reviewed april 2026|next review october 2026|88 physicians psi has verified|3096 published studies
LL-37
LL-37 is the only cathelicidin antimicrobial peptide found in humans, a 37-amino-acid peptide released by immune cells as a first line of defense against bacteria, viruses, and fungi, with over 3,000 published studies documenting antimicrobial, immunomodulatory, and wound healing mechanisms.
Evidence landscape: 3096 published studies
3,096 published items. 7 human studies and 159 animal studies. One of the most extensively studied antimicrobial peptides with a broad biological foundation.
- 7 Human
- 159 Animal
- 34 Reviews
- 2896 Other research
The only human cathelicidin. Over 3,000 published studies documenting antimicrobial, immunomodulatory, and wound healing mechanisms.
Vitamin D induces the body's own LL-37 expression because the cathelicidin gene contains a vitamin D response element.
On an FDA list that prevents licensed pharmacies from preparing it, limiting access through standard prescription channels.
PSI Assessment
The immune system produces exactly one cathelicidin antimicrobial peptide, and over 3,000 published studies have characterized what it does - from punching holes in bacterial membranes to orchestrating wound healing. LL-37 has one of the deepest biological foundations of any peptide on this platform. The gap between understanding what LL-37 does naturally in the body and proving that exogenous LL-37 works as a therapeutic remains wide. Early-phase human data exists for topical wound healing, but no large controlled trials have been completed. Here is what the evidence supports and where the gaps remain.
The only cathelicidin in humans. Over 3,000 published studies. One of the strongest biological foundations for any peptide on this platform.
The mechanism is amphipathic alpha-helical membrane disruption. LL-37 inserts into microbial phospholipid membranes, forming pores that kill bacteria, fungi, and enveloped viruses. Beyond direct antimicrobial activity, it orchestrates broader immune responses through FPRL1 and P2X7 signaling, modulates TLR4 (toll-like receptor 4) pathways, and promotes wound healing through EGFR (epidermal growth factor receptor) transactivation driving keratinocyte migration. A clinically important connection: vitamin D induces the body's own LL-37 expression because the cathelicidin gene contains a vitamin D response element.
What the evidence supports
LL-37 disrupts microbial membranes across bacteria, fungi, and enveloped viruses through amphipathic alpha-helical insertion. Biofilm disruption is documented across multiple independent groups. Wound healing promotion through EGFR transactivation and keratinocyte migration is mechanistically characterized. The vitamin D induction pathway is clinically relevant. Over 3,000 published studies provide one of the deepest biological foundations for any peptide.
What is not yet established
Whether topical or injectable LL-37 formulations produce clinically meaningful antimicrobial effects in humans beyond what the immune system achieves naturally. Optimal therapeutic dosing and delivery for wound healing applications. Whether LL-37 supplementation adds benefit beyond optimizing vitamin D status. Long-term safety of exogenous administration.
Research Evidence
The findings below cover the antimicrobial mechanism, wound healing data, and the vitamin D connection.
Evidence by condition
Evidence dimensions across LL-37's investigated applications. Wound healing has the earliest human data. Antimicrobial and immune modulation evidence is primarily from animal studies and cell culture.
| Condition | Mechanism | Animal evidence | Human evidence | Replication |
|---|---|---|---|---|
| Wound Healing | ||||
| Antimicrobial Activity | ||||
| Immune Modulation | ||||
| Biofilm Disruption | ||||
| Anti-Cancer Research |
LL-37 demonstrates broad-spectrum antimicrobial activity through amphipathic alpha-helical membrane disruption against gram-positive and gram-negative bacteria, fungi, and enveloped viruses. Biofilm disruption against P. aeruginosa is documented at sub-antimicrobial concentrations.
The antimicrobial mechanism is among the most replicated findings in peptide biology and the foundation of research interest.
Wound healing promotion occurs through EGFR transactivation driving keratinocyte migration. Heilborn et al. (2003) demonstrated that chronic wounds have impaired LL-37 expression, establishing a disease-state rationale for supplementation.
Early-phase human topical wound healing studies exist, but no large controlled trials have been completed.
Vitamin D is a confirmed inducer of LL-37 expression through a vitamin D response element in the cathelicidin gene. This provides an alternative, validated pathway for increasing LL-37 levels.
The vitamin D connection is clinically relevant: optimizing vitamin D status may be a safer first step than exogenous LL-37 administration.
7 Human|159 Animal|34 Reviews
View all 3096 indexed studiesHow LL-37 Works
LL-37 is a 37-amino-acid peptide cleaved from the hCAP-18 precursor protein. It is the only cathelicidin-derived antimicrobial peptide found in humans, expressed in immune cells, epithelial surfaces, and body fluids.
LL-37 is part of your immune system's first response to infection. When your body detects bacteria or other pathogens, immune cells release LL-37, which punches holes in microbial cell membranes, killing them directly. It also acts as a signal flare, recruiting more immune cells to the site and helping coordinate the broader immune response. In wound healing, it promotes the migration of skin cells to close the wound.
For a more detailed view of the biology, here is what researchers have observed at the molecular level.
LL-37 is an amphipathic, alpha-helical peptide that kills microbes by interacting with negatively charged phospholipids in microbial membranes, forming pores that disrupt membrane integrity. This mechanism gives it broad-spectrum activity against gram-positive and gram-negative bacteria, fungi, and enveloped viruses. Beyond direct antimicrobial action, LL-37 signals through multiple receptors including FPRL1 (formyl peptide receptor-like 1) and P2X7, modulating chemotaxis, cytokine production, and angiogenesis. It activates TLR4 signaling in immune cells and promotes keratinocyte migration through EGFR transactivation.
What is LL-37 being studied for?
Researchers are studying LL-37 across several health conditions. Each condition below is labeled with the strength of evidence that exists for that specific use, not for LL-37 overall. This means a compound can have human studies for one condition but only animal data for another.
Wound Healing
·Human TrialsLL-37 promotes wound healing by stimulating skin cell migration and blood vessel formation. Early-phase human studies exist for topical wound healing formulations.
Limitations: Human data is limited to early-phase topical studies. Large-scale controlled trials have not been completed. Whether topical LL-37 produces clinically meaningful improvements over standard wound care is not yet established.
Antimicrobial Activity
·Animal StudiesBroad-spectrum antimicrobial activity against bacteria, fungi, and viruses demonstrated in laboratory and animal studies. Kills pathogens by disrupting their cell membranes.
Limitations: All antimicrobial efficacy data is from cell culture and animal models. No controlled human trials exist for LL-37 as an anti-infective agent.
Immune Modulation
·Animal StudiesBeyond killing pathogens, LL-37 modulates the broader immune response by recruiting immune cells and regulating inflammation.
Limitations: Immune modulation data is primarily from cell culture and animal studies. Clinical applications have not been tested in controlled human trials.
Biofilm Disruption
·Animal StudiesLaboratory studies show LL-37 can prevent bacterial biofilm formation and disrupt established biofilms, particularly in Pseudomonas aeruginosa.
Limitations: Biofilm disruption data is entirely from cell culture. Whether LL-37 can disrupt clinically relevant biofilms in living organisms has not been demonstrated in human studies.
Anti-Cancer Research
·PreclinicalEarly laboratory studies suggest LL-37 may have direct anti-tumor activity through membrane disruption of cancer cells, but this research is at the earliest stage.
Limitations: Extremely limited data. Conflicting results across cancer types. No clinical relevance established.
Safety and Regulatory Status
FDA Status: Not FDA-approved for any therapeutic indication.
Regulatory status: Listed on an FDA list that prevents licensed pharmacies from preparing it for patient use. This reflects limited human safety and efficacy data, not confirmed harm.
Safety context: LL-37 is a naturally occurring (the body's own) antimicrobial peptide. Exogenous application at therapeutic concentrations appears well-tolerated in early-phase topical studies. At very high concentrations, LL-37 can damage host cells.
LL-37 is produced naturally by the immune system. Early-phase topical studies report good tolerability. At high concentrations in cell culture, LL-37 can be cytotoxic to host cells, meaning there is a dose-dependent toxicity threshold.
Peptide Structure
Technical molecular data for researchers and clinicians.
Questions and Comparisons
Questions the evidence raises for a LL-37 discussion.
Comparison and Related Research
LL-37 is most often compared with other immune-related peptides that serve fundamentally different roles.
Head-to-head comparisons
Full research comparisons covering LL-37 and another peptide side by side.
LL-37 vs Thymosin Alpha-1
Thymosin Alpha-1 has clinical approval in some countries. LL-37 is primarily preclinical. Evidence-graded comparison of two immune modulation peptides.
View full comparisonLL-37 vs KPV
KPV reduces inflammation via NF-kB. LL-37 kills pathogens directly. Both are early-stage. Evidence-graded comparison of two immune peptides.
View full comparisonRelated compounds
Frequently Asked Questions
References
Each citation links to the original study on PubMed, the U.S. National Library of Medicine database.
- 1.A comprehensive review of the cathelicidin family of antimicrobial peptides, including LL-37, the only human cathelicidin. The review details how these peptides serve as a first line of defense in the innate immune system, with roles that extend beyond direct antimicrobial killing to include immune cell recruitment, wound healing promotion, and modulation of inflammatory responses.Zanetti M, 2004 in J Leukoc Biol. View on PubMed
- 2.This study analyzed LL-37 expression in human wound tissue and found that the peptide is strongly upregulated during the re-epithelialization phase of normal wound healing. Critically, chronic non-healing ulcers showed a marked deficiency of LL-37 at the wound edge, suggesting that inadequate LL-37 levels may contribute to impaired wound repair in chronic wounds.Heilborn JD et al., 2003 in J Invest Dermatol. View on PubMed
- 3.A database resource paper describing APD2, the updated Antimicrobial Peptide Database containing over 1,200 entries including LL-37. The database catalogs the broad-spectrum activity of LL-37 against bacteria, viruses, and fungi, and provides structural parameters that help explain the peptide's mechanism of membrane disruption and its potential as a template for designing new antimicrobial agents.Wang G et al., 2009 in Nucleic Acids Res. View on PubMed
- 4.This study demonstrated that sub-inhibitory concentrations of LL-37 prevent Pseudomonas aeruginosa biofilm formation through multiple mechanisms, including reducing bacterial attachment, stimulating twitching motility, and downregulating biofilm-related genes. The findings are significant because biofilms represent a major clinical challenge in chronic infections that are resistant to conventional antibiotics.Overhage J et al., 2008 in Infect Immun. View on PubMed
Medical Disclaimer
This content is for educational and informational purposes only and does not constitute medical advice. The information presented reflects published research as indexed by PSI and should not be used to make treatment decisions. Always consult a qualified healthcare provider before starting, stopping, or modifying any treatment.