Other Blood Group Systems Lewis I MNS P
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What makes the Lewis blood group special
The antigens are not integral to blood cells, but are passively adsorbed onto the RBC from plasma
Where are Lewis antigens originally found before being adsorbed onto RBCs
On type 1 glycosphingolipids in plasma and other tissues
Which genes are involved in the formation of Lewis Antigens
Le, Se, H genes
What are the primary Lewis antigens
Le^a and Le^b
At what age are Lewis antigens fully expressed
7 years of age
How does pregnancy affect Lewis antigen expression
The Lewis antigen expression weakens resulting in Le(a-b+)
Cn Lewis antibodies be produced during pregnancy
Yes, but they typically disappear after delivery
Are Le^a and Le^b alleles
No they are not
Do le, se, or h produce any products
NO
What happens if the Le gene is inheirted
Le^a substance is produced
What genetic conditions must be met to convert Lea to Leb
Le, Se, and H genes must all be inheirted
How common is Le(a+b+)
It is rare
What gene is responsible for the production of Lewis antigens
The Lewis gene (Lu) or FUT3
How are Lewis genes similar to ABH genes
They control the production of specific transferases
What enzyme does the inherited genes encode
L-fucosyl-transferase
What is the function of L-fucosyl transferase in Lewis antigen formation?
It adds L-fucose to the subterminal N-acetylglucosamine precursor in a α1-3 linkage, converting the type 1 chain into a Lea antigen
How is the Lea antigen expressed on RBCs?
Le (a+b-)
What happens when both the Secretor gene (Se) and H gene are inherited?
The secretor transferase enzyme adds another L-fucose to the terminal D-galactose of the type 1 chain, forming the Leb antigen
What occurs when both Lea and Leb antigens are present in body fluids?
Leb antigens are more readily absorbed resulting in Le(a-b+) phenotype
Does any Lea substance remain in secretions when both Lea and Leb are present?
Yes, it remains unconverted in saliva
What is the structural difference between Lewis antigens in secretions and those on RBCs?
Those in secretions are glycoproteins, while those on absorbed on the RBC are glycolipids
Who commonly produces Anti-Lea and Anti-Leb antibodies?
Le (a-b-) phenotype
What type of immunoglobulin are Lewis antibodies typically?
IgM
At what temperature do Lewis antibodies react best?
At RT, and occasionally bind complement, which results in in vitro hemolysis
Do Le(a−b+) individuals produce Lewis antibodies?
No, because their body has both Lea and Leb structures
Which Lewis antibody is more commonly encountered?
Anti- Lea
How common is Anti-Leb compared to Anti-Lea?
Less common
Why do Lewis antibodies not cause hemolytic disease of the fetus and newborn (HDFN)?
Because Lewis antigens are not fully developed at birth
Where can Lewis gene products be found in newborns?
Because newborns inherit gene products they can be present in saliva and plasma
What are the transitional Lewis phenotypes during 2-6 years of age?
Le(a−b−) → Le(a+b+) → Le(a−b+).
Does Anti-Lea commonly cause hemolytic transfusion reactions?
No, however it can bind complement and may cause in vitro hemolysis
Is Anti-Leb clinically significant?
NO, it is clinically insignificant
How can Lewis antibodies be neutralized?
By saliva containing Lewis substances
What substances would be found in the saliva of a group B secretor who also the Lele genotype?
H, B, Leb
What is the probable genotype of a person who phenotypes as Le(a-b-)
LeLe, sese, HH, AA
The Leb phenotype is produced by the inheritance of which genes?
Lele, Sese, and Hh genes
What are the two major antigens in the I blood group system?
I and i
What precursor substance do I antigens share with the ABH system?
N-acetyl-glucosaminyltransferase (branching transferase)
How is the “I” antigen formed?
Through the sequential action of multiple gene products encoding transferases
Are I and i antigens antithetical (opposites)?
NO
Are I and i high-prevalence antigens?
YES
How do I and i antigen expression change from birth to adulthood?
Newborns have the i antigen which is linear, while adults have the I antigen which is branched this happens at about 2 years of age
Is there a true I-negative or i-negative phenotype?
NO, the strength of I and i antigens varies amongst individuals
What is the i adult phenotype?
A rare condition where the individual does not convert to the I antigen and retain the i antigen into adulthood
Where can I and i antigens be found besides RBC membranes?
In glycoprotein and glycolipids on the RBC membrane as well as plasma, breast milk, and amniotic fluid
At what temperature do I and i antibodies typically react?
They cold-reacting autoantibodies, typically reacting more strongly at 4°C or with enzyme-treated cells.
What is Autoanti-I, and is it harmful?
Found in the serum of normal individuals and is benign, meaning it is not harmful and doesn’t cause in vivo RBC destruction
What are the characteristics of benign Autoanti-I?
Weak
Naturally occurring
Saline-reactive IgM agglutinin with a titer less than 64 at 4°C.
How does pathogenic Autoanti-I differ from benign Autoanti-I?
It consists of strong IgM agglutinins with a higher titer and a broader thermal range, reacting up to 30°C. An example of this is cold agglutinin disease.
How does pathogenic Autoanti-I cause hemolysis?
When peripheral circulation cools in response to low ambient temperatures, leading the antibodies to attach in vivo, causing autoagglutination and resulting in hemolytic anemia.
How can potent cold autoantibodies interfere with transfusion testing?
They can mask clinically significant alloantibodies and complication pretransfusion testing which can be avoided by prewarming
What is meant by Autoanti-I "reacts as a compound antibody"?
It means because Autoanti-I is often found as an anti-IH, meaning it reacts more strongly with RBCs that have many H antigen sites such as O and A2 cells
How can Autoanti-I be distinguished in testing?
It will agglutinate all adult RBCs, including the autocontrol, but not the cord cells
Autoanti-I is associated with which infections or diseases?
Mycoplasma pneumoniae infection
Cold hemagglutinin disease
What diseases are associated with Anti-i antibodies?
Mono
Lymphoproliferative disease
Occasionally cold hemagglutinin disease
What are the three main antigens in the P Blood Group System?
P1, Pk, and P (GLOB)
What are the five phenotypes in the P Blood Group System?
P1, P2, p (null), P1k, and P2k
What are the P1 and P2 phenotypes in the P Blood Group System?
P1 have both P and P1 antigens, while P2 only have the P antigen and produce anti-P1 antibodies
How developed are the P Blood Group antigens at birth?
They are poorly developed
What happens to the strength of P antigens upon RBC storage?
It decreases
Where can P antigens be found in soluble forms?
In plasma and hydatid cyst fluid
What is one way to neutralize anti-P1 antibodies?
P1 substance found in hydatid cyst fluid
How are the Pk, P, and P1 antigens expressed biochemically?
The stepwise addition of sugars to lactosylceramide
How is the Pk antigen synthesized?
By adding galactose via galactosyltransferase 1 to lactosylceramide
What enzyme is responsible for converting the Pk antigen to the P antigen?
N-acetylgalactosaminyltransferase 1 which adds N-acetylgalactosaminyl to the terminal galactose on the Pk antigen to form the P antigen
How is the P1 antigen formed?
By adding a carbohydrate to the paragloboside precursor chain, which is a type 2 precursor that serves as the substate for both the P1 and Ha antigens
What happens when galactose is added to the paragloboside?
P1 antigen is produced
How is the H antigen formed from the paragloboside?
By adding fucose to the paraglobodise
What is Anti-P1, and who typically produces it?
Found in P2 people, and is a naturally occurring IgM antibody
Is Anti-P1 clinically significant?
NO, unless it is strong and reacts at 37
What is Auto Anti-P, and when is it produced?
A IgG autoantibody produced in people with paroxysmal cold hemoglobinuria
What type of antibody is Auto Anti-P, and what is its characteristic feature?
It is a biphasic antibody, which reacts with the antigen on the RBC at cooler temperatures and binds complement
How does a biphasic antibody cause hemolysis?
By binding to the antigen at cooler temperatures, and when the antigen-antibody complement complex warms up, the RBCs are hemolyzed
What is a key symptom of paroxysmal cold hemoglobinuria (PCH)?
HGB in the urine after exposure to cold
How is the Donath-Lansteiner test performed?
Incubating the patient’s serum with their own RBCs first at 4°C, then at 37°C, and looking for hemolysis.
What are the characteristics of the P2 phenotype?
It lacks the P1 antigen but expresses P antigen it is the second most common P blood group phenotype and is associated with Anti-P1 antibodies, which are IgM, react at room temperature, and are not clinically significant.
What are the characteristics of the P2k phenotype?
It expresses the P antigen and the P^k antigen, but lacks the P1 antigen. It is associated with Anti-P1 antibodies, which are typically IgM and react at room temperature. These antibodies are usually clinically insignificant, although they can occasionally cause mild reactions.
What are the characteristics of the P1k phenotype?
it expresses the P antigen and P^k antigen, along with Anti-P antibodies, which are clinically significant and have been associated with spontaneous abortions.
What is the P null phenotype?
It is negative for P, P1, and P antigens. It is a very rare phenotype and associated with hemolytic reactions. These antibodies can be separated into three specificities, and this phenotype is considered clinically significant.
What is the antibody for P null phenotype
Anti-PP1Pk
What is Anti-Pk, and how is it characterized?
It is not a pure antibody, and is found as a component of anti-Tja. It has a wider thermal range and can be enhanced by enzymes
What is Anti-Tja, and who produces it?
A rare antibody, also known as anti-PP1pk. It is produced by P null phenotype people
What clinical conditions are associated with Anti-Tja (Anti-PP1pk)?
Spontaneous abortion
HDFN
HTR
What are the four important antigens in the MNSs blood system?
M, N, S, and s.
When is the U antigen always present
When S or s antigens are inherited.
Where are the M and N antigens located?
Glycophorin A
Where are the S, s, and U antigens located?
Glycophorin B.
What is the membrane structure of the M and N antigens?
sialoglycophorin A.
How many amino acids are present in glycophorin A?
131 amino acids.
At which positions do M and N antigens differ on glycophorin A?
1 and 5 on glycophorin A (GPA).
What amino acids are found at positions 1 and 5 for M and N antigens?
M has serine and glycine at positions, while N has leucine and glutamic acid at those positions.
What is the inheritance pattern for M and N antigens?
They show dosage, meaning homozygous inheritance enhances agglutination. Phenotypes can be (M+N-) or (M-N+).
What is the membrane structure of the S, s, and U antigens?
sialoglycophorin B.
How many amino acids are present in glycophorin B?
72 amino acids.
At which position do the S and s antigens differ on glycophorin B?
position 29 on glycophorin B.
What amino acids are found at position 29 for S and s antigens?
S has methionine at position 29, while s has threonine at that position.
What is the inheritance pattern for S and s antigens?
S and s show dosage, meaning homozygous inheritance enhances the expression of these antigens.
How common is the U antigen?
It is present in 99% of individuals and is always present when S or s is inherited.
What percentage of Black individuals are U negative?
About 1%
How are M and N antigens controlled?
By codominant antithetical genes M and N.