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Nada Mohamed Ahmed , MD, MT (ASCP)i

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1 Nada Mohamed Ahmed , MD, MT (ASCP)i
ABO blood group system Nada Mohamed Ahmed , MD, MT (ASCP)i

2 Objectives Definition Characteristics of ABO blood group
Blood Group Genetics ABO Antigens ABO Antibodies ABO Subtypes Secretors and Non-Secretors Applications of ABO Grouping

3 Characteristics ABO BLOOD GROUP SYSTEM
discovered by Karl Landsteiner; locus on chr 9 most important blood group for the selection and transfusion of blood widely expressed  tissues & body fluids including red cells, platelets & endothelial cells three antigens: A, B, H two major antibodies: anti-A and anti-B four phenotypes: A, B, AB, O

4 Landsteiner’s Rule Individual’s will form immune
antibodies to ABO blood group antigens they do not possess. The body produce antibody to Antigen who lake it.

5 Phenotype The observable characteristic of an individual Which result from interaction between the genes he possesses. Genotype The genetic constitution of an individual or group as determinated by the particular set of genes it possesses. phenotype

6 Blood Group Genetics Blood group genetics are concerned with the way in which the different blood groups are inherited, that is passed on from parents to children. Blood group antigens are actually sugars attached to the red blood cell. The type of sugar added determines the blood group.

7 A and B genes do not directly produce antigens  produce an enzyme called transferase  attaches a sugar molecule to the chemical structure of the antigen  sugar molecule responsible for specificity O antigen  no transferase  no antigen produced A and B antigens on surface of RBC  protrude from outermost layer of cell membrane

8 Formation of A ,B& H Antigen
The ABO genes do not code for the production of ABO antigens, BUT rather produce specific glycosyl transferases ABO produces a specific glycosyl transferases that add sugars to a basic precursor substance on the RBCs H gene products is an enzyme that produce H substance The O gene is a silent allele It does not alter the structure of H substance.

9 The Role of H-Gene in the Expression of ABO Genes.
Each gene codes for the production of a specific transferase enzyme, , and enable us to convert the basic precursor substance to the particular blood group substance. the H gene (HH/Hh) encodes for an enzyme, which converts the precursor substance in red cells in to H substance (H antigen). A and B genes encode specific transferase enzymes which convert H substance in to A and B red cell antigens. Some H substance remains unconverted.

10 Gene Enzyme H L- fucosyltransferase A
3 N-acetyl- D- galactosaminyl transferase B 3-D- galactosyl transferase O None

11 ABO BLOOD GROUP SYSTEM

12 ABO BLOOD GROUP SYSTEM

13 ABO BLOOD GROUP SYSTEM

14 The Role of H-Gene in the Expression of ABO Genes
O gene encodes for an inactive enzyme, which results in no conversion of the substance in-group O red cells. This indicates group O individual contains the greatest concentration of H antigen. Persons who do not inherit H gene are unable to produce H substance This rare group is referred to as Oh (Bombay group).

15 inherited in simple Mendelian fashion from an individual’s parents
ABO Antigens present on the surface of red cells as well as tissue and endothelial cells in the body found in soluble form in plasma & other body secretions in people known as secretors inherited in simple Mendelian fashion from an individual’s parents 3 possible genes that can be inherited: A, B, O A and B genes produce a detectable product O gene does not produce a detectable product

16 GROUP A Express A antigen on RBC surface Genotypes AA or AO
Have naturally occurring, clinically significant, predominantly IgM (with a small amount of IgG) antibodies against type B (anti-B) Subgroups A1 (80%) A2 (20%) Significance: some with A2 have antibodies against the A1 subgroup (anti-A1)

17 GROUP B Express B Ag on RBC surface Genotypes BB or BO
Have naturally occurring clinically significant, predominantly IgM (with a small amount of IgG) antibodies against type A cells

18 GROUP O Have neither A nor B antigens on their RBC
Genotype OO (“universal donors”) Have naturally occurring, clinically significant, very high titer, anti-A, anti-B and anti-A,B antibodies Group O cells have the most H antigen

19 GROUP AB Express A and B Ag on RBC surface Genotypes A1B or A2B
have no ABO antibodies (“universal recipients”)

20 ABO BLOOD GROUP SYSTEM H Antigen
required to produce either A or B antigens possible genetic combinations: HH, Hh, or hh HH or Hh (+)  produce H Ag  99.99% of population. hh  does not produce H Ag  Bombay phenotype (Oh) anti-H antibodies rare – found only in individuals with Bombay phenotype

21 H Antigen Seen on RBC of ABO-Universal distributed
BOMBAY (Oh)PHENOTYPE Patients lack the H gene and therefore cannot make H antigen, A or B antigen on their red cells Have very strong anti-A, anti-B, and anti-H and can only receive cells from a Bombay donor

22 ABO System Phenotype Antigen Natural antibody Genotype A A only Anti-B
AA or AO B B only Anti-A BB or BO AB A and B None O Anti-A, OO

23 Example of determining offspring blood types from known or suspected genotypes:
Genotype parent #1 (AO) A O Genotype parent A AA AO #2 (AB) B AB BO Phenotypes of possible offsprings: A, AB, B

24 Frequencies of ABO Blood Groups:
Blood Group Frequency O % A 41% B 10% AB %

25 ABO Subtypes: A variants (A1, A2) A1 most common (80%) & most antigenic A1 and A2 differentiated using antisera specific for A1 Ag (anti-A1 lectin) prepared from seed known as Dolichos biflorus  (+) reaction with A1 but not A2 Anti-A  reacts with both A1 & A2 but more strongly with A2

26 ABO Subtypes: Weak A and weak B phenotypes Null phenotypes: (a) Bombay (Oh) No A, B or H Ag on red cells & secretions With anti-A, anti-B & anti-H in their sera (b) para-Bombay Absent or only trace A,B & H Ag’s detected on normal expression in secretions & body fluids

27 ABO Antibodies Natural antibodies  antigenic stimulus is environmental  exposure occurs from birth Newborns  without ABO antibodies of their own; begin to produce Ab with detectable titer at 6 months of age Other characteristics of ABO antibodies: IgM Reacts at room temp. after an immediate spin

28 Secretors and Non-Secretors
Refer to the presence or absence of water- soluble ABH antigen substances in body fluids (saliva, semen, urine, sweat, tears, etc). Secretors possess the water soluble (glycoprotein) form of antigen, which appears in most body fluids. The production of A, B & H antigens in saliva is controlled by a secretor gene. The relevant gene is called Se, and its allele which amorphic is se.

29 Applications of ABO Grouping
Pre-transfusion Testing Prenatal Testing Presurgical Testing Paternity Determination Transplant Matching Donor Testing


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