HEM 2133

Immunohaematology IImmunohaematology I

Lesson 13:

Other Blood Group Systems

Blood Group System

A group of related chemical determinants

(antigens) residing on the red blood cell (RBC)

membrane

The antigens associated with each system are

produced by the action of genes at a single produced by the action of genes at a single

locus or at loci situated so close together on

the chromosome that crossing over rarely

occurs

In most cases, the blood group antigens are

expressed as autosomal codominant traits

In some circumstances, the action of alleles at

separate loci may be required for the separate loci may be required for the

production of the final antigenic determinant

E.g. the products of A and B genes cannot be

fully expressed without collaborative action at

the Hh locus to produce H substance

Most blood group system antigens are integral

part of the RBC membrane

However, some antigens are simply absorbed

onto the membrane from surrounding plasma

These are recognized as also belonging to

blood group systemblood group system

Importance of red blood cell antigens

Antigens of the ABO and Rh systems

transfusion therapy

Hemolytic disease of the newbornHemolytic disease of the newborn

Autoimmune hemolytic anemia

Medicolegal serology aid in identification of

individuals in paternity testing as well as in

forensic investigation

The Lewis Blood Group System

Identified in 1946 by Mourant

Antigens in the Lewis system: Lea, Leb , Lec ,

Led , Lex

Three phenotypes commonly seen in the Three phenotypes commonly seen in the

system are Le(a-b+), Le(a+b-) and Le(a-b-)

Difference between the Lewis system and

other blood group system:

1. Lewis antigens are not intrinsic to the RBC

membrane produced during cell

development

The antigens are produced by tissue cells and The antigens are produced by tissue cells and

are found primarily in plasma and watery

secretions

RBCs subsequently acquire Lewis antigens by

adsorption from the surrounding plasma

2. An individuals Lewis phenotype is not

determined solely by genes at the Lele locus

but also by the action of genes at the Hh and

Sese loci.

3. The amount of Lewis antigen expressed on

the RBC varies according to the cells ABO the RBC varies according to the cells ABO

phenotype

Genetics of the Lewis system

Interactions of three genetic loci influence

production of the Lea and Leb antigens

The Lewis gene locus, with alleles Le and le,

determines whether an individual will develop

Lewis antigensLewis antigens

The nature of the antigens expressed depends

on activity by the secretor genes (Se and se)

and the Hh genes

Individuals with the lele genotype do not

produce Lea or Leb antigens regardless of the

other genes present

They type as Le(a-b-) and have no Lewis

antigens in their plasma or secretions

Nonsecretors (genotype sese) who have at Nonsecretors (genotype sese) who have at

least one Le gene produce only the Lea antigen

Their RBCs type as Le(a+b-) and their plasma

and secretions contain the Lea antigen

Expression of the Le(a-b+) RBC phenotype

depends on the presence of at least one Le

gene, one Se gene and one H gene

Le(a-b+) individuals have both Lea and Leb Le(a-b+) individuals have both Lea and Leb

antigens in their secretions

Because the Se gene is present, these

individuals also produce the appropriate A, B

and H antigens in their secretions

Acquisition of Lewis antigens by red blood cells

In the plasma, Lewis antigen activity is found

on glycolipids

RBCs acquire Lewis antigens by adsorbing

these Lewis-active glycolipids onto their

membranesmembranes

The Lewis phenotype of RBCs depends on the

phenotype of the plasma in which they are

suspended and can be changed by incubating

the cells in plasma containing different Lewis-

active glycolipids

If Le(a-b-) cells are incubated with plasma

containing Lea or Leb glycolipid, they adsorb

the available antigen from the plasma and

subsequently type as Le(a+b-) or Le(a-b+)

Similarly, Le(a+b-) or Le(a-b+) cells incubated

in plasma from an lele individual lose Lewis in plasma from an lele individual lose Lewis

antigens and convert to Le(a-b-)

The same change in phenotypic expression is

observed with transfused cells, which convert

to the phenotype of the recipient

Lewis System Antibodies

Anti-Lea

A very common antibody that is often

naturally occurring

Produced almost exclusively by the Le(a-b-)

phenotypephenotype

Le(a-b+) individuals do have small amounts of

Lea antigen in their plasma and RBCs, they

usually do not form anti-Lea

Usually IgM, reacts best at room temperature

Anti-Leb

Usually produced by Le(a-b-) individuals

May also be seen in Le(a+b-) phenotype

Usually an IgM, room temperature-reactive

Clinical significance of Lewis System

Antibodies

Hemolytic Disease of the Newborn

Lewis antibodies usually are not associated with

HDN

Most examples of anti-Lea and anti-Leb are IgM and Most examples of anti-Le and anti-Le are IgM and

are therefore incapable of crossing the placenta

Even examples of Lewis antibodies that are IgG and

able to cross the placenta do not cause destruction

of fetal RBCs because Lewis antigens are poorly

expressed on these cells

Hemolytic transfusion reaction

The most commonly seen forms of anti-Lea and

anti-Leb are reactive at room temperature only

and are not associated with HTR

However, Lewis antibodies that demonstrate in

vitro hemolysis or that are reactive in vitro hemolysis or that are reactive in

antiglobulin phase should be considered capable

of inducing increased clearance of transfused

cells

Routine (37C) compatibility testing should be

used to select appropriate donors for patients

with these potentially significant Lewis

antibodies

Selection of antigen-negative units for

transfusion does not appear to be necessary

The elution of Lewis antigens from cells

incubated in Le plasma may contribute to the

relative insignificance of Lewis system

antibodies in transfusion practice

If antigen-positive cells are transfused to an

antibody marker, the transfused cells readily

lose their antigens and are no longer a target

for destruction by Lewis antibodiesfor destruction by Lewis antibodies

Further, the antigens released from donor

cells into the plasma can neutralize Lewis

antibodies present in the recipient plasma

The I Blood Group System

I antigen is present on all red cells of all

human adults, but only a small amount is

present at birth

Its allele i is present in the red cells at birth, Its allele i is present in the red cells at birth,

and changes from i to I during the first 18

months

Adult cells show a very small amount of i

antigen

The i antigen also serves as a marker for

maturation of red cells

If a large number of immature red cells are

being released into circulation, the i activity is being released into circulation, the i activity is

enhanced

As a rare exception, the maturation of i

antigen to I does not take place and such i

adult individuals remain strongly positive for i

throughout life and show only traces of I

Antibodies Defining the I System Antigens

Anti-I

Usually seen as a benign, naturally occurring,

cold-reactive autoantibody

Encountered when testing is conducted at Encountered when testing is conducted at

room temperature or below

Can be detected in the sera of most normal

adults if the serum is tested at 4C

Almost exclusively IgM and binds complement

efficiently

The antibody elutes when the mixture is

incubated at 37C but the bound complement

remains and reacts with a polyspecific

antiglobulin serum

Occasional examples of anti-I are strongly

reactive autoantibodies that can cause a cold reactive autoantibodies that can cause a cold

autoimmune hemolytic anemia

Individuals of the adult i phenotype may

develop a strong alloanti-I that may be

strongly hemolytic

Anti-i

A rare antibody

Usually an IgM cold agglutinin

Development of a potent autoanti-i is

sometimes associated with infectious sometimes associated with infectious

mononucleosis and may cause a transient

hemolytic anemia

Clinical Significance of Anti-I and Anti-i

Hemolytic Disease of the Newborn

I system antibodies are primarily IgM in nature

They cannot cross the placenta to cause HDN

The weak expression of the I antigen on fetal The weak expression of the I antigen on fetal

RBCs protects those cells from anti-I-mediated

destruction

IgG anti-i has been implicated in at least one

case of HDN

Hemolytic Transfusion Reaction

The normally encountered benign autoanti-I

does not cause increased clearance of

transfused cells

More potent examples of anti-I and anti-i,

such as those associated with hemolytic such as those associated with hemolytic

anemias, may destroy transfused cells as well

as autologous cells

If transfusion is required in these instances,

the blood should be warmed and the patient

kept warm during the transfusion

The P Blood Group System

Discovered in 1927 when Landsteiner and

Levine

Immunized rabbits with human RBCs and

used the resulting immune sera to test for

antigenic differences among individual RBC antigenic differences among individual RBC

donors

Antigens of the P blood group system

Most common phenotypes: P1 and P2

analogous to the A1 and A2 phenotypes seen

in the ABO system

P1 individuals have two antigens on their

RBCs: P and PRBCs: P1 and P

P2 individuals have only the P antigen and can

produce anti-P1

The P1 antigen is poorly developed at birth,

but the P antigen is well developed

In adults, expression of the P1 antigen varies

widely from individual to individual

The strength of the antigen can deteriorate on

storage

3rd antigen Pk

P1k phenotype expressing both P1 and P

k

antigens

P2k phenotype P1 negative and P

k positive

Pk positive cells always lack the P antigen

p phenotype negative for P1, P and Pk antigens

Antigens of the P Blood Group System

Antibodies of the P Blood Group System

Anti-P1

Frequently encountered in the serum of P2individuals

Usually is naturally occurring as an IgM cold- Usually is naturally occurring as an IgM cold-

reactive agglutinin

Does not react above room temperature and

may often go undetected in samples tested by

routine techniques

Anti-P

Alloanti-P

Produced only by individuals of the P1k or P2

k

phenotypes

A potent hemolysin and must be considered

significant when selecting blood for transfusionsignificant when selecting blood for transfusion

Autoanti-P

Associated with an autoimmune hemolytic

anemia known as paroxysmal cold

hemoglobinuria

Potent IgG hemolysin

Anti-PP1Pk

Produced by all individuals with the p

phenotype

A potent, naturally occurring hemolysin that

may be either IgM or IgG

Women of the p phenotype have an increased

incidence of spontaneous abortion

Clinical Significance of P System Antibodies

Anti-P1 has little clinical significance

Usually an IgM antibody

P1 antigen is poorly expressed on fetal cells

has not been associated with HDNhas not been associated with HDN

Anti-P1 may be an in vitro hemolysin but it is

not reactive above room temperature

Rare examples of Anti-P1 that are reactive at

37C are capable of causing in vivo hemolysis

and have been associated with HTR

Anti-P and anti-PP1Pk

- produced by individuals with rare P system

phenotypes

- more potent antibodies and can be clinically - more potent antibodies and can be clinically

significant

- each can be hemolytic, both in vitro and in

vivo, and both have been associated with HDN

and HTR

The MNSs Blood Group System

Discovered in 1927 by Landsteiner and Levine

They used rabbit immune anti-human RBC

sera, they identified a second blood group

system, calling the two antigens M and Nsystem, calling the two antigens M and N

The MNSs blood group system rivals the Rh

system for number of antigens and complexity

interrelationships

Major antigens: M, N, S, s and U

Antibodies of the MNSs Blood Group System

Anti-M

Relatively common specificity in normal sera

Usually a naturally occurring antibody reacting

at room temperature or belowat room temperature or below

May be either IgM or IgG

Many examples of anti-M show dosage by

reacting stronger with homozygous (MM) cells

than with heterozyggous (MN)

Some weak antibodies may react only with

homozygous cells at room temperature

Many examples of anti-M react more strongly

in an acidified test system

Occasional examples of anti-M that are

reactive at 37C or in the antiglobulin test may reactive at 37C or in the antiglobulin test may

be clinically significant

Anti-M has rarely been reported to cause HDN

or HTR

Anti-N

An uncommon antibody

Usually a weak, cold-reactive, naturally

occurring IgM agglutinin produced by

individuals who are M+N- and who are

positive for S or spositive for S or s

Many anti-N sera demonstrate antigen dosage

on RBCs

It is not considered clinically significant unless

antibody reactions occur at 37C

Anti-S and anti-s

Uncommon antibodies usually seen as

immune antibodies reactive in the

antiglobulin phase

Anti-S is usually IgG, but IgM may also be seen

Anti-s is almost always IgG

Some anti-S sera may demonstrate antigen

dosage on the RBCs

Both specificities are considered clinically

significant

Anti-U

A rare antibody reactive at 37C and the

antiglobulin phase with the cells of most

normal individuals

Should be considered clinically significant and

has been associated with severe HDN and HTR

Identification can be difficult due to the

scarcity of U-negative cells for testing

Clinical Significance of MNSs System

Antibodies

Anti-M and anti-N

Not usually associated with HDN or HTR

because they are normally reactive at

temperature below 37Ctemperature below 37C

Examples of MNSs antibodies reactive at

higher temperatures or in the antiglobulin

phase of testing are considered clinically

significant

Anti-S, anti-s and anti-U

All have been associated with severe HDN and

HTR

Must be considered clinically significant

Antigen-negative blood should be selected for Antigen-negative blood should be selected for

transfusion to patients with one of these

antibodies

The Kell Blood Group System

First new blood group system discovered after

the development of the antiglobulin test

Antigens: K, k, Kpa, Kpb, Jsa, Jsb

Null phenotype K0 lack all Kell system

antigens0

antigens

McLeod phenotype weakened expression of

Kell system antigens is associated with

structural and functional abnormalities of

RBCs and leukocytes

Antibodies of the Kell Blood Group System

Anti-K

The Kell system antibody most commonly

encountered in routine blood bank practice

K antigen is a powerful immunogen, second K antigen is a powerful immunogen, second

only to D in its potential to induce

alloimmunization

Once stimulated, the immune system can

continue to produce detectable levels of anti-

K for years

Usually seen as an immune-mediated IgG

antibody reactive only in the antiglobulin

phase of testing

Autoanti-K has been reported Autoanti-K has been reported

Other Kell System Antibodies

Antibodies to k, Kpa, Kpb, Jsa, Jsb share the

serologic characteristics and clinical

significance of anti-K but occur much less

often because of the frequencies of these

antigensantigens

Kell system antibodies should be considered

whenever a serum reactive with most or all

cells is encountered

Clinical Significance of Kell System

Antibodies

Hemolytic Disease of the Newborn

Kell system antibodies are usually IgG and Kell

antigens are well expressed on fetal cells

- Must be considered capable of causing HDN- Must be considered capable of causing HDN

Anti-K is particularly potent causing disease

severe enough to require transfusion therapy

in 50% of cases in one study

Hemolytic Transfusion Reaction

Anti-K has been the cause of many transfusion

reactions

The reactions can be immediate or delayed The reactions can be immediate or delayed

Other antibodies in the Kell blood group

system also have caused HTRs

The Duffy Blood Group System

Antigens: Fya, Fyb, Fyx, FY3, FY4, FY5 and FY6

Antibodies defining the Duffy system

Anti-Fya and anti-Fyb

Most likely to be encountered in routine blood

bankingbanking

Often seen in combination with other RBC

antibodies

Usually are IgG antibodies produced after

transfusion or pregnancy and must be considered

clinically significant

Anti-FY3

Reacted equally well in with enzyme-treated or

untreated cells

Immune mediated, but transfusion appears to be a

much stronger stimulus than pregnancy

Anti-FY4

Resembles anti-FY3, reacted equally well in with Resembles anti-FY3, reacted equally well in with

enzyme-treated or untreated cells

Anti-FY5

Reacted only with cells having normal Rh antigens and

Fya or Fyb antigens

Like FY3 and FY4, the FY5 antigen is not destroyed by

proteolytic enzyme

Clinical Significance of Duffy System

Antibodies

Hemolytic Disease of the Newborn

Anti-Fya is an uncommon cause of HDN,

usually resulting in a mild disease

Occasional cases severe enough to require Occasional cases severe enough to require

exchange transfusion have been reported and

rare fatalities have occurred

Anti-Fyb has been implicated in only one case

of HDN, in which the infant is only mildly

affected

Anti-FY3 has been associated with a mild HDN,

whereas anti-FY4 and anti-FY5 have not been

implicated in HDN

Hemolytic transfusion reaction

Anti-Fya has often been implicated in

immediate and delayed HTR, which immediate and delayed HTR, which

occasionally have been fatal

Anti-Fyb has also been implicated in

immediate and delayed HTR, occasionally

causing severe cell destruction or death