Cathelicidin peptides (LL-37 in humans, CRAMP in mice) act as molecular bridges between gut mucosal immunity and brain inflammation, with context-dependent neuroprotective or pro-inflammatory effects depending on their cellular source.
Source determines functionThe same cathelicidin peptide is neuroprotective when produced by neurons but pro-inflammatory when delivered to the brain by peripheral immune cells — a critical insight for therapeutic targeting.
What the researchers found
The review synthesizes evidence that cathelicidin peptides serve multiple roles in gut-brain communication. In the gut, cathelicidin maintains intestinal barrier integrity, shapes microbiota composition, and regulates innate immune signaling. Gut-derived metabolites including short-chain fatty acids and vitamin D influence cathelicidin expression, creating feedback loops between diet, microbiome, and mucosal defense.
In the CNS, cathelicidin shows a striking functional dichotomy: when produced by neurons, it acts as a neuroprotective modulator, but when delivered by peripheral immune cells infiltrating the brain, it exacerbates glial-mediated inflammation. This context-dependent behavior — where the same peptide can protect or harm depending on its source and local environment — is a key insight for understanding neuroinflammatory disease mechanisms.
Why it matters
The gut-brain axis is increasingly recognized as central to neuroinflammatory and neurodegenerative diseases. Finding that a single peptide — LL-37 — can act as both a local effector in the gut and a systemic messenger reaching the brain fundamentally changes how we think about antimicrobial peptides. It suggests that gut health interventions (probiotics, vitamin D, dietary changes that boost cathelicidin) could influence brain inflammation, and that cathelicidin itself could be a therapeutic target or diagnostic biomarker for gut-brain axis disorders.
How the study worked
Narrative review synthesizing animal and human research on cathelicidin biology in the gastrointestinal and central nervous systems, with focus on the gut-brain axis communication pathways.
What this study cannot tell us
As a review, this synthesizes existing literature rather than presenting new data. Much of the mechanistic evidence comes from animal models (primarily rodent CRAMP studies), and the human relevance of all findings is not confirmed. The context-dependent effects of cathelicidin are complex and not fully characterized. The review proposes cathelicidin as a gut-brain mediator, but direct causal evidence for this communication pathway in human neuroinflammatory disease is limited.
How to read the evidence
This is a comprehensive narrative review synthesizing diverse animal and human research. The evidence for cathelicidin's individual roles in gut and brain immunity is well-established, but the gut-brain axis communication function proposed here is an emerging hypothesis supported by circumstantial rather than direct causal evidence.
When this study was published
Published in 2026, this is the most current review on cathelicidin's role in gut-brain communication, incorporating the latest research on LL-37 and the microbiome-neuroinflammation connection.
The bigger picture
This review reconceptualizes LL-37 from a simple antimicrobial peptide to an active molecular bridge between peripheral and central immunity. The implications extend across multiple fields: gastroenterology (gut barrier), neurology (neuroinflammation), immunology (innate immunity), and even nutrition (vitamin D regulation). The finding that the same peptide has opposite effects depending on its source adds important nuance to peptide therapeutic development — boosting LL-37 in the gut might help, but increasing it in the brain via immune cells could worsen inflammation.
Questions still open
- Could measuring LL-37 levels in blood or cerebrospinal fluid serve as a biomarker for gut-brain axis dysfunction in neuroinflammatory diseases?
- Would boosting intestinal cathelicidin expression (via vitamin D or probiotics) have measurable effects on neuroinflammation in human patients?
- Can the source-dependent neuroprotective vs. pro-inflammatory effects of cathelicidin be therapeutically exploited by targeting neuron-specific expression?
Common questions
What is LL-37 and why is it important?
How could gut health affect brain inflammation?
Read the original research
Immunomodulatory effects of cathelicidin in the gut-brain axis: A novel link between mucosal immunity and neuroinflammation.
Experimental physiology
Citation
Nourizadeh, Mehrdad; Ghahari, Amir Arsalan; Zandi, Ehsan; Rasouli, Seyedeh Zeynab; Davari, Shaghayegh; Hoseinzadeh, Mobina; Nourazar, Mir Alireza. (2026). Immunomodulatory effects of cathelicidin in the gut-brain axis: A novel link between mucosal immunity and neuroinflammation.. Experimental physiology. https://doi.org/10.1113/EP093221