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5. ABO Grouping

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    BLOOD GROUPS

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    Definitions

    Blood groups are determined by antigens

    structures on the surfaces or red cells and

    are detected by reactions with specific

    antibodies.

    A blood group system is defined by a.g that

    are regulated either by allelic genes orclosely linked genes.

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    The number or red cell blood groups now exceeds 400.

    (table1).

    Table 1. Survey of major Red Cell Blood Group System

    System Important antigensABO A1,A2,B,H,A3,Am,AxMNSs M,N,S,s,U,Mg,Mia,Hu,HeMta,Vw,M2,N2,S2P P1,p

    k,P2,(Tja)

    Rh D,C,E,c,e,Cw,Ew,ce,Ce,G,CE,cE,Du,Cu,Eu,LW

    Lutheran Lua,Lub

    Kell K,k,Kpa,Kpb,Jsa,Jsb

    Lewis Lea,Leb

    Wright Wra,Wrb

    Diego Di

    a

    ,Di

    b

    Cartwright Yta,Ytb

    Xg Xga

    Dombrock Doa,Dob

    Colton Coa,Cob

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    Antibodies : sources & properties

    1. Normal humans

    A.bodies to some blood group a.g occur in

    the serum of individuals who lack the a.g

    and have had no prior exposure to it

    natural isohemagglutinins.

    The major ones are directed against surface

    a.g such as the ABO, Ii and P systems

    controlled by oligosaccharides

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    Isohemagglutinins with ABO are always

    clinically significant

    Isohemagglutinins elicited by similar

    sequences on microbial surfaces >>Ig Ms

    effective hemolysins because they

    efficiently fix complement.

    Occasionally Ig G a.bodies specific for thesea.g also appear.

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    2. Immunized animals

    If animals are immunized with human red cells may form a.bodies to certain of the

    xenogeneic blood group a.g important

    source of blood group anti sera carefullyabsorbed with human red cells to establish

    specificity.

    Recently developed a.g specific monoclonala.bodies do not require such absorption.

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    3. Immunized humans

    The third major source of the blood group anti

    bodies are donors who have been allogenically

    immunized either by (1) prior bloodtransfusions or (2) previous pregnancies

    immune antibodies elicited by prior

    exposure to red cell a.g are commonly IgGs

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    Methods of detection

    1. Agglutination by specific antibody

    Under physiologic conditions of pH and ionic

    strength, normal red cells repel each other

    owing to their negative surface charge or

    zeta potential

    2. Enhancement of agglutination by antibody

    a. Reduction of zeta potential

    Can be reduced by addition of colloid (alb,

    polyvinylpyrrolidone or dextran).

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    b. Insertion of a.b red cells bridges

    Agglutinations may produced or enhanced

    by addition of Coomb reagent (i.e.,anti-

    globulin a.body)3. Use of lectins

    4. Automated techniques

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    Genetics

    According to mendelian laws Heredity is generally autosomal

    codominant i.e there is an expression of

    both alleles in the heterozygous individual1.Linked genes

    2.Interaction with other genes

    3.Loci of blood groups genes onchromosomes (table 2)

    4.Occurrence of blood group antigens

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    Table 2. Chromosome Assignment of Some Blood

    Group Loci

    Locus Chromosome

    ABO 9

    Rh 1

    Fy 1

    Chido, Rogers 6

    MNSs 4Xg X

    Sc 1

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    ABO SYSTEM

    a. Historical notesIn subsequent work Landsteiner recognized

    that the pattern of reactions could be

    explained by two a.g, which designated A

    and B. O signified the state of not having A

    or B.

    Table 3. The Landsteiner scheme

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    Table 3. The ABO system defined by Anti-A and Anti B

    Blood Groups Antigens on RC Antibodies in serum

    O

    A

    B

    AB

    None

    A

    B

    A and B

    Anti-A and Anti-B

    Anti-B

    Anti-A

    None

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    b. Subdivisions of A antigen

    A antigen and anti-A are complex. Anti-Aserum from a group B donor contains 2 types

    of a.b, anti-A and anti-A1 . (table 4)

    Group Antigens Reaction with

    Anti-A Anti-A1

    A1

    A2

    AA1

    A

    +

    +

    +

    -

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    Genetics

    Determining the blood group : genotype and

    phenotype. A child receives one of four genes

    from each parent : A1, A2, B1, or O. Six

    phenotypes are possible because the A a.g

    associated with group A2 and also A1.

    There are ten possible genotypes. Group A1 may

    have 3 genotypes (A1A1, A2 O, A1A2). Group A2can have either A2A2 or A2 O genotypes. Group

    B can have either BB or BO genotypes

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    Genotype :

    - specific genes that person carries

    - determined by family studies

    - AA, AO, BB, BO, AB and OO- see fig 1.

    F il 1

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    Family 1

    Phenotype B A1

    Genotype BO A1O

    Phenotype O O A1B

    Genotype OO OO A1B

    Family 2

    Phenotype A1 A2B

    Genotype A1A2 A2B

    Phenotype A2B A1

    Genotype A2B A1A2

    Fig 1. Illustration of usefulness of family studies in the elucidation of phenotype

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    Phenotype :

    Four phenotypes : A, B, AB and O

    Although there are ten possible genotypes,

    the absence of a specific anti-O prevents the

    serological recognition of more than four

    phenotypes. (table 5)

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    Table 5. Blood Type

    Phenotype Genotype Antigens

    on red cell

    Antibodies in

    plasma

    OA

    B

    AB

    OOAA or AO

    BB or BO

    AB

    OA

    B

    AB

    Anti-A, Anti-BAnti-B

    Anti-A

    None

    Fig 2 Synthesis of ABH antigens

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    Fig.2 Synthesis of ABH antigens

    R

    glc gal glcnac galH precursor

    Hh gen

    fucR

    glc gal glcnac gal H antigen

    A gene B gene

    fuc fucR R

    glc gal glcnac gal glcnac glc gal glcnac gal gal

    A antigen B antigen

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    H antigen

    The surfaces oligosaccharides thatconstitutes the H a.g is the precursor of the

    A and B a.g

    Gene A & B responsible for converting H

    substance into A & B substance

    The O gene is an amorph and doesnt

    transform the H substance

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    Rare variantBombay, the H precursor

    cannot be converted to H

    lack H ag &hence A or B phenotype cant be expressed.

    A terminal sugar molecules determine a.g

    specificity :

    A a.g : N acetylgalactosamine

    B a.g : galactosa

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    Other Carbohydrate Antigen

    a. Lewis system

    The Lewis a.g are made from the same

    precursors as the ABH a.g except that they

    are exclusively type 1 chain.

    The expression ag depends on the

    interaction of the H gene, Se gene and Legene

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    b. P system

    These ag were recognized by antisera

    developed in rabbits glycosphingolipids

    and originate on a ceramide dihexose (Gal-

    Gal-ceramide)c. Ii system

    Most cold a.bodies have specificity against

    the Ii a.g system. These a.g are found in red

    cells and nonhematopoietic tissue

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    Rhesus System

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    Rhesus a.b >> immune (previous

    transfusion or pregnancy), naturally

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    A. Nomenclature : relation to genetic models

    1. Fischer-Race theory (table 6) :Postulates 3 closely linked genes Cc,

    Dd and Ee. Rhesus a.g is renamed D.

    Rhesus positive presence of the Dantigen, also called Rh or Rh factor

    Rhesus negative absence of D but

    doesnt denote absence of other a.gof the Rh system (C,c,E or e)

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    2. Weiner system

    3. Rosenfield system

    B. Compound antigens

    C. Weakened antigens :

    - weakly reactive ag

    Du

    - formal terminology : Rh +, Du variant

    - for transfusion : Du is equivalent toRh +

    D. Deleted antigens : Rh null cells.E. Rh antigens structure

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    Table 6. Rh gene complexes

    Fischer-Race Wiener

    CDe R1

    cde r

    cDE R2

    cDe Ro

    CwDe R1W

    cdE ru

    Cde r1CDE Rz

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    Other clinically significant systems

    1. Kell system

    The Kell a.g system rivals the Rh system in itscomplexity and clinical importance. Appearing in

    response to prior immunization, anti-Kell a.b have

    caused hemolytic transfusion reactions and HDN.

    The main a.g pairs : K-k, Kpa-Kpb and Jsa-Jsb

    2. Duffy system

    Double negative phenotype red cells, Fy (a-b-) are

    totally resistant to invasion by Plasmodium vivax.Transfusion of incompatible blood into Duffy-

    sensitive individuals can cause severe hemolysis.

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    3. Kidd system

    Immunization to Kidd is caused mainly by

    transfusions. Kidd a.b are evanescent warm-activeincomplete a.b that may not be detected in red cell

    a.b screens. Consequently they often cause

    delayed transfusions rx, which may be severe.4. Lutheran system

    There are 2 common alleles, Lua and Lub and a

    silent one. The double-negative phenotype causedby either dominant inhibitor gene or a recessive

    silent allele.

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    5. Xga blood group

    This a.g is controlled by a gene on the Xchromosome. Its not clinically significant but

    is of interest as a marker for X chromosome

    that appear to escape inactivation by theLyon mechanism.

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    The ABO and Rhesus (Rh) groups are of major clinical

    significance. Some other systems of less overall

    importance are listed in table 7.

    Systems Frequency of a.body Cause of HDN

    ABO Very common Yes

    Rh Common Yes

    Kell Occasional YesDuffy Occasional Yes

    Kidd Occasional Yes

    Lutheran Rare No

    Lewis Occasional NoP Occasional Yes (rare)

    MN Rare Yes (rare)

    Ii Rare No

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    Uses of blood grouping data

    A. In clinical medicine

    1. Pretransfusion testing :

    Prior to transfusion, blood is typedand crossmatched to establish ABO and

    D compatibility

    2. Hemolytic disease of the newborn

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    B. In geneticschromosome mapping

    C. In forensic medicine :

    1. Identification studies

    2. Paternity testing

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    Thank you


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