Question of the Week Podcast

Question of the Week episode

Sun, 7th Jun 2015

Why does the immune system not attack foetuses?

Baby in Womb (c)  Sumlin

This week we've been sequencing Lorianna's question: if babies have different genetic sequences from their mother, and are technically foreign objects in the womb, why doesn't the mother's immune system attack? Ziyad Yehia asked Dr Lucy Fairclough, an immunologist from Nottingham University to find out... 

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Often the fetus IS rejected.

"Around half of all fertilized eggs die and are lost (aborted) spontaneously, usually before the woman knows she is pregnant. Among women who know they are pregnant, the miscarriage rate is about 15-20%. Most miscarriages occur during the first 7 weeks of pregnancy. The rate of miscarriage drops after the baby's heart beat is detected."

US National Library of Medicine

That's why Anne Boleyn got topped, you know. Pecos_Bill, Mon, 8th Jun 2015

This question was referring more specifically to the immune rejection of a developing foetus and what prevents this from happening, given the close contact between foetal and maternal tissues. Your point about early failure of embryos to implant is a good one though and points to a genetic selection process. chris, Sun, 14th Jun 2015

But can we be sure that the immune system is innocent in <<all>> if not most aspects of fetal wastage? If there is a genetic problem, what would suss that out but the immune system?

Certainly the mother's immune system is modified by normal cyesis.  "Pregnant women are considered to be a special population group due to their specific susceptibility to some infectious diseases because of the unique ‘immunological’ condition caused by pregnancy. " (1)

If those mods don't mesh with the pregnancy properly -- it might not be auspicious for either part of the dyad.

In my callow youth perinatal field nursing among "undocumented" hispanic women (with increased morbidity} was a large part of my rice bowl. In that population immunological screening? I once spent a whole day searching out an MD for a post dates prima para with NO prenatal care --- who was <<white>>. If I were not retired I would expect to find the same mileu in California today.

1. The Immune System in Pregnancy: A Unique Complexity,
Pecos_Bill, Sun, 14th Jun 2015

I've read that humans and other placental mammals make use of an endogenous virus carried in our DNA that is activated within the placenta. I had the impression that the virus had mastered the art of hiding from the immune system and our ancestors incorporated it as a tool enabling foetal growth within the body without sealing the baby in an egg.

Is this not correct? AndroidNeox, Tue, 27th Oct 2015

I would guess that the ovum, by containing the lion's share of the material needed to form the fetus, by being formed by the mother is is accepted by her body. The male DNA, upon fertilization, is only a small fraction of the total mass and becomes hidden away from her immune system, which sees only the bulk mass.

This hidden effect is connected to the mother originally having female DNA from her mother and male DNA from her father. When the ovum matures, the ovum extrudes half the DNA. When the male DNA from the sperm enters the ovum, the differences with the original full DNA is subtle; disguised and hidden.
puppypower, Thu, 29th Oct 2015

Another question in a similar vein (excuse the pun): why doesn't the immune system reject blood transfusions? vhfpmr, Mon, 16th Nov 2015

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