Transfusion - Rh Blood Group Flashcards
What is the ‘rhesus group’ now called?
Rh group
Why was the Rhesus group renamed?
(5)
Group was originally named rhesus due to a misunderstanding
an anti-rhesus monkey antibody was found to react with 85% of a panel of human red cells
The year prior to this a woman expeirienced HDFN and it was found tat her plasma reacted against the same 85% of red cells
Hence, the causative antibody in the HDFN case was thought to be this ‘anti-rhesus’ antibody
It was later discovered that this HDFN antibody was infact an anti-D and the anti-rhesus antibody was infact an anti-Lw -> both Lw and D are coexpressed hence the same reactivity of cells
What was the anti-rhesus antibody later found to be?
It was found to be an anti-Lw
What is clinically important about the D antigen?
How frequent is anti-D formation?
The D antigen is the next important antigen after A and B in transfusion practice
The formation of anti-D in a D- individual happens in approximately 80% of D+ to D- transfusions
The formation of anti-D happens in about 16% of D positive delivery from a D negative mother
What are the only circumstances where you would give D+ blood to a D- patient?
(3)
In order to induce anti-D in male volunteers to produce anti-D product for prevention of HDFN
Can be given to Males - often done in MMUH as long as no anti-D
Can be given to women over childbearing years
How immunogenic is D?
70%
What are the most immunogenic antigens?
D 70%
K 10%
c 4%
E 3.3%
k 1.6%
e 1.1%
Fya 0.5%
C 0.2%
What antibody class causes HDFN
IgG
What antibodies bind complement
ABO
KIDD
DUFFY
When was RhD discovered?
1939
Who discovered RhD
Levine and Stetson described the importance of the group in a case of HDFN in 1939
Karl Landsteiner and Alexander Wiener discovered the Rhesus factor
When were the RhCE antigens discovered?
They were discovered by the mid 1940s
Explain the genetic expression of the RhCE gene
Found on chromosome 1
four alleles for four antigens
Codominantly expressed
Talk about the production of anti RHCE antibodies
There are >55 antigens which stimulate antibody production
An anti-E can occur wihtout immunological stimulation -> tends to be IgM in nature (all others IgG)
Antibodies are tipically IgG, react at 37 degrees
What gene encodes the Rh group
Two highly homologous genes RhD and RHCE located on chromosome 1
What does the RhD and RHCE genes encoded?
non glycosylated membrane protein
These polypeptides span the membrane 12 times and have approx 417 amino acids
What does the RHAG encode?
It encodes for a similar, glycosylated protein which is necessary for rbc expression of Rh proteins
How did the RhD gene come about?
The RHCE gene was the original gene
The RhD gene later rose as a duplication of the RhCE gene
What does the RHAG do?
The RHAG helps structure of red cells
?? need more info on this
What happens in the Rhnull phenotype?
You will have no RhD or RhCE
You will have a mild haemolytic anaemia
Very rare but some people still have it in Ireland
What other antigens are found associated with the Rh structure and are therefore lost/expression decreased with Rhnull?
Diego
Duffy
LW
MNS
What is the function of the Rh as part of the red cell?
Ammonium ion transportation through the cell
Kind of redundant though as other structures also do this job
=> main function of Rh is red blood cell structure
What happens in the expression of D in a RhD-?
In almost all D negs the RHD gene is deleted
i.e. nothing where D should be on chromosome 1
Usually seen with Rhce expression i.e. most D- are D- C- E- c+ e+
There is also a D- that occurs due to unequal crossover
How does the RhD differ from the RhCE?
(2)
RhD polypeptide differs frm RhCE polypeptide by 36 amino acids
-> hence why immunogenicity of D is very high as the RhD protein is quite foreign in those that dont have it -> 36 amino acids that they dont have
Explain the unequal crossover mutation that results in 40% of RhD-
(3)
Recombination between an upstream and a downstream Rhesus box on two different chromosomes - termed unequal crossover
This mutation results in a part of the RHCE gene crossing over into the RhD region
It results in a perfetly healthy RHCE but a
Where is the RHAG found and what does it encode?
Found on chromosome 6
6 RHAG
Almost identical to RHCE but has a sugar added on
How does the RhD gene compare to the RhCE gene?
The two genes directly mirror each other
-> imagine a mirror between the RhD gene and the RhCE gene
How does the RhD gene compare to the RhCE gene?
The two genes directly mirror each other
-> imagine a mirror between the RhD gene and the RhCE gene
What are the two most common phenotypes if you are D+?
R1 is most common -> DCe
R2 is second most common -> DcE
How does C differ from c and E from e?
4 amino acids different between C and c
- only the serine matters
1 amino acid different between E and e
How does C differ from c?
4 amino acids different
serine 103 proline only significant change
How does E differ from e
only one amino acid difference at pro 226 to alanine
In the C to c change why does only the serine change matter?
This is because its the only change found on the outside of the red cells and thus the only antigenic
What is the Wiener Theory nomenclature?
R0 = Dce
R1 = DCe
R2 = DcE
Rz = DCE
r = dce
r’ = dCe
r’’ = dcE
ry = dCE
What are the four most common groups in caucasians vs Blacks?
R1, r, R2, R0
R0, r, R1, R2
What groups are rarely encountered?
r’
r’’
Rz
ry
What is the D dash dash
These patients have no C at all
Perfectly functional cells but the only polypeptide they produce is D
What happens in the Rhnull phenotype?
Missing or severly reduced Rh antigens as well as associated antigen LW, CD47, GPB antigens (SS, U), Fy5 etc
can either be due to mutation in RHAG glycoprotein or amorph type
What is Amorph type of Rhnull?
Caused by mutation in RHCE gene which results in loss of CE gene as well as individual being D-
-> this person has neither CE or D expression and is therefore RhNull without the traditional RHAG gene mutation seen in Rhnull
How does Rhnull affect the patient?
It affects cation transport and membrane phospholipid organisation
Its associated with a stomatocytosis and spherocytosis -> cell membrane defect
Patients suffer from constant low Hb -> due to a constant low grade haemolytic anaemia
How does Rhnull affect the patient?
It affects cation transport and membrane phospholipid organisation
Its associated with a stomatocytosis and spherocytosis -> cell membrane defect
Patients suffer from constant low Hb -> due to a constant low grade haemolytic anaemia
What groups are affected by Rh null?
MNSs are reduced
Duffy refuced
Lw reduced
Kell not really affected
What happens in weak D?
Antigen is all present but antigen expression is lower
Quantitative reduction in D so far that when you type them you type them as D- and thus receive D- blood -> if we give them D- they wont produce an antibody and if we give them D+ theyve been given the correct blood
Caused by missense mutations which result in a charged amino acid in the sequence -> this prevents the D antigen from sitting into the lipid bilayer of cell membrane which affects antigen expression
Normally D antigen amino acids are not charged -> if charged - the lipid in cell membrane rejets antigen like two magenets and forces the antigen out
RhC in trans to RhD results in lower expression of D as well -> RhC favoured -> not as common as the missense mutation but is seen
Why are weak Ds rarely seen now?
Our monoclonal agents are now strong enough to detect majority of weak Ds as positive
What is a partial D
This is where were missing certain parts of the D antigen
–> the person can produce antibodies against any antigenic parts they are missing so they must be given D- blood
How does Weak D differ from partial D?
If mutation is on exterior of cell then it can be antigenic and is therefore partial D but if missing internal amino acid then it is a weak D as all of antigen is present on external of cell
Talk a little about the D6 mutation
This is a parttial D variant
This is where there is crossing over between the RHCE and D gene
Some of D ends up in CE and vice versa
This is common -> occurs many times a year
Exons 4-7 from CE end up in D
A hairpin loop genetic structure is formed
Talk a little about immunogenicity in partial Ds
In some partial Ds there is only a small amino acid change that changes an epitope
This is less likely to produce an anti-D if only a single epitope missing
If a large section is missin e.g. 10 to 15 epitopes then the person is way more likely to produce anti-D
How do we detect d6?
Hospital gels use a D6
-> we would rather type a partial D as D- in the hospital but in the donor population or maternity we would rather type these as D positive -> want to pick up any D antigen
This can be a probel when group confirming units -> unit could be D+ from IBTS but you type it as D- when doing a group confirm -> will have to ring IBTS to confirm
What are Cis product antigens?
This is where the haplotype DCe express determinants additional to those defined as D, C and e
Ce is a cis product that almost always accompanies C and e when they are encoded by the same haplotype
Absent for example in a person of the genotype DCE/ce
Similar cis product antigens exist for c and e determined by the same haplotype (the antigen called ce or f), for c and E (cE) and for C and E (CE)
What is the G antigen?
The G antigen results from serine at position 103 of the Rh polypeptides
It is encoded by either RhD or RhCE
The G antigen is almost invariably present on red cells posessing either C or D
Antibodies against G appear to have anti-C+D specificity i.e. a combo anti-C+ and anti-D whose activity cannot be separated into anti-C and anti-D -> such as an anti-AB
When might the G antigen cause problems?
an anti-G can cause problems in a maternity setting due to its cross-reactivity with anti-D
i.e. an anti-G may appear as an anti-D
In maternity this can be dangerous as the mother still has potential to produce an anti-D ie. be immunised through pregnancy -> mother still a candidate for anti-D therapy
How would you investigate a G antigen
Most labs just send any query anti-Gs to the IBTS for investigation
Other las will carry out an elution to separate out the antibody and then test this antiody against reagent cells to type the antibody
What would a pan positive panel and positive auto indicacte?
AIHA ->
Reference lab can ID this using reference Rhnull blood which will comee up negative but we cant give out Rhnull blood
What would a pan positive panel with negative autoindicate?
This means there I an antibody present against a frequent antigen
Will need to figure this out
Antigen negative crosshatch units only
