Fetal Immunity

Question 1

Placentation

Answer 1

Placenta separates maternal from fetal blood. The more layers between the two, the more difficult it is for molecules (including antibodies) to cross the placenta
- Some species have no transfer before birth, some have limited

Question 2

What antibody class are mostly be transferred across the placenta?

Answer 2

Smaller antibodies such as IgG

Question 3

What newborns depend the most on colostrum?

Answer 3

The species where there is no transfer across the placenta before birth. So they depend on colostrum immediately after birth

Question 4

Fetal-maternal environment

Answer 4

Environment is almost sterile

Question 5

Placenta layers

Answer 5

• Maternal blood
• Maternal endothelium
• Endometrial connective tissue
• Uterine epithelium
• Chorion epithelium
• Fetal placental mesenchyme
• Fetal endothelium
• Fetal blood

Question 6

Types of placentation

Answer 6

1. Epitheliochorial
2. Endotheliochoral
3. Hemochorial

Question 7

Epitheliochorial

Answer 7

• Placentation with 6 layers (presence of uterus epithelium and endothelium on maternal side)
• Common for most livestock species (cow, pig, horses)
• Means no transfer of antibodies during gestation

Question 8

Endotheliochorial

Answer 8

• Placentation with 5 layers (endothelium on maternal side, but no uterus epithelium)
• Occurs in dogs and cats
• Means limited transfer of antibodies in gestation

Question 9

Hemochorial

Answer 9

• Placentation with 3 layers (no uterus epithelium and endothelium on maternal side)
• Occurs in humans and rodents
• Means transport of maternal IgG antibodies during gestation

Question 10

Immune cell migration across placenta

Answer 10

• Although antibodies can’t cross the placenta when there are many layers, the immune cells can. They will migrate back and forth
• The fetal immune cells will express MHC from their father and these cells would normally attack each other, but during pregnancy, the cytotoxic (Th1) immunity are suppressed and mothers have Treg/Th2-biased immunity.

Question 11

Antibody transfer in birds

Answer 11

• Maternal serum IgG (IgY in birds) is concentrated in the egg in the ovary and enters the bloodstream of the chick
• IgM and IgA enter the albumin in the oviduct and are swallowed by the chick (found in the hatchling GIT)

Question 12

Immune development in the fetus

Answer 12

Sterile environment in utero but the immune system slowly develops within the first trimester

1. Thymus develops first
2. Secondary lymphoid organs
3. Lymphocytes usually found within 40-60 days of gestation in larger animals
4. Recognition of self vs non-self in second trimester

Question 13

When is the fetus capable of responding to pathogens/having an immune response?

Answer 13

The fetus is capable to respond to pathogens and mount an immune response from the second trimester onwards. However, the cytotoxic immune response in both the fetus and mother are suppressed (Treg) to avoid killing of maternal and fetal cells due to the presence of the paternal MHC so few immune responses occur in utero

• Therefore fetuses are not fully protective and are susceptible to intrauterine diseases

Question 14

Fetal vaccination

Answer 14

Animals can respond to vaccine antigens in utero
- Routine practice in poultry (18 day chick embryos are routinely vaccinated for Mareks disease (herpes)
- Can also be demonstrated in mammals, but unlikely to have wide application because of mechanical challenges and risk of abortion

Can allows you to prevent diseases that are transmitted during labour

Question 15

Outcome of intrauterine infections

Answer 15

• Depend on the stage of gestation of the fetus and on the pathogen itself (type of infection and when it happens)
• The fetus is less capable than the adult in mounting an effective immune response

Question 16

Intrauterine infections during first trimester

Answer 16

More likely to result in death of the fetus because no effective immune response

Question 17

Intrauterine infections during second trimester

Answer 17

Results in variable damage to the fetus but fetus is more likely to survive

Question 18

Intrauterine infections during the third trimester

Answer 18

Can provoke effective immune responses and fetus is often undamaged

Question 19

Ranch South-West Sask clinical study

Answer 19

• Bull calf introduced illness (PVD) to the farmers herd
• If infection early on, then abortions and mummified calves
• If infection later on, calves were born but were smaller and some developed ulcers and stopped eating
  » Infection later on in gestation was found to result in persistently infected individuals (immunological tolerance)

Question 20

Porcine Reproduction and respiratory syndrome virus (PRRSV)

Answer 20

• Costly to pork industry
• Virus enters through macrophages and then breaks down the placenta as a result of infection

Question 21

Zika virus

Answer 21

• Another example of virus that infects during gestation
• Huge effects on humans; causes microcephaly in babies and higher levels of aggression in non-clinical babies. Generations of children born with non-clinical symptoms but have behavioural abnormalities (immunological tolerance)