genes are highly homologous and closely linked on chromosome 1.
Mother's Type
Rh Factor
Rh +(R)
Rh –(r)
Rh +(R)
Rh + Rh +(Rr)
Rh + Rh –(Rr)
Rh –(r)
Rh + Rh –(Rr)
Rh –(rr)
Father's Type
!‫أنت حر مالم تضر‬:‫الدعوة للحرية ليس معناها دعوة لإلنفالت والفوضى والهمجيةالحرية قيمة عظيمة ولكن القاعدة‬
Edited by :Mohammed J AlRawi
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