Lecture 19 + 20 - blood groups Flashcards
what are surface antigens composed of
glycoproteins
glycolipids
what chromosome are genes encoding ABO antigens on
chromosome 9
what do ABO genesdo
- produce glycotransferases
- add sugars to H substance (by making the enzymes that are responsible for adding it)
what does O gene add to H substance
no effect
what does group A gene add to H substance
N-acetyl galactosamine (GlcNAc)
what does group B add to H substance
D-galactose (Gal)
what is the cause of productions of antibodies
produced in response to the environemnt
as many things in nature have similar complexes to RBC sugars = elicit production of antibodies
what antibodies does AB type have
none
what antibodies does O type have
anti A and anti B
subtypes of type A and their prevelance
A1 = 80%
A2 = 20%
when might subtypes create an issue for transfusion
repeated transfusions can cause a reaction
what is the Bombay phenotype
- cant form 2-L-fucosyltransferase necassary for H substance formation
- so NO h substance
- and so present as O type
- but they have antibodies to A, B (like O) and H substance
- but when transfused with O = agglutinates
- can only have blood from eah other
all the antigens of Rh blood group system
C
c
D (biggest clinical influence)
E
e
what are the genes for the Rh blood system
RhD = codes proteins with D antigen
and RhCE = codes for RhCE protein with C, c, E and e antigens
RHD gene
on chromosome 1
is dominant
if you inherit even one Rh+ then you are positive
its either present or not
RHCE gene
can have 4 variations
what is R0 blood type
someone with R0 is always +ve, and has Dce
so always have the D gene
what happens when someone has medical conditions that require mutiple blood transfusions
need more extensively matched blood
so instead of just matching ABO and Rh +ve or -ve
they need to match the subtype also
e.g. R0 matching
which group are more donors needed
R0 subtype rare
and is 10x more common in Black african/black carribean backgrounds
so there’s a push for them to donate more
and theyre also at more risk of SCD, which need regular transfusions
in a Rh -ve mum and Rh +ve baby, what happens if the blood mixes and explain HDN
when blood mixes
mum’s immune system mounts a response against the Rh+ve antigens
But usually at delivery there’s no time for them to react ie an immune response to take place (usually takes 72hrs)
But the antibodies remain in the blood
So in first pregnancy theres no impact
BUT
In second, antibodies are already there
in second, when blood mixes, it can cause immune response and causes haemolytic disease of newborn
what can women be given for haemolytic disease of newborn
if baby is Rh +ve = anti d immunoglobulin is given
= destroys the foetus’ Rh +ve D cells before they can cause the mum to produce her own anti D
how might ABO haemolytic disease of newborn occur
happens to group A or B babies born to group O mothers (they have anti A and anti B antibodies)
how is blood group O associated with blood clotting
usually blood groups dont have any link with helath conditions
but blood group O will have 25% less efficient factor 8 and vWF
