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ABO blood group System By : Mr. Waggas Ela’as, M.Sc; MLT

Karl LandsteinerDiscovered by Karl Landsteiner; locus on chromosome 9 Single 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  A & B Ag’s autosomal co- dominant (expressed on group A, B and AB red cells; O phenotype autosomal recessive (most frequent) ABO BLOOD GROUP SYSTEM 3

4 People inherit H gene which will convert a “precursor Substance” into an H Substance. If the person –then – inherit A gene ; it will convert the H substance into A antigen. If he inherit B gene ; it will convert the H substance into B antigen. If he inherit both A & B genes ; they will convert the H substance into AB antigens. If he inherit NO A nor B genes; the H substance will remain unconverted. This is named “group O”. If the person didn’t inherit the H gene; he will not have an H substance. This is named “Bombay group”.

genes The A and B genes control the synthesis of specific enzymes (glycosyl-transferase) responsible for the addition of single carbohydrate residues (N-acetyl galactosamine for group A and D-galactose for group B) to a basic antigenic glycoprotein or glycolipid with a terminal sugar L-fucose on the red cell, known as the H substance. The O gene is an amorph and does not transform the H substance. 5

The H gene is converted to H substance. Subsequently the H substance is acted upon by specific transferases which is converted to either A or B antigen. Some H substance remains unconverted and is expressed as H antigen. Since there is no conversion of H substance in O blood group, the amount of H antigen is maximum on red cells (The O gene is a silent allele). 6

ABO Antigens Present on the surface of red cells as well as tissue and endothelial cells in the body (found on all the cells of the body tissues, hence the ABO compatibility is a prerequisite in cases of organ transplants). secretors.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 ABO BLOOD GROUP SYSTEM 7

PhenotypeAntigenNatural antibody Genotype AA onlyAnti-BAA or AO BB onlyAnti-ABB or BO ABA and BNoneAB ONoneAnti-A, Anti-B OO 8

ABO BLOOD GROUP SYSTEM 9

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ABO BLOOD GROUP SYSTEM 11

ABO BLOOD GROUP SYSTEM 12

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 Caucasians hh  does not produce H Ag  Bombay phenotype (Oh) anti-H antibodies rare – found only in individuals with Bombay phenotype 13

Example of determining offspring blood types from known or suspected genotypes: Genotype parent #1 (AO) AO Genotype parentA AA AO #2 (AB)B AB BO Phenotypes of possible offsprings: A, AB, B 14

Frequencies of ABO Blood Groups: Blood GroupFrequency O 45% A 41% B 10% AB 4% 15

ABO Subtypes: [Subgroups of A are of minor clinical significance]. 1.A variants (A 1, A 2 ) A 1 most common (80%) & most antigenic A 1 and A 2 differentiated using antisera specific for A 1 Ag (anti-A 1 lectin) prepared from seed known as Dolichos biflorus  (+) reaction with A 1 but not A 2 Anti-A  reacts with both A 1 & A 2 but more strongly with A 2 16

A2 red cells have fewer A antigen sites than A1 cells. In addition, the number of A antigens on A1 RBCs is approximately five times more than on A2 RBCs. The H antigen content of red cells depends on the ABO group and when assessed by agglutination reactions with anti-H, The strength of reaction tends to be graded O > A2 > A2B > B > A1 > A1B. Other subgroups of A are occasionally found (e.g., A3, Ax) that result from mutant forms. 17

ABO Subtypes: 2.Weak A and weak B phenotypes 3.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 RBCs with normal expression in secretions & body fluids 18

ABO Antibodies Natural antibodies  antigenic stimulus is environmental  exposure occurs from birth Newborns  without ABO antibodies of their own; begin to produce Abs with detectable titer at 6 months of age Other characteristics of ABO antibodies: 1.IgM :(complete Abs). 2.Reacts at room temp. after an immediate spin (cold Abs : react best at 4 o C, but can react also at 37 o C). 19

Summary Precursor substance No H gene H gene Bombay group H substance No A or B genes A or B genes Group O group A, B or AB 20

Inheritance of ABO ABO & RH genes are not linked Genotype: Sum of the genes. Phenotypes: product of the genes. 21

Allele from the mother Allele from the father Genotype of offspring Blood types of offspring A AAA A ABAB AO AOA BA AB BBBB B BO BOB O OOOO 22

Secretor Status 1. The presence or absence of the ABH antigens on the red blood cell membrane is controlled by the H gene. Se 2. Presence or absence of the ABH antigens in secretions is indirectly controlled by the Se genes. soluble form 3. In 80% of the population who possess secretor genes, these antigens are also found in soluble form in secretions and body fluids (e.g. plasma, saliva, semen and sweat). 23

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Think !! Is there any anti O Abs? why? A man with group O; married to a women with group O. Is there any possibility that they may have a group B child? Any group B person have B antigens in his body fluids. Is this correct?? 25