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 .

Figure (1)

Table (1)

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 .

Figure (2)

Figure (3)

The Origin of ABO Antigens

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 )

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 .

Figure (5)

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 ) .

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 .

Table (4)

Figure (7)