ABO Blood Grouping System

Dr. Niaz Ahammed A. 1st yr M.D.S Dpt of Prosthodontics

Contents

• Introduction• Classification of blood groups• Agglutinogens and Agglutinins• Landsteiner’s Laws• ABO blood grouping sysytem• ABO antigens• ABO antibodies• Types of ABO blood groups• ABO inheritance• Determination of blood groups• References

Introduction

• In 1901 Karl Landsteiner published his discovery of a blood group system and he grouped red cells into three categories; A,B and O

• A fourth blood group , AB was discovered later by Decastello and Sturli.

• Based on the type of antigen present or absent, various blood grouping systems are known

Classification

• Major blood grouping systems:- ABO blood grouping system- Rh (CDE) blood grouping system

• Minor blood grouping systems:- MNS blood group system- P blood group system

• Familial blood group systems:- Only in a few families. Ex: Kell, Duffy, Lutheran, Lewis, Deigo, Kidd etc.

Agglutinogens and Agglutinins

• Agglutinogens refer to antigens present on the cell membranes of RBCs

• Agglutinins: antibodies against the agglutinogens, are present in plasma

• Approximately 300 red cell antigens have now been identified

• 18 blood group systems have been recognized

Blood grouping systems

Landsteiner law

• If an agglutinogen is present on the red cell membrane of an individual the corresponding agglutinin must be absent in the plasma

• If an agglutinogen is absent from the cell membrane of RBCs of an individual, the corresponding agglutinin must be present in the plasma

ABO blood grouping system

• It was the first to be recognized and most important

• Based on the presence of antigens called A and B agglutinogens on the cell membrane of RBCs

• H antigen is also present usually in all individuals but it is non- antigenic

• Almost everybody over the age of 6 months has clinically significant anti-A and/or anti-B in their serum

ABO antigens

• A,B and H antigens are glycoproteins and the differences in terminal sugars determine the specificity of these antigensL- fucose for HL- fucose + N- acetyl-D- galactosamine for AL- fucose + D- galactose for B

• 15 amino acids make up the protein backbone and four sugars form side chains off this backbone

• A & B antigens are also present in many other tissues like salivary glands, pancreas, kidneys, liver, lungs and testis and in body fluids like saliva, semen and amniotic fluid

• H antigen- non antigenic

α- L – fucosyl transferase produced by H gene, attaches fucose and yields H activity (group O)α –N- acetyl- galactosaminyl transferase produced by A gene transfers N-acetylgalactosamine and results in A activityα- galactosyl transferase produced by B gene attaches galactose and confers B activity

• Expression of ABH antigens on red cells is controlled by genes that reside at two loci

• ABH antigens results from action of enzymes (tranferases) on the appropriate precursor substance

• The substrate is a product of H gene (chromosome 19) and converted to A or B by the action of A or B- transferases (chromosome 9)

Variants of A and B antigens

• The principal sub groups of A are A1 and A2• A1 constitute 80% of those in gp A• A1 individuals agglutinated by Dolichos biflorus

lectin but not agglutinated by anti-H lectin, Ulex europaeus

• A2 individuals are agglutinated by Ulex europaeus

• Variants of B are less common, but are recognized

ABO antibodies• Individuals develop antibodies or agglutinins against A or B antigen

missing from their red blood cells• Anti A /α agglutinin and Anti B/β agglutinins are present in the

plasma• O people also possess an antibody referred to as anti-A,B which

reacts with either A or B red blood cells• Bacteria with similar sugar moieties that confer A,B and H reactivity

provide antigenic stimulus• Anti A and anti B are globulins of IgM type • In individuals in O group, antibodies are of both IgM and IgG classes• α and β agglutinins act best at low temperature ( 5- 20 degrees

Celsius) and are called as cold antibodies

• Two kinds of Anti-H also exist – Oh (Bombay) group and other in group A1 and A1B individuals

• ‘Bombay’ blood is very rare but the antibody is active at 37 degree Celsius and only ‘Bombay’ blood can be transfused

Types of ABO blood groups

• Group A: A agglutinogen - B agglutinin-A1 and A2 sub groups

• Group B: B agglutinogen- A agglutinin• Group AB: A and B agglutinogen

- A1B and A2B sub groups• Group O: both anti A and anti B in plasma

ABO inheritance

• The inheritance pattern of ABO genes follows Mendalian autosomal genetics

• Four major alleles are located at the ABO locus on chromosome 9

• 6 common phenotypes described- A1, A2,B, A1B,A2B and O

• Most blood group genes are co-dominant (A and B)• O gene is a silent allele or amorph, with no

obervable expression

Co dominance: A state in which two diffrent alleles are equally expressedSilent genes or amorphs: those with no observable expression

Determination of ABO blood grouping

• ABO blood group can be determined by mixing one drop of suspension of red cells with a drop each of anti serum A and antiserum B seperately on a glass slide• Anti serum A will cause agglutination of RBCs having

antigen A and anti serum B will cause agglutination of RBCs having B antigen

Population distribution of Blood groups in India

A groupB groupAB groupO group

References

• Berne and Levy Physiology- Koeppan, Stanten• Guyton and Hall text book of medical

physiology- Hall• Text book of Physiology- A.K.Jain• Haematology clinical and lab practise – Bick,

Bennet, Bynes, Cline• Wintrobe’s clinical haematology- Less, Foester

Thank you