lecture 4 - blood: blood groups

Question 1

what are blood groups?

Answer 1

a classification of blood based on the presence (or absence) of inherited antigenic substances on the surface of RBCs

Question 2

what is an antigen?

Answer 2

a molecule that induces an immune response

those on RBCs will mount are red blood cell surface antigens

Question 3

how many blood group systems are there?

Answer 3

30

Question 4

how do we get our blood groups?

Answer 4

they are inherited and represent contributions from both parents

an individual always almost has the same blood group for life but it may change due to infection, malignancy, autoimmune disease or after a bone marrow transplant

Question 5

what is the ABO system

Answer 5

determined by the terminal sugar structure in the surface of RBCs

Question 6

what are the major sugars in the ABO system?

Answer 6

fucose
galactose 
N-acetylgalactosamine 
N-acetylglucosamine 
sialic acid

Question 7

what genes control the ABO system?

Answer 7

genes ABO and H

Question 8

what do the ABO and H genes encode?

Answer 8

glycotransferases

• enzymes that transfer monosaccharides to polysaccharide chains

Question 9

what are the alleles of the ABO gene?

Answer 9

A, B and O

A and B are dominant to O
O allele codes a truncated, non-functional proteins

Question 10

what are the alleles of the H gene?

Answer 10

H and h

Question 11

what does the H allele code for?

Answer 11

fucosyl transferase (FUT1) which converts precursor substance on RBCs to H antigen

H substance is required for A and B antigen production

adds a fucose to the terminal galactose

Question 12

what does the h allele code for?

Answer 12

a non-functional protein

Question 13

what substances do HH, Hh and hh individuals make?

Answer 13

HH make H substance
Hh make H substance
hh dont make H substance

Question 14

hh individuals

Answer 14

dont possess a functioning copy of the FUT1 gene

bombay phenotype

no ill effect but people with this blood group can only have transfusions from others with the same blood group

may have functional A or B genes but as they don’t have a functional FUT1 they cannot make substance H so can’t make ABO antigens

Question 15

where is the ABO gene located?

Answer 15

chromosome 9

the A and B alleles differ by 7 nucleotide substitutions

Question 16

what is the A transferase enzyme?

Answer 16

N-acetyl galactosamine transferase

Question 17

what is the B transferase enzyme?

Answer 17

galactose transferase

Question 18

what happens if an individual has both A and B transferases?

Answer 18

they add either galactose or N-acetyl galactosamine to the galactose on the glycoprotein H substance

results in blood cells having both sugar chains on their surface

Question 19

what are the 2 subgroups of blood group A?

Answer 19

A1 and A2

these react differently to a particular antibody (anti-A1)

in transfusion the A1 and A2 blood groups are interchangeable

Question 20

how does A1 react with anti-A1?

Answer 20

RBCs with the A1 phenotype react with anti-A1 and make up about 80% of blood group A

Question 21

how does A2 react with anti-A1?

Answer 21

RBCs with the A2 phenotype do not react with anti-A1 and make up 20% of blood group A

Question 22

functions of the A and B substances

Answer 22

unknown

O people are healthy, suggesting antigen function is not important

some disease susceptibility has been linked to ABO phenotypes

may have an evolutionary importance

Question 23

what are blood group antigens also known as?

Answer 23

agglutinogens

antibodies raised against them are agglutinins

Question 24

the rhesus group

Answer 24

system of greatest clinical relevance

named after the rhesus monkey

rhesus antigens are proteins unlike ABO antigens which are sugars

Question 25

what is the main antigen in the rhesus group?

Answer 25

the D antigen

Question 26

how are you Rh+?

Answer 26

``` homozygous domiant (DD) heterozygous (Dd) ```

Question 27

how are you Rh-?

Answer 27

homozygous recessive (dd)

Question 28

what do anti-Rh(D) antibodies do?

Answer 28

destroy any Rh(D)+ RBCs they come into contact with

Question 29

what blood type is the universal recipient?

Answer 29

AB+ | • has A, B and Rh antigens on the RBC surface

Question 30

what blood type is the universal donor?

Answer 30

O- | • has no antigens on the RBC surface

Question 31

what is haemolytic disease of the newborn?

Answer 31

destroys the RBCs causing anaemia and jaundice can kill the baby

Question 32

how does haemolytic disease of the newborn occur?

Answer 32

* Rh+ father * Rh- mother carrying her first Rh+ foetus - Rh antigens from the developing foetus can enter the mothers blood during delivery * in response to the foetal Rh antigens, the mother will produce anti-Rh antibodies * if the woman becomes pregnant with another Rh+ foetus, her anti-Rh antibodies will cross the placenta and damage the foetal RBCs

Question 33

how can you prevent haemolytic disease of the newborn?

Answer 33

Rh-ve mothers will be given anti-D immunoglobulin (normally in the third trimester) which will remove any foetal Rh+ve blood in her circulation before she can make her anti-D antibodies

Question 34

what are other blood group antigens?

Answer 34

* the lewis family of antigens * the P family * the Forssman antigen