Microchimeric mombie: Amy Boddy

Dave 00:52

It's like-- I don't know. [both laugh]

Athena 00:55

Cause you were, everybody was at one point inside their mother's wombs and mother's cells [Dave agrees] then could get around the baby-

Dave 01:04

Oh so then, my mom's cells might still be controlling my behavior? [Athena confirms] Really, that's a more direct method of my mom controlling my behavior. [Laughter]

Athena 01:14

We don't really know the extent to which, um, there is like behavioral manipulation happening, but we do know that microchimeric cells, um, from other individuals are replicating and expressing genes inside your tissues.

Dave 01:35

Interesting, wow.

Athena 01:35

Yeah. So the, that's what today's episode is about is microchimerism and in particular the transfer of cells between mother and fetus that happens in the womb and then what that might mean for life after the womb between family members, etc.

Dave 01:58

Wow, that's pretty interesting.

Athena 02:00

Yeah.

Dave 02:00

And so is there anything that stands out as particularly, uh, surprising?

Athena 02:06

Well, I think the coolest thing is the uh, if we think about, well, what would we expect to evolve in terms of what fetal cells can do in the brains and the bodies of moms? Like what would they evolve to control, right? Because like, you can think, you know, over, you know, such long evolutionary history, like since placental mammals came about, it's been possible for having this microchimerism. So, um, microchimeric cells like that. Like they could have evolved to actually do all sorts of crazy manipulation.

Dave 02:48

Okay, and does this go into sort of that like parent-offspring conflict of the babies trying to sap all the resources they possibly can?

Athena 02:54

Exactly. So it's a nice follow on from our last episode with David Haig about parent-offspring conflict and placentas and pregnancy and all of the weird things that happen in the womb.

Dave 03:10

All right. That sounds really exciting. Any useful takeaways for, uh, fetuses out there? [both chuckle]

Athena 03:18

While you're in the womb, that's your chance. [laughter] Alright, let's hear from Amy Boddy!

Intro 03:28

[Psychological by Lemi]

Athena 04:04

Amy, welcome to Zombified!

Amy 04:05

Thank you. I'm excited to be here!

Athena 04:08

Yeah, so we've known each other for a long time.

Amy 04:10

We have.

Athena 04:11

You, uh, came to work with me like, was it like 10 years ago? It was a while ago.

Amy 04:16

It was. It must have not been 10 years because my daughter was two. Oh no, she was a year and a half at the time.

Athena 04:24

Okay, so was...

Amy 04:25

And she's about to be eight, so-

Athena 04:27

Sevenish

Amy 04:28

Sevenish years ago.

Athena 04:30

Yeah. Alright, and then we worked together a bunch. And now you're here at UCSB.

Amy 04:34

Yes, correct.

Athena 04:34

And you're an assistant professor here...

Amy 04:36

Yes.

Athena 04:37

And can you like introduce yourself in your own words?

Amy 04:43

[Laughter] Yes, I can-- [both laugh] I think I can. Umm, so my name is Amy Boddy and, um, I'm an Assistant Professor in the Department of Anthropology at University of California Santa Barbara. Um, I got my training in, uh, Detroit, Michigan, um, in molecular biology and genetics, and I study, uh, evolution and human health and pregnancy in cancer.

Athena 05:13

Awesome. And mombies.

Amy 05:15

And mombies. Yeah. [laughter, both agree] The most important topic. [laughter]

Athena 05:19

That's right, yes. So, uh, when you came to the zombie apocalypse medicine meeting in the Fall of 2018... Right? That was--

Amy 05:31

Yes, 2018. Yeah.

Athena 05:31

Yeah. You came and you talked about fetal microchimerism.

Amy 05:36

I did.

Athena 05:36

And I remember and we're like going back and forth about it--

Amy 05:39

Uh-huh.

Athena 05:39

You're like, I didn't even realize there was a thing called a mombie!

Amy 05:44

Yeah. [laughs]

Athena 05:44

[Over laughter] Like can you tell us about that process? Like realizing, like, that there is a mombie thing?

Amy 05:50

Well, it was so fun because I've given microchimerism talks before, but um, I was very excited to put it together in terms of zombifying my talk. And I had planned like months ahead of time to like do this and, and put it in, but then obviously like life happens and a few days before I'm putting my talk together and I'm Googling it and I wanted cool images and then all of a sudden I fell into this like rabbit hole of memes of mombies where it's like zombified moms that need coffee and [Athena laughs] it's, are you training them? And there's a whole like--

Athena 06:29

Yeah.

Amy 06:30

--internet of mombies and mothers that identify as a mombie. [Amy chuckles]

Athena 06:36

So mombies are like taking over the internet basically?

Amy 06:38

Exactly. [Athena and Amy agree].

Athena 06:38

Yeah, yeah...

Amy 06:40

So that [Athena laughs] made my, putting my talk together quite easy.

Athena 06:44

So, so, um, what is microchimerism, and how does it relate to mombies?

Amy 06:49

Right. So microchimerism is a small transfer of cells from one genetic individual to another. Um...

Athena 06:57

So if like I have a small number of cells from someone who's not me--

Amy 07:02

Correct.

Athena 07:03

--then I'm microchimeric?

Amy 07:06

Correct.

Athena 07:07

Okay.

Amy 07:07

Right, right. And 'micro' being like a tiny amount of cellular exchange.

Athena 07:12

And, what's the 'chimera' part?

Amy 07:13

The chimera is the, um, from ancient Greece or whatever of the two different, you know, individuals or entities or organisms. So...

Athena 07:24

Right. Like the--

Amy 07:25

coming together.

Athena 07:26

--like a lion... And a bird... [Amy agrees] Aaand I wish I actually knew, I should know. [Amy laughs] Cause I'm, I'm Greek, right? [Amy laughs] And so I should know what chimera is.

Amy 07:35

I think there's one with like a dog?

Athena 07:38

Yeah. I think there's a lot of different ones--

Amy 07:39

--like creature with like...?

Athena 07:39

...with statues with...

Amy 07:41

...with like snake heads and stuff like that. [Athena agrees] So like, it's from, you know, ancient times of like two different organisms coming together like a head with like a different body, [Athena in agreement] but that's like 'chimerism' and then 'micro' is just maybe a, a few of those cells within a different--

Athena 07:59

Right...

Amy 08:00

--organism.

Athena 08:01

...it's like within species. Right? So like--

Amy 08:02

Yes.

Athena 08:02

--a mom having cells [Amy agrees] of her baby or a baby having cells of the mom.

Amy 08:08

Exactly, within species.

Athena 08:09

Yeah. [Amy affirms] Yeah, um, so... This happens in, in humans.

Amy 08:14

This happens in humans. It happens in organ transplantation, right? You have a different, you know, organ from an individual, umm, and they're shutting off cells along with the actual entire different organ. [Amy chuckles]

Athena 08:28

Yeah.

Amy 08:29

Um, and then it happens naturally during pregnancy. Um, the transfer of cells from the mother to the baby and from the baby to the mother.

Athena 08:38

So, the whole microchimerism thing is sort of even connected to like the Frankenstein idea, right? You're like putting a body together from like parts of like all different individuals. [Amy agrees]

Amy 08:49

Right, yeah, yeah, yeah, yeah...

Athena 08:51

...yeah. So, um uh, there are some primates that have even more chimerism than us, right?

Amy 08:59

Right. Yeah, so marmosets. They're... So, so the interesting thing is microchimerism happens during pregnancy, but it happens even more so during, during twinning, during pregnancy. So it's like a three-way transfer of cells, right.

Athena 09:14

Okay, so like if you're a mom, [Amy agrees] and you're pregnant with twins--

Amy 09:16

Yes.

Athena 09:17

--then the cells from you are going into the babies, the cells from the babies are going into you, and the cells from the twins are going into each other?

Amy 09:23

Yes. There's transfer of cells there too. Um, and uh, so, so there's some organisms that are natural twinners, uh, such as marmosets, so some new world monkeys, South American monkeys. Umm, and so, say you're a baby in utero and you're getting twin cells transferred to you.

Athena 09:48

A baby marmoset?

Amy 09:48

A baby marmoset, yeah--

Athena 09:49

Alright now, imagine you're in the, your mom, marmoset's womb...

Amy 09:53

And it's really tiny--

Athena 09:54

...and you've got a twin...

Amy 09:56

--and adorable and you have a little tiny, adorable twin with you. And their cells are being transferred to you. Your cells are their cellular exchange from you to your twin. Your mom's are being transferred to you. You're transferring some to your mother.

Athena 10:10

So cells are just going all over the place--

Amy 10:12

Yeah, all over the place. And then you grow up, right? So you come out of the moment--[Athena and Amy concur]

Athena 10:16

Okay so you're born...

Amy 10:16

--you're born.

Athena 10:17

...and you're a baby marmoset.

Amy 10:18

You're a baby marmoset, and you're maybe a female baby marmoset. And so you have your mother's cells, and you have your twin cells and you have your own cells and you grow up and then you have your own set of twins.

Athena 10:30

Wow.

Amy 10:31

And so there's a cellular exchange all over again--

Athena 10:35

Wait, wait, and like multiple generations...

Amy 10:37

multiple generations

Athena 10:38

...are getting all mixed up? So like how do you even say a marmoset is an individual? [Amy laughs]

Amy 10:44

Right, right. And it's been hard to quantify, right? And so this is a lot of, we know these processes happen. It's, it is happening on a small cellular level. And so it's really hard to, like, see how long cells from a different individual can persist in [Athena agrees] someone else's body. Um, but there's some studies in humans to show it lasts for decades to a lifetime.

Athena 11:09

Mmhmm. And we don't know about the intergenerational part.

Amy 11:11

And we don't know about the intergenerational [Athena agrees] part, which I think is like the coolest, most Sci-Fi, zombified version of, of human biology.

Athena 11:21

Right? Like I could have my great grandmother's cells in me...

Amy 11:24

Exactly.

Athena 11:24

...even though I don't really know her name.

Amy 11:26

Yeah, yeah, yeah. There could be. [laughter] I mean, there's a route for it and, and if we know, if there could be some kind of selfish cells that can hop generation to generation, I mean, why not?

Athena 11:38

Yeah, that's wild.

Amy 11:39

Right.

Athena 11:39

Yeah. Okay, so microchimerism is like this situation where cells are occupying an individual that is like genetically not the same as them.

Amy 11:49

Correct.

Athena 11:50

And it happens in marmosets, but it also happens in human pregnancies.

Amy 11:54

Right. And it happens across all, we think it happens across all placental mammals. So it has to do with the fact that we have internal gestation, and we have this organ that transfers nutrients back and forth between the mother and the baby. And there's some cells that get sloughed off into there. And it used to be that we thought that these cells just, it was a byproduct, right?

Athena 12:18

Yeah.

Amy 12:19

But these byproducts seem to be staying around in performing functions in the mother's body.

Athena 12:25

That's awesome. So, so can you like break down what happens? Like you get pregnant, the placenta starts growing--

Amy 12:32

Right, right.

Athena 12:32

--and the placenta is, um, attaching to the uterine wall...

Amy 12:36

Correct.

Athena 12:36

...and lika e sending out like these like tentacles, like extract resources [Amy agreeing with Athena] from the mom, or like they're getting like the blood vessels to come to it. Like what, what, what's actually happening, like, in that, that first stage and then like, where does the microchimerism come in?

Amy 12:53

Right. So we actually, it's, it's, it's complicated, and we don't know the exact process of it. So you get pregnant, implantation happens, right? [Athena agrees] So the embryo implants into the maternal, um, uterine wall, and then these specialized fetal cells called trophoblast cells start, um, invading the maternal endometrium and break down the, the tissue layer there. And they actually start developing, um, not only the, the, the embryo, but the placenta. And, um...

Athena 13:28

And the trophoblasts are the placenta, the ones that become the placenta?

Amy 13:32

Yeah. They're, they're, they're the invading cells and, and they, um, they also are super invasive. Right? And so like they're, they're, they're basically going through multiple tissue layers and then attaching onto the maternal's blood or the maternal bodies' blood vessels.

Athena 13:52

Yeah.

Amy 13:53

And opening them up.

Athena 13:55

Wow.

Amy 13:55

So it's like Game of Thrones, [Athena laughs] you know, when like the dragon comes? Oh, sorry. Spoilers. Maybe I shouldn't talk about. [laughter]

Athena 14:03

You can, you can talk about it.

Amy 14:04

And I'm like, they have the big ice wall and then the dragon comes and just like blows a hole through the ice wall--

Athena 14:10

And then the zombies come in?

Amy 14:11

And then the zombies come in. [Athena laughs] It's like that, only pregnancy. [Everyone laughs]

Athena 14:18

[Both joking around] So pregnancy is the zombie apocalypse...

Amy 14:21

Right! You open the, the, the arteries and then there's blood flow and cellular exchange that happens--

Athena 14:29

Yeah, yeah...

Amy 14:29

--across two different universes. [laughter]

Athena 14:34

Right. [laughter] Yeah. So you've got the placenta, which is actually, it comes from the cells of the fetus, right? [Amy agrees] So the placenta, like people say, "Oh, it's a maternal organ," but it's actually not, right? It's not genetically in the mom. It's genetically part of the baby.

Amy 14:48

When the placenta comes out, there's some layers of maternal tissue that has been shed.

Athena 14:54

Ohh.

Amy 14:54

So like when you go to like dissect a placenta or something, like you have to make sure there's, you get the fetal side because there is--

Athena 15:00

On the outside, there's a maternal layer?

Amy 15:03

Yeah there's like a maternal layer of where it was detached and, a-and shed. But it's mostly um, like 90% of it is like a "fetal-ly" derived tissue.

Athena 15:12

Yeah. So you've got like during pregnancy the you know placenta, which is from the fetus [Amy agrees throughout] and then the you know, uterine wall, which is like the mother and you have this like intersection point where um, I mean you would think like just first pass like, "Oh mom, baby mom wants to take care of babies". So like there should be cooperation at that intersection. And there is to a large extent, right? Because mom is allowing resources to flow to the baby, but it's also not 100% aligned interest, right? [Amy agrees with Athena].

Amy 15:47

Yeah. And the mom has specialized immune cells that tract to the uterus and help with this remodeling like overview things like reconstruct things. [Athena agrees throughout] So the mom has a way of like regulating this other way. So cooperation and in that sense, when you think about how that evolved, those policing cells of the mother's body might had to evolve because a placenta was invading too far. You know, like--

Athena 16:14

So from an evolutionary perspective, why like would the placenta be invading so far? Why like would there be conflict--

Amy 16:22

Mmhmm.

Athena 16:22

--between the interests of the fetus and the interests of the mom when like on a first pass it's like reproduction is like a super important thing, right? [Amy agrees] So, so why like is there conflict at all between the mother and the fetus? Like at this place where you know the placenta and the uterine wall are coming together?

Amy 16:41

Right. So that roots from like maternal-fetal conflict, right? Where the, the offspring's 100% related to itself and the mother's only half related to the offspring. So they have divergent interests and the fetus is always going to want to extract more. Right? Um, it's more interested in itself surviving. [Athena agrees] Right?

Athena 17:02

Yeah. So this relates a lot to the conversation that we had a few, uh, last episode with David Haig--

Amy 17:09

Correct, exactly.

Athena 17:09

--where he talked about maternal-fetal conflict and placentas and how like, I mean, if you think about it, an offspring, umm, is... it is potentially competing with its other siblings [Amy agrees] for resources from the parent, even if...

Amy 17:25

...and their potential siblings.

Athena 17:26

Exactly. Other future possible siblings [Amy agrees] or past sibling... You know, so, um, so... Anytime--

Amy 17:33

It's almost like that Christmas story, like siblings of the future and past or what is it like ghost of the past?

Athena 17:41

the...?

Amy 17:42

Do you know what I'm talking about? The Scrooge movie...

Athena 17:45

Oh yeah. I-I don't know which- what particular part of it we're talking about.

Amy 17:51

They go visit like future and past.

Athena 17:54

[Both recalling A Christmas Carol] Yeah. Right, right. Okay. Yeah. Right. So you imagine the future and past siblings [Amy agreeing] and every, you know, evolutionarily like every like you can compete with the future and past siblings too for the resources of the parent. And so like if you've ever seen like siblings, like fight over candy, it's basically the same thing that like mom has a certain amount of stuff--

Amy 18:18

Right.

Athena 18:18

--and both of the kids want more than their fair share. Like, I don't know if you see this with your kids ever, but like Vaughn, my, like youngest. So there's three of them and like Vaughn is like, well what would be fair is for me to have half of it and Yvonne and Monte to share the rest. [Amy laughs] And I'm like, what's your definition of fair? Right? Because... [laughter]

Amy 18:39

Right, right. You get half. [Athena agrees laughing]

Athena 18:43

So, so I feel like, I don't know for me, an intuitive way to kind of like understand the parent-offspring conflict is to like, think about like when there are multiple siblings, [Amy agrees] and that their siblings have conflict because they just want, they want more for themselves than for their siblings.

Amy 18:58

Exactly.

Athena 18:58

And then somehow like through the, you know, amazing properties of like, you know, the way evolution works, [Amy agreeing] that translates to like what's happening in the womb between the placenta and the uterine wall, so that you've got like, you know, the fetal cells... sort of advocating for the, you know, the fetal cells of the placenta advocating for the fetal interest and the cells of the mother kind of advocating for the mother's interests, which include like all past and future potential offspring and like saving some for them.

Amy 19:29

Right. And it's costly too, right? Like this, it would be so much easier if there, if there was like an aligned interest, but like [Athena agrees] there's all these defenses that the mother's body has evolved to have to defend against this like invading placenta type and the fetus has to put up these costly measures to invade. Umm...

Athena 19:54

Mmhmm, so there's like a lot of conflict.

Amy 19:56

So there's been a tug of war over evolutionary time. [Athena agrees] Um, and it's interesting because in the end the fetus does, at least in human pregnancies, tap onto the maternal arteries and be able to have like free access in the end. Umm, and so there's like this winning of the maybe tug of war in, in that sense. And in, in, at that point when you're pregnant, there is, there's things that the fetus can do, like ramp up the maternal blood pressure, right?

Athena 20:31

And turn up the pressure area, then the resources start pouring out for that, right?

Amy 20:36

Right. And that's not possible in a different placenta type that's not as invasive where they don't have direct access to the maternal arteries and blood flow and... and stuff like that.

Athena 20:48

So humans are like particularly vulnerable to being mombified?

Amy 20:52

Exactly, [Athena laughs] exactly. Because of our invasive placenta type and maybe our giving nature of allowing--

Athena 20:59

That's right.

Amy 20:59

The fetus.

Athena 21:00

Like yes, just latch onto me like a leech. It's fine. [laughter]

Amy 21:07

[Joking with Athena] It's totally fine. [Both laughing]

Athena 21:07

Yeah, it's like a little sucker actually...

Amy 21:08

Right, right.

Athena 21:11

Yeah... Umm, okay, so, we've kind of got like this, you know, evolutionary understanding of what's going on like with pregnancy and with the placenta. [Amy concurs] Um, and so, uh, full disclosure, Amy and I worked on this stuff about microchimerism together. So we have like sat around [Amy chuckles] and talked about it lot. Umm, what are your current thoughts about this? Like question, I know we've sort of like went back and forth a little bit about this when we were working on the paper. Um, so, when you go from like the invasive placental cells...

Amy 21:42

Mmhmm.

Athena 21:42

...to like the microchimeric cells, like, are those microchimeric cells just like cells that invaded and then just like kept going and then like got into the other systems of the body or do you think they're coming from like something other than like just the placenta invading and like going really far?

Amy 22:02

Right, I think they're different.

Athena 22:04

Yeah?

Amy 22:04

Because they can differentiate into a bunch of different cell types, they can make it. So it seems like they're STEM-like-cells going over so they're not specialized. Like I think the specialized cells do get sloughed off into the, the maternal blood stream...

Athena 22:17

So you think to be this like invasive trophoblast [Amy following] cells or having to like specialize and like commit to that in a way that it would be hard for those same cells to be the ones that like...? Yeah, but, okay, I'm going to push you on this.

Amy 22:33

Okay.

Athena 22:33

Because, um, if we now, I mean who wants to think about this in terms of cancer, but we do because we both study cancer, right? [Amy acknowledges Athena] Like you can also have like metastasis, like balls of cells growing that are differentiated, that like came from a tumor where...

Amy 22:51

...it was specialized.

Athena 22:52

...maybe, you know, they came from like invasive cells. So, so I don't know. I mean...

Amy 22:58

Right. I guess they could i-in this, the embryonic stage is very unique and there's differentiation, differentiation. Like it's like [Athena follows] creating all these different tissue types and it's a very controlled environment. And, and so...

Athena 23:16

Could they like go like could they like differentiate into like the trophoblasts like cells and then like go elsewhere and then differentiate and like a cancer-like way...

Amy 23:25

Right.

Athena 23:26

...and then grow and...?

Amy 23:28

Potentially, yeah. But there's so many cell types that come. [Athena agreeing] I mean there's immune cell types that we find in specialized liver and specialized heart cells... neurons...so...

Athena 23:39

S-so do you think they're just like going right into the blood? Like from somewhere in the fetus?

Amy 23:44

I-I think the theory out there, and I-I lean towards this is that there's STEM-like cells, so they're very like early [Athena audibly follows] stage cells that, that um, migrate to the maternal body and then they can, they probably differentiate based on what tissue type they're in, right? [Athena agrees] They get signals to say like, "Hey, you're in a liver, this is how you act in a liver." And they're able to differentiate and integrate into--

Athena 24:12

So it's almost like some point in the like, so if you think of like you start with one cell, right, [Amy following] and baby and then it divides and divides and divides and then you get like, you know the placenta from part of it and you get the fetus from another part of it. And maybe there's some part of it that actually is like destined to be the microchimeric cells and like finds its way into the maternal bloodstream and then like differentiates into the maternal tissue. So it's almost like a STEM cell transplant except from your baby in your womb.

Amy 24:43

Right, right. Yeah, and, and the interesting thing is we've, umm.... There's research out there that shows that these cells start transferring very early on in pregnancy before the placenta is completely established.

Athena 24:57

Hmm.

Amy 24:57

So, um, women that don't even know that they were pregnant. So with these early miscarriages [Athena follows] where very little is happening at that point in terms of placentation, um, still get a burst of, um, microchimerism in their blood.

Athena 25:15

Interesting.

Amy 25:15

Which makes it really challenging to study, because you don't, you don't know that history. If a woman is almost, didn't even know that there was, uh, a miscarriage, [Athena agrees] which happens quite often in humans, um, then it's very difficult to figure out which cells came from which person.

Athena 25:38

But it might be a way to better study spontaneous miscarriage.

Amy 25:42

Yes.

Athena 25:43

Right.

Amy 25:43

I think so. Yeah. I think it has, it could have really important clinical applications.

Athena 25:49

Interesting. Yeah. Okay. So I have to ask you, does it freak you out or creep you out that like microchimerism happens and that like you have kids and like their cells are in you and your cells are in them, or are you like, "Oh, we're just like a closer family [Amy laughs] because like we're sharing cells?" Like...

Amy 26:08

I- it doesn't creep me out. Yeah. It doesn't creep me out at all. I think it's fine. I've-I've met women that think it's actually really like sweet and they're, they, they get emotional knowing that they have like part of their baby in them type of thing.

Athena 26:24

Mmm.

Amy 26:25

So I think, I don't know. Like it doesn't creep me out at all. What about you?

Athena 26:29

Does it make you feel warm and fuzzy [Amy laughs] or it just doesn't?

Amy 26:32

I don't know. I guess I'm very like....

Athena 26:34

Practical. [laughter]

Amy 26:36

Practical. Like, it exists. So, yeah. [both laugh]

Athena 26:40

Yeah, I don't know. I don't think it creeps me out, but i-i-it is like very science fiction-y and to like, sometimes I'll think like, [Amy agreeing] 'Okay, how many potential other individual cells might be in my body right now?' Like, and, you know, obviously it's like right now there's not evidence to say like that it can be multiple generations transmitted but it also is possible given the things we do know and so, so I don't know. So I find that like kind of mind blowing like, yeah...

Amy 27:19

Like, and what if you like took a tissue dissection and you're like, oh, there's like Reagan's cells and their clumped next to like Sid's cells. Like I think that would actually like multiple generations of your kids like integrated like next to each other.

Athena 27:34

Yeah. [Joking] Oh and there's grandma next to Reagan. [Laughter]

Amy 27:38

Oh, their cells are like creating tight junction, saying they get along after all. [Athena laughs]

Athena 27:45

Awww [Both laughing]

Amy 27:46

They are cooperating and exchanging resources, but only in my body. [Laughter]

Athena 27:52

Yeah, I feel like it does kind of challenge our notion of like what is an organism too [Amy agreeing] and like, you know, in the faculty fields of, you know, like evolution and behavior, whether it's like evolutionary psychology or evolutionary anthropology or just straight like evolutionary biology. There is sort of this assumption that like the individual organism is like the unit of genetic uniqueness.

Amy 28:14

Right.

Athena 28:14

And therefore the unit that selection will act on. Um, but when you start mixing the cells up like that, it's like, well... Should we- do we need different theoretical approaches and models to actually predict what is going to happen and [Amy follows] how individuals are going to behave? And like, is there actually more, you know, interdependence, than we might have guessed?

Amy 28:48

Right, right. And in a cra-, like, not crazy. I think it's very Sci-Fi though, is to think that some of these cells could end up in germ cells. Right? So, as eggs or sperm.

Athena 29:01

Yes. So the reproductive line. So it's like, could there, like okay--

Amy 29:06

And what does that really mean [Athena audibly following] to be an organism? When you're, your germ cells, your reproductive line is hijacked.

Athena 29:14

Yeah. So this is like, so here, here's the scenario I think, right? Like great grandma's cells, like went into grandma went into [Amy follows] you. And then like when you were, um, conceiving somehow, like it was actually like, great grandma's egg. And so your daughter is actually half your great grandma or something. Right? That's the, that's the like crazy scenario and...

Amy 29:46

And it's biologically plausible within the women-like generations, because oocyte eggs are developed during fetal development. Right, where there's this cross-talk.

Athena 29:58

Yeah. Right. So it's crazy and bizarre, right? [Amy agreeing throughout] There's no- there's not evidence that that happens, but there would be like, there would be huge selective pressures for cells to evolve to do that. So there's probably, we probably have counter adaptations we don't even know about, right, to prevent that from happening.

Amy 30:18

Yeah, I'm sure.

Athena 30:19

So it's like we kind of just take for granted that that doesn't happen. But like if you think of the evolutionary logic, like selection pressures are going to be insanely high.

Amy 30:26

For that.

Athena 30:26

For that! Because you don't have to like build a whole body from scratch. You just like put your egg cell in the next generation or skip a generation or whatever. And then, yeah so....

Amy 30:38

Right.

Athena 30:38

Yeah, but, but there are some cases where like the mom of someone was not like, like she like you know gave birth to an offspring, [Amy follows] that did not look like her genetically from the blood test, right? It's- and there's some examples of that?

Amy 30:53

Yeah, yeah. So there's a few. And going back just before we go onto that, I always think it gives, like, when you hear people that are like, she looked just like her grandma. [Athena laughs] You're like, well maybe we should genetically test her [both laughing]. Let's go find those cases. But no. So there's, yeah--

Athena 31:11

But the thing is like, people don't really [Amy chuckles] look, I know. I mean now there's like, I guess all this genetic data that's online, so I wonder if anybody has tried looking for whether that happens.

Amy 31:24

Right, um, but there's, there's women who, there was a case study of, uh, uh, a woman named Lydia Fairchild, I believe. And it was a custody battle and so they had to do genetic paternal testing and they also did maternal testing. And what they found was the, the, the supposed father was indeed the genetic father, but the mother wasn't the genetic mother. She--

Athena 31:49

Whattttt-- [Amy laughs]

Amy 31:49

And she was pregnant at the time and, um...

Athena 31:52

With another baby.

Amy 31:54

With another baby. Yes. Not alien or zombie or [Athena laughs] dragon or, um, and then, uh, she gave birth and they immediately genetically tested her and her, um, her, they used her blood and I believe there was also a court-martial in the room.

Athena 32:16

Wow.

Amy 32:17

Because... yeah.

Athena 32:19

Wow. Okay.

Amy 32:20

Anyways, umm, and so what happened was, again, she wasn't the genetic mother and so they thought she was like scamming the system and surrogate and she almost lost her children and all of this stuff when eventually someone--

Athena 32:35

They took her kids away, right?

Amy 32:36

I believe her, her kids went away for a bit. It was like this horrific ordeal. And then someone finally, um, took a sample from her cervix and the sample from the cervix was genetically matched to all of her children.

Athena 32:55

Yeah.

Amy 32:56

So what they found was she was, um, something, not necessarily microchimeric but chimeric like full tissue integration and it seems like it probably happened--

Athena 33:08

So like her whole blood system was from another individual [Amy confirming] that was not the same as her reproductive system.

Amy 33:13

As her reproductive system. And so...

Athena 33:16

That's crazy.

Amy 33:17

The story goes that it was a twin of hers that was, um, absorbed or, or didn't make it in the womb. And so she was a singleton birth, but at some point, early in development, there were two fetuses and they had swapped a bunch of cells and then...

Athena 33:33

Wow.

Amy 33:33

Yeah.

Athena 33:35

Do we have any idea how common that actually is? Like in the general population?

Amy 33:38

No. It'd be so cool to figure out, right. Especially twins. How like how often during fetal development are these cells just kind of swapping back and forth, right?

Athena 33:49

Yeah.

Amy 33:50

Yeah.

Athena 33:51

It's crazy.

Amy 33:53

Mmhmm.

Athena 33:53

So, um, so can we talk about the zombie side of this?

Amy 33:56

Of course.

Athena 33:57

All right. So... [Amy laughs] So, like, earlier on we were talking about the conflict part, right? [Amy agreeing] Like how there's going to be some kind of battle over the resources and that the placenta does a bunch of this sort of, you know, trying to get more from the mom.

Amy 34:12

Right, right.

Athena 34:14

How does this kind of dynamic like translate into the microchimerism piece of things? Like what's, what is, what do we know is going on [Amy audibly follows] like where are the microchimeric cells going? Do we know what they're doing? Are they like advocating for the fetal interests? [Amy laughs] What, what, what's happening with these microchimeric cells in the maternal body?

Amy 34:41

Right. So great question. We don't, we don't know much, but what we do know is we do know that they transfer, they increase in frequency during pregnancy. So a woman is going to get the most microchimeric cells and just fetal DNA in her blood towards the very end of her pregnancy. And then she--

Athena 34:59

Okay, so the fetal cells, [Amy follows] they're like going from the baby, like into the mom's tissues. And as the pregnancy is progressing, there's like more and more and they're like going deeper and deeper [Amy laughs] into the mom's body and proliferating and invading [Amy agrees and laughs]. So it's like body snatcher's situation.

Amy 35:16

Right, right. And the maternal immune system is kind of dampened a little bit. It's modulated. It's not completely suppressed. It's just got a shift going on. And so there's tolerance of this, right? Umm, but then pretty quickly, I think one of the studies showed within 24 hours after labor, there is active clearance. So the maternal immune system kind of ramps back on and starts kicking them out.

Athena 35:44

They're like, "You know what, nine months long enough you're out of here."

Amy 35:48

And then also the reservoir is gone, right? Like the baby is gone. [Athena agrees] So there's no more to be like getting pushed into, into circulation. Ummm, and for a very long time we thought that was that and then all the cells just magically disappear....

Athena 36:06

Because the maternal immune system gets rid of them all.

Amy 36:08

Right. Um, and then, um, maybe 20 years ago it was discovered that these cells persist. Um, and so a lot of studies have been looking at what they're doing and where they're going since then. And it seems like during pregnancy they're floating, you get the highest amount in the blood, but also, the highest amount in the lung. And then they integrate into a bunch of different tissues, including the brain, which is just like--

Athena 36:34

And the lung might just be a byproduct, right? Because they're, the blood is flowing [Amy agreeing] and like you have these little capillaries and they're just getting stuck.

Amy 36:41

Exactly. Yeah. And after clearance, you know, like after pregnancy, most of them are cleared from the lung. It doesn't seem like they're persisting.

Athena 36:49

They're not sticking around long, but they are sticking around in the breasts?

Amy 36:55

Right, right.

Athena 36:56

In the thyroid, [Amy confirms for Athena] in the brain and the immune system, right? Is that right?

Amy 37:04

Yeah. I mean, almost all tissues that have looked at for this is like decades after a woman has given birth, they've found microchimeric cells. [Athena audibly following] So the ones that get embedded into tissues, stay. There's been a lot of research on it. So I don't know if it's a bias or if there are indeed more fetal cells in these interesting tissue types that are the breast in the thyroid in the brain. But a lot of these, um, tissue types, um, are important for diseases. [Athena agrees] So that's where we're the research is like directing it where, where women with breast cancer, they're finding fetal cells in tumors. And women with autoimmune diseases, they're finding fetal cells in the diseased tissue site. Um, and so it kind of opens up this idea of are they normally there or are they there causing this pathology, this disease.

Athena 38:05

Yeah. Well, and we kind of got interested in this whole microchimerism question actually because of the breast cancer link. [Amy agrees] Cause we started looking at, you know, is there some relationship with breast cancer and microchimerism and we found a bunch of papers and they were really inconsistent. Some were like, "Oh, it seems to be more cancer, right?" There's microchimerism. And others are like, "there seems to be less cancer!"

Amy 38:28

Yeah, there's less cancer, and everyone should have a fetal cell STEM therapy like injection type of because they're protective. And others others were like, "no, no, no, these women have more fetal cells and worse prognosis." So...

Athena 38:45

Yeah. So then we were kind of like sitting on this and we're like, you know, what's going on? Why are these studies contradictory? And of course one possibility is just that there's like no effect and it's just randomness, right? But the other possibility is that like there might actually be some times when the microchimerism is bad [Amy audibly agreeing] for the maternal health and other times when it's good for maternal health. Right? So then we were like, okay, well this sounds a little bit like some of the things that are going on with parent-offspring conflict where there's some alignment of interests, right? Like both the mom and the baby. Like they want each other to survive, right? But then there's also some conflict about just how many resources are going to be given to the offspring. Right. And so, so that's kind of where we were like, okay, I wonder if something is going on? We have maternal-fetal conflict and microchimerism, right? And maybe that explains why there's this like paradox with disease risk and microchimerism. Yeah. Is there also similar stuff happening with some of the immune conditions?

Amy 39:50

Right yeah the immune- every, every disease I looked at, it was all over the board on whether it was protective or.... So it was almost like, all right, that's the literature out there. Um, well what can we do from a theoretical framework then? Yeah, let's just move, we're going to assume that maybe there's like cooperation and conflict.

Athena 40:10

Right. Because we reviewed the literature and we're like, what? [Amy following] It's a paradox. What's going on, you know? So we're like, well, maybe maybe the maternal-fetal conflict framework could at least explain what's one possibility and it makes some new predictions too.

Amy 40:25

Right, right. And so you assume a cooperation, obviously for maternal health.

Athena 40:33

Right, so things like wound healing, for example.

Amy 40:34

Wound healing, yes.

Athena 40:34

Right? Like there's a cool example of seeing like, um, microchimeric cells involved in wound healing, right?

Amy 40:41

Yeah, so there's a few studies. One looked at, I believe it was mice and they were able to, uh, fluorescently label the microchimeric cells so they could watch them under a microscope in a mouse. And they saw that if they injured the ear of the mouse, that th-the fetal cells actually like migrated and helped repair the wound. Um, in humans. Umm, they've looked at women who have had C-sections and then just done a biopsy of this C-section wound and found that there were microchimeric cells embedded in the scar tissue and they were expressing things that were important for wound healing, like collagen to like, you know, repair that-that tissue.

Athena 41:28

So this is kind of consistent then with the cooperation side, right? [Amy agrees] Like, okay, fetal interests are babies and you know, mom's interests are aligned about like helping the mom to heal because baby wants mom to be around in the future.

Amy 41:42

Yeah. And then every- I still remember it was, we were sitting in an office at ASU and we're like, what about conflict? And it was just like, [Athena agreeing] it's gotta be over resources. It's just has to be and like, yeah. And then mapping out what, what kind of resources does a mom provide a baby postpartum?

Athena 42:01

Exactly.

Amy 42:04

Now we're not talking about the placenta. We're not talking about any-anything like that. It's what kind of resources does a mother give the baby once she's given birth?

Athena 42:13

Yep. Right. And then how could they possibly, right, how could those microchimeric cells that are staying in the mom almost be doing something like what the placenta does, [Amy follows] but after the baby is no longer attached and it's just like remote controlling the mom like through the microchimeric cells?

Amy 42:30

I know. I think about it as like an insurance policy. [Athena laughs] I don't know if you're going to love me after I'm out, so I'm just going to send a few of my friends to make sure that--

Athena 42:40

Into your brain, just flood you with oxytocin. [Athena laughing]

Amy 42:44

--just making sure that everything comes back to me. [both laughing] Um, so yeah, so the we have these predictions that maybe they would be involved in lactation.

Athena 42:57

Yep.

Amy 42:57

Ummm, helping women lactate or promoting, expressing important hormones that were important for lactation. Um, and you said earlier maybe, uh, migrating to the brain and expressing the love hormone, oxytocin. We know that's really important for bonding.

Athena 43:14

Yeah. Prolactin, so you know

Amy 43:17

Yeah, prolactin.

Athena 43:17

These are hypotheses, right? [Amy agreeing] These are speculations, but they're coming from this sort of framework.

Amy 43:22

And it's just like, it's so great. To think about rooting it in evolutionary theory that you can like have this like really novel predictions and framework [Athena agrees] that you can now go and test. So instead of testing whether these fetal cells in a tumor progress a disease or not, like understanding actually just the basic biology from first principles on evolutionary theory and maternal-fetal conflict.

Athena 43:52

And you can make predictions that, like, I mean really are like really in like Sci-Fi kind of world, right? [Amy agreeing] Like, well, what if the fetal cells are like manipulating the maternal bonding system, right? Like that's like super intense behavioral change. Or, or even if they're, you know, going into the breast and like, you know, forming, um, cause they, but they express genes and they differentiate into, um--

Amy 44:22

In Petri dishes, you can--

Athena 44:23

Mammary glands, don't they?

Amy 44:25

If you give them specific hormones, you can--

Athena 44:27

Get the fetal cells to actually make the mammary glands.

Amy 44:30

Yeah, they can differentiate into specialized cells [Athena agrees] that are part of the mammary gland. And so, and I mean cell signaling is quite amazing, right? You don't need, it's a cascade event where like you get a signal and then things follow instead of just having maybe a specialized cell that promotes and signals for prolactin could still have like very large effects.

Athena 44:52

Right.

Amy 44:53

Because like that's one of the criticisms of this, right? Is that like there's only a few cells. Do they really influence maternal physiological behavior and, you know, biological mechanisms? And I would argue that there, even if there's only a few of them, there still could be like a profound effect.

Athena 45:14

Right. If they're engaging with the signaling systems, then it could just be, [Amy follows] really large, right? And there's also the thyroid, right?

Amy 45:24

Right, yeah. We, um, yeah. So it-it's interesting and it leads back to like, you know, heat regulation for, for the baby, where the baby

Athena 45:33

So the thyroid is like really involved in like thermoregulation. [Amy agrees] So like if you're always cold or you're always hot, you should really go get your thyroid checked out. Like I should probably [Amy laughs] cause I'm always cold. Um, but it's like a really important part of how our bodies regulate heat and usually like when you're pregnant and when you're lactating, like your body temperature is higher. Right?

Amy 45:56

It is, it is. Yeah. And um...

Athena 45:59

And that helps keep the baby warm. Right? Because then the baby doesn't have to do the thermoregulation itself because it's actually metabolically expensive to stay warm.

Amy 46:06

And babies are not good at thermoregulating.

Athena 46:10

Yeah.

Amy 46:10

Right? And I don't know, this is completely anecdotal, but when I was nursing my daughters, I would be sweating. Like I would, just hearing them cry, would trigger my body to heat up.

Athena 46:22

That's interesting.

Amy 46:22

And so like, I felt like, and this was before I developed, we developed a framework. [Laughter] You know, like that I noted that like I would get so hot just hearing my baby cry, [Athena following] like it would create like a reaction in my core temperature.

Athena 46:38

Cool.

Amy 46:40

Um, but the other interesting thing is women have seemed to have a higher rate of thyroid disease in general in thyroid autoimmunity.

Athena 46:50

Yeah, right. And so the hypothesis is maybe fetal cells are getting into the thyroid. They've been found in the thyroid. Right?

Amy 46:57

Correct.

Athena 46:58

Um, have they been found to be associated with like thyroid disease in either direction? I don't remember now.

Amy 47:04

I think, um, there's a study looking at Hashimoto's, which is an autoimmune disease of the thyroid, and I don't remember which the outcome was.

Athena 47:11

Yeah. But, but anyway, the hypothesis is like maybe fetal cells are going into the thyroid [Amy audibly follows] and actually contributing to raising the maternal temperature so that the baby doesn't have to spend the energy to raise its temperature cause it's just draining the warmth from mom, so yeah.

Amy 47:30

Yeah. Yeah. And, and it's interesting to think about like in terms of that, but then thinking about each mom being a different, like--

Athena 47:38

Different environment?

Amy 47:41

A different environment, with a different immune system and a different need and a different reproductive value. And then the paternal interests, right, where the conflict comes from, which is like the fetal right [Athena agrees] might have a different reproductive drive or something like that as well. And so these conflicts might not be so much of a conflict in certain alignments. Right?

Athena 48:06

Yeah.

Amy 48:07

Certain gene alignments like maternal-fetal gene alignments.

Athena 48:10

Well and also like depending on the environment, right? [Amy agrees throughout] Like how many other siblings there are and like there can be situations where there are, you know, really aligned interests of all of the parties. Right? So you're probably going to get more cooperation and other situations where there's not as much. But then I guess it brings up like the question of like are these things that fetal cells might be doing to the maternal body? Like are they actually able to adjust depending on the environment that they're in to be more or less exploitative? And you might expect that, like they could evolve to do that.

Amy 48:50

Right. Do you want to hear-- I don't know if this is a good venue for talking about crazy ideas. [inaudible].

Athena 48:56

Yes! It is, it is totally a great venue for that.

Amy 48:58

I think- I keep thinking about this in terms of how humans used to have very large family sizes, [Athena follows] and a lot of children and that we might be at a mismatch where there used to be a lot of transfer of cells.

Athena 49:11

Yeah.

Amy 49:11

And so that's maybe had, uh, um, basically development of the immune system in a certain way to tolerate, you know, [Athena agrees] the number of cells being transferred and the different genetic.... Now we're seeing a lot less of that and it could have some, what we expect calibrated from our evolutionary past to now what we see could be at a mismatch in that--

Athena 49:38

Right so our immune systems might not be really calibrated in the right way [Amy agrees] for how genetically undiverse we are inside.

Amy 49:45

Yes, yes. [Athena laughs]

Athena 49:47

Yeah. They're like expecting us to be like filled with like 17 children. [Athena laughs]

Amy 49:52

Right, right, right, yeah. And it's like, it's, it basically parallels to the microbiome, you know, stuff right?

Athena 49:57

Hmmm, that's interesting,

Amy 49:58

Where we think about it in terms of like, you know, we used to have all this pathogen exposure until our immune systems calibrated to deal with all that pathogen exposure. But if we don't get that challenge, then it just kind of develops a little bit wonky. And can, you know...

Athena 50:14

That's really interesting. Yeah. Um...

Amy 50:16

So I, yeah, I don't know where to go with that? [laughter]

Athena 50:19

[inaudible] It's a fun thing...

Amy 50:22

Its a fun thing to think about. [Athena agrees] We're like, we think we think about like, Oh microchimerism. We could be really genetically diverse and things like that, but like we used to maybe be a lot more radically diverse, especially the transgenerational effect if there were a lot of cells getting passed on.

Athena 50:39

Yeah. So, um, so I have to ask, what is your version of the like zombie apocalypse of, of microchimerism.

Amy 50:51

oooh.

Athena 50:52

Like what is the like, you know, if you take the things that, you know, w-w-we know are happening [Amy audibly follows] with microchimerism the things that we speculate might be happening with microchimerism and you like ramp it up. Like what, what is that scenario where like the cells inside of us like get even more power over our physiology and behavior? [Laughter]

Amy 51:20

Yeah. I-I mean, yeah, I, yeah, I immediately went to like, well the cells would transfer to the brain and like manipulate behavior. [Athena agrees] Right? Right? And manipulate how we interact with other humans or something. 'Cause it'd be a different genetic entity taking over the brain.

Athena 51:37

So would like our, our kids be like, you know, con--

Amy 51:41

Basically.

Athena 51:41

remote controlling us, basically?

Amy 51:43

Yeah, yeah. The kids are remote controlling us... I feel like I live in that life though. [Laughter]

Athena 51:49

You're in the mombie apocalypse?

Amy 51:49

I have two young kids. I think they control me. I sometimes am like, why am I doing this right now? You can get your own water. [Athena laughs] You're standing right next to the water resources element. I am, I am the one.

Athena 52:03

Right. Who's like, who's spending the metabolic resources [Amy laughing] to transport the water, right?

Amy 52:08

Yes. Yes. Yes. Um, I also think about it in terms of immediately when you ask that is just like that, um, hopping into the germ cell, [Athena follows audibly] so hopping in the reproduction, so hijacking the body so the body's still protecting the germ cells and it's the body's multi-cellular like interest to protect themselves and pass on different generations.

Athena 52:31

Yeah.

Amy 52:31

You know, just getting a free ride and being able to [Athena agrees] get passed on.

Athena 52:37

Right. So it could be like a future of just like clones.

Amy 52:44

Right, right. [Amy laughs] But, but mombie clones.

Athena 52:45

Yeah. But, but I guess it would be like there'd be, well cause at some point well like even if they like the offspring then mate with other [Amy audibly follows] individuals, then the next generation can still be a clone, but then they might be more susceptible to disease. Right? If you just have a lot of clones. So I don't know, there might be some countervailing pressures to like not just be parthenogenetic, right. That's what that's called. When you just make a clone of yourself?

Amy 53:14

Right, I think there's probably some pretty strong evolutionary pressures to make sure that there's no hopping generations. Right?

Athena 53:24

Yeah.

Amy 53:24

We just don't know what they are yet, which would be cool to figure out.

Athena 53:28

Yeah. Yeah. So, do you have any other, um, sort of mombie apocalypse thoughts? Like what, you know, what we should be--

Amy 53:36

I think mombies will survive the apocalypse. [laughter] We're more, we're more robots. We're good at dealing with crazy things [Athena agrees] and hungry things and... [Amy laughs]

Athena 53:50

Managing the conflict.

Amy 53:53

Managing conflict, and maybe doing it with part of us that may not even--

Athena 53:56

Be us. Right? [laughter] We need like, you know, we need like inclusion and genetic diversity like [Amy agrees] even inside us in order to deal with the apocalypse maybe.

Amy 54:09

Definitely. Yeah.

Athena 54:10

Yeah. So just another reason, that inclusion and diversity--

Amy 54:14

And you know, the more cells you have in you the more, you know, you might be able to figure out a way out of the apocalypse, maybe your kid controlling your brain might have a very creative way to survive a zombie.

Athena 54:26

Right. In fact, I mean, we're literally talking about sharing brains, right?

Amy 54:30

Right!

Athena 54:30

Brains that are made of like different organisms. [Amy agrees] So it's like a hybrid Frankenstein brain. [Amy agrees] So that the mombie brain is actually a hybrid Frankenstein brain. Yeah.

Amy 54:44

The interesting thing, and we can end on this, it-it's unclear whether when we find microchimeric cells in the brain who they're from.

Athena 54:54

Oh, because we're not doing like the single cell kind of.

Amy 54:59

We can assume that they're from her pregnancies. So what if it was from her mother?

Athena 55:05

Yeah.

Amy 55:05

Or her older brother?

Athena 55:07

So there's just like, so much we don't know about microchimerism. Like we know what happens and we know from like an evolutionary perspective that sometimes there's going to be aligned interest and you'll expect like positive effects on health. [Amy agrees] Sometimes there'll be conflicting interest and you might expect negative effects on health. But in terms of where the microchimerism is coming from, what exactly the cells are doing. I mean we know they're expressing genes and like becoming parts of the tissues, but like what is their actual effect on the viability of the organism and the behavior of the organism? There's just so many open questions.

Amy 55:45

So many, and we only discussed fetal microchimerism but there's maternal where the maternal cells get transferred to the fetus and it seems like those cells are very important for developing the immune system and [Athena agrees] doing really important health benefits for the fetus early in life. Right. And that's happening both like during pregnancy and also during breastfeeding. Right? [Amy agrees] If cells are going into the baby through the breast feeding. So, yeah, so we're just made of like so many different things like, you know, other cells from other humans, all these microbes, like we really are not just one thing, even though sometimes we feel like it.

Right. Exactly.

Athena 56:27

Yeah. Well, Amy, thank you so much...

Amy 56:28

Thank you.

Athena 56:28

...for sharing your brain. [Amy laughs]

Amy 56:31

I like that.

Athena 56:34

It was great to have you on Zombified.

Amy 56:36

Yeah, this was fun! Thanks!

Outro 57:23

[Psychological by Lemi]

Athena 57:54

Zombified is a production of Arizona State University and the Zombie Apocalypse Medicine Alliance. Thank you to the Department of Psychology, the Interdisciplinary Cooperation Initiative and the President's Office at ASU. Also, thanks to the Lincoln Center for Applied Ethics. Thank you to all the brains that helped make this podcast to Tal Rom, who does our sound, to Neil Smith, our illustrator, to Lemi, the creator of our awesome song, "Psychological", and to the entire Z-team - all of our amazing undergraduates. You can follow us and support us. Um, if you go on Twitter and Instagram, you'll find us at Zombified Pod, Zombified Podcast on Facebook. Our website is zombified.org and you can support us by, uh, joining us on Patrion. You can just $1 a month will help support us making more awesome episodes. And if you can give us $5 a month, we will be super, super grateful.

You can also support us by buying merchandise. Um, you'll find our stickers and our T-shirts on our website, www.zombified.org. You can also support us by reviewing us. Um, definitely let us know what you think of Zombified. As I do at the end of every episode after the credits, I share some of my brains. So, um, today I'm going to offer a wild speculation and, um, this is something that I've been thinking about ever since Amy and I started working on the issues of, you know, how microchimerism might be affecting maternal health. So here's the question: is it possible that microchimerism could be a contributor to postpartum mental health issues like postpartum depression and postpartum psychosis? So given what we know about the involvement of the immune system in depression and also the involvement of the immune system in clearing fetal cells after birth, I think it's something that we should be looking at. So, you know, my understanding is that both postpartum depression and postpartum psychosis can involve ambivalent feelings about one's new baby.

So to me this suggests that there could potentially be some conflict that's happening, um, between the maternal fetal cells or between the fetal cells and the maternal cells in the brain. So if the fetal cells are kind of trying to upregulate the maternal bonding systems and the maternal immune system is trying to clear them out, um, then you might actually sort of see a almost volatility of, um, you know, sometimes, uh, the woman maybe being very positively emotional towards her child and other times maybe negatively emotional. And it makes actually, you know, really concrete predictions about what we would be expecting to be going on with the immune system. So, um, I think that this is potentially a hypothesis that should be followed up on. Um, of course it's just a speculation at this point, but given how big of an issue postpartum mental health is, and given the fact that there aren't really good, any good theories out there right now for what is going on, I think we should be looking. Thank you for listening to Zombified - your source for fresh brains.

Outro 1:01:24

[Psychological by Lemi]