The cells we share

Summary

Unexplainable (Vox)

Episode: “The cells we share”
Date: June 1, 2026
Host: Bird Pinkerton
Guests: Amy Boddy (Biologist, UC Santa Barbara), Anne Bird Platt (Bird’s mother), Lee Nelson (Researcher)

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Episode Overview

This episode dives into the mysterious biological phenomenon of microchimerism: the surprising discovery that cells can be exchanged between pregnant people and their fetuses, and those exchanged cells can persist in both bodies for decades, possibly for life. Host Bird Pinkerton weaves personal narrative, a conversation with their mother, and scientific interviews to explore what these cells do, why they exist, and how this deepens the mystery and complexity of pregnancy. The episode offers a blend of awe—at the wonder and weirdness of biology—and frustration—at how much science still doesn’t know.

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Key Discussion Points & Insights

1. Personal Beginnings: “You can’t have them back”

• Bird calls her mother, Anne, to break the news that Bird’s cells are still inside Anne decades after pregnancy (01:22).
  • Memorable quote:

    “You can’t have them back. You want to use a quote? Use that quote. You can’t have them back. They’re mine.” (Anne, 02:00)

• Introduces the core mystery: why and how could cells from a child persist in a parent’s body for decades?

2. Chimerism & Microchimerism Explained

• Definition and myth:
  • Chimerism in myth: hybrid creatures like griffins, sphinxes (06:05).
  • Chimerism in biology: “multiple individuals existing in one host body” (Amy Boddy, 07:02).
• Microchimerism:
  • The transfer of a small number of cells between genetically distinct individuals, e.g., child to parent during pregnancy (07:34).
• Potential numbers:
  • As many as 30 million cells from a child might linger in a parent’s body (08:23).

    • “…could potentially be 30 million cells from me floating around in you.” (Bird, 08:23)

3. How Cells Move & Stay

• Stem cells at the center:
  • Fetal stem cells are versatile and can integrate into different organs (09:19).
  • “It’s this super highway.” — describing the placenta (Amy, 09:48)
• Cell journey:
  • Fetal cells enter the parent’s bloodstream, travel throughout the body, and can become different cell types in tissue (09:50-10:29).

    • “They can reshape themselves into a heart cell or a lung cell or a brain cell, whatever.” (Bird, 10:22)

4. What Are These Cells Doing?

(A) Possibly… nothing?

• Some think the cells just hang around like “tchotchkes” (Bird, 11:30).

(B) Helpers & Healers

• Studies have found fetal cells at wound sites (like C-section scars), suggesting a possible role in wound healing (12:39-13:05).
  • Mouse studies:
    • Cells move to help heal ear injuries; may help with heart repair post-pregnancy (Amy, 14:11, 14:51).
    • The heart of a pregnant person works like an endurance athlete’s, and fetal cells may help recover from pregnancy-induced strain (15:06-15:40).

      • “You could just be pregnant and be like, I’m basically an endurance athlete.” (Amy, 15:35)

• Narratively, Bird and her mom playfully discuss Bird’s cells as “scar healing helpers” (16:50-17:08, 33:27-33:33).

(C) Troublemakers & Harms

• The parent-fetal cell relationship isn’t always positive—there are signs these cells may play a role in diseases (17:18-17:48).

i. Autoimmune Disease

• Those who’ve been pregnant have a higher risk for autoimmune diseases, possibly due to these “foreign but not so foreign” cells that confuse the immune system (20:10-22:45).
  • Cells may express proteins the parent’s immune system hasn’t seen, potentially triggering mistaken attacks (22:45).

    • “Maybe... 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.” (Amy, 22:45)

• Current evidence is correlational, not causal (23:55-24:17).

  • “We don’t know the root cause... The cells, again, just happen to be there.” (Amy, 24:07)

ii. Cancer

• Sometimes higher amounts of fetal cells are found in cancer patients; sometimes they appear to help fight tumors (25:27-26:17).

  • “We don’t know what they’re doing. Are they fighting the tumor or are they making...this cancer worse? And we—we don’t know the answer to that.” (Amy, 25:48)

(D) Therapeutic Hopes

• If better understood, microchimerism could help predict or even treat diseases by harnessing stem cells’ healing powers (26:43-27:03).

5. Why Are Answers So Elusive?

• Technical barriers:
  • Microchimeric cells are rare (sometimes 1 in a million), hard to spot, and look extremely similar to the host’s own cells (29:03).

    • “It’s kind of like looking for a needle in the haystack. If the needle looked a lot like hay, right?” (Bird, 29:03)

• Human study limitations:
  • Mouse models are more accessible (can use fluorescent tracers), but pregnancy in mice is different (multiple pups) (28:30-28:41).
• Funding limitations:
  • Reproductive science is historically underfunded (27:58).

6. It’s Even More Complex: Generational Tangle

• Microchimerism is not just one way: cells also flow from parent to child, meaning every person is a collective blend—including possible traces from grandmothers or previous generations (29:59-30:29).

  • “So any researcher...would be saying, is this cell from Anne 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?” (Bird, 30:29)

  • “There’s actually multiple generations happening all at once.” (Amy, 30:51)
  • “You’re getting...two of a thousand piece puzzle... and you haven’t seen the rest of the body...” (Amy, 31:26)

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Notable Quotes & Memorable Moments

• On the emotional resonance:
  • “It's possible it’s always going to remain kind of like a, like a parent child relationship. Right? ... There’ll be sort of pushing and pulling and hurting and healing...” (Bird, 32:13)
• Optimism in research:
  • “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. Strikes me as a good enough reason to pursue it.” (Anne, 32:30)
• Mother’s affectionate summary:
  • “Oh, sweetheart, you are a scar healing helper.” (Anne, 33:27)

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Key Timestamps

• 01:17 — Bird introduces the idea to her mom.
• 02:00 — Anne claims the cells as her own (“You can’t have them back...”).
• 06:05–07:22 — Chimerism explained (myth to biology to pregnancy).
• 08:13–08:23 — How many fetal cells are in a parent?
• 09:19–10:29 — What are stem cells and how do they travel into the parent?
• 12:23–13:05 — Fetal cells in C-section scars and wound healing.
• 14:11–14:51 — Mouse studies show fetal cells' healing abilities.
• 15:22–15:40 — The parent’s heart as an “endurance athlete.”
• 17:29 — The “strained relationship”—when fetal cells aren’t benign.
• 20:10–22:45 — Potential link to autoimmune disease.
• 25:08–26:17 — Cancer: still a mystery, possibly helper or harm.
• 29:59–31:04 — Generational persistence of microchimerism.
• 32:13 — The analogy to long-term, untangleable parent-child relationships.
• 33:27–33:33 — “You are a scar healing helper.”

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Flow and Tone

• Warm and personal: Bird’s conversation with her mother throughout grounds the science in relatable family dynamics, humor, and affection.
  • Lively back-and-forth, playful teasing, but underpinned by curiosity and care.
• Wonder and humility: The episode balances awe at the complexity of biology with frustration at how little is understood, often highlighting the limits of current studies with candid expert commentary.
• Accessible science: Technical topics are explained through analogies and stories (e.g., tchotchkes, endurance athletes, puzzle pieces).

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Further Reading & Resources

• Research of Dr. Lee Nelson on microchimerism and autoimmune disorders.
• Amy Boddy’s 2015 article in BioEssays.

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Final Thoughts

Pregnancy, one of the most ordinary experiences on Earth, hides deep biological mysteries. Microchimerism—these “cells we share”—is a window into the incredible complexity of living bodies, and especially into the unseen connections between parents, children, and even generations. As Bird’s mother concludes, the surprises in research are themselves a reason to keep searching—and no matter what science uncovers, some mysteries may always remain beautifully interwoven with family life.

Transcript

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[Bird Pinkerton]

So good, so good, so good.

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[Bird Pinkerton]

Okay, so I am recording. Do you want to just first start by, can you say your name and how you know me?

[Anne Bird Platt (Bird Pinkerton's mother)]

My name is Anne Bird Platt and I am Bird Pinkerton's mother.

[Bird Pinkerton]

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 and become a part of you. And I am curious what you make of that.

[Anne Bird Platt (Bird Pinkerton's mother)]

You can't have them back. You want to use a quote? Use that quote. You can't have them back. They're mine.

[Bird Pinkerton (continuation or alternate label)]

Thanks, mama.

[Commercial Announcer]

Oh my.

[Amy Boddy (Biologist at UC Santa Barbara)]

Great.

[Bird Pinkerton (continuation or alternate label)]

Thank you for telling me how to do my job.

[Bird Pinkerton]

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.

[Bird Pinkerton (continuation or alternate label)]

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?

[Anne Bird Platt (Bird Pinkerton's mother)]

Can I ask it as a statement?

[Bird Pinkerton (continuation or alternate label)]

What do you mean? Can you ask it as a statement?

[Anne Bird Platt (Bird Pinkerton's mother)]

I hope these cells are behaving themselves that, you know, they're playing nicely with my cells.

[Bird Pinkerton (continuation or alternate label)]

Well, so here's the fun twist. Researchers don't know.

[Bird Pinkerton]

It seems like, you know, maybe something

[Bird Pinkerton (continuation or alternate label)]

like a parent child relationship.

[Bird Pinkerton]

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.

[Anne Bird Platt (Bird Pinkerton's mother)]

Define less good.

[Bird Pinkerton (continuation or alternate label)]

All right, well, let's get into it.

[Bird Pinkerton]

Do you want me to tell you

[Bird Pinkerton (continuation or alternate label)]

a little bit about, like.

[Bird Pinkerton]

Okay, so I'm gonna. I wasn't actually. I was just gonna walk you through that intro, but why don't I just

[Bird Pinkerton (continuation or alternate label)]

tell you the whole episode? Let's see what happens.

[Bird Pinkerton]

Okay.

[Bird Pinkerton (continuation or alternate label)]

Do you have something.

[Anne Bird Platt (Bird Pinkerton's mother)]

No.

[Bird Pinkerton (continuation or alternate label)]

Yeah, you definitely. Something is happening.

[Anne Bird Platt (Bird Pinkerton's mother)]

It's Chris.

[Bird Pinkerton (continuation or alternate label)]

Can you just put your phone on silent?

[Anne Bird Platt (Bird Pinkerton's mother)]

Yes, I can put my phone on silent, thank you. It's on silent.

[Bird Pinkerton]

It's unexplainable. I'm Bird Pinkerton, and we originally aired this episode a few years ago when we did a series on pregnancy and parenting. But we've recently had a bunch of people on the team become parents. So I have been thinking about pregnancy a lot, and especially about the idea that even though pregnancy is one of the most common experiences on Earth, right, this thing that we all participate in in order to be alive, pregnancy is still very mysterious. It's mysterious in ways that are amazing and awe inspiring, obviously, but also in ways that can hurt parents or at least confuse them. And so the story that I was telling my mom is kind of this perfect example of a lot of the things I learned about pregnancy over the course of my reporting. Like, it has got a wonder element, but it also has an element of just the frustrating reality that we are still very, very far from satisfying.

[Anne Bird Platt (Bird Pinkerton's mother)]

Answer.

[Bird Pinkerton]

All right, so let's just start with. With the basics here. This whole, like, idea of my giving you my cells, right. It's. It's actually a subset of something called chimerism, which. You know what a chimera is, right?

[Anne Bird Platt (Bird Pinkerton's mother)]

Yes, I do.

[Bird Pinkerton]

You want to describe that for me?

[Anne Bird Platt (Bird Pinkerton's mother)]

Well, it's like a. It's like a replication of the real thing.

[Bird Pinkerton (continuation or alternate label)]

Not exactly.

[Bird Pinkerton]

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 and, like, a snake tail and like a go body.

[Anne Bird Platt (Bird Pinkerton's mother)]

Okay.

[Bird Pinkerton]

Like a griffin's, a chimera, a sphinx, a manticore.

[Anne Bird Platt (Bird Pinkerton's mother)]

It's the composite. Right. Okay.

[Bird Pinkerton]

Right. Let the record show that my mother

[Bird Pinkerton (continuation or alternate label)]

did know what a chimera was and was unfairly put on the spot.

[Anne Bird Platt (Bird Pinkerton's mother)]

Doesn't sound like your mother knew what a chimera was.

[Bird Pinkerton]

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 this biologist at UC Santa Barbara. And Amy says that in biology, the definition of chimera is a little bit broader than in myth.

[Amy Boddy (Biologist at UC Santa Barbara)]

It's multiple individuals existing in one host body.

[Bird Pinkerton]

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.

[Amy Boddy (Biologist at UC Santa Barbara)]

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.

[Bird Pinkerton]

So this is not like the goat, lion, hybrid version of a chimera. Right. It's just bits of two genetically different people. 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 microchimera. Cause 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.

[Anne Bird Platt (Bird Pinkerton's mother)]

So how many cells do I have from you?

[Bird Pinkerton]

So according to Amy, it can be

[Amy Boddy (Biologist at UC Santa Barbara)]

infrequently as one in a million cells, but we have 30 trillion cells in our body.

[Bird Pinkerton]

So a trillion's. Like a million million. Right. So if you're doing the math, could potentially be 30 million cells from me floating around in you. Oh, yeah. But so some people have more, some people have fewer. 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?

[Anne Bird Platt (Bird Pinkerton's mother)]

Yeah, after my implosion with chimera, I am not hazarding, I guess.

[Bird Pinkerton]

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. Like, 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.

[Amy Boddy (Biologist at UC Santa Barbara)]

It's this super highway.

[Bird Pinkerton]

So the fetus cells sort of travel along this highway into the parent's body hitching a ride in the circulatory system probably. 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.

[Anne Bird Platt (Bird Pinkerton's mother)]

I'm intrigued, but I'm also puzzled. It basically opens up more questions than it even begins to answer.

[Bird Pinkerton (continuation or alternate label)]

Welcome to the show.

[Bird Pinkerton]

So Starting around the 1990s, these researchers were sort of like, all right, like,

[Bird Pinkerton (continuation or alternate label)]

what is going on here?

[Bird Pinkerton]

Like, if these cells are sticking around and becoming part of the body, are they affecting it in some way?

[Bird Pinkerton (continuation or alternate label)]

Like, what are they doing?

[Amy Boddy (Biologist at UC Santa Barbara)]

We don't know, but we have some ideas.

[Bird Pinkerton]

First of all, Amy told me that it is very possible that at least potentially they are doing nothing.

[Amy Boddy (Biologist at UC Santa Barbara)]

I have to admit it, even though I think there are some functional properties of these cells, but they could just be hanging out.

[Bird Pinkerton]

Like, it is possible that my cells are just like the tchotchkes that you

[Bird Pinkerton (continuation or alternate label)]

love to collect, right? Like your little figurines that don't really do anything. They're just kind of there. It's possible that my cells are just the equivalent of that. Like, like you have some tiny little cell sized tchotchkes of me inside of you.

[Anne Bird Platt (Bird Pinkerton's mother)]

I don't do like little things anymore. I bought this huge piece of granite the other day in Berren and I lugged it all the way home, which was kind of silly.

[Bird Pinkerton (continuation or alternate label)]

You bought granite like you. You can find granite on the ground.

[Anne Bird Platt (Bird Pinkerton's mother)]

Well, but this was polished. Okay, anyway, keep going.

[Bird Pinkerton (continuation or alternate label)]

So again, there is a possibility that

[Bird Pinkerton]

these cells are just hanging out like polished granite.

[Bird Pinkerton (continuation or alternate label)]

But researchers have some good reasons to

[Bird Pinkerton]

think that these cells are potentially doing other things.

[Amy Boddy (Biologist at UC Santa Barbara)]

There's 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.

[Bird Pinkerton]

So for example, there have been studies to look at. If someone has a C section and

[Amy Boddy (Biologist at UC Santa Barbara)]

they look at the tissue in the

[Bird Pinkerton]

C section, they found cells from the baby in the parent's scar tissue, essentially

[Amy Boddy (Biologist at UC Santa Barbara)]

suggesting that they are there helping heal the gestational parent's body.

[Anne Bird Platt (Bird Pinkerton's mother)]

Uh huh.

[Bird Pinkerton]

And again, it's possible that they're just sort of randomly there. Right. Because as Amy was saying, like, 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 like in this scar site than anywhere else in the body.

[Amy Boddy (Biologist at UC Santa Barbara)]

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.

[Bird Pinkerton]

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, cells that fluoresce.

[Amy Boddy (Biologist at UC Santa Barbara)]

It's like a glow in the dark feature.

[Bird Pinkerton]

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.

[Amy Boddy (Biologist at UC Santa Barbara)]

If a mouse gets an ear injury, the fetal cells will migrate up to the tissue. Seems like they're primed to be able to go in and kind of have help recover and heal the maternal body.

[Anne Bird Platt (Bird Pinkerton's mother)]

Huh?

[Bird Pinkerton (continuation or alternate label)]

Which is cool.

[Anne Bird Platt (Bird Pinkerton's mother)]

That's cool.

[Bird Pinkerton]

And again, like, 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.

[Amy Boddy (Biologist at UC Santa Barbara)]

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.

[Bird Pinkerton]

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.

[Bird Pinkerton (continuation or alternate label)]

This will be no surprise to you,

[Bird Pinkerton]

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.

[Amy Boddy (Biologist at UC Santa Barbara)]

So you could just be pregnant and be like, I'm basically an endurance athlete.

[Anne Bird Platt (Bird Pinkerton's mother)]

No wonder I hated it.

[Bird Pinkerton (continuation or alternate label)]

But because the heart is doing this, this sort of nine month long workout,

[Bird Pinkerton]

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 are 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.

[Amy Boddy (Biologist at UC Santa Barbara)]

So it's quite fantastic, I think, in thinking about the coolest, weirdest biology.

[Bird Pinkerton]

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.

[Anne Bird Platt (Bird Pinkerton's mother)]

I think your cells need to get their act together. Let's get going here.

[Bird Pinkerton (continuation or alternate label)]

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.

[Anne Bird Platt (Bird Pinkerton's mother)]

You have not been a disappointment. Your cells are just, you know, let's get moving.

[Bird Pinkerton]

This feels like a perfect transition to the next thing here, which is that sometimes the parent fetus cell relationship becomes

[Bird Pinkerton (continuation or alternate label)]

strained in certain ways. Like any communication between parent and child,

[Bird Pinkerton]

it's not all sort of heart healing and scar knitting. Sometimes the cells from the kid can be somewhat obnoxious.

[Anne Bird Platt (Bird Pinkerton's mother)]

This is deplaying less well with others, right?

[Bird Pinkerton (continuation or alternate label)]

Yes.

[Bird Pinkerton]

So up next, how these cells might actually play a role in a whole range of pretty serious diseases.

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[Bird Pinkerton]

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 Body says that there are trade offs.

[Amy Boddy (Biologist at UC Santa Barbara)]

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.

[Bird Pinkerton]

And one of the main complications that researchers have been exploring is related to autoimmune disease.

[Anne Bird Platt (Bird Pinkerton's mother)]

Wow.

[Bird Pinkerton]

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 mycochimera or this 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?

[Amy Boddy (Biologist at UC Santa Barbara)]

Typically, your body recognizes self by specific markers on your cell that says, you know, like, hey, I am me.

[Bird Pinkerton]

And it leaves those cells alone. But then if it comes across cells that don't look like itself, then my

[Amy Boddy (Biologist at UC Santa Barbara)]

immune system might say, nope, let's get rid of this.

[Bird Pinkerton]

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 microchimaera 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. 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 microchimaera, and they were thinking, like, okay, people who are getting pregnant are bringing kind of foreign cells into themselves that look a lot like. 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 kid's cells.

[Amy Boddy (Biologist at UC Santa Barbara)]

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?

[Bird Pinkerton]

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 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,

[Anne Bird Platt (Bird Pinkerton's mother)]

huh?

[Bird Pinkerton]

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.

[Amy Boddy (Biologist at UC Santa Barbara)]

There's a few different studies looking at individuals with autoimmune disease, and they find these fetal cells in the tissue.

[Bird Pinkerton]

But once again, like, these are mostly sort of correlations. Like, we saw these cells and we saw this problem. Maybe they're related.

[Amy Boddy (Biologist at UC Santa Barbara)]

We don't know 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.

[Bird Pinkerton]

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.

[Anne Bird Platt (Bird Pinkerton's mother)]

Okay. I am fascinated by this. I wish there were more information, but what an interesting possibility.

[Bird Pinkerton]

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 gonna like, is that these microchimaera might also play a role in cancer.

[Anne Bird Platt (Bird Pinkerton's mother)]

Lay it on. Just lay it on.

[Bird Pinkerton]

So basically, cancer is almost one of the best examples of maybe this is helpful. Maybe this is harmful. Right now, it's just kind of deeply confusing. Amy was saying she actually got interested in microchimaera when she was studying breast cancer. So she was sort of reading through

[Amy Boddy (Biologist at UC Santa Barbara)]

these papers, and some women had higher amounts of fetal cells in their body and were diagnosed with cancer, which would

[Bird Pinkerton]

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.

[Amy Boddy (Biologist at UC Santa Barbara)]

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 or are they making, you know, the immune system more aggressive and making this cancer worse? And we. We don't know the answer to that.

[Bird Pinkerton]

So again, there. 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 that microchimaera 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.

[Amy Boddy (Biologist at UC Santa Barbara)]

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 BO of stem cells to actually help fight a disease or help heal right

[Bird Pinkerton]

now, because this is all such a mystery, 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?

[Anne Bird Platt (Bird Pinkerton's mother)]

That is a good question.

[Bird Pinkerton]

Lee Nelson agrees with you. That's a good question. Lee Nelson is. Is actually one of the researchers that I mentioned before who first started diving into microchimaera in the 1990s, and she's been doing a lot of work for. For many decades on the autoimmune stuff specifically. So I asked her essentially, like, why we are still so far from answers.

[Anne Bird Platt (Bird Pinkerton's mother)]

The most direct two answers to that are technical. So it's the techniques, and the other one is funding.

[Bird Pinkerton]

Reproductive health in general is very underfunded. But this work is also just very hard from a technical perspective.

[Anne Bird Platt (Bird Pinkerton's mother)]

The big challenge is very simple.

[Bird Pinkerton (continuation or alternate label)]

There are all these little chimerical cells

[Bird Pinkerton]

that are very hard to track. And, you know, you can put tracers in mice like we mentioned before, but mice are not humans. Like, mouse pregnancy just looks different than human pregnancy, which could lead to different effects.

[Anne Bird Platt (Bird Pinkerton's mother)]

I mean, routinely, mice are multiple gestations.

[Bird Pinkerton]

They're routinely having, like, eight pups all at the same time.

[Anne Bird Platt (Bird Pinkerton's mother)]

For example, I don't know anybody that's had eight or nine kids.

[Bird Pinkerton]

And meanwhile, you can't, like, inject human fetuses with glow in the dark tracers or cut up human parents in the

[Bird Pinkerton (continuation or alternate label)]

same way as mice to see what's going on.

[Bird Pinkerton]

And so as a result, when you're

[Bird Pinkerton (continuation or alternate label)]

looking at some of these cells in

[Bird Pinkerton]

human tissue, you can't really know both

[Anne Bird Platt (Bird Pinkerton's mother)]

where it came from and where it went to and kind of everything about it.

[Bird Pinkerton]

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. 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 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.

[Anne Bird Platt (Bird Pinkerton's mother)]

Of course.

[Bird Pinkerton]

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 Mari's cells swimming around inside of you as well.

[Anne Bird Platt (Bird Pinkerton's mother)]

That makes perfect sense. How far back does it go?

[Bird Pinkerton]

So it is also possible that your mom.

[Bird Pinkerton (continuation or alternate label)]

So my grandmother gave you some of your grandmother's cells.

[Bird Pinkerton]

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.

[Amy Boddy (Biologist at UC Santa Barbara)]

So we've been talking very simply about this because it is so complex that our minds can even wrap around the fact that there's actually multiple generations happening all at once.

[Bird Pinkerton]

And so studying microchimaera is so hard because you have to find just like a few cells in a million, untangle

[Bird Pinkerton (continuation or alternate label)]

this whole intergenerational jumble, and then figure out what those cells are doing, what they're up to.

[Bird Pinkerton]

And that's part of why this research is going so slowly.

[Amy Boddy (Biologist at UC Santa Barbara)]

You're getting these like two of, you know, a thousand piece puzzle, right? 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.

[Bird Pinkerton]

And I find it. I mean, I find it like, I guess there's something about it that like, 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 the cells from your miscarriages have affected your body. Like, it's possible. It's always going to remain kind of like a, like a parent child relationship. Right.

[Bird Pinkerton (continuation or alternate label)]

Like on a tiny scale. There'll be sort of pushing and pulling and hurting and healing and you know,

[Bird Pinkerton]

it's a relationship we can explore forever and never fully untangle, to be sure.

[Anne Bird Platt (Bird Pinkerton's mother)]

But to me, the whole benefit of this kind of research is that what you know. Now let's say you really the 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. Strikes me as a good enough reason to pursue it.

[Bird Pinkerton (continuation or alternate label)]

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.

[Anne Bird Platt (Bird Pinkerton's mother)]

Ye.

[Bird Pinkerton (continuation or alternate label)]

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?

[Anne Bird Platt (Bird Pinkerton's mother)]

Oh, sweetheart, you are a scar healing helper.

[Bird Pinkerton (continuation or alternate label)]

It's on the record

[Anne Bird Platt (Bird Pinkerton's mother)]

and I'm so happy you're here.

[Bird Pinkerton]

Seem happy you're here.

[Bird Pinkerton (continuation or alternate label)]

Mama, we love you.

[Bird Pinkerton]

I love you too.

[Anne Bird Platt (Bird Pinkerton's mother)]

And I assume that's it, we're done.

[Bird Pinkerton]

Yeah, I think that's it. I think we're done.

[Anne Bird Platt (Bird Pinkerton's mother)]

No kidding.

[Bird Pinkerton (continuation or alternate label)]

Thank you for doing this.

[Bird Pinkerton]

You're very welcome.

[Anne Bird Platt (Bird Pinkerton's mother)]

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.

[Bird Pinkerton]

This episode was reported and produced by me, Bird Pinkerton. It was edited by Brian Resnik and Catherine Wells as well as Meredith Hodnot who runs the show. We had sound design and mixing for from Christian Ayala, music from Noam Hassenfeld, Serena Solon checked our facts and Manding Nguyen is just really lovely to have nearby. I want to say a special thank you this episode to Lee 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 microchimaera 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 if you would like to support the show and the journalism that Vox does. We would love it if you would become a member. It is very easy to do. Just go to vox.commembers and you will get access to all of Vox's journalism. But you will also know that you are supporting all of Vox's journalism. And for those of you who have emailed to let us know that you see signed up because of Unexplainable. Thank you. And thank you to those of you who have left us a nice review on your podcast platform or told someone in your life about the show. You are all excellent. Unexplainable is part of the Vox Media Podcast network and we will be back very soon with another episode about everything that we do not yet know.

[Anne Bird Platt (Bird Pinkerton's mother)]

Sam There's a new way to sweetgreen

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