Download (H antigen). - INAYA Medical College

• Definition
• Characteristics of ABO blood group
• ABO Antigens
• ABO Antibodies
• ABO Subtypes
•
• Individual’s will form immune
antibodies to ABO blood group antigens
they do not possess.
The body produce antibody to Antigen who
lake it.
Result from interaction between the genes it possesses.
• The genetic constitution of an individual or group as
determined by the particular set of genes it possesses.
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.
• 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 transerase  no
antigen produced
• A and B antigens on surface of RBC 
protrude from outermost layer of cell
membrane
• 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
• Each gene codes for the production of a specific Transferase enzymes 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.
Gene
Enzyme
H
L- fucosyltransferase
A
3 N-acetyl- D- galactosyl transferase
B
3-D- galactosyl transferase
O
None
H substance.
A antigen
B antigen
• 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).
• The H antigen is present on the red cells in the following diminishing quantity.
– O > A2 > B > A2B > A1 > A1B.
•
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
• 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 (antiA1)
16
– 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
17
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
18
– Express A and B Ag on
RBC surface
– Genotypes A1B or A2B
– have no ABO antibodies
(“universal recipients”)
19
• 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
• 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
AB
O
None
Anti-A,
Anti-B
OO
Example of determining offspring blood types from
known or suspected genotypes:
Genotype parent #1 (AO)
Genotype parent
#2 (AB)
A
O
A
AA
AO
B
AB
BO
Phenotypes of possible offspring: A, AB, B
Frequencies of ABO Blood Groups:
Blood Group
O
Frequency
45%
A
41%
B
10%
AB
4%
1. 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
2. weak B phenotypes
2-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
•
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:
1. IgM
2. Reacts at room temp. after an immediate spin
• 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.
• Pre-transfusion Testing
• Prenatal Testing
• Presurgical Testing
• Paternity Determination
• Transplant Matching
• Donor Testing
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