ABO Blood Group System

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ABO Blood Group System
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History Karl Landsteiner

• Discovered the ABO Blood Group System in 1901
• He and his five co-workers began mixing each
  others red cells and serum together and
  inadvertently performed the first forward and
  reverse ABO groupings

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Why is it important?

• ABO compatibility between donor cell and patient
  serum is the essential foundation of
  pretransfusion testing
• It is the only system with expected antibodies
• Whether they are IgG or IgM, ABO antibodies can
  activate complement readily
• This means that incompatibilities can cause life
  threatening situations (transfusion reactions)

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ABO antigens

• Biochemical Genetic Considerations

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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

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• 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

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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

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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)

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RBC Precursor Structure
RBC
Glucose
Galactose
Precursor Substance (stays the same)
N-acetylglucosamine
Galactose
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Formation of the H antigen
RBC
Glucose
Galactose
H antigen
N-acetylglucosamine
Galactose
Fucose
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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 a sugar
  to the H antigen
• Immunodominant sugars are present at the terminal
  ends of the chains and confer the ABO antigen
  specificity

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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

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

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H antigen

• Certain blood types possess more H antigen than
  others
• OgtA2gtBgtA2BgtA1gtA1B

Greatest amount of H
Least amount of H
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The O allele

• Why do Group O individuals have more H antigen
  than the other groups?
• The O gene is a silent allele. It does not alter
  the structure of the H substance.that means more
  H antigen sites

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

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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

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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

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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

A antigen
Se gene (SeSe or Sese)
H antigen in secretions
and/or
B antigen
No antigens secreted in saliva or other body
fluids
se gene (sese)
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ABO Group ABH Substances
Secretors (SeSe or Sese) A B H
A 0
B 0
O 0 0
AB
Non-secretors (sese)
A, B, O, and AB 0 0 0
Sese h/h (no H antigen) ? no antigens in
secretions
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Type I and Type II Precursors

• There are two potential precursors substances for
  ABH antigens Type I and Type II
• Both are comprised of identical sugars but the
  linkage of the terminal sugars differs in the two
  types
• Type I precursor has a terminal galactose linked
  to a subterminal N-acetylgluosamine in a 1-3
  linkage
• These same sugars combine in a 1-4 linkage in
  type II precursor

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Type II H

• After fucose is added to Type II chains, the
  structure is termed Type II H
• Four kinds of Type II H have been identified
• H1, H2 are simple straight chain glycolipids
• Whereas H3 H4 have branched chains

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ABH Ags on red cells are derived from Type II
chains whereas the ABH Ags in plasma are made
from both types I II precursors
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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

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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

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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)
• Whats the difference between the A1 and A2
  antigen?
• Its quantitative
• The A2 gene doesnt convert the H3 H4 to A very
  well
• The result is fewer A2 antigen sites compared to
  the many A1 antigen sites

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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
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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

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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

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Other ABO conditions

• Bombay Phenotype (Oh)
• Inheritance of hh
• The h gene is an amorph and results in little or
  no production of L-fucosyltransferase
• Originally found in Bombay (now Mumbai)
• Very rare

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Bombay Phenotype
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Bombay

• The hh causes NO H antigen to be produced
• Results in RBCs with no H, A, or B antigen
  (patient types as O)
• Bombay RBCs are NOT agglutinated with anti-A,
  anti-B, or anti-H (no antigens present)
• Bombay serum has strong anti-A, anti-B and
  anti-H, agglutinating ALL ABO blood groups
• What blood ABO blood group would you use to
  transfuse this patient??

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ANSWER

• Another Bombay
• Group O RBCs cannot be given because they still
  have the H antigen
• You have to transfuse the patient with blood that
  contains NO H antigen

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Important Issue ?
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ABO Blood Group

• ABO Antibodies

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Landsteiners Rule

• Normal, Healthy individuals possess ABO
  antibodies to the ABO antigen absent from their
  RBCs

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ABO Blood Group System

• The ABO Blood Group System was the first to be
  identified and is the most significant for
  transfusion practice
• It is the ONLY system that the reciprocal
  antibodies are consistently and predictably
  present in the sera of people who have had no
  exposure to human red cells

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Blood Group Systems

• Most blood group systems (ABO and others) are
  made up of
• An antigen on a red cell and the absence of its
  corresponding antibody in the serum (if youre A,
  you dont 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

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ABO

• Remember
• 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
• Titer of ABO Abs is often reduced in elderly and
  in patients with hypogammaglobulinemia
• Infants do not produce Abs until 3-6 months of age

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ABO antibodies
RBC Phenotype Frequency () Serum Ab
A 43 Anti-B
B 9 Anti-A
AB 4 --------
O 44 Anti-A,B
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Anti-A1
Anti-A1 Anti-A1
Clinically Significant Sometimes Abs class IgM
Thermal range 4 - 22 HDNB No
Transfusion Reactions Transfusion Reactions
Extravascular Intravascular
No Rare

• 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.

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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

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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)

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ABO antibody facts

• Complement can be activated with ABO antibodies
  (mostly IgM, some IgG)
• High titer react strongly (4)

Anti-A, Anti-B, Anti-A,B Anti-A, Anti-B, Anti-A,B
Clinically Significant Yes Abs class IgM, less IgG
Thermal range 4 - 37 HDNB Yes
Transfusion Reactions Transfusion Reactions
Extravascular Intravascular
Yes Yes
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ABO Antibodies

• Usually present within the first 3-6 months of
  life
• Stable by ages 5-6 years
• Decline in older age in hypogammaglobulinemia
• Newborns may passively acquire maternal
  antibodies (IgG crosses placenta)

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Nature of antibodies

• Non-red blood cell stimulated
• ABO antibodies
• Red blood cell stimulated
• Antibodies formed as a result of transfusion, etc
• Usually IgG
• Active at 37C
• Can occur in group O (may occur in group A or B)
• These antibodies also occur in the other Blood
  Group Systems

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Anti-H
Auto-Anti-H Auto-Anti-H
Clinically Significant No Abs class IgM
Thermal range 4 - 15 HDNB No
Transfusion Reactions Transfusion Reactions
Extravascular Intravascular
No No
Allo-Anti-H Allo-Anti-H
Clinically Significant Yes Abs class IgM, IgG
Thermal range 4 - 37 HDNB Yes
Transfusion Reactions Transfusion Reactions
Extravascular Intravascular
Yes Yes