ABO Blood Group System Lecture Notes PDF

ABO Blood Group System  ABO Blood Group System THE ABO BLOOD GROUP SYSTEM ❖ Most important of all blood groups in transfusion practice ❖ It is the only blood group system in which individuals have antibodies in their serum to antigens that are absent from their RBCs. This occurs without any...

ABO Blood Group System  ABO Blood Group System THE ABO BLOOD GROUP SYSTEM ❖ Most important of all blood groups in transfusion practice ❖ It is the only blood group system in which individuals have antibodies in their serum to antigens that are absent from their RBCs. This occurs without any exposure to RBCs through transfusion or pregnancy (naturally occurring) EX. BLOOD GROUP/TYPE A → ANTI-B ❖ Due to the presence of these antibodies, transfusion of an incompatible ABO type may result in immediate lysis of donor RBCs. This produces a very severe, if not fatal, transfusion reaction in the patient ❖ Testing to detect ABO incompatibility between a donor and potential transfusion recipient is the foundation on which all other pre-transfusion testing is based.  1901 – ABO discovered HISTORICAL PERSPECTIVE  Karl Landsteiner → Discovery of the first human blood group system.  First to conduct reverse and Forward typing  A,B, and O Blood group  Sturli and Von Decastello → AB Blood group  I gene – code for the ABO allele’s: 1. IA 2. IB 3. i THE LANDSTEINER LAW ❖ The antigen is present on the RBC surface and determines the blood group/type ❖ The corresponding antibody is NEVER FOUND in the individual’s serum ❖ The OPPOSITE naturally occurring antibody is always present in the individual’s serum Blood Antigens on the Naturally Percentage in the groups RBC surface occurring antibody American in serum population A A Anti-B 40% B B Anti-A 10% AB A and B None 5% O H Anti-A and Anti-B 45%  Importance of ABO ✓ Almost all normal healthy individuals above 3-6 months of age have “naturally occurring Abs” to the ABO antigens that they lack ✓ These Abs termed naturally occurring because they were thought to arise without antigenic stimulation  Importance of ABO ✓ These “naturally occurring” Abs are mostly IgM class. ✓ Thatmeans that, they are Abs capable of agglutinating saline/ low protein suspended red cell without enhancement and may activate complement cascade; can cause strong rapid intravascular hemolysis  Inheritance of the ABO blood group Theoryfor Inheritance of the ABO blood group was first described by BERNSTEIN in 1924 He demonstrated that an individual inherits one ABO gene from each parent (CODOMINANCE) and these two genes determine which ABO antigens are present on the RBC membrane One position, or locus, on each chromosome 9 is occupied by an A, B, or O gene  Inheritance of the ABO blood group The O gene is considered an amorph, as no detectable antigen is produced in response to the inheritance of the genes AA, BO and OO – denotes genotype A and B – denotes phenotype Inthe case of Blood type O individual they possess homozygous OO genotype. That’s why the phenotype is Blood type O Inheritance of ABO antigens from PARENTS Parent A B O alleles A AA AB AO B AB BB BO O AO BO OO Parents’ blood type is O and A, what are the possible blood types of their offspring? Parents’ blood type is B and AB, what blood type would not be expected in their offspring?  Formation of A, B and H Red cell antigen Formation of ABH antigens results from the interaction of genes of three separate loci (ABO, Hh and Se) These genes do not actually code for the production of antigens but rather produce specific enzymes (glycosyltransferase) that add sugars to a basic precursor/precursor substance called paragloboside or glycan GENE → ENZYME → SUGAR (PS) → ANTIGEN  Formation of A, B and H Red cell antigen o H and Se genes - located on chromosome 19 Not part of ABO blood group system; but their inheritance affect the ABO blood group H gene ✓ must be inherited to form ABH antigens on the RBCs ;codes for the H antigen ✓ Enzyme produced acts on Type II precursor substance ✓ Most individuals are homozygous HH ✓ The hh genotype is extremely rare and is referred to as the Bombay phenotype Se gene ✓ must be inherited to form ABH soluble antigens in secretions ; codes for the H substance ✓ Enzyme produced acts on Type I precursor substance o ABO genes – located on chromosome 9  Formation of A, B and H Red cell antigen o H antigen precursor structure on which A and B antigen are made  Formation of A, B and H Red cell antigen The precursor substance on erythrocytes is referred as Type 2 precursor substance. Means that the terminal galactose on the precursor substance is attached to the N- acetylglucosamine in a beta 1-4 linkage Type 1 precursor substance means that the terminal galactose on the precursor substance is attached to the N- acetylglucosamine in a beta 1-3 linkage  Formation of A, B and H Red cell antigen ❖ Type I and Type II precursor substances; both are composed of 4 sugars: 2 molecules of D-galactose 1 molecule of glucose 1 molecule of N-acetylglucosamine ❖ Differ only in the linkage of the terminal sugars (terminal D-galactose is attached to N- acetylglucosamine) ❖Type 1 precursor substance is water soluble and is found in plasma and in tissues and body secretions ; glycoproteins ❖Type 2 precursor substance is fat soluble and is found as an integral part of the red cell membrane ; glycolipids Type 2 precursor substance H Antigen α-2-L- fucosyltransferase L-fucose L-fucose, will attached to TYPE 2 PS  A Antigen A gene codes for the production of α-3- N-Acetylgalactosaminyltransferase Will attached to the H antigen to expressed A N-Acetylgalactosamine antigen B Antigen B genes code for the D-galactose will production of α-3-D- attached to H antigen to galactosyltransferase expressed B Antigen  OCCUPIED H ANTIGENIC SITES BLOOD TYPE 810,000 to 1,170,000 A 610,000 to 830,000 B A: 600,000 AB B: 720,000 None O NOTES ✓Amount of H-antigen / reaction with anti-H: ✓O > A2 > B > A2B > A1 > A1B  ABO ANTIBODIES ✓ ABO antibodies is initiated at birth, but titers are generally too low ✓ ABO testing before 3-6 months of age cannot be considered valid because some or all antibodies present maybe IgG maternal antibodies ✓ More logical to perform forward typing on cord blood from newborns  ABO ANTIBODIES ✓ Antibody production peak: 5-10 years of age ✓ Decline: later in life ✓ Elderlypeople usually have lower levels of Anti-A and Anti-B; therefore antibodies may be undetectable in Reverse grouping.  ABO ANTIBODIES They are present in some animals and plants as lectins. Lectins are plants or seed extracts diluted to agglutinate specific human blood group antigens ✓Dolichos biflorus: agglutinates A1 or A1B cells (anti-A1 lectin) ✓Bandeiraea simplicifolia: agglutinates B cells (anti-B lectin) ✓Ulex europaeus: agglutinates O cells (H specificity) and other ABO blood groups depending on the amount of H antigen (anti-H lectin) REMEMBER! GROUP Antigen Antibody O A B AB  NOTES: ✓ L-fucose is the sugar responsible for H specificity (blood group O) ✓ Amount of H-antigen/reaction with anti-H: O > A2 > B > A2B > A1 > A1B ✓ The term Bombay has been used to refer to the phenotype that lacks normal expression of the ABH antigens because of the inheritance of the hh genotype. ✓ The hh genotype does not elicit the production of α-2-L-fucosyltransferase. Therefore, L- fucose is not added to the type 2 chain, and H antigen is not expressed on the RBC BLOOD GROUP “O” BOMBAY PHENOTYPE (hh) REACTION WITH ANTI-H 4+ 0 (NEGATIVE) 4+ ONE SOLID AGGLUTINATE 3+ SEVERAL LARGE AGGLUTINATE; CLEAR BACKGROUND 2+ MEDIUM SIZED AGGLUTINATES; CLEAR BACKGROUND 1+ SMALL AGGLUTINATES TURBID BACKGROUND W+ TINY AGGLUTINATES TURBID BACKGROUND 0: NO AGGLUTINATION OR NO HEMOLYSIS  Two Methods in determining blood type oForward/Direct/Cell blood typing ✓Defined as using known sources of commercial anti-sera (anti-A and anti-B) to detect antigens on an individual RBC Specimen: Patient’s red cell (RCS) Reagent: Anti-sera oReverse/Indirect/Back blood typing ✓Defined as detecting ABO antibodies in the patient’s serum by using known reagent RBC’s namely A1 cells and B cells (Known cells) ✓Only unique to the ABO blood group system; checks results of forward typing Specimen: Patient’s serum/plasma Reagent: Known cells Procedure in Blood Typing FORWARD TYPING REVERSE TYPING Reagents for Forward typing Anti A Anti B Anti A,B Reagents for reverse typing A1 cells B cells O cells FORWARD/DIRECT TYPING REVERSE/INDIRECT TYPING TEST YOURSELF! FORWARD REVERSE Anti A Anti B A1 cells B cells Patient Forward: Reverse:  SERUM Group O Type O individuals contains Anti-A, Anti-B and as wells Anti-A,B Anti-A,B – will react with A and B cells. Originally thought to be just a mixture of anti-A and anti-B Anti-A,B is not part of ABO testing, but some believe that anti-A,B is more effective at detecting weakly expressed A and B antigens than Anti-A and Anti-B. INTERACTIONS OF THE Sese, Zz and ABH GENES  Sese system regulatesthe formation of H antigen and subsequently, of A and B antigens in secretory cells (ABH soluble substances) Genotypes: SeSe, Sese, sese ✓Secretors: SeSe , Sese ✓Non-secretors: sese  Zz system regulates production of H antigens on erythrocytes DISTINCTION OF ABH ANTIGENS AND ABH SOLUBLE SUBSTANCES ABH Antigens ABH Soluble substances RBC, epithelial cells, All body secretions except Found where? platelets, CSF lymphocytes, endothelial cells, Secreted substances Glycolipids Glycoprotein 1st sugar in the precursor Glucose N-acetylgalactosamine substance Precursor chain Type 2 Type 1 Linkage Beta 1-4 linkage C1-C3 (Beta 1-3 linkage) Regulating Gene Zz gene Se gene Test for ABH soluble substances/Determination of secretor status SALIVA NEUTRALIZATION TEST Principle: Hemagglutination Inhibition (+) reaction: without agglutination (-) reaction: with agglutination Test for ABH soluble substances/Determination of secretor status SALIVA NEUTRALIZATION TEST Principle: Hemagglutination Inhibition (+) reaction: without agglutination = soluble substance is present (-) reaction: with agglutination = soluble substance is absent Protocol: 1. Saliva heated to boil (560C for 10 mins to denature salivary amylase to prevent interference ; prolonged heating may cause destruction of soluble substance) 2. Dilute saliva using NSS (1:2) to reduce non-ABH soluble substances present in saliva 3. Dilute anti-sera (1:4) to reduce potency not to cause false positive reaction   B substance is present because it has 2 steps procedure been neutralized first by anti sera, not reacting to the B cell = without agglutination  A substance is not present because anti A was not neutralized, so anti A Step 1: Saliva + Antisera/ Lectin reacts with a cell – agglutination Step 2: Mixture of step 1 + Known Red cell suspension Example result:  Therefore, The saliva is from an individual which is a B secretor Antisera A cell B cell O cell with Saliva Anti – A + - - Anti – B - - - Anti - H - - -  2 steps procedure Step 1: Antisera/ Lectin only Example result: Antisera A cell B cell O cell with Saliva Anti – A + - - Anti – B - - - Anti - H - - -  2 steps procedure Step 2: Mixture of step 1 + Known Red cell suspension Example result: Antisera A cell B cell O cell with Saliva Anti – A + - - Anti – B - - - Anti - H - - - END