Lecture 1 - Blood Groups Flashcards
what are blood group systems considered as?
antigens on membranes of cells
how are red cells agglutinated?
when they are joined together by cross linking of antibodies
what blood group is the most clinically significant?
ABO
what is landsteiners law?
that antibodies in plasma match with antigens that are not on the surface of the red cells
what is the cause of almost all serious transfusion reactions?
ABO incompatability
what is the difference between the A and B antigens?
different terminal carbohydrates to the H antigen
how is a H antigen made?
H allele produces H transferase which converts a precursor substance to a H antigen
what converts a H antigen to an A or B antigen?
A or B transferase
what does A transferase add to the H antigen?
N-acetyl-D-galactosamine
what does B transferase add to the H antigen?
D-galactose
what is the features of the transferase of OO genotype?
no functional transferase so H left unchanged
what is the name for the carbohydrate chains added to a H antigen?
immunodominant sugars
what is the H immunodominant sugar?
Fuc
what is the A immunodominant sugar?
GalNAc
what is the B immunodominant sugar?
Gal
how is blood grouping linked to natural selection?
certain blood groups cause susceptibility with certain diseases
what antibodies are in the plasma of a type A patient?
anti-B
what antibodies are present in the plasma of a type B patient?
anti-A
what antibodies does an AB patient have?
none, yet A and B antigens
what antibodies does a O patient have?
anti-A and anti-B yet no antigens on red blood cell
what antibodies can cause intravascular lysis and how?
anti A and B and anti A,B by activating the complement pathway
what group is the universal red cell donor and why?
O as no antibodies on the surface
what group is the universal red cell recipient and why?
AB as they have no antibodies in the plasma
what group is the universal plasma donor?
AB as will not give patient any antibodies
what group is the universal plasma recipient?
group O as no antigens to reject the antibodies in the plasma
what is HDFN?
haemolytic disease of the foetus and newborn
how is blood grouping carried out in present years?
antiserum is contained in a gel matrix and the blood is passed through, if the blood cells contain the matching antigen they are trapped in the matrix
what are the blood subgroups?
A1, A2, A3 and Ax
how does a subgroup form?
there is a quantitative reduction in the number of A antigens on the surface of red cells
how can you tell that there is a subgroup?
if there is a slight positive reaction to the A antibody
what is anti-A1?
this is the formation of ability to produce anti-A1
what is an acquired B blood type?
group A patients who produce a B like antigen so therefore start grouping as a B
what diseases is acquired B linked to?
GI bacterial diseases and colon cancer patients due to the action of bacterial enzymes
how is acquired B caused?
bacterial enzymes nibble off the end of the carbohydrate chain, transforming it into a B chain
how is loss of ABO antigens caused?
due to malignancy
what disease causes loss of ABO antigens?
usually myeloid leukaemia
what does loss of ABO antigens indicate is changing?
genetic changes in the stem cell line at the ABO gene level
how is loss of ABO antigens detected?
flow cytometry which marks the different antigens showing different populations
what is an Oh blood group?
Hh group people cannot make H, A or B antigens as no H antigen produced
what grouping features does an Oh group have?
may be genetically A or B but groups as an O
what blood does group Oh react with?
have strong anti H antibodies so will react with all blood except its own
what is the second most important blood group?
Rh
what are the 5 antigens belonging to Rh?
D, C, c, E and e
what antigens does D produce?
D antigens
what antigens does the CE gene produce?
ce, Ce, cE or CE
why is the D antigen the most important?
most immunogenic
why is the D antigen the most immunogenic?
large membrane protein so even small amount of exposure with RhD positive blood if patient is negative still causes production of anti-D antibodies
what does it mean if you are rhesus positive?
have the D gene
what is weak D?
quantitative difference in number of antigen sites on the red blood cell, do not form anti-D antigens
how is weak D caused?
mutation of interior of D molecule, causing less D antigens on the surface
is weak D still R+?
yes but have a weak positive reaction to the antiserum
what is partial D?
qualitative difference in the antigen, can still form anti-D with the missing parts of the antigen
how is partial D formed?
mutation on the outside of the D molecule
are partial D patients still R+?
as a donor yes, as they do still have part of the molecule, yet not as a recipient in case they may form anti-D antibodies with the blood they receive
