Expecting: Pregnancy souvenirs 36:44

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Listen to commentary from the Council twice a week by subscribing on your favorite podcast app. That's Council, C-O-U-N-S-E-L. Okay, so I'm recording. Do you want to just first start by, can you say your name and how you know me? My name is Anne Bird Platt, and I am Bird Pinkerton's mother. That's my mom.

And I called my mom after I found out this fascinating thing. Basically that some cells from my body are probably hanging out inside of her body and have likely been there for three decades, like ever since she carried me in her womb. And as I told her, those cells, cells that are genetically me, it seems like some of them might have stuck around in your body forever.

And become a part of you. And I am curious what you make of that. You can't have the thing.

You want to use a quote, use that quote. You can have them back. Thanks, Mama. Oh, my. Great. Thank you for telling me how to do my job. So my plan here was to explain to my mom very briefly sort of what those cells could be doing inside her and what similar cells are doing to parents all over. And that plan went without a hitch.

Can you, I mean, now, since you're helping me out, can you ask me what are they doing inside my body? What are these cells doing inside my body? Can I ask it as a statement? What do you mean, can you ask it as a statement? I hope these cells are behaving themselves. You know, they're playing nicely with my cells. Well, so here's the fun twist.

Researchers don't know. It seems like, you know, maybe something like a parent-child relationship. Some of the things that these cells might be doing might be good. Some of them might be somewhat less good. Some of them might be totally neutral. And researchers just don't know. Define less good. LAUGHTER

All right, well, let's get into it. Do you want me to tell you a little bit about all, like, okay. So I'm going to, I wasn't actually, I was just going to walk you through that intro, but why don't I just tell you the whole episode and see what happens. Okay. Do you have something? No. Yeah, you definitely, something is happening. It's Chris. Can you just put your phone on silent? Yes, I can put my phone on silent. Thank you. It's on silent. Okay.

It's unexplainable. I'm Bird Pinkerton, and this is the first episode of Expecting, a three-part series on pregnancy and parenting. I cover reproductive health a lot on the show, and one thing I noticed about a lot of the research on pregnancy is that even though it's one of the most common experiences on Earth, literally this thing that we all participate in to be alive, pregnancy is still very mysterious.

It is mysterious in ways that are amazing or awe-inspiring, but also in ways that can hurt parents or at least confuse them. And the other thing that I noticed kind of reading through the literature is that a lot of research on pregnancy kind of focuses on the fetus, like what's happening to the fetus, what is best for it, et cetera, et cetera. So we at Unexplainable decided to do

a series of episodes that looks at mysteries about pregnancy from the parents' perspective. Like, how is pregnancy and parenting reshaping parents' bodies and their brains and their lives? And the story that I've been telling my mom, it's kind of a perfect example of all the things that I have learned about pregnancy. Like, it has got the wonder element, but it also has an element of mystery

Just the frustrating reality that we are still very, very far from satisfying answers. All right. So let's just start with the basics here. This whole idea of my giving you my cells, right? It's actually a subset of something called chimerism, which you know what a chimera is, right? Yes, I do. You want to describe that for me? Yeah.

Well, it's like a, it's like a replication of the real thing. Not exactly. So a chimera is like a, it's the mythical creature from like Greek myth. So you have like, it has like a lion head, like a snake tail and like a goat body. Okay. Like a griffin's a chimera, a sphinx, a manticore. It's the composite, right? Okay. Right.

Let the record show that my mother did know what a chimera was and was unfairly put on the spot. Doesn't sound like your mother knew what a chimera was. So that is a chimera in myth.

But to understand a chimera in biology and what it has to do with pregnancy, I reached out to Amy Boddy, who is a biologist at UC Santa Barbara. And Amy says that in biology, the definition of chimera is a little bit broader than in myth.

It's multiple individuals existing in one host body. And so she was telling me that basically whenever you have a living thing that's made up of pieces of more than one individual, that's a chimera. So you can find them in plants, you can find them in animals.

You can even find them in humans. Like if you see organ transplantation or something like that, where you have a large tissue, right, that's from someone that is a completely different individual, you can consider that person a chimera. So this is not like the goat-lion hybrid version of a chimera, right? It's just bits of two genetically different people. Mm-hmm.

But so technically, Mama, Amy was telling me that this process that you and I went through, where some of my cells left my body, kind of went into your body, that is considered chimerism on like a tiny scale. So they literally call it micro chimera because you just have like a few cells. So cells from me, cells from my sister, Chloe, and also potentially from any like miscarriages that you might have had.

So how many cells do I have from you? So according to Amy, it can be infrequently as one in a million cells, but we have 30 trillion cells in our body. So a trillion is like a million million, right? So if you're doing the math, could potentially be 30 million cells from me floating around in space.

You? Oh. Yeah, but so some people have more. Some people have fewer. They're actually they're usually more during pregnancy. And then your immune system kind of gets rid of a lot of them. But around the 1990s is when researchers started to realize that some cells were really sticking around in the parent long term, like potentially for the parent's whole life.

which was surprising, right? And a lot of these cells are probably stem cells. So do you know what a stem cell is? After my implosion with chimera, I am not hazarding a guess. Okay, so a stem cell is like the...

the really basic cells that then develop into other tissues. So they're kind of like a jack-of-all-trades flexible cells. They can turn into any kind of cell.

So you can basically imagine, like, the fetus has these flexible cells, right? And then some of those cells travel into the placenta, which Amy was telling me is kind of like the main connector between the fetus and the parent. It's this superhighway. So the fetus's cells sort of travel along this highway into the parent's body, hitching a ride in the circulatory system, probably, right?

And they finish their road trip eventually in the heart, say, or the lungs or the brain, sort of all over the body. And then they can reshape themselves into a heart cell or a lung cell or a brain cell, whatever they're around, and kind of braid themselves into that tissue. So they're doing work in the parent's body, even though genetically they're different from the cells around them.

I'm intrigued, but I'm also puzzled. It basically opens up more questions than it even begins to answer. Welcome to the show. So starting around the 1990s, these researchers were sort of like,

All right. Like, what is going on here? Like, if these cells are sticking around and becoming part of the body, are they affecting it in some way? Like, what are they doing? We don't know. But we have some ideas. First of all, Amy told me that it is very possible that

At least potentially, they are doing nothing. I have to admit it, even though I think there are some functional properties of these cells, but they could just be hanging out. Like, it is possible that my cells are just like the tchotchkes that you love to collect, right? Like your little figurines that don't really do anything. They're just kind of there. Yeah.

It's possible that my cells are just the equivalent of that. Like, you have some tiny little cell-sized tchotchkes of me inside of you. Okay.

I don't do like little things anymore. I bought this huge piece of granite the other day in Barron and I liked it all the way home, which was kind of silly. You bought granite? Like you can find granite on the ground. Well, but this was polished. Okay. Anyway, keep going. So again, there is a possibility that these cells are just hanging out like polished granite.

But researchers have some good reasons to think that these cells are potentially doing other things.

There are some studies that show that these cells actually help the host body. And so there's ideas out there that, yeah, this is a good feature to have. So, for example, there have been studies to look at if someone has a C-section and they look at the tissue in the C-section. They've found cells.

from the baby in the parent's scar tissue, essentially. Suggesting that they are there helping heal the gestational parent's body. Uh-huh. And again, it's possible that they're just sort of randomly there, right? Because as Amy was saying, these studies in humans aren't super firm evidence because we don't know

what they would be doing to heal a body. It's not clear that there are necessarily lots more fetal cells in this scar site than anywhere else in the body. And that's maybe one of the biggest criticisms of they're just there. There's a few of them. You're just trying to find a purpose to this randomness of cells there. But if you just sort of step away from humans for a second, there is some more definitive research that has been done in mice.

So in mice, they'll breed female mice with these special males so that some of their fetuses can create cells that fluoresce.

It's like a glow-in-the-dark feature. And then the researchers can sort of dissect the mice or use machines to sort of track these glow-in-the-dark mouse fetus cells as they move through the mouse parent body. If a mouse gets an ear injury, the fetal cells will migrate up to the tissue. It seems like they're primed to be able to go in and kind of help recover and heal the maternal body. Yeah.

Which is cool. That's cool. And again, something like that could also be happening in other mammals, including humans. So it's not just sort of like C-section scars, healing injuries...

There's also been some research on how these cells that the parent gets from their fetus could potentially help with heart health. There was a mouse model where the heart was injured and they saw these cells, these fetal cells migrating to the injury, specializing in helping repair.

So this is in mice, but it would actually help explain a phenomenon that doctors have seen in humans, which is basically like a lot of pregnant people develop heart issues. So your heart is actually doing like a huge workout during pregnancy. This will be no surprise to you, but, you know, it's pumping a lot of blood. There's just

like more of you and your body is working a lot harder. And so researchers have actually compared it to athletes who do long distance sports. So you could just be pregnant and be like, I'm basically an endurance athlete. No wonder I hated it. But because the heart is doing this, this sort of nine month long workout, it makes sense that a lot of pregnant people develop problems with their heart during this time. What's interesting is that

Sometimes these problems just kind of fix themselves. Like, they go away and researchers aren't totally sure why. And some are wondering if the cells from the fetus actually help fix things. Like, if the cells from the fetus are traveling to the heart and giving it some kind of boost that could explain the sort of heart healing that is happening here. So...

It's quite fantastic, I think, in thinking about the coolest, weirdest biology. And again, like, this is just one example of the ways that researchers think that these cells could be helping a parent's body sort of heal or fix issues, right? So maybe, you know, my cells at some point helped heal something in you as well. I think your cells need to get their act together. Let's get going here.

Okay, I'll work on it. Nothing wrong with your heart, but I'll work on curing your various other ailments and diseases. Sorry. Sorry I've been such a disappointment to you. You have not been a disappointment. Your cells are just, you know... Let's get open. This feels like a perfect transition to the next thing here, which is that...

Sometimes the parent-fetus-cell relationship becomes strained in certain ways. Like any communication between parent and child. It's not all sort of heart healing and scar knitting. Sometimes the cells from the kid can be somewhat obnoxious. This is the playing less well with others. Yes. So up next...

how these cells might actually play a role in a whole range of pretty serious diseases. Support for Unexplainable comes from Greenlight. People with kids tell me time moves a lot faster. Before you know it, your kid is all grown up, they've got their own credit card, and they have no idea how to use it. But you can help. If you want your kids to get some financial literacy early on,

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Hey, unexplainable listeners. Sue Bird here. And I'm Megan Rapinoe. Women's sports are reaching new heights these days, and there's so much to talk about and so much to explain. You mean, like, why do female athletes make less money on average than male athletes?

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So, Mama, when I was in your womb, I gave you a bunch of my cells. This happens whenever there's a fetus inside a pregnant person for a while. And in this exchange, Amy Boddy says that

there are trade-offs. It might be helpful during pregnancy. It might be helpful in the postpartum period. But long-term, there could be some trade-offs where actually at some point it can lead to health complications. And one of the main complications that researchers have been exploring is related to autoimmune disease. Wow. So like...

To be really clear from the get-go, right, like this is all very much theoretical, right? It's something researchers are still trying to figure out. So I would not want anyone with sort of an autoimmune disease to immediately assume that it comes from microchimera or this like exchange of cells, right? But basically, the way that Amy explained it to me is that

We have this immune system, and its whole job is to sort of cruise around, check up on various cells, and say, like, is this me?

Typically, your body recognizes self by specific markers on your cell that says, you know, like, hey, I am me. And it leaves those cells alone. But then if it comes across cells that don't look like itself. Then my immune system might say, nope, let's get rid of this. But in an autoimmune disorder, the immune system kind of goes haywire, right? Like it starts attacking cells that are part of the body.

that are part of itself in some way. And that leads to sort of the swelling, the pain, tiredness, like a whole bunch of different issues that are associated with autoimmune disorders. And so the way that this is potentially linked to microchimera is it turns out that people who have carried fetuses at some point in their lives do seem to be at higher risk for autoimmune diseases. Mm-hmm.

The data that we have now focuses on women, but it shows that these diseases are significantly more likely to affect women as compared to men. And some studies have found that the chances of getting some of these diseases actually increases after women's reproductive years. So researchers were kind of looking at microchimera.

And they were thinking like, okay, people who are getting pregnant are bringing kind of foreign cells into themselves that look a lot like them. Because usually half our DNA comes from each of our parents. So these cells come in, they become part of the body, sort of part of the tissue.

And then down the line, one scenario is that they do something that the body cells wouldn't usually do, right? Something more unique to the kids' cells. So maybe, for example... They're expressing a protein you've never seen before.

then your immune system might say, hey, that's not self. We need to go ahead and get rid of this. And that can, you know, elicit an autoimmune response. I don't know if we can call it autoimmune because that means self, right? Like, is it autoimmune? Because it's not attacking the self. It's attacking these foreign cells. And that's kind of the whole problem here, right? Like, these cells are both immune.

part of the parent self and also genetically foreign. So maybe, and again, emphasis on maybe, this could be contributing to autoimmune diseases. Like maybe these foreign but not so foreign cells are why the body starts attacking itself. Yeah.

And there have been a few studies to sort of look at people with autoimmune diseases to look for proof that this might be happening. There's a few different studies looking at individuals with autoimmune disease and they find these fetal cells in the tissue. But once again, like these are mostly sort of correlations. Like we saw these cells and we saw this problem. Maybe they're related. We don't know exactly.

the root cause. We don't know if these individuals would have gone on to get autoimmune diseases anyways and the cells, again, just happen to be there. So, like, there's still work to be done here to sort of tease this relationship out and figure out what's going on. But it is sort of one way, at least, that people think that some of these sort of cells from, like, fetuses could be causing issues. Okay. I am fascinated by this.

I wish there were more information. But what an interesting possibility. I think so, too. Right? So there's this possibility, this possibility that they're involved in autoimmune diseases. And then the other possibility, which you are not going to like, is that these microchimera might also play a role in

Lay it on. Just lay it on. So basically, cancer is almost one of the best examples of maybe this is helpful, maybe this is harmful. Like right now, it's just kind of deeply confusing. Amy was saying she actually got interested in microchimera when she was studying breast cancer. So she was sort of like reading through these papers. And some women had higher amounts of fetal cells.

in their body and were diagnosed with cancer. Which would suggest that there could be some kind of a connection again, or like a correlation, right? Like more cells from the fetus, more cancer potentially. But then there's other papers. This is where it gets really confusing. There's other studies showing that no, actually those cells might be in there trying to help fight the cancer.

And actually, these cells are protective. And so it's a big like, we don't know what they're doing. Are they fighting the tumor? Are they making, you know, the immune system more aggressive in making this cancer worse? And we don't know the answer to that.

So, again, there are a lot of questions here, right? But if we can figure this stuff out, like if we can figure out exactly the effects that microchimera have on our body in terms of cancer or also autoimmune diseases, like,

That could potentially be huge, right? Amy was saying that maybe we could figure out if people are high risk for certain issues and help them early, for example. The other exciting thing is some people are, again, seeing these potential fetal cells

helping with wound healing. And the thought is that it could be a therapy as well, providing a boost of stem cells to actually help fight a disease or help heal. Right now, because this is all such a mystery, like we are, we're still a very long way away from these kinds of applications, right? Which

I guess kind of just left me wondering why, right? Like, why do we still have so many questions instead of answers here and know so little? That is a good question. Lee Nelson agrees with you. That's a good question.

Lee Nelson is actually one of the researchers that I mentioned before who first started diving into microchimera in the 1990s. And she's been doing a lot of work for many decades on the autoimmune stuff specifically. So I asked her essentially, like, why we are still so far from answers. The most direct two answers to that are technical. So it's the techniques.

And the other one is funding. Reproductive health in general is very underfunded, but this work is also just very hard from a technical perspective. The big challenge is very simple. There are all these little chimerical cells that are very hard to track. And, you know, you can put tracers in mice, like

like we mentioned before, but mice are not humans. Like mouse pregnancy just looks different than human pregnancy, which could lead to different effects. I mean, routinely mice are multiple gestations. They're routinely having like eight pups all at the same time, for example. I don't know anybody that's had eight or nine kids. And meanwhile, you can't like inject human fetuses with glow-in-the-dark tracers.

or cut up human parents in the same way as mice to see what's going on. And so as a result, when you're looking at some of these cells in human tissue... You can't really know both where it came from and where it went to and kind of everything about it. And then even if you do have sort of some tissue that you're looking at from a human, finding these cells isn't easy, right? It's a couple of cells in a million, right?

And so it's kind of like looking for a needle in the haystack if the needle looked like a lot like hay, right? Because it's actually got half the hay's DNA. And then one extra wrinkle that I talked about with both Lee and Amy, but which I've sort of been saving for the end is

is that microchimerism isn't just about fetuses passing cells to their parents. It's actually a lot more complicated because it goes both ways. So not only am I kind of giving you my cells, but when I was in your womb, you gave me some of your cells as well. Of course. Which means that

You're not just sort of a chimera of me and my sister Chloe and any miscarriages that you might have had. You also have my grandmother, Muddy's, cells swimming around inside of you as well. That makes perfect sense. How far back does it go? So it is also possible that your mom, so my grandmother, gave you some of your grandmother's cells...

So any researcher sort of looking, Mama, at your tissue would be saying, is this cell from Ann Bird Platt? Or is it from her daughter Chloe or her daughter Bird or her mother or her grandmother or a miscarriage she had?

Or, like, what? And so Amy says it's just hard to parse. So we've been talking very simply about this because it is so complex that our minds can't even wrap around the fact that

There's actually multiple generations happening all at once. And so studying microchimera is so hard because you have to find just like a few cells in a million, untangle this whole intergenerational jumble, and then figure out like what those cells are doing, what they're up to. And that's part of why this research is going so slowly. You're getting these like two of,

you know, a thousand piece puzzle, right? And you're like, I think it's a horse, but then you haven't seen, you know, the rest of the body or something like that. And I find it, I mean, I find it like, I guess there's something about it that like there, there might be things that we'd never fully understand here, right? Like we are potentially never going to be able to completely untangle the way that like my cells and my sister's cells and

that sells from your miscarriages have affected your body. Like, it's possible it's always going to remain kind of like a parent-child relationship, right? Like, on a tiny scale, there'll be sort of pushing and pulling and hurting and healing and, you know, it's a relationship we can explore forever and never fully untangle. To be sure, but...

To me, the whole benefit of this kind of research is that what you know now, let's say you really, not you, one, was really able to go into this into a lot more depth. There are always surprises. That's the reason everybody does research. They're always like, oh, we were looking for X and we found a whole different section of the alphabet. It strikes me as a good enough reason to pursue it.

I'm beginning to realize where I came from. It's beginning to make sense that I have maybe some of your cells in my body and our brain. Question, would you say I'm overall more of like a scar healing helper or an autoimmune disease trigger of a child? Oh, sweetheart, you are a scar healing helper.

It's on the record. Um, and I'm so happy you're here. I'm happy you're here, mama. Um,

I love you. I love you, too. And I assume that's it. We're done? Yeah, I think that's it. I think we're done. Okay. Thank you for doing this. You're very welcome. In a separate space, I will bring you up to date on certain postal events coming your way soon. And you can bring me up to date on other events in your life.

That's it for this episode. But next week, we will continue our expecting series with a story about how children don't just leave a mark on a parent's body, but also potentially change their parents' minds. Until then...

This episode was reported and produced by me, Bird Pinkerton. It was edited by Brian Resnick and Catherine Wells, as well as Meredith Hodnot, who runs the show. We had sound design and mixing from Christian Ayala, music from Noam Hassenfeld, Serena Solon checked our fax, and Mandy Nguyen. It's just really lovely to have nearby.

I want to say a special thank you this episode to Leigh Nelson, who sent so many articles that just really helped orient me and deepen my knowledge here. So if you want to read more about microchimera and autoimmune disorders, look up her body of research. I would also recommend the article that Amy Boddy co-authored in Bio Essays in 2015.

We will also be rolling out a whole bunch of articles about pregnancy unknowns on the site in the next few weeks. So check out vox.com slash unexplainable to read those. And then just email us your thoughts, your questions. We're at unexplainable at vox.com and we love to hear from you. Unexplainable is part of the Vox Media Podcast Network. And we'll be back next week with another episode of Expecting. So...

Expect that.