LL-37
Also known as: Cathelicidin, hCAP-18, Human Cathelicidin Antimicrobial Peptide, CAMP
LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino acid peptide with broad-spectrum antimicrobial activity against bacteria, viruses, and fungi. Beyond direct antimicrobial action, it modulates immune responses, promotes wound healing, and has anti-biofilm properties.
LL-37 is a 4,493.33 Da research peptide. LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino acid peptide with broad-spectrum antimicrobial activity against bacteria, viruses, and fungi. Beyond direct antimicrobial action, it modulates immune responses, promotes wound healing, and has anti-biofilm properties.
Also called: Cathelicidin, hCAP-18, Human Cathelicidin Antimicrobial Peptide
4,493.33
Molecular Weight
Daltons
3
Strong Evidence
benefits
5
Studies Cited
peer-reviewed
0-0
Typical Dose
Varies
Overview
LL-37 is a 37-amino acid amphipathic, alpha-helical peptide that represents the only member of the cathelicidin family of antimicrobial peptides in humans. It is cleaved from its precursor protein hCAP-18 (human cationic antimicrobial protein, 18 kDa) by proteinase 3 in neutrophils and by kallikreins in keratinocytes. LL-37 is produced by neutrophils, macrophages, epithelial cells, and mast cells, and is found in various body fluids including sweat, saliva, wound fluid, and airway surface liquid. Its name derives from its two N-terminal leucine residues and 37-amino acid length. LL-37 has broad-spectrum direct antimicrobial activity against gram-positive and gram-negative bacteria, enveloped viruses, and fungi. However, its biological significance extends far beyond direct pathogen killing; LL-37 is a multifunctional immune regulator that modulates inflammation, recruits immune cells, promotes angiogenesis and wound healing, and disrupts bacterial biofilms. Deficiency or dysregulation of LL-37 is associated with increased susceptibility to infections, while overexpression is linked to inflammatory conditions like rosacea and psoriasis. LL-37 is being investigated as a therapeutic agent for chronic infections, biofilm-associated infections, wound healing, and as an anti-cancer agent.
Key Takeaways: LL-37
- Strongest evidence supports LL-37 for broad-spectrum antimicrobial and anti-biofilm activity
- Research doses typically range from 0 to 0 Varies via topical application (wound dressings, gels)
- 3 benefits with strong evidence, 2 moderate, 1 preliminary
- Half-life: Minutes to hours depending on tissue environment (susceptible to proteolytic degradation)
- 5 cited research studies in this guide
Mechanism of Action
LL-37's antimicrobial mechanism involves its amphipathic alpha-helical structure, the positively charged face interacts with negatively charged bacterial membranes (via lipopolysaccharide in gram-negative and lipoteichoic acid in gram-positive bacteria), while the hydrophobic face inserts into the lipid bilayer. This creates pores or disrupts membrane integrity through a 'carpet' or 'toroidal pore' model, leading to bacterial lysis. Against biofilms, LL-37 penetrates the extracellular polymeric matrix, disrupts quorum sensing, and kills biofilm-embedded bacteria at sub-inhibitory concentrations. As an immunomodulator, LL-37 acts through multiple receptors including formyl peptide receptor-like 1 (FPRL-1/FPR2), P2X7 purinergic receptor, and EGFR transactivation. Through FPRL-1, it functions as a chemoattractant for neutrophils, monocytes, and T-cells. LL-37 modulates Toll-like receptor signaling — it can both amplify (by chaperoning nucleic acids to endosomal TLR3/7/8/9) and suppress (by neutralizing LPS at TLR4) inflammatory responses depending on context. For wound healing, LL-37 promotes keratinocyte and fibroblast migration, stimulates angiogenesis through VEGF-dependent and FPRL-1-dependent pathways, and enhances re-epithelialization. Anti-cancer mechanisms include direct membrane disruption of tumor cells, induction of apoptosis, and immune cell recruitment to tumor microenvironments.
Research Benefits
LL-37 at a Glance
LL-37's antimicrobial mechanism involves its amphipathic alpha-helical structure, the positively charged face interacts with negatively charged bacterial membranes (via lipopolysaccharide in gram-negative and lipoteichoic acid in gram-positive bacteria), while the hydrophobic face inserts into the lipid bilayer.
Broad-Spectrum Antimicrobial
Strong EvidenceDirect killing activity against gram-positive bacteria (MRSA, Staphylococcus), gram-negative bacteria (Pseudomonas, E. coli), enveloped viruses, and fungi. Effective against drug-resistant organisms.
Anti-Biofilm Activity
Strong EvidenceDisrupts bacterial biofilms at concentrations below those needed for planktonic killing. Penetrates biofilm matrix, inhibits biofilm formation, and kills biofilm-embedded bacteria, relevant for chronic and device-associated infections.
Immune System Modulation
Strong EvidenceRecruits immune cells to infection sites, enhances antigen presentation, modulates TLR signaling, and bridges innate and adaptive immunity. Can both amplify and resolve inflammation depending on context.
Wound Healing Promotion
Moderate EvidenceStimulates keratinocyte migration, fibroblast proliferation, and angiogenesis. Promotes re-epithelialization and vascularization in wound models. Combines antimicrobial protection with active tissue repair.
Synergy with Conventional Antibiotics
Moderate EvidenceLL-37 shows additive antimicrobial effects when combined with conventional antibiotics, potentially restoring sensitivity in resistant strains and reducing required antibiotic doses.
Anti-Cancer Properties
PreliminaryPreclinical studies show direct cytotoxicity against cancer cells, induction of apoptosis, and immune cell recruitment to tumors. Being investigated as an anti-cancer immunotherapy agent.
Research Dosing Protocols
Research Purposes Only: All content is for informational and research purposes only. This site does not provide medical advice, diagnosis, or treatment. Consult a qualified healthcare professional before using any peptide or supplement.
| Research Protocol | Dose Range | Route |
|---|---|---|
| Topical wound/infection research | 0–0 Varies | Topical application (wound dressings, gels) |
| Subcutaneous immune research | 50–200 mcg | Subcutaneous injection |
| Inhalation research (respiratory infections) | 0–0 Varies | Nebulized/intratracheal |
Frequency
Varies by application; daily for wound applications, variable for systemic
Timing
No specific timing requirements
Cycle Length
Application-dependent; wound healing: until resolution; systemic: 2-4 week courses in research
Research Notes
- 1LL-37 is primarily a research compound — no standardized clinical dosing exists yet.
- 2Topical applications (wound care, biofilm disruption) are the most developed use case.
- 3Susceptible to proteolytic degradation in vivo; delivery systems and analogs are being developed.
- 4Vitamin D supplementation increases endogenous LL-37 production (via CAMP gene transcription).
- 5Salt concentration affects activity, LL-37 may have reduced efficacy in high-salt environments.
- 6Modified LL-37 analogs and delivery systems are under active development for clinical use.
Reconstitution Guide
Standard Reconstitution
Vial Size
5 mg
Bacteriostatic Water
2 mL
Concentration
25 mcg
per 0.1 mL (10 units)
Step-by-Step Guide
Gather Materials
LL-37 vial, bacteriostatic water, alcohol swabs, insulin syringes.
Equilibrate Temperature
Remove the vial from storage and allow it to reach room temperature (5-10 minutes).
Sanitize
Swab the rubber stopper of both the peptide vial and bacteriostatic water vial with alcohol.
Draw Water
Draw 2 mL of bacteriostatic water into a syringe.
Add Water to Vial
Insert the needle into the peptide vial and direct the water stream against the glass wall — not directly onto the powder.
Mix Gently
Swirl the vial gently until the powder is fully dissolved. Never shake. The solution should be clear and colorless.
Store Properly
Refrigerate at Frozen (-20°C) for long-term; refrigerated (2-8°C) short-term after reconstitution. Use within 7-14 days of reconstitution (peptide is somewhat labile).
Storage Temperature
Frozen (-20°C) for long-term; refrigerated (2-8°C) short-term after reconstitution
Shelf Life
Use within 7-14 days of reconstitution (peptide is somewhat labile)
Important Notes
- •Reconstitute with sterile water or bacteriostatic water.
- •LL-37 is an amphipathic peptide — may adhere to plastic surfaces. Use low-binding tubes/vials.
- •Store lyophilized peptide at -20°C or -80°C for long-term stability.
- •Avoid repeated freeze-thaw cycles.
- •Solution should be clear; aggregation may occur at high concentrations.
LL-37 Dosing Calculator
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LL-37 Reconstitution Calculator
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Safety & Side Effects
Reported Side Effects
- !Local irritation at injection or application site (dose-dependent)
- !Potential for mast cell activation and histamine release at high local concentrations
- !Overexpression is associated with inflammatory skin conditions (rosacea, psoriasis), dose must be balanced
- !Possible hemolytic activity at very high concentrations (typically well above therapeutic range)
- !Limited clinical safety data; most evidence is preclinical or early-phase
- !Theoretical risk of autoimmune activation through TLR signaling amplification
Potential Interactions
- ⚡Vitamin D induces endogenous LL-37 production — supplementation may enhance natural levels.
- ⚡complementary with conventional antibiotics (beta-lactams, fluoroquinolones) against resistant bacteria.
- ⚡Salt concentration affects antimicrobial activity; high NaCl can reduce efficacy.
- ⚡May interact with heparin and other glycosaminoglycans which can bind LL-37.
- ⚡Potential interaction with immunosuppressive drugs (LL-37 enhances immune recruitment).
- ⚡Butyrate (from gut microbiome or supplements) can induce LL-37 expression in colonocytes.
Important: Side effects and interactions listed here are compiled from published research and community reports. This is not a complete list. No formal drug interaction studies have been conducted for most research peptides. Always consult a qualified healthcare provider.
Research Studies
The following studies are referenced in this profile. PubMed IDs are provided where available for independent verification.
LL-37, the only human member of the cathelicidin family of antimicrobial peptides
thorough review of LL-37's structure, antimicrobial mechanisms, immunomodulatory functions, and roles in wound healing. Established LL-37 as a multifunctional host defense molecule beyond simple antimicrobial activity.
LL-37 disrupts bacterial biofilms and promotes wound healing
Demonstrated LL-37's anti-biofilm activity against Pseudomonas aeruginosa at sub-MIC concentrations, showing biofilm disruption, inhibition of bacterial attachment, and stimulation of twitching motility.
Vitamin D induces cathelicidin antimicrobial peptide gene expression
Landmark study showing vitamin D directly induces LL-37/CAMP gene expression, providing a molecular link between vitamin D status and innate immune defense against infections.
The human antimicrobial peptide LL-37 as an immunomodulator
Detailed review of LL-37's immunomodulatory functions including chemotactic activity, TLR modulation, cytokine regulation, and bridging innate and adaptive immune responses.
Cathelicidin antimicrobial peptides in clinical development for MRSA infections
Clinical development of cathelicidin-based therapeutics for drug-resistant infections, demonstrating efficacy against MRSA in wound models and establishing the translational potential of LL-37-derived agents.
Note: This is not an exhaustive list of all published research. Studies are selected for relevance and quality. Click PubMed IDs to verify sources independently. Inclusion does not imply endorsement of the peptide for any clinical use.
Frequently Asked Questions
LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino acid peptide produced by immune and epithelial cells. It has broad-spectrum antimicrobial activity, disrupts biofilms, promotes wound healing, and modulates immune responses.
Yes. Vitamin D is a direct inducer of LL-37 gene expression. Maintaining adequate vitamin D levels (through sunlight, supplementation, or diet) supports natural LL-37 production. Butyrate from dietary fiber/gut microbiome also induces LL-37 in the colon.
Yes. LL-37 has demonstrated activity against methicillin-resistant Staphylococcus aureus (MRSA) both in planktonic (free-floating) and biofilm forms. Its membrane-disrupting mechanism is less susceptible to the resistance mechanisms that render conventional antibiotics ineffective.
LL-37 kills bacteria by physically disrupting their cell membranes (rather than targeting specific metabolic pathways), making resistance development much more difficult. It also disrupts biofilms, modulates immune function, and promotes wound healing — none of which conventional antibiotics do.
Yes, directly. Vitamin D activates the vitamin D receptor (VDR) which binds to the LL-37/CAMP gene promoter, inducing its expression. This is one of the key mechanisms by which vitamin D supports immune defense, and helps explain why vitamin D deficiency is associated with increased infection risk.
LL-37 can both promote and resolve inflammation depending on context. Overexpression is linked to inflammatory skin conditions (rosacea, psoriasis). At therapeutic doses, it recruits immune cells and enhances pathogen clearance, but its immunomodulatory actions typically support appropriate inflammation rather than excessive inflammation.
Research & Educational Use Only
All content is for informational and research purposes only. This site does not provide medical advice, diagnosis, or treatment. Consult a qualified healthcare professional before using any peptide or supplement.
The information presented here is compiled from published research studies and is intended for informational purposes only. Individual results may vary. Always consult with a licensed healthcare provider.