[RADIOLAB INTRO]

LATIF NASSER: Hey, I'm Latif Nasser. This is Radiolab. Today, I'm handing over the reins to our senior correspondent Molly Webster.

MOLLY WEBSTER: Hi.

LATIF: Hey. So what do you got for us, Molly?

MOLLY: Okay, so I think you know that for the last couple of years, I've been doing a lot of reporting on immunity.

LATIF: Yeah.

MOLLY: It's like, with COVID and vaccines and everything, it just kind of feels like the waters we've all been swimming in.

LATIF: For sure.

MOLLY: For today I have a story that's not exactly about COVID and vaccines, but it is about this part of the body that feels like one of the most elemental and mysterious parts of the immune system, if not certainly the most philosophical.

LATIF: Ooh! Like, I have no idea what you're about to say. What is it?

MOLLY: Well, it is a tiny organ called the thymus. And I want us to—I don't know, shall we say dissect this? [laughs]

LATIF: Oh!

MOLLY: Get into this by going back to a conversation that I had with Jad about a year ago.

LATIF: Okay.

MOLLY: When I first learned some of this stuff.

LATIF: Okay.

MOLLY: Are you ready?

LATIF: Go for it.

MOLLY: Cool.

JAD ABUMRAD: All right. So yeah, start me—start where you want to start. I'm here.

MOLLY: I feel like this story is kind of like a bad joke where a protein, a cell and a funny little molecule walk into the thymus. And then—and then a joke ensues is what I feel like this story is.

JAD: [laughs] That was a—that's a joke that would land with only a certain group of people.

MOLLY: What the [bleep] is even the thymus?

JAD: [laughs] I don't even know what the thymus is.

MOLLY: Oh, that's so great.

JAD: I'm gonna say it's in the brain, but I'm not even sure. No, no, no. No, it's not in the brain. It's in the—it's in the throat?

MOLLY: This is great that you said that because you're actually talking about a different organ.

JAD: Oh, I am?

JENNI PUNT: People mix it up with thyroid.

JAD: Thyroid!

JENNI PUNT: Yeah, the thyroid is higher up and does different things.

JAD: Oh!

JENNI PUNT: Yeah.

MOLLY: So the woman setting the record straight is immunologist Jenni Punt.

JENNI PUNT: I'm professor of immunology at the University of Pennsylvania, School of Veterinary Medicine.

MOLLY: And she's an expert on the thymus.

JENNI PUNT: Okay, so the thymus is an organ right above your heart.

MOLLY: It literally lays on top of the heart. There are these two lobes that drape over the heart.

JAD: Okay.

MOLLY: In kids, it's about the size of an adult person's palm, and people say it has the texture of a moist cornbread.

JENNI PUNT: People do eat thymus.

MOLLY: Really?

JENNI PUNT: Oh, yeah. The thymus of a cow can be quite big, and people say it's tasty. I think I've had some, but because I know about the cells in it, it's a little bit too freaky.

MOLLY: It's freaky because the thymus, and this is how scientists have put it to me, the thymus teaches the body what is you and what is not you.

JAD: Oh, I love that sentence!

MOLLY: Right? It's, like, so existential.

JAD: Yeah.

JENNI PUNT: It is existential.

SHARON STRANFORD: It is like the metaphysical thing of all of us. Like, how do we know what belongs to us?

MOLLY: But the thing is, according to Jenni and then our new friend who just popped in here, Sharon Stranford ...

SHARON STRANFORD: Professor at Pomona College, and I'm also an immunologist.

MOLLY: When it comes to the work of the immune system, this is actually a real world practical question.

SHARON STRANFORD: Because somehow, your immune system only attacks when it notices something foreign, and doesn't attack your own tissues and cells.

JAD: If you're a—if you're a little immune thing in the body, like, you don't know anything. You're just a cell. So, like, how do you figure out, like, "Oh, that's a bit of liver. That's good."

MOLLY: Mm-hmm.

JAD: "Whereas that thing over there, that weird globule, that looks foreign."

SHARON STRANFORD: Right. And how does it know when something is foreign unless it knows what's self?

MOLLY: And that is what the thymus does: it teaches the immune system the difference between self and not self.

SHARON STRANFORD: Yeah.

JAD: Okay, good, good. I'm in.

MOLLY: Perfect. We're gonna kick off with a little Immune System 101.

JAD: Okay.

MOLLY: So the immune system ...

SHARON STRANFORD: Has lots of different cells.

MOLLY: ... is made of so many different types of cells, right? There's ...

SHARON STRANFORD: B-cells and T-cells.

MOLLY: The ones we've heard of: the T-cells, the B-cells.

SHARON STRANFORD: Then there's all the other white blood cells.

MOLLY: There's also, like, natural killer cells, and these other ones called dendritic cells. Or ...

JAD: Yeah. This is funny. I mean, this just like—I'm sorry to interrupt ...

MOLLY: No, interrupt!

JAD: It's just like every time I hear about the immune system, it's a little bit like learning about the 15 different types of Navy SEALs or something. Like, there's like ...

MOLLY: Yeah.

JAD: Seven—like, there's the JSOC unit, and there's the Special Ops unit. There's just such a crowd of different specialized things.

MOLLY: There are so many, but for our purposes I'm just gonna focus us on the T-cells.

JAD: Okay.

MOLLY: Which are famously, you probably know this, like, the warrior cells, the ones that go out and fight viruses or bacteria or pathogens.

JAD: Mm-hmm.

MOLLY: But T-cells do not start as these warrior cells. They start like all immune cells do, in the bone marrow where they are sort of like ...

SHARON STRANFORD: Wannabe T-cells.

MOLLY: ... baby T-cells. And what happens is, at some point they sort of leave the bone marrow, they head out into the bloodstream, and in ways people don't fully understand, they get called to the thymus. And it turns out the "T" in T-cells is "Thymus."

JAD: Really?

MOLLY: Yeah. It's "Thymocyte cell" because the thymus is the training ground for the cell.

JENNI PUNT: Yes. Its primary and almost pure function is to generate your T-cells and to test them.

MOLLY: So the first thing these baby T-cells need to do before anything else is just be able to grab onto things around them, which means right when they get to the thymus, they have to ...

JENNI PUNT: Make a receptor. A real T-cell receptor.

MOLLY: Which is sort of like a tower or an arm that comes off the surface of the cell and lets them grab things.

JAD: What does it look like?

MOLLY: So it was described to me as: take your arms, push your forearms together from your elbows to your wrists.

JAD: Okay.

MOLLY: And you can sort of think of your arms as what's sticking out from the surface of the cell. And then you have the fists of your hands on top, and the fists of your hands are really like the receptor part that lock into things.

JAD: So it's just this thing protruding outward?

MOLLY: Yeah. It can, like, match with another molecule or object floating around.

JAD: Got it.

MOLLY: Like a lock and key.

SHARON STRANFORD: That fits somebody else.

MOLLY: That is designed to grab onto some particular thing around it, but ...

SHARON STRANFORD: But you don't know who else.

MOLLY: Now each T-cell only gets one receptor, so the trick for the thymus and the T-cells is if anything super random from the outside ever gets into the body. We're talking, like, little viruses, bacteria ...

SHARON STRANFORD: A billion different things that we haven't even anticipated ...

MOLLY: Things we've never even seen before, the T-cells have to have a receptor to potentially catch that thing. It's like they have to plan for the unexpected.

SHARON STRANFORD: And so the way that you plan for the unexpected is to create the unexpected in the genome.

MOLLY: In the DNA you can think that there's something like a recipe for making these receptors. The ingredients are nucleotides: As, Cs, Gs, Ts. But what the T-cells can actually do is they rearrange the recipe.

JENNI PUNT: Loop that out and get rid of it. Add a few nucleotides, it's like dashes of pepper, dashes of salt.

MOLLY: Allowing each T-cell to create a receptor unlike any other.

JENNI PUNT: Randomly generate what can be up to a billion different receptors. And they're all different. They're like snowflakes, as my mother used to say.

JAD: So now each one of them knows one thing.

MOLLY: One thing.

JAD: The thing that—that my receptor will click into.

MOLLY: Yeah.

JAD: And if we make enough of these things with enough variations, we might be covered.

MOLLY: Yeah.

JENNI PUNT: If you go forward a million years to grab a virus from there, give it back to us now ...

MOLLY: There should be a receptor in there that recognizes it.

JENNI PUNT: We would develop an immune response to it.

JAD: Whoa!

MOLLY: So you've got all of these baby T-cells trying to make these receptors, prove their worth, but it's actually very hard to make these receptors. And so if it doesn't work, you're just killed.

JAD: Damn! [laughs]

MOLLY: Because you're useless. You're useless to the body.

JAD: Wow, okay.

SHARON STRANFORD: It's pretty draconian. It's a killing.

MOLLY: It's like a culling.

SHARON STRANFORD: It's a culling. It's a culling.

MOLLY: Now if you can make a good receptor, you are rewarded by getting to go onto the second round of training. Because if an army of billions of T-cells is ready to attack anything, by random chance some will have receptors that will want to glom on and attack you. And so this is where knowing what is self and not self comes into play. Because what the thymus does next is it creates something that's like a shadow version of you.

SHARON STRANFORD: Part of it—the self-shadow stuff is very cool. It's able in this shadow kind of way to mimic and imitate things in your body.

JAD: What?

MOLLY: I know! It sounds so trippy, but even, like, one of the biggest science papers on the thymus talks about "An immunological self-shadow."

JAD: Ooh!

MOLLY: So what the thymus actually does ...

JENNI PUNT: Yeah, so now we're at AIRE.

SHARON STRANFORD: AIRE.

MOLLY: Which starts with this thing with a very mysterious name.

MOLLY: AIRE!

JENNI PUNT: [laughs]

JAD: Like, air that we breathe, air?

MOLLY: It's spelled A-I-R-E, and it stands for autoimmune regulator.

MOLLY: Maybe tell me what AIRE is.

JENNI PUNT: Oh, it's a good question. So AIRE is a protein. AIRE is a big, long protein, and it's not simple.

MOLLY: So AIRE lives inside certain cells in the thymus, and it gives these cells like a superpower, which is that every cell in the body has a full copy of DNA, but each cell uses only the part that applies to it. So the heart uses the heart stuff and the liver uses the liver stuff. But AIRE allows the thymus cells to access almost any part of the DNA.

SHARON STRANFORD: AIRE is something that sort of runs around the DNA, helps to unwind things and open it up.

MOLLY: Which means that those cells can make ...

SHARON STRANFORD: Every possible protein that your body could make.

JENNI PUNT: Proteins that should be only in the brain, or proteins that should only be in your big toe—I don't think there are any of those—proteins that only should be in—you know, in your gut ...

MOLLY: You're literally creating a version of yourself in this little spot above your heart.

SHARON STRANFORD: Yeah.

JENNI PUNT: Yeah.

JAD: Whoa!

MOLLY: Now all that you stuff is in there, now this is where the tests comes in: the thymus puts this line-up of these little pieces of you in front of the T-cells.

SHARON STRANFORD: And as T-cells pass by ...

MOLLY: I imagine, like, the T-cells with their receptors kind of gently just sniff and touch.

SHARON STRANFORD: ... all of self.

MOLLY: And then meanwhile, you have the thymus just sitting there watching, waiting to see what happens, because if any of those T-cells bond too strongly to the tiny bits of you that are being presented to them ...

SHARON STRANFORD: Like, "Hey, that piece looks super exciting. I'd bind to it really strongly."

MOLLY: Then once again the body will kill that T-cell.

SHARON STRANFORD: The idea is you want to eliminate that T-cell because it sees self.

MOLLY: Because it's just latched onto, and in a sense attacked a part of "self."

JAD: Who—who does the killing?

MOLLY: Well, they actually get signals just to commit suicide.

JAD: Oh. And if you say the right word they blow up, kind of?

MOLLY: Yes.

SHARON STRANFORD: Literally there are lots of dead wannabe T-cells in the thymus.

JAD: [laughs] Oh my God!

MOLLY: Yeah. And so, billions of T-cells go through this process of making receptors and getting tested. And 90 to 95 percent of them are killed.

JAD: 90 to 95 percent?

MOLLY: Yeah.

JAD: God!

MOLLY: But, you know, if you're in the five percent that didn't get killed ...

JENNI PUNT: You're let loose.

MOLLY: You become one of these super badass warrior cells off in the immune system protecting us.

JAD: Okay this is—I have a whole new appreciation for thymus.

MOLLY: Yeah, now you know what the thymus actually is.

JAD: [laughs]

MOLLY: One of the coolest parts of this for me is that there's this whole idea that the thymus and these T-cells know you, but really what you've got is a bunch of cells that know everything but you.

SHARON STRANFORD: We keep the things that don't bind to self. We get rid of the things that do bind to the self.

MOLLY: So in an interesting way, there's some sense that self-knowledge—at least as it applies to the immune system—is really all about the negative space.

LATIF: Oh, man! I just won't be able to stop picturing, like, a dissembled version of myself. I had never even heard of this organ, and now this is like in the running for the—for the coolest one.

MOLLY: Well, I'm very glad you dig it because I am about to take this thymus up a notch because that was a conversation I had with Jad awhile ago, but a few months ago, I learned a whole other part of this story, which is while the thymus has this ability to know you and save your life day in and day out, we are just now figuring out how to use this part of you that knows you to save the life of someone else.

LATIF: What?

MOLLY: Boom, boom, boom.

LATIF: How is that even possible?

MOLLY: Well, you will find out after the break.

LATIF: Hey, this is Latif Nasser. We're back with our very own Molly Webster telling us all about the thymi, which is the plural of thymus, the kind of unsung hero of the immune system that teaches our body how to know itself so that it doesn't kill itself.

MOLLY: Yes. Exactly. So we've been talking about how the thymic sense of self protects you, but now we're gonna see how that sense of you could actually protect someone else.

LATIF: Okay.

MOLLY: It'll make sense in a minute.

LATIF: Okay.

MOLLY: Okay.

JOSEPH TUREK: Hey, Molly!

MOLLY: Hi!

JOSEPH TUREK: Have a seat wherever works best for you.

MOLLY: So to start, a few months ago I went to Duke University to talk to a guy named Joe Turek.

JOSEPH TUREK: So I'm chief of pediatric heart surgery here. And I'm one of the executive co-directors of our pediatric and congenital heart center. And I ...

MOLLY: Joe does a lot of heart surgeries on babies. And for him, the thymus, this organ that lays on top of the heart, was always just sort of an annoyance.

JOSEPH TUREK: Yeah.

MOLLY: So when you were doing anything with the heart, you were like, "Thymus? Meh!"

JOSEPH TUREK: Yeah. Move over. [laughs] Yeah, it's in the way.

MOLLY: But then about five years ago, something happened that completely changed his relationship with the thymus.

JOSEPH TUREK: It's actually a neat story.

MOLLY: He was actually just sitting in his office one day, and he got a message from one of his colleagues.

JOSEPH TUREK: Dr. Markert asked to have a meeting with me.

LOUISE MARKERT: Hi, Molly.

MOLLY: [laughs] How are you?

MOLLY: This is Dr. Markert.

LOUISE MARKERT: Mary-Louise Markert.

MOLLY: She goes by Louise.

LOUISE MARKERT: I have been at Duke for a very long time. Since 1975, actually.

LATIF: Whoa!

LOUISE MARKERT: Until my retirement in 2021.

MOLLY: Oh, you just retired!

LOUISE MARKERT: Yes.

MOLLY: But at the time that she called Joe, she was sort of science famous for this technique that she developed where you could take a bit of thymus from one person and you could put it in another.

LOUISE MARKERT: Yes.

MOLLY: The idea is sometimes kids are born with no thymus or with a thymus that doesn't work right, and so what if you get a bit of thymus from a heart surgery ...

LOUISE MARKERT: The surgeon will have to cut out some of it in order to get to where he or she is operating on the heart.

MOLLY: So you could take that little bit of thymus that's normally probably tossed in the trash, and then take it back to the lab, do some fancy lab work stuff on it to flush out existing T-cells.

LOUISE MARKERT: Then we could put these little slices in the patient.

MOLLY: Put it into the kid that didn't have the working thymus, and the idea is that thymus is gonna, you know, kick into gear ...

LOUISE MARKERT: The process of making T cells.

MOLLY: And hopefully a healthy immune system.

LATIF: Wow!

MOLLY: So when Louise called up Joe that day ...

JOSEPH TUREK: She said, "Do you know why I want to talk to you?" And I said, "Oh sure, Louise. You know, we take out part of the thymus because it's in our way when we're trying to do aortic surgery."

MOLLY: And you need thymus for your work, and so I'm just kind of assuming you're coming to me for some thymus.

JOSEPH TUREK: And she said, "No, but it's more than that, Joe. I don't just want you to just be getting me thymus." She said, "I've been looking for a partner to collaborate with because I've got an idea."

LOUISE MARKERT: I was, you know, just thinking that ...

JOSEPH TUREK: "We can combine this work that we've done culturing thymus, along with organ transplantation."

LOUISE MARKERT: Combine it with a heart transplant.

MOLLY: Because the problem with a heart transplant—or any organ transplant—is that the body's immune system will attack the new organ because it's not part of self. So Louise is suddenly thinking, "Wait a second. I think the big problem here is the thymus, this thymus sense of self." Because once you put in an organ, you're no longer just self, right? So she said to Joe, "What if, when we're doing a heart transplant, we also get a little bit of the donor's thymus and we transplant the heart and the thymus together into a recipient, and then maybe the recipient's body wouldn't reject the heart, because the thymus would be there too.

LOUISE MARKERT: So that they would not need to be on immunosuppression the rest of their lives.

JOSEPH TUREK: And that makes a big difference.

MOLLY: And basically Joe said, "Yes, I'm in. I think we should try this." And from there, they just had to, you know, wait until the right case came along where they could test this out.

JOSEPH TUREK: And Louise and I, from that day on just started working on this project. And, you know, that was early in— that was in 2017.

MOLLY: And then just last year ...

LOUISE MARKERT: This patient came along.

MOLLY: Named Easton.

JOSEPH TUREK: Baby Easton, who has single-ventricle-type heart disease, so pretty severe.

MOLLY: So Easton was waiting for a heart transplant, and then at the same time, they had figured out ...

JOSEPH TUREK: Easton needed an immune system.

MOLLY: He wasn't really making that many T-cells.

LATIF: In addition to the heart problem.

MOLLY: In addition to the heart problems.

LATIF: Right.

JOSEPH TUREK: I mean, clearly the—the light bulb goes off.

MOLLY: Here's a baby that needs a new immune system and needs a new heart.

JOSEPH TUREK: We know how to treat each of those individually, and it would be an opportunity to actually treat them together.

MOLLY: Try the dual thymus-heart transplant.

LATIF: Ah!

MOLLY: And we can actually see if we're able to bring this baby off immune-suppressant drugs under the guidance of the new thymus.

LATIF: Mm-hmm.

MOLLY: So last summer, 2021, they got a heart and they got a bit of thymus from the same donor. They did the heart transplant right away.

JOSEPH TUREK: We just dealt with the heart. Easton recovered very well, did great.

MOLLY: But as for the thymus, they take out Baby Easton's original thymus with the heart, but for the new thymus, they actually had to wait for that, because they need to prep the thymus first. So they take that chunk they got from the donor ...

LOUISE MARKERT: And then slice it.

MOLLY: Chop it into these really, really paper-thin ...

LOUISE MARKERT: ... sections.

MOLLY: Letting them sit in a lab, feed them with nutrients.

LOUISE MARKERT: Daily for 12 to 21 days.

MOLLY: 18 for Easton.

LOUISE MARKERT: And then ...

MOLLY: In that two-week time span, they sort of shed the T-cells that are packed inside of them. And so by the end of it, you get ...

JOSEPH TUREK: The scaffolding.

MOLLY: The thymus training structure, but missing T-cells from the donor because the T-cells that are trained in the donor's body would see Easton's body as an outsider and attack it. So you basically end up with chunks of cleaned-up thymus from the donor.

LATIF: How big are the chunks?

MOLLY: Oh my gosh, they're so small.

JOSEPH TUREK: You know, probably half the size of a dime. It's almost like a piece of snot, to be honest with you.

LATIF: Okay.

LOUISE MARKERT: But the thing was, initially it was like, where would we put them?

MOLLY: It seems very dangerous to, like, re-crack open the chest and then try and, like, weave this little bit of thymus tissue back onto this new fragile heart. And at the same time ...

LOUISE MARKERT: You need to have a good blood supply.

MOLLY: You need a lot of blood to, like, turn these little bits of tissue back on again.

JOSEPH TUREK: So the location where they do this, do you know?

MOLLY: I feel like there's a drum roll ...

JOSEPH TUREK: Oh, a drum roll. Please! Yeah, yeah! So the location where they do this is the thigh.

MOLLY: Really? Thigh-thymus.

JOSEPH TUREK: Yeah, that's why they joke that they call it the thymus, right?

LATIF: What? No!

LOUISE MARKERT: And so you go down to the thigh muscle, and then it's like planting tulips. Now when you plant a tulip ...

MOLLY: I heard you were a gardener.

LOUISE MARKERT: Yeah. [laughs] You poke a hole in the ground, and you put in the bulb, and then you fill in the dirt.

JOSEPH TUREK: So yeah, this is us taking these off these filter papers. Those are the little pieces of thymus. That's me.

MOLLY: That's you?

JOSEPH TUREK: Yeah, yeah. Dunking it down there. Planting tulips, like Louise would say. And we actually used both of his thighs just to make sure that we gave ourselves the best opportunity possible to make sure that this thymus would engraft.

MOLLY: And the idea is is that these bits of thymus from the thigh would actually start training up new T-cells.

LATIF: Wow!

MOLLY: How old was Easton by the time the transplants happened?

JOSEPH TUREK: I think he was five months old when he—when he got his transplants.

MOLLY: That was in August. The thymus tissue did start working again, and the thymus is now releasing new T-cells to the body.

JOSEPH TUREK: He's able to produce T-cells now. The levels were where we wanted them, so the next step that we have is to start to slowly pull back on our immunosuppression.

MOLLY: And then they will know if the new T-cells with the thymus, the donor thymus, that knows this heart as its own ...

LATIF: Mm-hmm.

MOLLY: ... will allow Easton's body to fully accept it, and fully accept it as self.

JOSEPH TUREK: You know, recognizes both his transplanted heart and his body as self.

LATIF: So that part of it, do we know if that works yet?

MOLLY: I mean, not exactly. They can tell right now that the immune system doesn't appear to be attacking the heart, even though it's on immunosuppressant drugs, nothing, no funny business seems to be happening.

LATIF: Or the rest of the body, for that matter.

MOLLY: Or the rest of the body for that matter. And so it's like, right now they're, like, counting it as a success.

LATIF: Yeah.

MOLLY: But by the end of the summer is when they're gonna start taking Easton off the immune suppressants.

LATIF: Hmm.

JOSEPH TUREK: If those T-cells recognize both his new heart and his body as self then, you know, this could change everything. It's not just for children who need hearts, but it could be for adults who need hearts or adults who need liver or children who need kidneys or yeah, it would change everything.

LATIF: I'm—I'm—I'm ...

MOLLY: Puzzled?

LATIF: It's, like, really smart to pull in the new thymus, but I'm still kind of confused about ...

MOLLY: Okay.

LATIF: Okay, so thymus and heart are both coming from the donor. The thymus is training T-cells based on the donor DNA.

MOLLY: Yes.

LATIF: Now they're both in—thymus and heart—in the recipient's body. Now when the T-cells come out of the thymus, they look at the heart, they're like, "I recognize you. No problem." But then when they look at the rest of the body, that's all recipient DNA, which they theoretically won't recognize. Like, won't they now attack the rest of the body, the recipient body?

MOLLY: No. I mean, this can all get pretty gnarly, like, the closer you stare at it, and I'm not sure that anyone would say this is, like, exactly how it works, but I think the general idea is that, you know, part of the training is in the thymus with thymus cells, which are from the donor, but it seems like there's another part of the training which is in the way the thymus is actually interacting with the body that it's in—which is the new body. So in a way, it's like the T-cells are being trained on two selves.

LATIF: Oh, wow. So it's, like, training it to be bilingual or, like, bi-self-al. It's like a two-for-one.

MOLLY: Yeah. You know, it's funny. Like, it's on the first hand it sounds like it's two becomes one—I haven't been able to get the Spice Girls out of my head, like, the whole time I've been reporting this. But I've also been thinking that it's more than that, that there's a sense that what we know of as "self" can be extended. It's not that two becomes one, it's just that two is one—or it could be. Or who knows? Like, maybe even more. That you can pull in other selves and they can pull in you. Suddenly "you" is just a lot less singular.

MOLLY: As I was reporting this episode, one of the things that became really to me as a reporter was, like, I needed to see a thymus. I wanted to be able to explain it to people. And so to do that, I went out to Cold Spring Harbor Laboratory on Long Island, to the lab of Hannah Meyer.

HANNAH MAYER: Have you seen mice before?

MOLLY: Where they study the thymus and the AIRE protein and all that stuff.

HANNAH MAYER: It's hard to put gloves on. [laughs]

MOLLY: And I want to play for you now two bits of my time out at the lab. And the first part I want to share starts with a dissection.

HANNAH MAYER: And so we just took two different mice and this one is about eight weeks old.

MOLLY: And the person who showed this to me is second year PhD student ...

SALOMÉ CARCY: Salomé Carcy. I'm a medical student from France and I came here to do a PhD.

MOLLY: That day, as part of a training with a new lab tech, Salomé was dissecting mice to get to their thymus. And I got to watch.

SALOMÉ CARCY: Just pinch the skin and I cut.

MOLLY: And then—and then I see the heart, which is like, almost looks like a ruby or a garnet.

SALOMÉ CARCY: And you can see—oh, I'm going to cut this. You can see the thymus.

MOLLY: Is it ...

SALOMÉ CARCY: Sitting just on top.

MOLLY: Is it kind of like that extra pinky fleshy part at the top?

HANNAH MAYER: It's a white with two little lobes sitting on top of the heart here, one and two. All of this.

MOLLY: It's funny, I guess it maybe it's supposed to be white, but it comes as a little opaque pink in my mind.

SALOMÉ CARCY: Yeah. Really feels like a hat on top of the heart.

MOLLY: Kind of almost as big as the top half of the heart.

SALOMÉ CARCY: Yeah. So in young mice, sometimes I've even in, like, three weeks old mice, I've even seen sometimes the thymus is bigger than the heart.

MOLLY: Oh, wow!

SALOMÉ CARCY: Wow! Clean dissection. Look at this. And so when you remove the thymus, you can really see there's this, like, emptiness above the heart.

MOLLY: Wow. There really is a hole where you took the thymus out.

SALOMÉ CARCY: It's a huge hole.

MOLLY: I had—that's insane.

MOLLY: So they did this dissection in a young mouse. And the thymus, you can tell it was huge. And then Salomé did a second dissection in an older mouse, and that's where I saw something that I had been hearing about but never fully got.

MOLLY: So we're cutting up through the sternum again.

SALOMÉ CARCY: I'm going a bit quicker this time. I'm quite curious actually, to see how big—if we're going to find the thymus or not. [laughs] Oh, I think I see it, actually. Yeah, it's tiny tiny.

MOLLY: You can hear me just, like, breathing quietly there because I just can't see it.

SALOMÉ CARCY: So it's tiny tiny tiny. Like, it's even hard to distinguish it from, like, random connective tissue.

MOLLY: Wow. So we just pulled it out.

SALOMÉ CARCY: But look how tiny it looks.

MOLLY: This looks like a little bit of skin I could have pulled off of me and, like, wouldn't do anything.

SALOMÉ CARCY: And you can also see compared to earlier, remember how there was a huge hole when we removed the thymus? Here it looks like a tiny little hole.

MOLLY: What I saw in the lab is that when we're born, the thymus starts big and fat and juicy, but as we age, it actually starts to shrink.

SALOMÉ CARCY: There's actually quite a lot of fat.

MOLLY: So that by the time we're adults, it's super small and it has turned basically into fat.

SALOMÉ CARCY: Like, yeah, here if there was no thymus, we would not be shocked.

MOLLY: It's just crazy to me an organ can just disappear or, like, melt into fat, you know?

SALOMÉ CARCY: Exactly. It's not ...

MOLLY: I asked Hannah, Hannah Meyer, the head of the lab, about this very stark age difference.

HANNAH MEYER: So people—initially, whenever people saw thymus, it was in an adult setting, such that when they did surgeries on kids, they thought maybe the thymus was actually causing the illness because the thymus was so big. And they thought, "Oh, my goodness, the enlargement must have got something to do with why they're sick." And sometimes, like, there is some studies where the kids were actually prescribed radiation therapy because they thought the thymus is actually—yeah, the thymus is the trouble. Until when the thymus research properly picked up, they realized having a large thymus in childhood is exactly what you would expect. And the surprise is why is it so small and the adult stage.

MOLLY: So, like, these kids would go in because of some presumable illness, and then they were, like—doctors were doing surgery on them, and they'd see this giant thing on top of the heart and think, like, "Oh, is that a cancer or something?"

HANNAH MEYER: Yeah. They thought that might actually be related to the illness and not this is what it should look like. The adult is unusual that this organ is all of a sudden vanishing.

MOLLY: But I don't understand, like, if it really starts going away by the time you're in puberty, how do you have any T cells at all? Like, when you're 39 or 59 or 89?

HANNAH MEYER: So your T cells, there's a process called homeostatic proliferation, which just means that the T cells that have left the thymus can divide when they're in a periphery. So they age, but they can also make copies of themselves. And because they have already been screened in the thymus, the copies they make of themselves have the same properties. So you know they're safe to be out there. And therefore you can keep up a T cell pool even though the thymic output diminishes rather quickly with age.

HANNAH MEYER: There is a—there's a scientist out there now, Jacques Miller, who I believe is the only sort of living scientist that can claim he's discovered the function of an organ. And only in the '60s. Which is crazy that he figured out first off, there is immune cells in the thymus that have a function, and they need to leave the thymus to do their function. And if we don't have these cells throughout the body, what I refer to as the periphery, then the mice get ill.

MOLLY: What captivates you about this organ and its function being fully discovered in the '60s? Because there's, like, a magic twinkle that comes to your eye every time you sort of gesture towards, like, "It was only the '60s."

HANNAH MEYER: Yeah. I just feel like, you know, we managed to, like, transplant organs before, and there's an organ in our body that we even don't know what it does. Like, that just puzzles me, like, how far medicine had come. And then there is this big organ sitting right in the center, and it's sort of being ignored.

MOLLY: So it wasn't until the '60s that we even knew the thymus had anything to do with the immune system. And then it was just over 20 years ago when researchers discovered AIRE, that protein I told you about at the beginning of the episode, that is just vital to training T cells. And so now I want to go back to AIRE one last time to unpack a maybe one minute bit of conversation I had with Hannah that was so interesting I just want to tell everybody about it.

HANNAH MEYER: Can I throw one more idea there in the hat—whatever you say. Yes.

MOLLY: And it has to do with why the AIRE protein may actually choose to not show the T cells every single part of the body.

HANNAH MEYER: Yes. So imagine this process was perfect. We're covering all the little snippets. We have no T cells that go out there and could detect the body. We might create a different problem, namely that pathogens use the same amino acids as we do. So their proteins are composed of the same parts as ours. So maybe pathogens have similar sequences. So if we are super stringent and kicking out everything that might be mildly reactive, we now might not be able to detect the pathogens anymore.

MOLLY: To underline what Hannah is saying there, it's that because of evolution, our bodies and pathogens, things like viruses and bacteria, they have very similar proteins—if not the same proteins. So if AIRE trained the T cells on every single protein that we humans have, then the T cells, there's a chance they wouldn't actually be able to see and attack some pathogens. Which means that there are some T cells that are sent out into the body that can attack pathogens but can also attack us. And that's on purpose.

HANNAH MEYER: Exactly. It's not black and white.

MOLLY: So there's a world in which, like, maybe I have—maybe I have multiple sclerosis because there's something about those diseases, something about the presentation in the body that might actually be similar to a pathogen. And maybe it actually would make sense for the thymus to not train a T cell to, like, fight that thing Because fighting the pathogen is also important.

HANNAH MEYER: Exactly.

MOLLY: It's reminding me of the whole, like, sickle cell malaria thing, which is like, malaria is terrible, but, like, sickle cell helps you. You have less of a chance of getting and dying of malaria. So it's been positively selected for even though it itself is also terrible.

HANNAH MEYER: Exactly. There's a little—it's definitely a tug of war between, well, the pathogen and the host.

MOLLY: This is a very complicated thymus!

HANNAH MEYER: Yes, thymus—and I think if you also just—the immune system is mind blowing. Like, the immune system is like all these disparate cells all over the body, and somehow they still function as a whole and manage to communicate with one another.

MOLLY: I want to give a thousand special thanks to Hannah Meyer, Salomé Carcy and Joshua Torres. They're all part of Hannah's lab at Cold Spring Harbor Laboratory. Hannah and her team just published their latest research in the journal Nature Communications. It's actually all about what we've been talking about. It's about what proteins are being made inside the thymus. So essentially what parts of the body the T cells are being trained on. It's interesting. Go check it out.

MOLLY: And thank you to Natalie Middleton for fact-checking help.

MOLLY: Stay tuned. We've got another story of our body's weird and wild and wonderful inner workings after the break.

JAD: I don't know what we're doing today, so you go.

ROBERT: Well, because here's what we're doing: maybe six years ago, I'd just returned to National Public Radio, and for the first story I did ...

JAD: Can we just put that in context? I mean, you started National Public Radio.

ROBERT: [laughs] I didn't start it.

JAD: You did kind of start it.

ROBERT: I was at it near the beginning.

JAD: And then you went away to do great things on TV.

ROBERT: For 23 years I was missing.

JAD: And then you came back.

ROBERT: Then I just popped back again, yes.

JAD: Okay.

ROBERT: When I popped back, I brought this puzzle back with me. It was about motherhood, actually. And it's—we'll you'll hear. Why don't I just play you the piece that I aired back in—gosh ...

PRODUCER: 2006.

ROBERT: 2006?

JAD: That's another time.

RADIO HOST: NPR's Robert Krulwich has the story.

ROBERT: For years, it was thought as soon as a baby is conceived, once it starts to grow inside a mom, it gets its own very private space.

KIRBY JOHNSON: There is. There's a placenta. A placenta was thought to be a fairly impenetrable barrier.

ROBERT: So, says Dr. Kirby Johnson of Tufts University, the baby and its cells stay on the baby's side. The mommy's cells stay on the mommy side, and nature keeps them separate until it's time to go. But here's the surprise: when scientists at Tufts took blood from ordinary pregnant moms ...

KIRBY JOHNSON: We would find, for example, in a teaspoon of blood, dozens, perhaps even hundreds of cells.

ROBERT: From the baby.

KIRBY JOHNSON: From the baby.

ROBERT: So baby cells were slipping out of the placenta into the moms. But because babies do have different genes ...

KIRBY JOHNSON: One would expect them to be attacked fairly rapidly. You would expect them to be cleared within hours if not days. What we've found is that that is not the case, not anywhere near the case.

ROBERT: It turns out that baby cells stay in their moms not for days or weeks, but for decades.

KIRBY JOHNSON: Four to five decades following the last pregnancy.

ROBERT: So 40 years after conception, that son or daughter who can now be a middle-aged pharmacist or something, yet their fetal cells, their baby cells are still floating around inside the mother?

KIRBY JOHNSON: Yes.

ROBERT: Even his 60-year-old mother? 70?

KIRBY JOHNSON: 70, 80, perhaps 90-year-old women.

ROBERT: You're sure of this?

KIRBY JOHNSON: Absolutely.

CAROL ARTLETT: Yeah, these cells last essentially forever.

ROBERT: In the mom?

CAROL ARTLETT: In the mom.

ROBERT: And, says Carol Artlett who studies fetal cells at Thomas Jefferson University in Philadelphia, even if a woman has a miscarriage or an abortion, even if there is no baby, the cells of an unborn child will stay in the mother for decades. But why? What exactly are they doing in there for years and years and years?

CAROL ARTLETT: That's a good question.

ROBERT: [laughs]

ROBERT: Well, one early hypothesis, and it's not the nicest idea, says Kirby Johnson, is that certain autoimmune diseases ...

KIRBY JOHNSON: Such as lupus, rheumatoid arthritis, scleroderma are much more common in women than men. And that's one component of the hypothesis is that this prevalence in women is due to fetal cells.

ROBERT: So later in life, when the mother's joints inflame, maybe it's her fetal cells, her own babies taking a poke at her. In fact, Kirby's mom did have an autoimmune disease. It was a bad one, and for a while Kirby thought well, his cells were responsible.

KIRBY JOHNSON: So I apologized immediately and said, "Well, there's nothing much I can do about it."

ROBERT: Yeah, yeah. But it's like, "Stop it, Kirby!"

KIRBY JOHNSON: But you know what? I was always doing that to my mother. Always causing problems, and it was just another on the long line of those kinds of things.

ROBERT: But happily, the folks at Tufts proposed an alternative, a second theory to explain what fetal cells are doing in the moms.

KIRBY JOHNSON: Well, theory number two is the polar opposite of theory number one.

ROBERT: The "good" fetal cell hypothesis proposes that the son or daughter's cells stay in mom not to hurt her, but to protect, defend and repair her for the rest of her life, whenever she gets seriously ill. And that's a more attractive idea.

KIRBY JOHNSON: It's such a personal thing, and it does touch the heartstrings of even the most hard-nosed research scientist.

ROBERT: But they all have mothers.

KIRBY JOHNSON: But they all have mothers.

ROBERT: And happily, they now have evidence. More and more evidence, says Kirby Johnson, that looks like the good hypothesis may be correct. For example, here's a case ...

KIRBY JOHNSON: Well, this was a woman who came into a neighboring hospital in Boston with symptoms of hepatitis. She was an intravenous drug user.

ROBERT: And she had had five conceptions. She'd had one child, two miscarriages, two abortions—that's five in all. She could be carrying, therefore, a lot of fetal cells. And they examined her.

KIRBY JOHNSON: And in the process, she had a liver biopsy.

ROBERT: And the doc said, "Well, why don't we send her liver to the lab to see if there are any fetal cells gathering where she's got trouble?" And when they looked ...

KIRBY JOHNSON: We found hundreds and hundreds of fetal cells.

ROBERT: Normally, they'd expect five or ten cells.

KIRBY JOHNSON: But this was a very large—we saw literally sheets of cells, whole areas that seemed to be normal.

ROBERT: Meaning that those fetal cells had gathered at the liver, and like stem cells, they just turned themselves, in this case, into healthy liver cells.

KIRBY JOHNSON: And most interestingly, this woman did not desire to have any further treatment done. In fact, she wanted to get back to her normal life and be left alone.

ROBERT: And she left the hospital with hepatitis, but when they checked months later, they learned ...

KIRBY JOHNSON: That she is completely healthy. No signs of further liver damage.

ROBERT: So no medical intervention, but just a huge number of her baby's fetal cells. Could that lead you to think the poetic thought that she was saved by her kids?

KIRBY JOHNSON: We want to think that.

ROBERT: I know you do. [laughs]

KIRBY JOHNSON: There—it's the most likely explanation.

ROBERT: But in science, there is such a thing as a too-dangerously beautiful idea.

KIRBY JOHNSON: That's right. Right. And we say the same thing to ourselves because it shows such a basic wonderful thing, but it has to be right, and we can't be led astray by our own desire for it to be true.

ROBERT: So they are systematically testing the good hypothesis and the bad hypothesis, all these ideas, on laboratory mice. And when they see mother mice with all kinds of diseases: infectious disease, cancer ...

KIRBY JOHNSON: Ovarian cancer, endometrial cancer, cervical cancers, we find fetal cells there. We know that fetal cells don't ...

ROBERT: Over and over and over and over.

KIRBY JOHNSON: Over and over and over and over.

ROBERT: Suggesting that fetal cells regularly rush to the places where they're needed in the mom, and says Carol Artlett ...

CAROL ARTLETT: There's a lot of evidence now starting to come out that these cells may actually be repairing tissue.

ROBERT: That is, protecting the mom. While the other hypothesis, that fetal cells hurt the moms, there, the more they look the less they find.

KIRBY JOHNSON: I can't recall a single study that's been truly reproduced to verify the bad fetal cell hypothesis.

ROBERT: So while no one knows in the end which way it'll go ...

KIRBY JOHNSON: I think that that's something that we're going to see within the next five years or less.

ROBERT: So far, a sense is building that fetal cells probably stay in mothers for decades to defend and to protect them, which increasingly is a quiet consolation to Kirby Johnson because it's now more likely that his cells and his brother's cells were helping their mom, not hurting. And even though his mother did die, Kirby's beginning to feel differently.

KIRBY JOHNSON: Well, maybe if it wasn't for my brother and I, she may have passed a few years earlier. Maybe we bought her a couple of extra years of time so she could have a few more birthdays and a few more Mother's Days. And that, if I can just say that, that there's some way where I can even have the remotest thought that I contributed to the extension of my mother's life, even if it was a few days, that would make all of the years that I've spent doing this research worthwhile.

ROBERT: Robert Krulwich, NPR News, New York.

JAD: Hmm.

ROBERT: So it's been more than five years, as I said, since I talked to Kirby Johnson, six years, really. So I figured he might have an answer by now.

KIRBY JOHNSON: Hello?"

ROBERT: Hi, Kirby.

KIRBY JOHNSON: Hi, Robert. How are you?

ROBERT: I wanted to know, what do you now know about what those fetal cells are really doing?

KIRBY JOHNSON: Right.

ROBERT: So when we last left it, you were tipping between two possibilities: one is that they do some harm, that they aggravate conditions later in the mother's life, or the opposite, that they help in the mother's life.

KIRBY JOHNSON: Right.

ROBERT: And do you now have a sense of which was right?

KIRBY JOHNSON: Well, I think it's more complicated than we originally thought. Like, you would expect ...

ROBERT: Isn't that always the case? [laughs]

JAD: Yes.

KIRBY JOHNSON: But what we're able to do though now, is more specifically argue for or argue against one of those different hypotheses. For example ...

ROBERT: So here's how he's addressed the question—because this is a completely new development. He's working with mice, and he's taken the glow from another animal.

KIRBY JOHNSON: ... comes from some sort of fish.

ROBERT: A greenish glow ...

KIRBY JOHNSON: The green fluorescent protein.

ROBERT: ... that exists in nature. He's plucked it onto the fetal cells of a pregnant mouse.

KIRBY JOHNSON: Right. Exactly.

ROBERT: So what is that like? Is that if you do a tummy scan on a pregnant lady mouse, can you look inside, and is that like going to the movies and see a little ...?

KIRBY JOHNSON: Absolutely. It is like the movies. It is shiny, glowing green, and it's extremely easy to see. I mean, a child could say that, "Oh, that's green."

ROBERT: So he can look at the mouse, and he can see from the little bits of green glow where the fetal cells are.

KIRBY JOHNSON: And we find these cells virtually anywhere we look, like the lung, the spleen, liver, bone marrow, the heart. We even find them in brain tissue.

ROBERT: Which will help figure out what they're doing.

JAD: So he can track them.

ROBERT: Yeah.

KIRBY JOHNSON: Yes.

ROBERT: Here I am!

KIRBY JOHNSON: And we've removed ...

ROBERT: And now that he has tracked them, he says, "All right, what I said before about fetal cells probably helping moms, I think that in many cases is still true. If you've got a mom who's suffering, say, from some liver disease or something, you can see fetal cells doing something there."

KIRBY JOHNSON: And these cells may be able to contribute to tissue repair after an injury or chemical or environmental assault. So these are helpers.

ROBERT: Helpers.

KIRBY JOHNSON: Definitely, yeah. But ...

ROBERT: But unlike six years ago, now he suspects that if a mother has, let's say rheumatoid arthritis or some kind of autoimmune disease ...

KIRBY JOHNSON: Where the maternal immune system seemingly attacks itself in this autoimmune fashion.

ROBERT: ... now he sees other kinds of fetal cells, that ...

KIRBY JOHNSON: Seem to be causing a problem.

ROBERT: Their behavior seems to suggest that they are attacking the mom.

KIRBY JOHNSON: Actually attacking maternal tissue.

ROBERT: So that's the go-get-Mommy group.

KIRBY JOHNSON: Right. And the unfortunate go-get-Mommy group.

JAD: Wait, so there are some kinds of fetal cells that are good, some that are bad, and it seems to depend on what again? On, like, where it is in the body or what disease?

ROBERT: Well, it seems to depend on a longer and longer list of variables, so including, for example, who the father was. That turns out to be ...

JAD: Why does that matter?

ROBERT: Well remember, every fetal cell is half mom and half dad.

KIRBY JOHNSON: We actually do see differences in the cells that are present in the mother, depending upon the genetic background of the father.

ROBERT: Oh, so you can have bad daddies and good daddies?

KIRBY JOHNSON: That is entirely possible. I think we would say good daddies and less-good daddies. But what we're finding ...

ROBERT: [laughs] Is that because you're at a university, and you never like to call daddies bad?

KIRBY JOHNSON: Yes. No one's a bad daddy.

JAD: But wait a second. Does he know how to explain the difference? Like, why one dad would be good and one wouldn't be good?

ROBERT: I don't think he knows yet. No.

KIRBY JOHNSON: We haven't been able to quite delineate why one cell may be doing something good or maybe be doing something bad. It may be the very same cell type.

ROBERT: Ooh, so it might even switch sides during the course of life?

KIRBY JOHNSON: It possibly could. I mean, it's sort of like behavior. You got good kids and you got bad kids.

ROBERT: [laughs] You got good days, you got bad days.

KIRBY JOHNSON: Bad days. You got good cells and you got bad cells.

JAD: This is getting complicated. So the cells can be good or bad, depends on the disease, the location, and the dad, but we're not really sure what.

ROBERT: And that's not the end of the list. It actually gets longer.

KIRBY JOHNSON: There's a number of other variables. The number of pregnancies, also pregnancy loss—whether it's through miscarriage or through termination. Maternal age. That's another very important variable.

ROBERT: So who's your daddy? How old are you when you're pregnant? How many times have you been pregnant before?

KIRBY JOHNSON: Yes. And many other influences. It's impossible to quant ...

ROBERT: Well, wait a second. So this—so when we got to the poetry part of our interview back then, you said to yourself, "My brother and I either roughed up our mother or gave her a few more, you know, birthdays."

KIRBY JOHNSON: Right. It's possible that one of us had a more positive impact than the other. I mean, there's obviously no way of knowing that, but any normally inquisitive mind would start to wander to say, "Well, what if this or under what circumstances ..."

ROBERT: Well see, my mind is wandering wildly now because when we last did this story ...

KIRBY JOHNSON: Yeah. And that's what we want you to do. We want people in our ...

ROBERT: No, I don't want to. It'll be a much better story if it was—if it had been—for me, if it had been—if it had gone clearly one way or the other. But the story you're now telling me is that you and your brother can now meet for coffee, and you can look into each other's eyes, and you will not know between the two of you, whether you helped your mom, whether you hurt your mom, whether you did both, whether your contribution was bigger or less than the happenstance of your dad's genetic makeup, and and and and—this is getting to be a much harder story to tell.

KIRBY JOHNSON: It is much harder to tell.

ROBERT: SO as the story gets blurrier and blurrier, why are you still in the game?

KIRBY JOHNSON: A lot of this is driven, as you know, by the issues that my mother has or had. And I still have that in the back of my mind, and I can't get that out of my mind that a lot of the issues that my mother had recur in the literature.

ROBERT: What that means is that the diseases that killed his mom are the very kinds of diseases that show up in his research.

KIRBY JOHNSON: And then we—towards the end, we had conversations about fetal cells, and it made us closer. And I could share my scientific background and the work that I was doing in a way that comforted her, I think to a certain degree, to know that I was investigating something that was directly related to her health issues. And towards the end, we had a lot of real nice conversations about the work that I was doing and the latest discoveries. And she would always ask—after she would ask how I was, she would say, "How's the work?"

ROBERT: Well, here's what—I think there's a chance that your fetal cells in your mom sometimes helped and sometimes hurt. So you're not gonna come out the hero, you might even come out the villain. Doesn't that sap your enthusiasm for this a little bit at some level?

KIRBY JOHNSON: Well, of course I would want to think that my cells contributed in some small way to some improvement to my mother's health. If I find out that it wasn't the case, well that's the truth. And as a scientist, I want to find the truth. Whether or not the truth is wonderful or the truth is horrible, that's what I want to find out, regardless of what the end personal outcome is.

ROBERT: And what if the truth is well, some of the time you helped, some of the time you hurt, much of the time it didn't matter? Doesn't that hurt you a little bit? Can you get up the next morning and say, "Let's find out how unimportant I am?"

KIRBY JOHNSON: [laughs] Well, that's—that is a very difficult question. I know if I were to be able to go to my mother, if I put my best effort forward to finding the truth, and even if it was a negative or was a mixed bag, or perhaps was even not really much of anything, at least I know what the truth is. And both as a son and as a scientist, that would be of value to me. I may feel unfortunate that I wasn't able to do something more than the emotional support that I could provide my mother, but I have to look at it as finding the truth.

ROBERT: Yeah.

JAD: That's nice.

ROBERT: So that's where we land.

JAD: You've written about this on your blog, right?

ROBERT: I have, yeah. I should say ...

JAD: You should say where that is.

ROBERT: It's called Krulwich Wonders. So you just write K-R-U-L-W-I-C-H Wonders into any search engine, and there it is.

JAD: Yeah.

ROBERT: And this issue and other things many times a week.

JAD: Yeah, check it out. It's pretty good.

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[LISTENER: Hi, my name's Tom Geffen Jones from Denver, Colorado. I am a Radiolab listener. Radiolab is supported in part by the National Science Foundation, and by the Alfred P. Sloan Foundation, enhancing public understanding of science and technology in the modern world. For more information about Sloan, at www.sloan.org. Thanks.]

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