The Cloak of Invisibility

December 6, 2013. Marta Wegorzewska, PhD candidate.

We learned that fetal DNA can be found in the mother’s blood. Companies are using this finding to create new prenatal screening tests. This finding also raises some interesting questions we will examine in a two part series.

Once the fetal DNA is swimming in the mother’s blood, does the mother’s immune system know it is there?

A baby receives half of her DNA from her mother and half from her father. The DNA from her father, different from her mother’s, should alarm the mother’s immune system a foreigner is present.

The mother’s immune system is made of troops that defend against invading bacteria, viruses, and cancer. They could attack the fetus, but they do not. Why not?

Nature has developed multiple ways to protect the fetus from the mother’s immune system.

Fetal DNA wears a cloak of invisibility.1 It goes unnoticed when passing surveilling troops in the mother’s blood. If the cloak of invisibility slips off, the fetus gets help from the mother’s immune system!

Wait! The mother’s immune system can harm and protect the fetus at the same time?

You guessed it! The mother’s immune system can also protect the fetus. Regulatory officers oversee the surveilling troops. In some cases, the officers can stop the troops from attacking the fetus. The officers can only help the fetus when fetal DNA is found in very small amounts in the mother’s blood (as is the case during healthy pregnancy). An excess of fetal DNA may be responsible, scientists think, for problems during pregnancy.2

Now it is your turn to be a scientist.

Companies are using the finding that fetal DNA is swimming in the mother’s blood to create tests that screen fetal DNA for genetic abnormalities. But that is not the reason why nature allowed for this phenomenon to evolve. Can you come up with a reason as to why nature allows fetal DNA to swim in the mother’s blood knowing that the mother’s immune system could potentially see that DNA and harm the fetus?

There is no wrong answer. Nobody knows!

My guess is that by exposing the mother to small doses of fetal DNA (remember fetal DNA is found in the mother’s blood in very small amounts), her immune system learns the fetus is not an invader but a welcomed guest. What is your guess?

This work is funded in part by the Graduate Student Internships for Career Exploration (GSICE) program at UCSF

This post is checked by the following science articles:

1. Madeja, Z., H. Yadi, R. Apps, S. Boulenouar, S. J. Roper, L. Gardner, A. Moffett, F. Colucci, and M. Hemberger. 2011. Paternal MHC expression on mouse trophoblast affects uterine vascularization and fetal growth. Proc Natl Acad Sci 108: 4012-4017.

2. Saadai, P., T. H. Lee, G. Bautista, K. D. Gonzales, A. Nijagal, M. P. Busch, C. J. Kim, R. Romero, H. Lee, S. Hirose, L. Rand, D. Miniati, D. L. Farmer, and T. C. Mackenzie. 2012. Alterations in maternal-fetal cellular trafficking after fetal surgery. J Peds Surg 47: 1089-1094.

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