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A story about two people sharing one body - maybe even three people. A baby's cells can hide out in a mother's body after birth. A German scientist found this out back in the 1800s, and now scientists are trying to figure out what these cells are doing. NPR's Michaeleen Doucleff reports these findings could have implications for cancer and immune system diseases.
MICHAELEEN DOUCLEFF, BYLINE: When I announced at work that I was pregnant, I got this response from my colleague, NPR's Laura Sydell.
LAURA SYDELL: Oh, wow, it's like an alien invaded your body.
DOUCLEFF: OK, I knew that was a joke. But as the months went on, I started wondering if it's true. Has an alien really invaded my body? So I called up Hilary Gammill, an OB/GYN at the University of Washington, and asked her.
HILARY GAMMILL: (Laughter) That's an interesting question. Well, so I guess you could say that (laughter). It's not the way we typically would think about things.
DOUCLEFF: Gammill is a leading expert in fetal medicine. She says pregnancy does have all the elements of an alien invasion. She says the baby's genes are different than mine, so in a sense, she's a foreigner. And when the placenta grows, it actually invades the mom's body.
GAMMILL: The human placenta is one of the most invasive placentas. So I guess you could say that there's invasion happening.
DOUCLEFF: The placenta reaches out and grabs onto the mom's arteries to control blood flow. This ensures the fetus has nutrients. But in the process...
J. LEE NELSON: There's a very large amount of fetal material that is sloughed into the mother's circulation, especially in the third trimester. I mean, it's widely circulated throughout the mother's body.
DOUCLEFF: That's J. Lee Nelson, also at the University of Washington. She has been studying this rogue fetal material for more than 20 years. It contains DNA, pieces of the placenta and potent fetal cells. They travel around the mom's bloodstream and sneak into the mother's organs.
GAMMILL: They can be in the liver, and they can become, for example, a liver cell - or in the heart, where they can become a muscle cell.
DOUCLEFF: So the fetus is integrating itself into the mom's body. These cells are also found in the mom's scar tissue, specifically scars of C-sections. So scientists think these cells can help moms recover after giving birth by helping to repair wounds. Nelson says fetal cells can also go into the mom's brain and turn into neurons.
Then the fetus could be actually controlling your mind through these neurons?
NELSON: Well, that's a bit of a jump (laughter). I think we have a connotation with alien that's not necessarily positive. But I think you've got to consider them as friends.
DOUCLEFF: These cells got a bad reputation when scientists first started studying them. They have been linked to immune system diseases and preeclampsia, a deadly complication during pregnancy. But Nelson says as time went on, more studies began to suggest fetal cells are beneficial to moms. They're linked to a reduced risk of rheumatoid arthritis and thought to protect against breast cancer. One hypothesis is that fetal cells may act like little sentinels, watching out for breast cancer cells and killing them.
NELSON: Being an optimist, I think that the benefits outweigh the times when they're problematical. So it's actually kind a beautiful cooperation.
DOUCLEFF: And it's not just the moms that get an extra set of cells. Amy Boddy is an evolutionary biologist at Arizona State University. She and her colleagues recently wrote a review on this topic.
AMY BODDY: We've been talking on a very one-sided story. But this is a bidirectional transfer of cells. Cells from the mother also cross the placenta and enter the fetal body.
DOUCLEFF: Which, if you think about it, means you've got your mom's cells inside you. But it also means something else, something that's a bit mind-boggling. Since your mom had cells in her body from all her other pregnancies and her mom, that means you likely have cells from your older siblings and from your grandmother, maybe even your great-grandmother.
BODDY: You can keep going up the family tree pretty far.
DOUCLEFF: So far, scientists haven't actually seen these grandma cells in anyone's body. But if they do exist, it means we're all walking around with a whole family tree inside of us. Michaeleen Doucleff, NPR News.
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