LL-37
Also known as: Cathelicidin LL-37, hCAP18-derived LL-37, CAMP-derived peptide
3 notable studies · 4 references
TLDR
LL-37 is an endogenous human cathelicidin peptide studied for antimicrobial defense, immune regulation, biofilms, inflammation, angiogenesis, and wound repair, with extensive laboratory evidence but limited therapeutic human evidence and a larger Phase II wound trial that failed to show significant benefit in its overall population.
Research Supports
- Studied for antimicrobial activity against Gram-positive and Gram-negative bacteria, fungi, and some viruses
- Investigated for antibiofilm activity, including against multidrug-resistant organisms
- Studied in topical wound-healing trials for hard-to-heal venous leg ulcers
- Examined for roles in innate immunity, endotoxin binding, and immune-cell chemotaxis
- Investigated for context-dependent roles in inflammation, angiogenesis, and cancer biology
Observations Reported in Research
- Turner et al., 1998: active in vitro against E. coli, P. aeruginosa, S. aureus, and vancomycin-resistant enterococci
- First-in-human trial (2014, n=34): lower topical concentrations showed encouraging wound-healing signals
- Phase IIb trial (2021, n=148): no significant overall healing benefit vs. placebo; post-hoc large-wound subgroup appeared to benefit
- Altered circulating LL-37 has been observed in bacterial pneumonia, but this is observational, not treatment evidence
These are brief summaries of what the referenced research examined or reported — not conclusions about safety or effectiveness, and not medical advice. See Notable Studies and Sources & References below for the full context and citations.
At a Glance
Classification: Human cathelicidin antimicrobial peptide; cationic host-defense peptide; innate immune peptide
LL-37 is a naturally occurring 37-amino-acid human antimicrobial peptide and the only known human member of the cathelicidin family. It is generated from the precursor protein hCAP18, encoded by the CAMP gene. Unlike many compounds in the research market, LL-37 wasn't invented as a drug. Your body already makes it. LL-37 is part of innate immune defense and has been investigated for: • Bacterial defense • Viral defense • Fungal activity • Biofilms • Wound healing • Immune signaling • Inflammation • Angiogenesis • Tissue repair • Cancer biology. The phrase “antimicrobial peptide” is accurate—but incomplete. LL-37 can also influence immune-cell recruitment, inflammatory signaling, blood-vessel formation, tissue repair, and host-cell behavior. That complexity creates a major caution: More LL-37 is not automatically better. Depending on context and concentration, LL-37 can have antimicrobial, inflammatory, anti-inflammatory, tissue-repair, and cytotoxic effects.
What Is LL-37?
Humans produce a precursor protein called hCAP18. Proteolytic processing releases its C-terminal active peptide, LL-37. The name comes from: LL → its first two amino acids are leucines; 37 → the mature peptide contains 37 amino acids. LL-37 is expressed by several cell types and tissues involved in host defense, including neutrophils, epithelial cells, skin, respiratory tract, gastrointestinal tissues, and immune cells. It therefore sits at an interesting intersection between direct antimicrobial defense and immune regulation.
What Are Researchers Studying?
Antimicrobial activity
LL-37 was initially characterized largely because of its ability to damage microorganisms. Experimental studies demonstrate activity against numerous Gram-positive bacteria, Gram-negative bacteria, some fungi, and some viruses. Classic laboratory work found activity against organisms including E. coli, Pseudomonas aeruginosa, S. aureus, Salmonella, Listeria, and vancomycin-resistant enterococci. But antimicrobial activity is highly dependent on the experimental environment. Salt concentration, peptide concentration, bacterial strain, host proteins, and other conditions can dramatically alter activity. Therefore: Kills bacteria in vitro ≠ proven systemic antibiotic in humans.
Biofilms
Biofilms are structured microbial communities attached to surfaces and surrounded by protective extracellular material. They can be much harder to eradicate than freely circulating bacteria. LL-37 and shorter LL-37-derived peptides have therefore been investigated for preventing bacterial adherence, disrupting biofilms, killing organisms inside biofilms, and enhancing conventional antimicrobial activity. Laboratory studies have reported antimicrobial and antibiofilm activity against multidrug-resistant Acinetobacter baumannii. Other LL-37-derived fragments have shown experimental synergy with vancomycin against resistant S. aureus. These findings are interesting for antimicrobial-drug development but do not establish injectable LL-37 as a treatment for human infections.
Wound healing
This is one of the most important areas because actual randomized human trials exist. A first-in-human randomized trial involving 34 people with hard-to-heal venous leg ulcers evaluated topically administered LL-37. Lower tested concentrations showed promising wound-healing signals and treatment was generally well tolerated. That led to a larger Phase IIb study involving 148 patients. However, the larger trial did not find a statistically significant healing advantage over placebo in the overall study population. A post-hoc subgroup of people with larger ulcers appeared to benefit, but that requires prospective confirmation. Small trial: promising. Larger trial: primary overall efficacy result negative.
Innate immunity
LL-37 is increasingly described as a host-defense peptide, rather than merely an antibiotic produced by humans. It can influence chemotaxis, immune-cell recruitment, endotoxin responses, cytokine signaling, cellular activation, and innate immune recognition. LL-37 can bind and neutralize bacterial endotoxins while also recruiting immune cells to sites of infection or injury. This helps explain why LL-37 biology cannot be reduced simply to punching holes in bacterial membranes.
Inflammation
LL-37 has both pro-inflammatory and anti-inflammatory properties. Which effect dominates depends on tissue, concentration, disease state, cellular environment, and other inflammatory signals. That makes statements such as “LL-37 reduces inflammation” too broad. In some contexts it may suppress inflammatory signals. In others it may amplify immune activation.
Angiogenesis and tissue repair
LL-37 can influence endothelial-cell behavior and angiogenesis. This provides another plausible connection to wound healing because repair requires development and remodeling of blood vessels. But angiogenesis isn't universally beneficial. Abnormal vascular growth can also participate in disease. Therefore, “promotes angiogenesis” should be described as a biological property, not automatically a health benefit.
Cancer biology
LL-37 has an unusually complicated relationship with cancer. Depending on tumor type and biological context, research has associated LL-37 with tumor-cell proliferation, immune responses, cell migration, angiogenesis, and direct cytotoxicity. Recent reviews emphasize that LL-37 can be cytotoxic to multiple human cell types at certain concentrations. That makes simplistic claims that LL-37 is either “anticancer” or “cancer-promoting” scientifically inadequate.
How Does It Work?
LL-37 is cationic, meaning it carries a positive charge. Many microbial membranes contain negatively charged components. This allows LL-37 to associate with microbial membranes and potentially disrupt their integrity. But that's only part of the story. Membrane disruption: LL-37 can interact directly with microbial membranes and increase permeability. Endotoxin binding: It can bind bacterial products such as lipopolysaccharide and modify host inflammatory responses. Chemotaxis: LL-37 can influence recruitment of immune cells. Receptor interactions: Research suggests interactions with several host-cell receptors and signaling systems rather than one dedicated “LL-37 receptor.” Cellular signaling: LL-37 can alter intracellular calcium and numerous inflammatory pathways. This makes LL-37 much closer to a multifunctional host-defense signaling molecule than a conventional antibiotic.
What Does the Research Show?
Human research
Human evidence exists but is surprisingly limited compared with LL-37's popularity. The best interventional evidence comes from topical wound-healing studies. The 34-person first-in-human trial was encouraging. The subsequent 148-person Phase IIb study failed to demonstrate significant improvement over placebo in the overall population, although an exploratory large-wound subgroup appeared to benefit. Observational studies also measure endogenous LL-37 in human disease. For example, altered circulating LL-37 concentrations have been documented in people with bacterial pneumonia. But: Measuring naturally occurring LL-37 during disease ≠ evidence that administering synthetic LL-37 treats the disease. That's an important Aminodex distinction.
Animal research
Animal research is extensive and includes models of infection, wound healing, sepsis, lung injury, skin disease, inflammation, cancer, and angiogenesis. These studies provide substantial biological plausibility but also demonstrate LL-37's context-dependent effects.
In-vitro research
This is where LL-37 has its strongest evidence base. Laboratory experiments demonstrate antibacterial activity, antibiofilm activity, membrane disruption, endotoxin interactions, immune-cell signaling, chemotaxis, cytotoxicity, and angiogenic signaling. A classic study demonstrated substantial antimicrobial activity against numerous bacterial species. But laboratory antimicrobial potency varies substantially with environmental conditions.
Notable Studies
Activities of LL-37, a Cathelin-Associated Antimicrobial Peptide of Human Neutrophils
in-vitroResearchers compared LL-37 with other antimicrobial peptides and demonstrated activity against numerous Gram-positive and Gram-negative organisms, including P. aeruginosa, E. coli, S. aureus, and vancomycin-resistant enterococci. Activity varied with experimental conditions and organism.
Limitations: Laboratory antimicrobial activity does not establish efficacy or safe dosing in human infections.
View publication →Treatment with LL-37 Is Safe and Effective in Enhancing Healing of Hard-to-Heal Venous Leg Ulcers: A Randomized, Placebo-Controlled Clinical Trial
humanThirty-four participants with venous leg ulcers received topical LL-37 at different concentrations or placebo. The 0.5 and 1.6 mg/mL groups showed encouraging wound-healing signals, while the highest concentration did not show the same benefit. No major local or systemic safety concern emerged.
Limitations: Very small trial, short treatment period, and surrogate wound-healing measurements. The unusual dose-response relationship also required confirmation.
View publication →Evaluation of LL-37 in Healing of Hard-to-Heal Venous Leg Ulcers: A Multicentric Prospective Randomized Placebo-Controlled Clinical Trial
humanResearchers randomized 148 patients with difficult-to-heal venous leg ulcers to topical LL-37 or placebo alongside compression treatment. In the overall population, LL-37 did not significantly improve healing versus placebo. Post-hoc analysis suggested possible benefit among participants whose ulcers were at least 10 cm² at baseline.
Limitations: The primary overall efficacy result was negative. The apparently responsive large-wound subgroup was identified post hoc and requires prospective confirmation.
View publication →What We Still Don't Know
• Whether systemic LL-37 administration is clinically useful • Safe systemic exposure ranges • Long-term human safety • Human pharmacokinetics • Whether antimicrobial effects translate into treatment of human infections • Whether biofilm effects translate clinically • Which infections might benefit • Whether wound-healing subgroup findings replicate • Which immune effects are beneficial versus harmful • How concentration changes its biology • Clinical importance of its pro- versus anti-inflammatory effects • Whether angiogenic activity creates disease-specific risks • Long-term implications of its complex cancer biology
Related Compounds
Recent publications
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Sources & References
- Turner J, Cho Y, Dinh NN, Waring AJ, Lehrer RI. Activities of LL-37, a Cathelin-Associated Antimicrobial Peptide of Human Neutrophils. Antimicrobial Agents and Chemotherapy. 1998;42:2206–2214.
- Grönberg A, Mahlapuu M, Ståhle M, et al. Treatment with LL-37 Is Safe and Effective in Enhancing Healing of Hard-to-Heal Venous Leg Ulcers. Wound Repair and Regeneration. 2014;22:613–621.
- Mahlapuu M, Sidorowicz A, Mikosinski J, et al. Evaluation of LL-37 in Healing of Hard-to-Heal Venous Leg Ulcers. Wound Repair and Regeneration. 2021;29:938–950.
- Svensson D, Nilsson BO. Human Antimicrobial/Host Defense Peptide LL-37 May Prevent the Spread of a Local Infection Through Multiple Mechanisms: An Update. Inflammation Research. 2025.
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