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Blood Group The Objective : To give information about :
1- Types of blood group systems present on the surfaces of red blood cells ( RBCs ) .
2- Types of ABO blood group systems depending on ABO antigens present on the surfaces of RBCs .
3- The inheritance of ABO blood group system by ABO genes which located on chromosome 9 .
4- The origin of ABO antigens through ABO genes that encoded specific enzymes that added specific sugars ( antigens ) on the RBCs receptors .
5- Types of laboratory tests used for the donor and recipients blood before blood transfusions :
* Bloob typing tests * Cross match .
Twenty five blood group systems have been defined on the
bases of antigens located on the surfaces of red blood cells .
(Figure 1) and ( Table 1 ) . Each system is a series of red cell
antigens determined by either a single genetic locus or very closely
linked loci .
The ABO- system and RH- systems are both of key
importance in determining the compatibility of blood transfusions and
tissue grafts .
ABO – System : ABO – System :
Discovery of the ABO system by the Austrian Karl Landsteiner in
1901 marked the beginning of safe blood transfusion . There are 4 major ABO- blood types designated by the antigens
present on RBCs: 1 -Blood group A:
Individuals have the A antigen on the surface of their RBCs , and blood serum containing Anti-B antibodies . Therefore , a group A individual can only receive blood from individuals of groups A or O ( with A being preferable ) and can donate blood to
individuals of groups A or AB .
2- Blood group B : Individuals have the B antigen on their surface of their
RBCs , and blood serum containing Anti-A antibodies . Therefore , a group B individual can only receive blood from individuals of groups B or O ( with B being preferable ) and can donate blood to individuals of groups B or AB .
3- Blood group AB : Individuals have both A and B antigens on the surface of
their RBCs , and their blood serum does not contain any antibodies against either A or B antigen . Therefore , an individual with type AB blood can receive blood from any group ( with AB being preferable ) , but can only donate blood to another group AB individual . (Universal recipient)
4- Blood group O : Individuals do not have either A or B antigens on the
surface of their RBCs , but their blood serum contains Anti- A and Anti-B antibodies . Therefore , a group O individual can only receive blood from a group O individual , but they can donate blood to individuals of any ABO blood group ( A , B , O , or AB ) . ( Universal donor ) . ( Table 2 ) .
Table 2 : Blood Transfusion Compatibilities for the ABO Blood Groups
Blood Group
Antigens present on
RBCs
Antibodies present
in serum
Transfusion can be
accepted from
Transfusion can be
given to
AA
(galactosamineAnti- BA , O A , AB
BB (galactose)Anti- A B , O B , AB
ABA
(galactosamine) galactose Plus B
None A , B , AB , O AB Universal
recepient
ONone Anti-A plus
Anti- BO
O , A , B , AB Universal
donor
Blood groups are inherited from both parents . The
ABO blood type is controlled by a single gene . This gene
responsible for the producing of the A and B antigens and the
gene is donated by the letter I . It has 3 alleles IA , IB , IO . The
gene is located on chromosome 9 . The gene encodes a
glycosyltransferase enzyme .
Inheritance : Inheritance :
Individuals with the IA allele have the A antigen on
their erythrocyte surfaces ( blood type A ) , while those
with IB have the B antigen on their cell surfaces ( blood
type B ) , those with both alleles express both antigens
(blood type AB ) , and those with only two copies of the
IO allele have neither antigen ( type O blood ) . Because
the IO allele produces no antigen , Individuals who are IA
IO or IB IO heterozygotes have blood types A and B
respectively . ( Table3 ) .
Table 3 : Genotypes and the Corresponding Phenotypes ( Blood Group Types ) for the ABO Locus in Humans .
Genotype
Activity
Phenotype
Frequency inPopulation
IA IA, IA IOα-3-N-acetyI-D-galactosaminyltransferase
A42%
IB IB, IB IOα-3-D-galactocyltransferase
B8%
IA IB Both enzymesAB3%
IO IO None O47%
The genetics of ABO antigens were once used to rule
out paternity .as in table 4. A child inherits genes from each parent that determine his blood type . This makes blood typing useful in paternity testing . Paternity testing compares the ABO blood types of the child , mother , and
alleged father.
Inheritance of Blood TypesThese charts show the possible blood type results for offspring.
Blood Type Mothers's Type
OABAB
Fathers' Type
OOO, AO, BA, B
AO, AO, AO, A, B, ABA, B, AB
BO, BO, A, B, ABO, BA, B, AB
ABA, BA, B, ABA, B, ABA, B, AB
Rh FactorMother's Type
Rh +Rh -
Father's TypeRh +Rh +, Rh +Rh +, Rh -
Rh -Rh +, Rh -Rh -
The Origin of ABO Antigens :
The A and B genes each code for an enzyme (glycosyl
transferases ) that adds aterminal carbohydrate to RBC receptors
during maturation . ( Figrue 2 ) .
RBCs of type A contain an enzyme that adds N – acetyl
galactosamine to the receptor ; RBCs of type B have an enzyme
that adds D – galactose ; RBCs of type AB contain both enzymes
that add both carbohydrates ; and RBCs of type O lack the genes
and enzymes to add a terminal molecule . ( Figure 3 ) .
Then the ABO antigens are not primery gene products but
instead they are the enzymatic reaction products of enzymes called
glycosyltransferases which is encoded by the ABO gene .
Codominance :Codominance :
When both alleles of pair are fully expressed in a heterozygote
, they are called Codominants .
In humans , the ABO blood group antigens are a good
example .
Amating between a homozygous A- type person ( IA IA ) and a
homozygous B- type person ( IB IB ) would result in all heterozygous
AB- type ( IA IB ) offspring . ( Figure 4 )
Mating between heterozygoutes ( IA IB x IA IB ) would result in
a ratio of : 1 A- type ( IA IA ) : 2 AB- type ( IA IB ) : 1 B- type ( IB IB).
Aphenotypic ratio of 1 : 2 : 1 has thus replaced the 3 : 1 ratio ,
because the alleles are codominant .
The functional alleles A and B provide activities that are
codominant with one another and dominant over O group .
(Antibodies are proteins produced by the immune system that
comnine with specific antigens ; Hence , anti A combines with antigen
A) . Because of their specificity for the corresponding antigens these
antibodies are used in standard tests to determine blood type .
The Source of these ( anti A ) and ( anti B ) antibodies: The Source of these ( anti A ) and ( anti B ) antibodies:
It appears that they develop in early infancy due to exposure
to certain heterophile antigens that are widely distributed in nature .
These antigens are surface molecules on bacteria and plant cells that
mimic the surface of A and B antigens . Exposure to these sources
stimulates the production of corresponding antibodies (IgM).
Blood Transfusions : Blood Transfusions :
A number of laboratory tests must be completed before blood can be transfused : 1- Blood Typing :
The individual blood types of donor and recepient must be
determined .Using a standard technique , drops of blood are mixed with
antisera that contain antibodies against the A and B antigens , and are
then observed for the evidence of agglutination . ( Figure 5 ) .
2- Screening for possible infectious agents that could be transmitted by blood
transfusion such as : Human Immunodeficiency Virus ( HIV ) 1 and 2 , Hepatitis B
Virus (HBV) , Hepatitis C Virus (HCV) and some bactria and parasites .3- Crossmatch ( Compatibility Test ) :
The general rule of compatibility is that the RBC antigens of the donor
must not be agglutinated by antibodies in recepient’s blood .
For example : If the donor is A type and the recepient is B
type .The RBCs of the type A donor contain antigen A , while the serum
of the type B recepient contains anti-A antibodies that can agglutinate
donor RBCs (agglutination : aggregation by antibodies of RBCs into
clumps that settle
Agglutinated RBCs can clog blood vessels and stop circulation in
vital organs . And the activation of complement by antibodies on the
RBCs can cause hemolysis and anemia , fever , jaundice .
(Transfusion reaction :occurs When incompatibile blood is transfused ,
specifically if antibodies in the recipient’s serum cause rapid RBC destruction in
the proposed donor ). ( Figure 6 ) .
The ideal practice is to transfuse blood that is a perfect match ( A to A , B to B ) . But even in this event blood samples must be cross matched prior to transfusion because other blood group incompatibilities can exist . The primary purpose of the major cross match or compatibility test , is to prevent a possible transfusion reaction . The aim of cross matching is to ensure that the blood of a recepient does not contain antibodies that will be able to react with and destroy transfused ( donor ) RBCs . To begin the crossmatch , blood from adonor with the same ABO and Rh type as the recipient is selected . In atest tube , serum from the patient is mixed with RBCs from the donor . If clumping occurs , the blood is not compatibile . If clumping does not occur the blood is compatibile . ( Figure 7 ) .
In an emergency , when there is not enough time for blood typing and crossmatching O red blood cells may be given . preferably Rh- negative . O- blood type is called the Universal donor because it has no ABO antigens for a patient’s antibodies to attack . In contrast , AB+ blood type is called the Universal recipient because it has no ABO antibodies to attack the antigens on transfused red blood cells . If there is time for blood typing , RBCs of the recipient type ( type specific cells ) are given . In either case , the crossmatch is continued , even though the transfusion has begun .
Blood donors and blood recepients must have compatible blood types .
( Table 4 : Blood compatibility chart ) illustrates how people with different
blood types can receive or donate blood . An A- person , for example ,
can receive either O- or A- , and can donate to people with AB+ , AB- ,
A+ or A- blood . An O-person can donate blood to people with any type ,
and is termed a Universal donor . An AB+person can receive blood of
any type , and is termed Universal recepient .