Human epidermal Langerhans cells exposed to Ixodes ricinus tick saliva and Borrelia burgdorferi adopt a tolerogenic state with CXCR4/CCR7-driven emigration that impairs T cell priming.
0:00Welcome to Base by Base, the paper cast that brings genomics to you, wherever you are. Thanks for listening, and don't forget to follow and rate us in your podcast app. Today we are diving into something really special.
0:10Please produce a comprehensive and engaging scientific podcast episode based on the attached paper, human epidermal Langer Hand cells, induced tolerance and hamper T cell function, upon tickborne pathogen transmission, by Johanna Strobel, Lisa Kleisel at all, published on 13 November 2025 in nature communications.
0:30It's great to be here. This paper is just a fascinating look at how nature can, well, hack our own biology. Let's get right into it. I want to start with a scenario that, you know, practically everyone listening has experienced, or at least feared.
0:42You're hiking, maybe walking through some tall grass, you get home, and you find it, a tick attached to your leg. It's a universal dread, isn't it? That little black dot? And usually our concern is immediate and, well, physical.
0:54Is the head still in? Is it going to itch? Did I get it all? We tend to view the bite itself as a mechanical act. Like a tiny pair of draws breaching the perimeter fence. Exactly. But what this paper forces us to realize is that the physical pinch is actually the least dangerous part of the whole interaction.
1:10That is such a great way to frame it. The physical breach is just the delivery mechanism. Because while that tick is feeding, it isn't just taking blood out, it's pumping a complex chemical cocktail in.
1:23And I don't just mean the bacteria, like the stuff that causes Lyme disease. Right, not at all. I'm talking about the saliva itself. It's essentially a pharmacological hacking tool designed to rewire the security system of your skin.
1:35It's biological espionage. I mean if you think about the immune system as a high security facility. The tick isn't dynamically fighting the guards. No. It's impersonating a superior officer. That's the image I can't get out of my head.
1:48Imagine a burglar who doesn't blow up the safe. Instead, he walks up to the head of security, whispers a code word, and convinces the guard to not only unlock the door, but to call the police and report that.
1:58That everything is fine, false alarm. Right. He gets the guard to do the cover up for him. And that analogy gets right to the heart of a massive medical mystery. Why is it so hard for humans to develop immunity, to tick born diseases like lime.
2:12You can just get it again and again. Exactly. You can get infected, take antibiotics, clear the infection, and then go out next summer, get it all over again. Your body just refuses to learn the lesson.
2:22Precisely. The immune system usually builds a wanted poster for invaders, so it can stop them faster next time. Both tick bites, that memory is often weak or, you know, non-existent. So this research suggests the reason isn't just that the bacteria are tricky.
2:38And they are. They are very tricky. But it suggests that ticks live itself has fundamentally brainwashed the skin's 1st responders before the war even began. A complete subversion of our defenses. And we have a specific group of people to thank for uncovering this whole mechanism.
2:53We do. Today we're celebrating the work of Johanna Strobel, Lisa Kleisel, Jorks Derry, and their wider team at the Medical University of Vienna, and the CMM Research Center for Molecular Medicine. They took a problem that has baffled immunologists for decades and just threw the kitchen sink at it.
3:11Clinical data, high-tech sequencing, and some really creative tissue models. And that's actually where we need to pause and talk about context, because to understand why this paper is such a big deal. We have to look at how we usually study Lyme disease.
3:24Right. Usually when we talk about immunology studies. We were talking about mice. Almost exclusively. And Mice are fantastic for many things. But when it comes to Lyme disease caused by the bacteria. Borelia Bergdorf fury mice are actually a pretty poor model for humans.
3:39Because mice are natural reservoirs, right? They carry the bacteria, but don't get the same severe disease we do. Exactly. Their immune response to borelia is fundamentally different. So if you cure a lime in a mouse or see an immune reaction in a mouse, it doesn't necessarily tell you what's happening in a human hiker's leg.
3:55Which brings us to the sentinels. The stars of today's deep dive are the Langer hen cells. The LCs, yes. These are the dendritic cells of the epidermis, which is the very outer layer of your skin. I always picture them as the guards on the castle wall, the very 1st line of defense.
4:11Their job is to stand, watch, spot an invader, grab a piece of it, and then run. Run to the headquarters to sound the alarm. That's their classical function. They capture the antigen, the piece of the invader, and migrate to the draining lymph nodes.
4:26And there they present that evidence to the T cells and say, we are under attack, mobilize the army. Exactly. But scientists have known for a while that when a tick bites, these Langer hand cells do something strange, they, well, they disappear from the bite site.
4:42They vanish. And for a long time, the assumption was quite dark. We assume the tick bite was just toxic and was killing them. Collateral damage. Or, you know, on the flip side, we assumed they were rushing off to do their job, running to the lymph nodes to start the fight.
4:55But nobody knew for sure. It's incredibly difficult to track individual cells in a human patient. Until this team decided to get creative with their methodology. And this is the part of the paper that really impressed me.
5:07They didn't just rely on mice. No, they went straight to the source. human data. They used a combination of approaches. First, they took biopsies, actual skin punches, from healthy volunteers who had been bitten by ticks within the last week.
5:20Which is great for a snapshot, but it's hard to control, right? You don't know exactly when the tick attached or how long it fits. Exactly. So they needed a controlled environment. Enter the ex Vivo model.
5:31Okay. They obtained surplus human skin from plastic surgeries. Tommy tucks specifically. Abdominoplasties. It sounds a bit macarb, but it is scientifically gold. This is living, functional human skin with its immune system completely intact.
5:48They could take this skin into the lab and inject it with tick salivary gland extract or SGE. So they're simulating the chemical component of the bite without the variable of a live bug crawling around.
6:01Correct. And then, and this is the key, they used single cell RNA sequencing. The technology that changes everything. It really does. Instead of grinding up the skin and looking at the average of all the cells.
6:11They could look at the genetic diary of every single cell individually. They could see exactly which genes the Langer hand cells were turning on and which ones they were turning off. And to close the loop, they didn't just look at the skin.
6:23They built immune spheroids. Essentially, mini lymph nodes in a dish to see what happened when those skin cells arrived at headquarters. Wow, so they had the crime scene, the skin and the police station, the lymph node.
6:35Okay, let's walk through the findings. Finding number one. The disappearing act. They confirmed it. After exposure to tick saliva, the Langerhand sells vanish from the epidermis, but the sequencing revealed something crucial.
6:50What was that? They weren't dying. They looked for death markers, right? Things like GH2AX. Yes, markers of DNA damage or apoptosis. And they were absent. These cells were perfectly healthy. They were just leaving voluntarily.
7:03So the ticks bit tells them to pack their bags. Gives them travel orders. The sequencing showed a massive upregulation of genes like CXCR 4 and CCR 7. Let's decode that alphabet soup. What are CXCR4 and CCR 7?
7:16Think of them as transit passes. CXER 4 allows the cell to navigate through the deeper layer of skin, the dermis, and CCR 7 is the key that opens the door to the lymphatic vessels. Siway system. The highway to the lymphad, yes.
7:29The tick saliva specifically hands these keys to the Langer hand cells and says, go, go to the lymph node and go now. Okay, so the Sentinel leaves the wall and goes to headquarters. That sounds helpful.
7:41Isn't that what we want? If I'm the commander, I want my scout to come back and tell me what's happening. You do, but only if the scout is telling you the truth. And this is where the hack comes in. This is finding number two.
7:50The reprogramming. Because when these cells arrive, they aren't screaming attack. Far from it. The researchers looked at the attitude of these cells. Normally, if a Langerhand cell encounters a bacteria, say, staphylococcusorius, it enters a pro-inflammatory state.
8:08It turns on genes like NFKB. It's angry. Ready for war? But under the influence of Tickspit? They become tallerogenic. The saliva forces them to switch on a completely different set of transcription factors.
8:21So basically ideal one in IRF 4. Ideal one and IRF 4. These are the pacifier genes, essentially. In a way, yes. Under normal circumstances, idea one and IRF 4 are vital. They prevent your immune system from attacking your own body or overreacting to harmless things like pollen.
8:38They are the keep common carry on signals. So the tick is coopting a safety mechanism. It tricks the immune system into thinking the bite is something harmless that should be ignored. It creates a false flag operation.
8:49And get this, even when the researchers added berylia bacteria, the actual lime pathogen into the mix. The tick saliva was so potent that it overruled the bacteria. The Langerhand cells just ignored the pathogen and kept singing the song of peace.
9:04That is terrifyingly efficient. The bacteria are literally standing right there, waving a flag, but the security guard is looking the other way because the burglar told him to. It gets worse. When these brainwash Langer hand cells reach the lymph node, or the spheroid model in the lab, they interact with the T cells.
9:20This is finding number three, the consequence. The griefing at headquarters. Exactly. Now, in a fight against bacteria like borelia, you want the body to produce TH 17 cells. TH17. These are the special forces.
9:33Yes. They recruit neutral fills, they drive inflammation, they kill bacteria, they are the killers. But the reprogrammed Langer hand cells, they don't ask for TH 17s. They induce the formation of regulatory T cells or TREGs.
9:47Intregs are the diplomats. They are the suppressors. Their whole job is to shut down inflammation. So you have a situation where the bacteria are multiplying in the skin, but the immune headquarters is issuing orders to stand down.
9:58It effectively creates an immunosuppressive bubble around the infection site. And this explains the clinical reality of Lyme disease. The memory that's formed is a memory of tolerance, not a memory of defense.
10:09That's why you can get reinfected. That is why your body remembers the standdown order, not the attack order. So it's not just that the system failed. It's that the system was actively turned against itself.
10:19This fundamentally changes how we have to think about prevention. It really does. It suggests that our focus on just killing the bacteria might be too narrow. The bacteria are just the passengers. The tick saliva is the vehicle that gets them past the border guards.
10:35Exactly. So if we look at the implications here, If the saliva is the key to the heist, can we? Can we change the locks? This is the most exciting part of the discussion section. This research provides a rock solid foundation for the concept of a tick vaccine.
10:52Wait, we aren't talking about a vaccine against lime. We are talking about a vaccine against the tick. Exactly. Imagine if we could vaccinate you with those specific salivary proteins, maybe targeting the ones that trigger IDO one or IRF 4.
11:06Your immune system would then develop antibodies against the saliva itself. So the moment the tick bites and start spitting, my body recognizes the hack attempt. And neutralizes it. The calming signal is blocked.
11:16The Langer hand cells don't get brainwashed. They see the bacteria, they stay angry, and they run to the length node to demand the TH17 special forces. You stop the sabotage before it starts. And the beauty of this approach is that it is pathogen agnostic.
11:32Right, because the tick uses the saliva trick to feed, regardless of what diseases it's carrying. Correct. Whether that tick is carrying lime or tickborne encephalitis or BBziosis or anaplasmosis, they all rely on this immunosuppressive saliva to survive the feeding process.
11:48If you block the saliva. You potentially block the transmission of all of them. You do. That is a massive shift. Instead of playing whack-a-mole with every new disease that emerges from the forest, you just take away the mallet.
12:00There are limitations, of course. The study used SGE, the whole extract. It's a soup of 100s of proteins. We still need to identify the specific molecule responsible for flipping that idea one switch. They mentioned candidates like Celt 15, but it's probably a team effort by multiple proteins.
12:18It is, but with MRNA technology, the same tech we use for the COVID vaccines. We can screen these proteins so much faster now. We can theoretically create a vaccine cocktail that targets the most potent immusuppressants in the spit.
12:32It brings up a vision of the future that is honestly pretty wild. We usually think of tick proof clothing or tick proof repellent, but this could lead to a tick proof human. The human host where a tick bite is just a minor annoyance, a mechanical pinch, rather than a gateway for chronic disease, it effectively disarms the vector.
12:52It really highlights why this base by base approach matters. If they hadn't looked at the single cell RNA. If they had just looked at the whole tissue, they might have missed that the LCs were migrating.
13:01They might have missed the idea one switch. The granularity of the data is what revealed the mechanism. And understanding the mechanism is the only way to break the cycle. So to synthesize this for everyone listening, the tick is not a passive syringe.
13:15It is an active immunologist. It has evolved a sophisticated chemical weapon that targets the specific command and control centers of our skin, turning our sentinels into traders to ensure its own survival.
13:27And in doing so, it holds the door wide open for pathogens like beryllia. Which leaves us with a final thought to mull over. We've spent the last century of medicine declaring war on germs. We fight bacteria, we fight viruses, but this paper suggests that in the arms race of evolution, the delivery system is just as dangerous as the payload.
13:46It really prompts the question, if we can immunize ourselves against the saliva of a tick. What else could we apply this to? Mosquito saliva for malaria, sandfly, saliva for leash maniasis. It changes the battlefield from the pathogen to the vector.
13:58A shift from fighting the soldiers to blocking the transport ships. It's a brilliant strategy. This episode was based on an open access article under the CCBY 4.0 license. You can find a direct link to the paper and the license in our episode description.
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