blood group antigens and antibodies Flashcards
Proteins present on the surface of red cells
Red cell antigens
Red cell antigens are
Inherited
Most important red cell antigens
ABO and Rh
Antigen A has antibody
B in plasma
Antigen B has antibody
A in plasma
Antigen AB has antibody
No antibodies present
Blood group O has antibody
AB in plasma
What are blood group antigens
Complex structures present on red cell membrane that contain proteins and carbohydrates and often have a role
How are antigens produced
By the inheritance of certain genes which produce different antigen systems
Where are blood group antigens located on membrane
Glycolipid, glycoprotein molecules on RBC
The carbohydrate chain of membrane glycolipids carry antigens of
ABO,Hh,Li and P systems
Band 3 contains ABO,Hh, Li antigens
Glycophorin A contains these antigens
MN
Glycophorin B contains
Ss and U antigens
antibodies also called
immunoglobulins
What are antibodies
Protein molecules found in the plasma/serum , produced by the immune system following exposure to foreign antigens
An antibody binding to an antigen on the surface of the red cell results in
Red cell destruction
What stimulates Antibodies
Blood transfusion, i.e blood carries antigens foreign to patient
Fetal antigen entering maternal circulation in pregnancy/ birth
Environmental factors
Co dominant antigen include
A,B
Most clinically important blood group system
A,B
How are the ABO genes inherited
One from each parent, where the position 9 on each chromosome is occupied by either A,B OR O
Blood group O antigen
Has no detectable antigen
Blood group AB antibody
Has no detectable antibody
Blood group O mode of inheritance
Autosomal recessive
Why cant you inherit two O genes
Because it is inherited as autosomal recessive and doesnt code for any enzyme to add unto the terminal end of O antigen. Hence they just have H antigen
Phenotype A can express genotypes
AA and AO because O has no antigens to be expressed
Phenotype B has genotype
BB and BO
Phenotype AB has genotype
AB
pHENOTYPE OO has genotype
OO
H antigen and blood grouping
It is the foundation upon which A and B antigens are built
H gene function
It codes for an enzyme that adds a sugar i.e fucose to terminal sugar of a precursor substance to form H antigen
How is precursor substance formed
On an oligossacharide chain, and contains lipids and carbohydrates
How does H antigen become the foundation of A,B antigens
A and B genes code for enzymes that add sugar to the H antigen
The does A gene add onto A ntigen
Codes for the enzyme N- acetylgalactosaminyltransferase which adds N-acetylgalactoseamine to the terminal sugar of H antigen
How does B gene add on to H antigen
B gene codes for the enzyme D-galactosyltransferase that adds D galactose to the terminal sugar of the H antigen
Enzyme that codes for conversion of H gene to H antigene
L-fucosyltransferase
ABO antibodies show in humans from age
6 months
IgM antibodies location
only in plasma , do not cross placenta
IgM and compliment
Igm antibodies fix complement to C9 so transfusion is very severe
Bombay phenotype
H gene not inherited and cant form H antigen to form ABO genes
Bombay phenotype can be likened to this phenotype
Phenotype O and can be differentiated using anti-H i.e cos they dont have H antigen
Varieties of rhesus
Dominant- C,D,E
Recessive - c,d,e antigens
What is the rhesus factor
A group of agglutinogens that are also present on the surface of RBC
Antigen with the strongest antigenic effect
Antigen D
If antigen D is present
Rhesus positive
If antigen D is absent
Rhesus negative
Rhesus locus is located on
Long arm of chromosome 1 containing 2 genes RHC, RHCE
Rh gene inheritance
Inherited as codominant alleles
Most important blood grouping system after abo
Rhesus
There is no
d antigen
Rh (D) STAUS OF AN INDIVIDUAL IS USALLY EXPRESSED AS
Blood group antigen and the positive or negative suffix after ABO type
Rh D frequency
5-10% in blacks
15% in UK
0.3% in chinese
What happens when D negative people are exposed to D antigen
They produce anti-D
When is anti -D stimulated
Transfusion
Feto maternal hemorrhage
mOST IMPORTANT BLOOD GROUPING IN REGARDS TO HEMOLYTIC DX OF NEWBORN
RHESUS
Most commonly produced Rh antibody after anti-D
ANTI-c
Anti-c usually produced in these people
D positive cos they are highly likely to have antigen c
In rhesus is you have the antigen
you will have the antibody
