Short Wave - Why Daylight Boosts Immunity

Episode Date: May 30, 2025

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. 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 [e-mail]. 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.See 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

You're listening to Shortwave from NPR. Hey, Shorewaver is Regina Barbara here. And Burley McCoy. With our biweekly science news roundup featuring the hosts of All Things Considered. And today we have one of our favorites, Ari Shapiro. Only one of your favorites? It's always an honor to be here. One of our five favorites.

Well, let's get to the stories. I hear today we've got one on the immune system telling time. Contact lenses that allow you to see infrared light. And a hawk they may be using traffic to hunt for prey. All that on this episode of Shortwave, the science podcast from NPR. All right, Ari. Where do you want to start? 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 the immune system telling time? Yes. I'm going to let Burley start, though, but yes, that's sweet. 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. Wild. How does the immune system know whether it's day or nighttime? 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. 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. This is immunologist Jennifer Hurley at Rensler 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? Why even bother having a circadian rhythm and something that's not going to be very long lived? Fascinating question. How did scientists go about trying to answer it? 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. So during the day, they killed the bacteria faster. But if we removed completely, opponents of the neutrophils circadian clock that removed their ability to kill the bacteria faster because the neutrophils didn't know that it was daytime. The team published their work in the journal Science Immunology. How could this knowledge be useful for people trying to fight diseases? 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. Or a scientist could look at how to do the opposite. So like how to modify these clock immune genes to lower inflammation. 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?

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. How did scientists make them? 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. 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 also. 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. 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? 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 without scattering on fog particles. 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 died. 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. 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. 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.

And then at 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. Yeah, so explain how this hawk knew in advance when the line of cars would become long. 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. So Vladimir spent a couple 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 a about it in the journal Frontiers and Ethology. So what's the takeaway here? Just like hawks are smart? Well, so people who train raptors like hawks wouldn't be surprised by this behavior. 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 Zumutskutner, a professor of behavioral ecology at the University of Vienna, who didn't work on the study, she was excited about

this behavior, but she was skeptical that this hawk was being queued by this crosswalk sound. She does welcome more observations. Unfortunately, Vladimir says the crosswalk button no longer makes sounds and the family no longer leaves crumbs. So the hawk hasn't returned. Oh, that's such a sad ending, but I hope the hawk is living a fulfilling life wherever it is. We're all hoping for that. But, you know, we might not see see the hawk again, but we're probably going to see you again, Ari. Thank you for coming and hanging out with us. Thank you for having me. I always love this. Come back anytime. You can hear more of Ari Shapiro on Consider This and P.R.'s afternoon podcast about what the news means for you.

Also, make sure you never miss an episode of our podcast, Shortwave, by following us. It really helps the show out, just like sharing it with a friend. This episode was produced by Jordan Marie Smith and Burley McCoy. It was edited by Rebecca Ramirez and Christopher and Taliatta. Tyler Jones, check the facts. Jimmy Keely and Tiffany Vera Castro were the audio engineers. I'm Burley McCoy. I'm Regina Barber. Thank you for listening to Shortwater. The Science Podcast from NPR.