Blood: Blood Groups L4 Flashcards
define blood group
classification of blood based on presence of inherited antigenic substances on surface of red blood cells
define antigen
a material not found in the host and is considered as foreign provoking an immune response
describe the antigens on the surface of red blood cells
mixture of proteins, glycoproteins and glycolipids
they are found on all red blood cells and a range of other cells in the body
can the antigens on red blood cells that have been inherited change
yes
- those inherited tend to be life long but ca be changed by infection, malignancy, autoimmune disease or after a bone marrow transplant
what are the two main blood groups systems
- ABO
- Rhesus
who discovered ABO blood group system
Karl Landsteiner
what are the blood types in ABO blood group system
A , B, O, AB
- A and B are codominant
- A and B are dominate to O
what are the 5 sugars involved in the ABO system
Fucose*
galactose*
N-acetylgalactosamine*
N-acetylglucosamine
Sialic Acid
what type of enzymes are used and what are the 3 main ones used in ABO system
glycosyl transferases
1. Fucosyl transferase (FUT1)
2. N-acetylgalatosamine transferase (A transferase)
3. Galactose transferase (B transferase)
what are the two genes involved in ABO system
- ABO
- H
what is the ABO blood group determined by
terminal sugar structure of substances found on surface of red blood cells
what do the ABO and H genes encode and what is the products function
they encode specific glycosyltransferases
- transfer monosaccharides to polysaccharide chains
what are the possible alleles of ABO and H genes
ABO: A, B or O
- O encodes a non-functional protein so no enzymatic activity
H: H or h
what does the H allele encode and what is its function
encodes for fucosyl transferase (FUT1)
- Adds fructose to terminal galactose molecule of precursor substance forming H antigen
where is H gene located
what is the function of H and h and which is dominant
chromosome 19
H: dominant, encodes for FUT1
h: recessive, encodes non-functional protein
-HH make H antigen
- Hh make H antigen
- hh do not make H antigen
what name is given to the hh genotype and describe it
Bombay phenotype
No symptoms or related disease but hh people can receive transfusions only from others with the same blood group.
where is ABO gene found
what causes O allele
how do A and B alleles differ
which residues determine A and B to encode different glycosyltransferase
found in seven exon gene on chromosome 9
O allele caused by deletion in 6 of the exons causing a frameshift therefore protein is inactive
A and B differ by 7 nucleotide substitution
- 4 of these substitutions cause different amino acids to form
residues 266 and 268
A allele encodes A- transferase (N-acetyl galactosamine transferase) while B allele encodes B transferase (galactose transferase)
what do A and B transferase do
A transferase turns H antigen to A antigen
- adds N-acetyl galactosamine to terminal galactose
B transferase turns H antigen to B antigen
- adds galactose to terminal galactose of H antigen
both use UDP to do this
describe blood group O
people who have neither A or B transferases and make only H substance
hh May posses functional A or B transferases but can not make ABO antigens
- why is this
they don’t have functional FUT1 they can not make substance H
(can not turn precursor substance to A or B antigen)
describe AB blood group
person has both A and B transerases
- some of the H antigens will have galactose added and some will have N-acetylgalactosamine added
- forms blood cells with both A and B sugar chains on their surface.
what are the 6 genotypes of ABO blood group system
- AA- only makes A antigens
- BB - only makes B antigens
- AO- only make A antigens
- BO- only make B antigens
- AB- make both A and B antigens
- OO- makes only H antigen
What is the function of A and B antigen
unknown
- those with O do not have A or B antigen but are still healthy
give examples of diseases linked with ABO blood group
- gastric cancer for blood group A
- gastric and duodenal ulcers in group O individuals
- ABO phenotype correlates with level of factor VIII and von Willebrand factor (vWF). Blood group O individuals have about 25% less factor VIII and vWF in their plasma.
which is the most common blood group across ethnicities and which is the rarest
most common: O
rarest: AB
A,B,O are glycoproteins so are antigenic
- what can this provoke
an immune response
what kind of antibodies will blood group O develop
A and B (alpha and beta)
what antibodies will blood group A make
B (beta)
what antibodies will blood group B make
A (alpha)
what antibodies will blood group AB make
none
Note that blood group antigens are also known as agglutinogens and the antibodies raised against them are known as agglutinins
what will happen if blood group A mixes with B
B antibodies from A’s plasma will agglutinate red blood cells
what does agglutination lead to
lysis of red blood cells in the blood vessels, complement system is activated. Leads to kidney failure, uncontrolled clotting and circulatory shock; can be fatal.
why is donated blood less clinically significant
Donated blood also contains antibodies that can agglutinate recipient RBCs - Clinically of less significance as are quickly diluted in the recipient’s blood.
what molecule are rhesus antigens and how many can be present on RBL
proteins
- not glycoproteins
49
which is the most common type of rhesus antigen
D
Individuals who are homozygous dominant (DD) or heterozygous (Dd) are Rh+.
Individuals who are homozygous recessive (dd) are Rh-ve
- positive is most common of all ethnicities
what are anti-Rh antibodies
antibodies that destroy rhesus positive blood they find
- RBC bound by IgG, engulfed by macrophages, transported to liver and spleen for removal.
- Less serious than intravascular haemolysis
who can O- blood be given to
and who can they receive blood off
everyone
- has no antigens on surface
only receive off O-
- has all antibodies
who can AB+ be given to and who can they take blood off
they can receive from anyone
- have all antigens so have no antibodies
can only donate to AB+
read the rest using pp table
what is Haemolytic disease of the newborn
a father is Rh+ mother is Rh-
during first pregnancy, mother will make Rh antibodies as baby is Rh+
during second pregnancy and baby is Rh+, anti-Rh antibodies made by mother will cause agglutination of babies RBC causing anaemia and jaundice, can kill the foetus
how can haemolytic disease of a newborn be prevented
Rh-ve mothers given anti-D immunoglobulin which removes any foetal Rh+ve blood from her circulation before she can make anti-D antibodies
Mothers may make antibodies to a baby’s ABO antigens
why is this not an issue like anti-Rh antibodies
These antibodies are of the IgM class and do not cross the placenta thus the foetus can not be harmed.
