For many people living with Lewy body dementia (LBD) digestive problems such as constipation can appear years before changes in memory, thinking, movement, or perception. This pattern has led researchers to look more closely at the connection between the gut and the brain.
 

A recent study titled “Intestinal macrophages modulate synucleinopathy along the gut–brain axis” adds important new detail to this work. Rather than focusing solely on nerves in the gut, the researchers examined nearby immune cells and how they respond to alpha-synuclein, a protein that misfolds and builds up abnormally in LBD.
 

Their findings suggest a role for immune cells in the intestine as a link between alpha-synuclein changes in the gut and those in the brain.
 

The gut has its own nervous system
 

Inside the wall of the intestine is a large network of nerve cells called the enteric nervous system. This network helps control digestion and bowel movements.  
 

Living alongside these gut nerves are immune cells called macrophages. Macrophages are part of the body’s defense system. Their job is to remove damaged cells and debris, respond to infection, and help keep tissues healthy. In simple terms, they help with cleanup and maintenance in the body.
 

The study examined what happens to these intestinal macrophages when misfolded alpha-synuclein is present.
 

Macrophages interact directly with alpha-synuclein
 

Using mouse models of synuclein-related disease and human tissue samples, the researchers found that intestinal macrophages can take up and contain misfolded alpha-synuclein. They also showed signs that their internal “recycling” systems were under stress. These recycling systems normally help cells break down and dispose of unwanted material.
 

Importantly, the macrophages did not simply store the protein. Their activity appeared to influence the surrounding immune environment.
 

When the researchers reduced the number of intestinal macrophages in their models, they observed several changes:

• Lower levels of alpha-synuclein buildup in both the gut and the brain
• Less expansion of certain immune cells called T cells (a type of white blood cell that helps coordinate immune responses)
• Improvements in measures of nerve cell damage and motor function
   

These findings suggest that intestinal macrophages may affect how synuclein-related disease processes unfold, not only in the gut but potentially along the pathway connecting the gut and the brain.
 

Communication between gut and brain immune systems
 

The study also looked at T cells more closely. In the setting of alpha-synuclein buildup, T cells increased in number in the gut. Some evidence suggested that these gut-related T cells could travel toward areas surrounding the brain, including the dura mater, a protective membrane that covers the brain and also contains immune cells.
 

This does not prove that LBD begins in the gut or that disease simply “moves” from gut to brain. However, it supports the idea that immune activity in the intestine may influence immune responses near the brain. The gut and brain are connected through nerves, blood vessels, and immune signaling, and these systems may interact more closely than once thought.
 

What related research shows
 

Other recent research helps provide additional context. A separate study found that intestinal macrophages use part of the complement system, a group of proteins in the immune system that help tag harmful material so it can be removed. One of these proteins, called C1q, appeared to help macrophages recognize and engulf alpha-synuclein in early stages of disease models.
 

However, this protective response seemed to weaken over time. In some situations, changing complement activity affected gut function in ways that did not perfectly match changes in alpha-synuclein buildup. This highlights an important point: immune responses can be complex. They may be helpful at one stage of disease and less helpful, or even harmful, at another.
 

What this means for people living with LBD
 

These findings do not change clinical practice now, but they offer clues for earlier detection and better treatment in the future.
 

Most of this research was conducted in mouse models, and translating findings from animals to people requires careful study. These results do not prove that LBD starts in the gut. They also do not show that changing intestinal immune cells would prevent or treat disease in people.
 

What they do show is that immune cells in the gut appear to participate actively in processes related to alpha-synuclein misfolding and buildup, and that this may influence alpha-synuclein changes in the brain. Understanding these processes more clearly gives researchers better information about where and how to look for early signs of disease and possible future treatment targets.
 

This study provides a clearer picture of how immune cells in the intestine may influence synuclein-related changes along the gut–brain connection. Over time, that clearer picture may help guide more precise approaches to diagnosis and treatment.


REFERENCES

De Schepper S, Konstantellos V, Conway JA, et al. 2026. Intestinal macrophages modulate synucleinopathy along the gut–brain axis. Nature. https://doi.org/10.1038/s41586-025-09984-y
 

Mackie PM, Koshy JM, Bhogade MH, et al. 2026. C1q-dependent clearance of alpha-synuclein allows macrophages to transiently limit enteric synucleinopathy in male mice. Nat Commun. https://doi.org/10.1038/s41467-026-68641-8