2. Introduction
• The system determine the formation of ABH antigens. The formation
of A B and H antigen depends on the presence of genes A, B & H
• Genes at three separate loci (ABO, Hh, and Se) control the occurrence
and the location of the A and B antigens. Three common alleles (A, B
and O) are located on the ABO locus on chromosome 9.
3. Transferases: An enzyme that catalyses addition of specific
sugar units to give A B and H. The enzymes are also specific for A B
and H. –
• The H gene acts on the precursor substance by addition of its terminal
sugar L-fucose and thus making it H active substance.
• The H active substance forms a substrate to which another Transferase
specific enzyme adds its sugar.
• After the addition of another sugar there is the formation of A and/or B
antigen.
• The H-active substance must be formed first by the formation of at least
one H-gene in order for the sugars to be attached in response to an
inherited ABO genes
• A and B transferases add specific sugars to oligosacchide chains that have
been converted to H by the fucosyltransferase produced by the H gene.
• The number of potential A, B and H sites on the red cells is thought to be
in excess of two million
4. Role of Gene H
• H gene is inherited independently of ABO system. It is the first gene
that acts on the basic material (macromolecules) and is therefore
responsible for the formation of A, B & H antigens.
• Basic materials are precursor substances ( macro-
molecules)composed of peptide backbone on which many relatively
short carbohydrate chains are attached.
• Irrespective of specificity within ABO blood group system, each
macromolecule contains the sugars L-fucose, N- acetylgalactosamine,
D-galactose and about 15 amino acid.
• The actual specificity of the molecule is determined by the terminal
sugar occurring at the end of the chain.
5. Role of Gene H
• The primary products of the A B and H gene are specific transferase
enzymes which catalyse the addition of specific sugar unit to give
varied ABH antigen.
• H gene, therefore, acts on the Precursor substance I by addition of L-
fucose and converting it H-active precursor substance II.
• H active precursor substance II forms the substrate for another
transferase enzyme to add its respective sugar thus forming
respective antigen.
• H antigen like A & B antigen is capable of stimulating the formation
of an antibody.
6. Role of Gene A
• In the presence of H gene the A gene adds its terminal sugar to H
active substance II. N-acetylgalactosamine is the sugar added by A
gene. This sugar converts the molecule and antigen consequently
Blood Group A. N-acetylgalactosamine inhibits the accessibility of the
sugar L-fucose and therefore A cell reacts weakly with anti H.
• The A-gene tends to elicit higher concentration of glycosyltransferase
than the B-gene. This leads to one conversion of all the H-antigens on
the red cells to A-antigens sites as many as 1,000,000 to 1,700,000
antigens sites exist on any adult red cells in response to inherited A-
genes.
7. Role of B Gene
• In the presence of H gene B gene adds its terminal sugar (D-
galactose) to H- active precursor the substance to form B antigen on
the surface of RBC consequently Blood Group B.
• Anywhere between 600,000 and 830,000 B-antigen sites exist on B-
adult red cells, in response to the conversion of the H-antigen by the
glycosyltransferase elicited by the B-gene.
8. Role Gene AB
• In the presence of H gene AB gene adds their terminal sugar (N-
acetylgalactosamine and D galactose) forming A B antigen on the
surface of RBC consequently Blood Group AB.
9. Role of Gene O
• O Gene does not add any sugar on the H active precursor II and
therefore not able to change H-active precursor substance II.
• It is considered as an amorph and got no effect on H-active precursor
substance. The only antigen present is the H-antigen.
• Blood group O has the highest concentration of H antigen
• The terminal sugar is the one that determines the specificity of the
antigen and blood group an individual.
10. Bombay Phenotype ( Oh )
• It was discovered in Bombay India among Marathi speaking people, by Dr
Bhende in 1952.
• It is due to sanguineous marriages.
• It is a very rare blood group.
• Lacks A, B and H antigen.
• The symbol Oh has been selected to denote the phenotype because results
of routine ABO typing tests mimic those of blood group ‘O’ persons. Oh red
cells are not agglutinated by anti H, anti A and anti B reagents, and the
serum contains a strong anti H, anti A and anti B.
• art of the world.
• Bombay serum contains anti A anti B anti-AB and anti H.
11. Bombay Phenotype ( Oh )
• The Bombay individual lack H gene to convert the macromolecule to
H. active precursor substance II.
• H-active precursor substance II serves as the acceptor molecule or
precursor substance for the product of the A or B gene specified
transferases.
• Bombay individual lack all normal expression of the A, B or O genes
they inherited. More than 30 Bombay phenotypes have now been
reported in various p
12. Bombay Phenotype ( Oh )
• Unlike the anti H found occasionally in the serum of A, B and AB
individuals, the Bombay anti H is active over a wide thermal range (4 -
37oC).
• It is an IgM antibody that can bind complement and cause red cells
lyses. Since the H antigen is common to all ABO blood group Bombay
blood is incompatible with all ABO blood groups.
• Bombay can only receive blood from another Bombay .
• NB/ giving normal group O (with the highest concentration to H
antigen) would cause immediate cell lyses due to the potent of anti H
of the Bombay individual.
13. Inheritance
• The genotype hh usually occurs in the children of consanguineous
marriage. When family studies demonstrate which ABO genes are
inherited in the Bombay phenotype then the genes are written as
superscripts.
• At the genotype level, the Oh phenotype arises from the inheritance
of hh at the H locus and se/se at the Se-locus.
• Bombay phenotypes are all non-secretors of ABH substances
• The genotype hh is usually with individuals of consanguineous
(relatives) marriages.
14. Difference between group O and Bombay
• Group the two blood groups with Anti-H
• Bombay blood group –
• Blood group O +++
Blood group O contains H antigens and hence will react with Anti H in a
Bombay individual. Thus a Bombay individual should be cross –
matched and transfused with blood from another Bombay individual
15. Characteristics of Anti-H in Bombay individuals:
• It has a wide reacting range. +4oC-37oC
• It reacts weakly or not at all with A1 or A1B cells due to the little H
antigens present but reacts strongly with O cells.
• O>A2>A2B>B>A1>A1B
• Anti H can also be found in the serum of blood group A1 and blood
group A1B individuals
• Anti H can be obtained from Lectins e.g. Ulex europaeus
