Why doesn't an expectant mother's immune system damage her growing baby - since it has 'foreign' DNA?
This fundamental phenomenon has yet to be fully explained.
“During pregnancy, the maternal immune system is exposed to a major challenge. The fetus expresses paternal alloantigens, yet it is not rejected”
“Pregnancy represents a major challenge to immunologic tolerance. How the fetal 'semiallograft' evades maternal immune attack is unknown.”
Source (Journal of the American Society of Hematology, 2011 vol. 117 no. 6 pp 1861-1868)
It's known that a specialised type of immune response cell called uerine Natural Killer cells (uNK cells) play a part in supressing the mother's immune response. They make up about 70% of the leukocytes (white blood cells) in the uterus druing early pregnancy. Their precise function, method of action, and their origin, is currently unknown. (see Int. J. Dev. Biol. 54: 281 - 294)
Similarly, the developing baby also has its own (developing) immune system - which somehow accepts the presence of the mother's cells, even though they have differing DNA to its own.
Also see :
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