Haemolytic diseases of foetus

Question 1

What is an antibodies structure?

Answer 1

4 polypeptides made up of 2 identical long chains and 2 identical short chains

Question 2

What are the 5 classes of antibodies with distinct functions?

Answer 2

MADGE - IgM, IgA, IgD, IgG, IgE. These are distinguished by the type of heavy chain found in the molecule

Question 3

How are antibodies produced?

Answer 3

They can be expressed on the surface of B-lymphocytes, can also be secreted by them

Question 4

Describe IgM

Answer 4

It is a pentamer that can not cross the placental barrier as it is too large. It makes up approximately 5-10% of serum antibodies, is the first antibody class to be synthesised in a neonate. It is effective against microbes and agglutinating agents

Question 5

Describe IgG

Answer 5

It is a monomer that can cross the placental barrier, It makes up approximately 80% of serum antibodies. It enhances phagocytosis and neutralises toxins and viruses as well as protecting the foetus and new-born

Question 6

What is opsonization?

Answer 6

A cell labelled with antibody for destruction

Question 7

What is a foetal maternal haemorrhage (FMH)

Answer 7

The rupture of the placental barrier that happens during birth

Question 8

What is class switching?

Answer 8

The B-lymph cells start to produce IgG after enough IgM has been produced. IgG

Question 9

Why can IgG cross the placental barrier?

Answer 9

Due to its size and presence of Fc receptors on the membrane of placental cells. IgG binds tot he foetal RBC resulting in sensitisation and destruction carried out by the reticuloendothelial system

Question 10

What antibody is most effective at activating the complement system?

Answer 10

IgM, IgG can activate it in high quantities but is less effective than IgM

Question 11

What happens to RBC coated with IgG when they enter the spleen?

Answer 11

They cannot pass through it and end up getting haemolysed, this can also activate the complement system

Question 12

What are the most severe cases id IgG crosses the placental barrier? (7 outcomes)

Answer 12

Foetal anaemia, extravascular haemolysis, hepatosplenomegaly (enlarged liver and spleen), subcutaneous oedema (fluid build-up), pleural and pericardial effusions (fluid moving into the heart or lungs), kernicterus (build-up of bilirubin in the brain tissue causing brain damage) and hydrops foetalis (total body swelling)

Question 13

When is a blood sample taken from the pregnant mother to determine risk of HDFN

Answer 13

Between 12-16 weeks

Question 14

what is the Kleihauer-Betke test?

Answer 14

The determination if an FMH has occurred by adding acid to a blood sample, HbA will be eluted, if there is any HbF it will remain intact as HbF is more acid-resistant. The eluted cells will appear as ghost cells under microscopy

Question 15

How can flow cytometry be used to determine if an FMH has occurred?

Answer 15

By adding fluorescent anti-HbF, they will bind to any HbF present in the sample

Question 16

What do DAT and IAT look for in blood sample?

Answer 16

DAT - looks if there are any antibodies bound to the babies red cells
IAT - determines whether the mother is producing any antibodies

Question 17

What is an alternative method to determine if the mother is producing antibodies?

Answer 17

Can carry out an antibody titre, which dilutes the maternal plasma. A greater ratio of 1:32 is considered high giving a greater risk of HDFN

Question 18

What test can be done on the foetus to help against HDFN?

Answer 18

Antenatal ultrasound - detects signs of hydrops foetalis
Doppler ultrasound - measures speed of blood flow, fast flow indicating anaemia
Amniocentesis - measures bilirubin in amniotic fluid

Question 19

What is RhD immunoprophylaxis?

Answer 19

Injecting the mother with large amounts of anti-RhD, destroying any foetal RBC present in the mother’s blood before and antibody response can be mounted

Question 20

What other protein can cause HDFN?

Answer 20

Anti-E and Anti-C can also cause it but is less common