This document discusses the ABO blood group system. It notes that there are over 20 known blood group systems that are genetically determined. The ABO and Rh systems are most important for blood transfusions. The ABO system involves antigens on red blood cells and corresponding antibodies in plasma. People are categorized into one of the main blood groups - A, B, AB, or O - depending on which antigens are present on their red blood cells and which antibodies are present in their plasma. The exact genetic basis and inheritance of the ABO system is also described.

1. The Blood Group Systems
Dr. Yogendra Vijay
Resident doctor
SMS Medical college,Jaipur
(Rajasthan)

2. •The blood group you belong to depends on
what you have inherited from your parents.

3. • There are more than 20 genetically determined
blood group systems known today
• The AB0 and Rhesus (Rh) systems are the
most important ones used for blood transfusions.
• Not all blood groups are compatible with each
other. Mixing incompatible blood groups leads to
blood clumping or agglutination, which is
dangerous for individuals.

4. Blood group A
If you belong to the blood
group A, you have A
antigens on the surface of
your RBCs and B
antibodies in your blood
plasma.
Blood group B
If you belong to the blood
group B, you have B
antigens on the surface of
your RBCs and A
antibodies in your blood
plasma.
AB0 blood grouping system

5. Blood group AB
If you belong to the blood group
AB, you have both A and B
antigens on the surface of your
RBCs and no A or B antibodies
at all in your blood plasma.
Blood group O
If you belong to the blood group O,
you have neither A or B antigens on
the surface of your RBCs but you have
both A and B antibodies in your blood
plasma.

6. • The "A“ and "B" antigens are also produced
by some other plants and microorganisms.
Thus, individuals who do not recognize one or
more of these antigens as "self" will produce
antibodies against the plant or microbial
antigens.
• These antibodies will also react with human
antigens of the same kind whether introduced
via a blood transfusion or a tissue graft.

7. Significance of ABO Group
 ABO mismatched transfusions:
 Rare
 May be life threatening
 Can be caused by technical or clerical error
 Intravascular haemolysis
 More severe in group O patients
7

8. ABO inheritance and genetics
• 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
• Each person has two copies of genes coding for their ABO blood
group (one maternal and one paternal in origin)

9. Principles of Heredity
 Antigens and enzymes are genetically controlled
 Genes: responsible for transfer of hereditable material
 Genes are found on chromosomes, which are found in the nucleus of every cell
 Human Cells contain 46 chromosomes with the exception of the egg and sperm,
which contain only 23.
 23 of these chromosomes are inherited from mother
 23 of these chromosomes are inherited from father

10. Genes Come in Pairs
 The position a gene occupies on a chromosome is called a
locus.
 Genes for the same trait are located at the same locus on
both the mother and the father’s chromosomes.
 Alternative forms of genes that influence a given
characteristic are called alleles.
 Father: allele for brown eyes
 Mother: allele for blue eyes

11. Blood Types are Genetic
 A and B Blood Types are Dominant
 Dominant: Characteristic is shown
 Blood Type O is Recessive
 Recessive: Characteristic is hidden
 Recessive characteristics only appear when both alleles are recessive
 Homozygous recessive OO

12. Phenotype V. Genotype
 Phenotype: individual’s outward characteristics
 Genotype: individual’s pair of allele genes together
 Example:
 Phenotype Genotype
Type B Blood Could be BO or
BB depending
on parents

13. Important Parts for Forensic Science
 Red Blood Cells—because of their importance in blood typing
 Serum—because of its’ importance in carrying antibodies

14. ABO and H Antigen Genetics
 Genes at three separate loci control the occurrence and
location of ABO antigens
 The presence or absence of the A, B, and H antigens is
controlled by the H and ABO genes

15. Location
 The presence or absence of the ABH antigens on the red
blood cell membrane is controlled by the H gene
 The presence or absence of the ABH antigens in
secretions is indirectly controlled by the Se gene

16. ABO Antigen Genetics
 H gene – H and h alleles (h is an amorph)
 Se gene – Se and se alleles (se is an amorph)
 ABO genes – A, B and O alleles

17. H Antigen
 The H gene codes for an enzyme that adds the sugar
fucose to the terminal sugar of a precursor substance
(PS)
 The precursor substance (proteins and lipids) is formed
on an oligosaccharide chain (the basic structure)

18. RBC Precursor Structure
Glucose
Galactose
N-acetylglucosamine
Galactose
Precursor
Substance
(stays the
same)
RBC

19. Formation of the H antigen
Glucose
Galactose
N-acetylglucosamine
Galactose
H antigen
RBC
Fucose

21. H antigen
 The 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 the H antigen
 Immunodominant sugars are present at the terminal ends
of the chains and confer the ABO antigen specificity

22. A and B Antigen
 The “A” gene codes for an enzyme
(transferase) that adds N-acetylgalactosamine
to the terminal
sugar of the H antigen
 N-acetylgalactosaminyltransferase
 The “B” gene codes for an enzyme
that adds D-galactose to the terminal
sugar of the H antigen
 D-galactosyltransferase

23. Formation of the A antigen
Glucose
Galactose
N-acetylglucosamine
Galactose
RBC
Fucose
N-acetylgalactosamine

24. Formation of the B antigen
Glucose
Galactose
N-acetylglucosamine
Galactose
RBC
Fucose
Galactose

25. Genetics
 The H antigen is found on the RBC when you have the
Hh or HH genotype, but NOT from 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

26. A A
A A
Group O Group A
Many H
antigen sites
Fewer
H antigen
sites
A
Most of the H antigen sites in a
Group A individual have been
converted to the A antigen

27. ABO Antigens in Secretions
 Secretions include body fluids like plasma, saliva,
synovial fluid, etc
 Blood Group Substances are soluble antigens (A, B, and
H) that can be found in the secretions. This is
controlled by the H and Se genes

28. Secretor Status
 The secretor gene consists of 2 alleles (Se and se)
 The Se gene is responsible for the expression of the H
antigen on glycoprotein structures located in body
secretions
 If the Se allele is inherited as SeSe or Sese, the person is
called a “secretor”
 80% of the population are secretors

29. Secretors
 Secretors express soluble forms of the H antigen in
secretions that can then be converted to A or B antigens
(by the transferases)
 Individuals who inherit the sese gene are called
“nonsecretors”
 The se allele is an amorph (nothing expressed)
 sese individuals do not convert antigen precursors to H
antigen and has neither soluble H antigen nor soluble A or
B antigens in body fluids

30. Secretor Status Summary
 The Se gene codes for the presence of the H antigen in
secretions, therefore the presence of A and/or B
antigens in the secretions is contingent on the
inheritance of the Se gene and the H gene
Se gene (SeSe
or Sese)
H antigen in
secretions
A antigen
B antigen
se gene (sese) No antigens secreted
in saliva or other
body fluids
and/or

31. ABO Subgroups
 ABO subgroups differ in the amount of
antigen present on the red blood cell
membrane
 Subgroups have less antigen
 Subgroups are the result of less
effective enzymes. They are not as
efficient in converting H antigens to A
or B antigens (fewer antigens are
present on the RBC)
 Subgroups of A are more common than
subgroups of B

32. Subgroups of A
 The 2 principle subgroups of A are: A1 and A2
 Both react strongly with reagent anti-A
 To distinguish A1 from A2 red cells, the lectin Dolichos
biflorus is used (anti-A1)
 80% of group A or AB individuals are subgroup A1
 20% are A2 and A2B

33. A2 Phenotype
 Why is the A2 phenotype important?
 A2 and A2B individuals may produce an anti-A1
 This may cause discrepancies when a crossmatch is done
(incompatibility)
 What’s the difference between the A1 and A2 antigen?
 It’s quantitative
 The A2 gene doesn’t convert the H to A very well
 The result is fewer A2 antigen sites compared to the many
A1 antigen sites

34. A1 and A2 Subgroups*
Anti-A
antisera
Anti-A1
antisera
Anti-H
lectin
ABO
antibodies
in serum
# of
antigen
sites per
RBC
A1
4+ 4+ 0 Anti-B 900 x103
A2
4+ 0 3+ Anti-B &
anti-A1
250 x103
*Adapted from Flynn, J. (1998). Essentials of Immunohematology

35. Other A subgroups
 There are other additional subgroups of A
 Aint (intermediate), A3, Ax, Am, Aend, Ael, Abantu
 A3 red cells cause mixed field agglutination when
polyclonal anti-A or anti-A,B is used
 Mixed field agglutination appears as small agglutinates
with a background of unagglutinated RBCs
 They may contain anti-A1

36. B Subgroups
 B subgroups occur less than A subgroups
 B subgroups are differentiated by the type of reaction
with anti-B, anti-A,B, and anti-H
 B3, Bx, Bm, and Bel

37. ABO Blood Group:
ABO Antibodies

38. Landsteiner’s Rule:
Normal, Healthy
individuals possess
ABO antibodies to
the ABO antigen
absent from their
RBCs

39. Blood Group Systems
 Most blood group systems (ABO and
others) are made up of:
 An antigen on a red cell and the
absence of it’s corresponding antibody
in the serum (if you’re A, you don’t
have anti-A)
 If you do NOT have a particular antigen
on your red cells then it is possible (when
exposed to foreign RBCs) to illicit an
immune response that results in the
production of the antibody specific for
the missing antigen

40. ABO
The ABO Blood Group System
does NOT require the presence of
a foreign red blood cell for the
production of ABO antibodies
 ABO antibodies are “non-red
blood cell stimulated” probably
from environmental exposure and
are referred to as “expected
antibodies”

41. Anti-A1
 Group O and B individuals contain
anti-A in their serum
 However, the anti-A can be
separated into different
components: anti-A and anti-A1
 Anti-A1 only agglutinates the A1
antigen, not the A2 antigen
 There is no anti-A2.

42. Anti-A,B
 Found in the serum of group O
individuals
Reacts with A, B, and AB cells
 Predominately IgG, with small
portions being IgM
 Anti-A,B is one antibody, it is
not a mixture of anti-A and
anti-B antibodies

43. ABO antibodies
 IgM is the predominant antibody in Group
A and Group B individuals
 Anti-A
 Anti-B
 IgG (with some IgM) is the predominant
antibody in Group O individuals
 Anti-A,B (with some anti-A and anti-B)

44. ABO antibody facts
 Reactions phase: Room
temperature
 Complement can be activated with
ABO antibodies (mostly IgM, some
IgG)
 High titer: react strongly (4+)

45. ABO Antibodies
 Usually present within the first 3-6
months of life
 Stable by ages 5-6 years
 Decline in older age
 Newborns may passively acquire maternal
antibodies (IgG crosses placenta)
 Reverse grouping (with serum) should
not be performed on newborns or cord
blood

46. Paternity Tests
 No blood group can be present in a child without being
present in one of the parents
 Paternity tests can be resolved in this way unless disputed
fathers have the same blood type
 Paternity tests can also be determined by using DNA testing

47. Blood as Evidence
 Blood typing not so useful anymore because of DNA technology
 Scientists can now characterize biological evidence by
selecting regions of our DNA

48. AUTOSOMAL CHROMOSOME
Dad
Mom
The alleles for Blood
group are in the same
place on the
A B
chromosome 9. However
the genes have a
different code giving the
different blood group

49. What do co-dominant genes mean?
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)

50. Possible Blood group Genotypes
Parent
Allele
A B O
A
B
O

51. Possible Blood group Genotypes
Parent
Allele
A B O
A AA AB AO
B AB BB BO
O AO BO OO

52. The ABO blood groups
• The most important in assuring a safe blood transfusion.
• The table shows the four ABO phenotypes ("blood groups") present
in the human population and the genotypes that give rise to them.
Blood
Group
Antigens
on RBCs
Antibodies in Serum Genotypes
A A Anti-B AA or AO
B B Anti-A BB or BO
AB A and B Neither AB
O Neither Anti-A and anti-B OO

53. The ABO Blood Group System
Laboratory Determination of the
ABO System

54. METHODS OF ABO BLOOD GROUPING
1.SLIDE METHOD
2.TUBE METHOD
3.GEL SYSTEM
4.MICROPLATE TECHNIQUE
5.GLASS MICROBEAD METHOD
6.GALILEO METHOD

55. Several methods for testing the ABO group of an
individual exist. The most common method is:
Serology: This is a direct detection of the ABO
antigens. It is the main method used in blood
transfusion centres and hospital blood banks.
This form of testing involves two components:
a) Antibodies that are specific at detecting a
particular ABO antigen on RBCs.
b) Cells that are of a known ABO group that
are agglutinated by the naturally occurring
antibodies in the person's serum.

56. • Illustration of the forward and reverse
grouping reaction patterns of the ABO
groups using a blood group tile

57. Blood
Group
Antigens Antibodies Can give
blood to
Can
receive
blood from
AB
A
B
O

58. Blood
Group
Antigens Antibodies Can give
blood to
Can
receive
blood from
AB A and B None AB AB, A, B, O
A A B A and AB A and O
B B A B and AB B and O
O None A and B AB, A, B, O O