Why Daylight Boosts Immunity

Depending on what time it is, your body responds differently to an injury or infection. During the day, you're likely to heal faster and fight infection better than at night. And historically, scientists weren't entirely sure why. That picture is starting to clear up thanks to a new study published last week in the journal Science Immunology https://www.science.org/doi/10.1126/sciimmunol.adn3080. The research finds a missing piece of the puzzle in neutrophils, powerful immune cells that — despite living less than 24 hours — know the difference between day and night. Got a question about how the body works? Let us know at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:16Speaker 01

  You're listening to Short Wave from NPR.

• 0:21Regina Barber?

  Hey, Short Wavers. Regina Barber here.

• 0:23Speaker 03

  And Burleigh McCoy.

• 0:24Regina Barber?

  With our biweekly science news roundup, featuring the hosts of All Things Considered. And today, we have one of our favorites, Ari Shapiro.

• 0:31Speaker 04

  Only one of your favorites? It's always an honor to be here.

• 0:35Speaker 03

  One of, one of our five favorites.

• 0:38Speaker 04

  Well, let's get to the stories. I hear today, we've got one on the immune system telling time.

• 0:44Speaker 03

  Contact lenses that allow you to see infrared light.

• 0:47Regina Barber?

  And a hawk, they may be using traffic to hunt for prey.

• 0:51Speaker 03

  All that on this episode of Short Wave, the science podcast from NPR.

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• 2:26Regina Barber?

  All right, Ari, where do you want to start?

• 2:28Speaker 04

  It sounds to me like your immune system may be in overdrive right now, Gina. So out of solidarity and sympathy, you want to tell us about

• 2:35Regina Barber?

  Aww.

• 2:35Speaker 04

  the immune system telling time?

• 2:37Regina Barber?

  Yes, I'm going to let Burley start, though, but yes, that's sweet.

• 2:40Speaker 03

  Yeah, so scientists have known that our immune responses are different depending on what time it is and that we're actually better at mounting an immune response in the daytime. And this makes sense, since we evolved to be more active in the day and so more likely to get an injury or infection. So by day, the immune system is primed to fight potential invaders, which it does by causing inflammation, and at night, it goes anti-inflammatory to recover.

• 3:08Speaker 04

  Wild. How does the immune system know whether it's day or nighttime?

• 3:11Regina Barber?

  Yeah, many immune cells have a built-in circadian clock, like a lot of cells in our body, but there's some immune cells that don't even live a full day. Scientists wanted to know if they could tell time.

• 3:21Speaker 06

  They're the frontline responders, right? They show up with all the energy, they try and kill off everything that they can, and then they book it out of here, and then they die.

• 3:29Speaker 03

  This is immunologist Jennifer Hurley at Rensselaer Polytechnic Institute. She's talking about a special immune cell called a neutrophil that's really important at fighting off infections. And she says scientists hadn't really studied circadian rhythms and neutrophils because they die so fast.

• 3:46Speaker 06

  Why even bother having a circadian rhythm in something that's not going to be very long-lived?

• 3:51Speaker 04

  Fascinating question. How did scientists go about trying to answer it?

• 3:55Regina Barber?

  Well, a different group of researchers used baby zebrafish, which are transparent, to watch how fluorescent bacteria interacted with fluorescent neutrophils. And they found that neutrophils can indeed tell whether it's day or night. We talked to immunologist Chris Hall, who was part of that research team.

• 4:09Speaker 07

  So during the day, they killed the bacteria faster. But if we removed components of the neutrophils' circadian clock, that removed their ability to kill the bacteria faster because the neutrophils didn't know that it was daytime.

• 4:26Speaker 03

  The team published their work in the journal Science Immunology.

• 4:29Speaker 04

  How could this knowledge be useful for people trying to fight diseases?

• 4:33Speaker 03

  Yeah, so Chris says they're interested in seeing if they can freeze neutrophils in the daytime state in the case, for example, you have a really bad infection and need all hands on deck.

• 4:43Regina Barber?

  Or scientists could look at how to do the opposite. So like how to modify these clock immune genes to lower inflammation.

• 4:49Speaker 04

  Cool. Okay, next up, let's talk about these contact lenses that let the wearer see infrared light, which sounds to me like something out of James Bond or Mission Impossible. Are we talking about like night vision goggles in a contact lens?

• 5:02Speaker 03

  Kind of, but with some big caveats. So right now, these prototype lenses aren't very sensitive. They can only pick up infrared light sources in the lab, so not out in the real world from a person or a car engine. But the lenses do have some advantages. They're less bulky than night vision goggles, and they can be worn in the daytime. And the big difference is that the contacts convert infrared into color vision instead of the mainly green or gray that night vision goggles do.

• 5:29Speaker 04

  How did scientists make them?

• 5:30Regina Barber?

  Yeah, they embedded tiny microscopic particles in contact lenses that convert certain wavelengths of infrared light to specific wavelengths of visible light. So using a few versions of these particles, they could convert a range of infrared light into different colors.

• 5:44Speaker 03

  But the images they saw were blurry. And that's because the direction the infrared light was originally traveling gets lost when the contact lenses convert it to visible light. So that means making out the shape of the object also gets lost. So the researchers coupled the contact lenses with eyeglasses, and the eyeglasses were able to focus the infrared light in a way that participants can make out letters and shapes. And they described all this in the journal Cell.

• 6:09Regina Barber?

  And Ari, one really cool thing, it kind of blew my mind about these contact lenses, is that participants could see infrared light when their eyes were closed. And this is because the longer wavelength can actually go through eyelids.

• 6:21Speaker 04

  Wow, that's amazing. Now, it sounds like these might not be ready for prime time yet, but once they are on the market, what do you think people are going to do with them?

• 6:29Regina Barber?

  Well, as we mentioned before, these won't pick up infrared in like the environment just yet, so scientists need to work on their efficiency. Like turning infrared to visible light. But if they could do that, one advantage of wearing them would be able to see when it's foggy or if there's low light. For example, if you're like driving across a bridge when it's foggy, infrared light can travel farther like without scattering on fog particles.

• 6:51Speaker 03

  You could also use this in like a security setting. So a concert or any other crowded place. If communication systems went down, security guards could communicate with each other quickly by shining infrared light that only they could see. Or doctors could use these to see edges of tumors that have infrared dyes.

• 7:08Speaker 04

  Wow. Okay, for the third story, you've got this hawk that I'm personally obsessed with. I've read all about this young Cooper's hawk in New Jersey. Set the scene for us.

• 7:17Speaker 03

  Right, so there's a house in New Jersey near an intersection with a big front lawn. And sometimes the family that lives there eats outside and that leads to crumbs. And the crumbs attract little birds that peck around at the leftovers. And those little birds attract this Cooper's hawk, which preys on them.

• 7:34Regina Barber?

  But if the hawk just swoops in, the prey will fly away. The hawk needs cover for this ambush. And that's when the story like really starts. Zoologist Vladimir D. Nitz observed a hawk waiting for a long string of cars to line up at this traffic light.

• 7:46Speaker 01

  And then it's the last moment it would cross between two cars and grab a bird from that flock. But what was really interesting is that it seemed to know in advance when the line of cars would become particularly long.

• 7:58Speaker 04

  Yeah, so explain how this hawk knew in advance when the line of cars would become long.

• 8:04Regina Barber?

  Yeah, so Vladimir noticed that whenever the crosswalk button was pushed, it would make this like beeping sound. And the hawk would position itself in a tree down the street from the crumb house, like staging this attack. And he says that when the crosswalk button was like activated, the red light lasts a bit longer. And this would make the line of cars get like just long enough to give the hawk proper coverage for this like surprise attack.

• 8:26Speaker 03

  So Vladimir spent a couple of weeks watching this and saw the hawk attack six different times. And Vladimir's theory here is that the hawk just listens for the beeping sound to know when it can launch its attack. He wrote about it in the journal Frontiers in Ethology.

• 8:40Speaker 04

  So what's the takeaway here? Just like hawks are smart?

• 8:45Speaker 03

  Well, so people who train raptors like hawks wouldn't be surprised by this behavior.

• 8:50Regina Barber?

  Yeah, still, it's important to keep in mind that this is like one hawk. This was only observed by Vladimir. It's not been filmed. So when we talked to Petra Zumutz-Kutner, a professor of behavioral ecology at the University of Vienna, who didn't work on this study, she was excited about this behavior, but she was skeptical that this hawk was being cued by this crosswalk sound. She does welcome more observations.

• 9:11Speaker 03

  Unfortunately, Vladimir says the crosswalk button no longer makes sounds and the family no longer leaves crumbs. So the hawk hasn't returned.

• 9:19Speaker 04

  Oh, that's such a sad ending, but I hope the hawk is living a fulfilling life wherever it is.

• 9:25Regina Barber?

  We're all hoping for that. But, you know, we might not see the hawk again, but we're probably going to see you again, Ari. Thank you for coming and hanging out with us.

• 9:33Speaker 04

  Thank you for having me. I always love this.

• 9:35Speaker 03

  Come back anytime.

• 9:37Regina Barber?

  You can hear more of Ari Shapiro on Consider This, NPR's afternoon podcast about what the news means for you.

• 9:43Speaker 03

  Also, make sure you never miss an episode of our podcast, Short Wave, by following us. It really helps the show out, just like sharing it with a friend.

• 9:52Regina Barber?

  This episode was produced by Jordan Marie Smith and Burleigh McCoy. It was edited by Rebecca Ramirez and Christopher Intagliata.

• 9:59Speaker 03

  Tyler Jones checked the facts. Jimmy Keely and Tiffany Vera Castro were the audio engineers. I'm Burleigh McCoy.

• 10:05Regina Barber?

  I'm Regina Barber. Thank you for listening to Short Wave, the science podcast from NPR.

• 10:20Speaker 05

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