Summary: Researchers have mapped the precise molecular “phone line” that allows the gut’s immune system to talk to the brain during a parasitic infection. The study identifies a unique relay between two rare cell types: tuft cells and enterochromaffin (EC) cells.
When tuft cells detect a parasite, they release a slow-burn signal of acetylcholine—a chemical usually used by neurons—which triggers EC cells to release serotonin. This activate the vagus nerve, telling the brain to shut down the appetite. This elegant “molecular logic” explains why we often don’t feel sick until a few days into an infection, once the immune response has fully ramped up.
Key Facts
- The Two-Cell Relay: Tuft cells act as the “scouts” (detecting parasites), while EC cells act as the “transmitters” (sending signals to the brain).
- Neuronal Mimicry: Surprisingly, tuft cells use acetylcholine to communicate, but they do so without the typical machinery found in actual nerve cells.
- The Delay Factor: Appetite loss isn’t instant because tuft cells release acetylcholine in two phases. The second, “sustained” phase only happens after the immune system has confirmed the threat is persistent.
- Beyond Parasites: This same pathway—found in the airways and gallbladder as well as the gut—may be the culprit behind chronic conditions like Irritable Bowel Syndrome (IBS) and severe food intolerances.
Source: UCSF
Anyone who has weathered a bad stomach bug knows the feeling: a loss of appetite that sets in and lingers, even after the initial illness. For the millions of people around the world who are chronically infected with parasitic worms, the same thing happens. But scientists have long puzzled over exactly why.
Now, researchers at UC San Francisco have traced the molecular pathway that connects the gut immune system to the brain during a parasitic infection, explaining how the immune system triggers a loss of appetite.
“The question we wanted to answer was not just how the immune system fights parasites, but how it recruits the nervous system to change behavior,” said co-senior author David Julius, PhD, professor and chair of Physiology at UCSF and recipient of the 2021 Nobel Prize in Physiology or Medicine. “It turns out there’s a very elegant molecular logic to how that happens.”
The findings, published in Nature on March 25, reveal an unexpected communication system between two cell types, and could shed light on a range of conditions involving gut discomfort — from food intolerances to irritable bowel syndrome.
Two cells communicating
The new study focused on two rare cell types in the gut. Tuft cells detect parasites and trigger immune defenses, while enterochromaffin (EC) cells release signals that activate nerve fibers leading to the brain. EC cells are known to cause sensations like nausea, pain, and gut discomfort but whether they communicate with tuft cells was unknown.
“My lab has long been interested in how tuft cells, after they initially respond to a parasitic infection, release signals to other cell types,” said co-senior author Richard Locksley, MD, a UCSF immunologist.
First author Koki Tohara, PhD, a postdoctoral researcher at UCSF, found the answer by positioning genetically engineered sensor cells directly next to tuft cells under a microscope. When tuft cells were exposed to succinate, a molecule produced by parasitic worms, the sensor cells lit up, revealing that tuft cells were releasing acetylcholine, a chemical messenger used primarily by neurons.
When acetylcholine was added to lab-grown gut tissue containing EC cells, they released serotonin. This activated vagal nerve fibers that carry signals from the gut to the brain.
“What we found is that tuft cells are doing something neurons do, but by a completely different mechanism,” Tohara said. “They’re using acetylcholine to communicate, but without any of the usual cellular machinery that neurons rely on to release it.”
The team also discovered that tuft cells release acetylcholine in two distinct phases — explaining why people often don’t develop a loss of appetite until days into an infection. In the first phase, a brief burst of acetylcholine is released. Later, after the immune system has mounted a full response, tuft cells multiply and produce a slow, sustained release of acetylcholine that is sufficient to activate EC cells.
“This explains why you feel fine at first but then start to feel sick as the infection becomes established,” Julius said. “The gut is essentially waiting to confirm that the threat is real and persistent before it tells the brain to change your behavior.”
Implications beyond parasites
To test whether the pathway matters beyond the lab, the researchers infected mice with a parasitic worm and tracked their food intake. Mice with normal tuft cell function ate less as the infection took hold. Mice engineered to lack acetylcholine-producing machinery in their tuft cells kept eating normally, confirming that the molecular chain drives the behavioral response. The new findings could have relevance for treating the symptoms of a parasite infection.
“Controlling the outputs of tuft cells could be a way to control some of the physiologic responses associated with these infections,” Locksley said, adding that the study also could have broader implications.
Tuft cells are found throughout the body — not just in the gut, but also the airways, gallbladder, and reproductive tract — and disruptions to the newly identified pathway could contribute to conditions like irritable bowel syndrome, food intolerances, and chronic visceral pain.
The work was carried out in collaboration with Stuart Brierly, PhD, and his lab group at the University of Adelaide in Australia.
Key Questions Answered:
A: Your gut is “fact-checking” the threat. The study found that tuft cells only send the strong “stop eating” signal to your brain after the infection is established and persistent. It’s a biological safety to ensure you don’t stop eating for a false alarm.
A: In many ways, yes! This research shows that your immune cells can act like neurons, using the same chemical language (acetylcholine) to tell your brain when you’re under attack, leading to feelings of nausea or discomfort.
A: High probability. Because tuft cells and this signaling pathway are active in many gut disorders, doctors might be able to develop drugs that “mute” these signals, helping patients with IBS or food allergies manage chronic nausea and pain.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this neurology and aging research news
Author: Laura Kurtzman
Source: UCSF
Contact: Laura Kurtzman – UCSF
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Parasites Trigger Epithelial Cell Crosstalk to Drive Gut-Brain Signaling” by Kouki K. Touhara, Jinhao Xu, Joel Castro, Hong-Erh Liang, Guochuan Li, Mariana Brizuela, Andrea M. Harrington, Sonia Garcia-Caraballo, Tracey O’Donnell, Daniel Neumann, Nathan D. Rossen, Fei Deng, Gudrun Schober, Yulong Li, Richard M. Locksley, Stuart M. Brierley & David Julius. Nature
DOI:10.1038/s41586-026-10281-5
Abstract
Parasites Trigger Epithelial Cell Crosstalk to Drive Gut-Brain Signaling
Parasitic infections modulate both immune and sensory responses, but how these systems collaborate to elicit protective behaviours remains incompletely understood.
The gut epithelium contains specialized sensory cells that detect pathogens and irritants. These include cholinergic tuft cells, which sense parasites and initiate type 2 immune responses, as well as serotonergic enterochromaffin (EC) cells, which detect irritants and communicate with afferent nerve fibres to transmit nociceptive signals.
Here we show that paracrine signalling between these cells constitutes a mechanism for neuro–immune interaction and gut–brain communication.
We find that tuft cells use two distinct mechanisms of acetylcholine (ACh) release despite lacking synaptic vesicles and excitable membranes. These include acute release in response to parasite-derived metabolites, followed by constitutive ‘leak-like’ release, which occurs with type 2 inflammation.
Although both mechanisms can activate muscarinic receptors on crypt-residing EC cells, only the sustained mode of ACh release elicits levels of serotonin sufficient to stimulate vagal afferent neurons that suppress food intake.
This two-phase paracrine signalling mechanism explains how parasitic infection progresses from an initial asymptomatic phase to symptomatic established disease, in which type 2 immune and sensory signalling pathways within the gut–brain axis collaborate to evoke protective behaviours.
