Blood Groups Flashcards
Identify the main blood group systems.
ABO
Rhesus
How many blood group systems are there ?
26
What property distinguishes different blood groups ?
Antigens on Surface of Red Blood Cells
Describe Antibody-Antigen reactions.
Antibody from B cells in response to non-self antigens presented to T cells
• IgG antibodies occur mainly after exposure to blood transfusions or foeto-maternal transmission
(after exposure to blood group antigens which we do not have, for instance kKell negative person transfused Kell positive blood)
• IgM antibodies (naturally occurring) occur due to components in food which mimic A and B antigens
(for instance, O has naturally occurring anti A and anti B, not formed as a result of exposure to other blood groups, formed naturally early on in life)
Describe the structures of antibodies.
2 heavy chains with N terminal and C terminal end of proteins
2 Light chains attached to each heavy chain
FC portion (the first portion of the 2 heavy chains together) FAB portion (2 of them, the second portion of each of a heavy and light chain together)
What are the functions of the Fc and Fab portions of an antibody ?
Fab portion: binds antigen
Fc portion: binds phagocyte, complement activation
Are antibodies specific for particular antigens ?
Yes
Describe the structure of IgM.
IgM antibody normally circulates as 5 antigen recognising sites (pentamer)
Has J chain linking all 5 single antibodies
Describe the transfusion reactions which may arise following the recognition of an antigen on a blood cell by IgM and IgG respectively.
In both cases, immune haemolysis (
IgG
As a result of binding with IgG antibodies, red cells have shortened survival but are at least not destroyed in circulation (Fc receptors on splenic macrophages bind Ig-G coated red cells, which may then gradually be destroyed)
IgM
IgM antibodies agglutinate red cell, then activates complement and the membrane attack complex rapidly destroys red cells
Describe the main features of the ABO blood group system.
- FUT1 and FUT2 genes (chromosome 19) code for H substance
- H antigen is a precursor to each of the ABO blood group antigens
- Virtually everyone will produce this H substance
- Some people will, in addition, have genes for blood group A or B or one of each.
- Naturally occurring anti-A and/or B IgM antibodies in individuals lacking these antigens
- A and B genes (chromosome 9) code for glucosyl transferases which add further sugar groups
How may ABO antigens be distinguished ?
- ABO antigens differ in their sugars
- FUT1 and FUT2 genes will code for string of 5 sugars (lipid tail then glucose, galactose, N-Acetylglucosamine, galactose, fucose) which virtually everyone has. Lipid tail attached to red cell membrane whilst sugars sick out into plasma.
- O antigen is just an H antigen (5 sugar chain) without additional A or B antigens
- People who also have genes for A or B antigen, that codes for one more sugar (galactose for B antigen, and N-acetylgalactosamine for A antigen)
State the naturally occurring antibodies produced for each of the existing blood antigens (as part of the ABO system), and the frequency of each antigens.
O antigen - anti-A and anti-B - 46% frequency
A antigen - anti-B - 42% frequency
B antigen - anti-A - 9% frequency
AB (A and B antigens) - no naturally occurring antibodies - 3% frequency
What is the shelf life of RBCs, platelets, and plasma ?
RBCs: 35 days
Platelets: 7 days
Plasma: 2 years
Describe the main features of the Rhesus system.
- Antigens c C D e E
- coded for on chromosome 1 and inherited as a triplet eg cDe (inherit a triplet of those from each parent, those two together will determine Rhesus type)
- ‘Rhesus negative’ implies D negative (negative for Rhesus D antigen)
- No naturally occurring antibodies but can develop in response to pregnancy or transfusion
Define haemolytic disease of the newborn.
- Foetal red cells carrying antigens from the father transferring to maternal circulation (not meant to but always small number of foetal cells which escape during childbirth, abortion, trauma)
- Mother produces IgG antibodies to eg D, c, E, Kell
- Antibodies cross the placenta and attack foetal cells possessing said antigens causing anaemia and jaundice due to haemolysis. Bilirubin may then get into the brain causing brain damage. Foetal death is also possible.
- Usually, the antibodies develop as a result of exposure to the antigen from an initial pregnancy in childbirth or abortion or trauma, but only affect a foetus from a subsequent pregnancy (assuming same antigens are present on the second foetus to which the mother has developed antibodies)