LL-37
The only human cathelicidin antimicrobial peptide - with broad-spectrum antibacterial, antiviral, and wound-healing properties beyond its antimicrobial role.
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Compound Profile
LL-37
Key Data
Research reference only
Research Focus
Preclinical data
⚠ Research & Educational Use Only. LL-37 is a research chemical documented here for scientific education. All information references peer-reviewed literature and preclinical/clinical study data. Not for human consumption. Not medical advice. Consult a licensed researcher or healthcare professional before any laboratory use.
- The only human cathelicidin antimicrobial peptide - part of the innate immune first line of defence against bacteria and viruses
- Broad-spectrum antimicrobial: kills gram-positive and gram-negative bacteria, drug-resistant organisms (MRSA, ESKAPE pathogens), fungi, and viruses
- Wounds healing through keratinocyte migration and proliferation stimulation - accelerates re-epithelialisation
- LL-37 is not FDA-approved for human use. It is a research chemical for scientific study only.
Research At a Glance
- The only human cathelicidin antimicrobial peptide - part of the innate immune first line of defence against bacteria and viruses
- Broad-spectrum antimicrobial: kills gram-positive and gram-negative bacteria, drug-resistant organisms (MRSA, ESKAPE pathogens), fungi, and viruses
- Wounds healing through keratinocyte migration and proliferation stimulation - accelerates re-epithelialisation
- Anti-biofilm activity - disrupts established bacterial biofilms that are resistant to conventional antibiotics
In Plain English
Simple summaryLL-37 is the only member of the cathelicidin family of antimicrobial peptides found in humans. Your body produces it in neutrophils, macrophages, mast cells, and epithelial cells -- basically at any surface where pathogens might enter. It's a 37-amino acid peptide (the LL refers to the two leucine residues at the N-terminus) and it works primarily by disrupting bacterial cell membranes. What makes it more than just an antibiotic peptide is its range of immunomodulatory functions: it promotes wound healing, regulates inflammation, stimulates blood vessel formation, and has shown activity against viruses, fungi, and cancer cells in lab settings. In vivo, LL-37 is one of the body's first responders to infection.
- The only human cathelicidin antimicrobial peptide - part of the innate immune first line of defence against bacteria and viruses
- Broad-spectrum antimicrobial: kills gram-positive and gram-negative bacteria, drug-resistant organisms, fungi, and viruses
- Wounds healing through keratinocyte migration and proliferation stimulation - accelerates re-epithelialisation
The full scientific detail, mechanisms, citations, and dosing data, follows below.
What is LL-37?
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LL-37 is a 37-amino acid cationic antimicrobial peptide and the only known human member of the cathelicidin family. It is produced primarily by neutrophils, macrophages, epithelial cells, and keratinocytes as a first-line innate immune defence against bacterial, viral, and fungal pathogens.
What It Is
- A 37-amino acid amphipathic alpha-helical peptide (Leu-Leu-Gly-Asp-Phe-Phe-Arg-Lys-Ser-Lys-Glu-Lys-Ile-Gly-Lys-Glu-Phe-Lys-Arg-Ile-Val-Gln-Arg-Ile-Lys-Asp-Phe-Leu-Arg-Asn-Leu-Val-Pro-Arg-Thr-Glu-Ser) cleaved from the hCAP18 precursor protein by serine proteases
- Charged, amphipathic structure enables direct membrane disruption of bacterial membranes and immunomodulatory receptor binding
- Acts on FPR2 (formyl peptide receptor 2), EGFR, CXCR2, and toll-like receptors in human cells
- Deficiency in LL-37 is associated with increased susceptibility to atopic dermatitis, recurrent skin infections, and respiratory infections
How It Works
- Direct antimicrobial: positively charged residues bind anionic bacterial membranes; amphipathic helix inserts into and disrupts the lipid bilayer, causing membrane depolarisation and bacterial lysis; effective against Gram-positive, Gram-negative, and antibiotic-resistant organisms including MRSA
- Example: LL-37 at MIC of 2-4 mcM kills MRSA within 4 hours; equivalent to gentamicin at the MIC
- Immunomodulation: activates FPR2 on immune cells; promotes macrophage phagocytosis of pathogens; stimulates pro-inflammatory cytokines for pathogen clearance while also resolving inflammation post-clearance
- Wound healing: activates EGFR on keratinocytes and fibroblasts; promotes cell migration, proliferation, and angiogenesis (synergises with VEGF)
- Antiviral: disrupts enveloped virus membranes (influenza, HSV, RSV); concentrations of 5-20 mcM inactivate influenza A in vitro within 30 minutes
Key Research Findings
- Chronic wound therapy: topical LL-37 gel (0.5 mg/mL) applied to venous leg ulcers increased complete closure rates at 12 weeks vs vehicle (Phase 2: 33% complete closure vs 5% placebo, n=20)
- MRSA infections: LL-37 at 2 mcg/mL eliminated MRSA biofilms in catheter models within 24 hours; synergistic with rifampicin (4-fold MIC reduction when combined)
- Acne vulgaris: overproduction of LL-37 in acne patients (from sebaceous gland keratinocytes) has been identified as a driver of the inflammatory component of acne; LL-37 activates TLR-2 on macrophages, explaining the immune response to Cutibacterium acnes
- Psoriasis: LL-37 forms complexes with self-DNA released from dying cells, activating TLR-9 in plasmacytoid dendritic cells, triggering the IFN-alpha production cascade central to psoriasis pathology
Dosing From the Literature
- Topical: 0.1-1 mg/mL in gel or cream
- Intravenous (sepsis research models): 2-5 mg/kg
- Inhaled (respiratory infection research): 1-3 mg/kg in nebuliser solution
Storage and Handling
- Lyophilised: -20 degrees C; stable 12 months
- Reconstituted: 2-8 degrees C; use within 5 days
- Aggregates at neutral pH and low salt concentrations; reconstitute in mild acidic buffer (pH 5-6) or saline to maintain solubility
By the Numbers
Key Research Benefits
Documented effects observed in preclinical and clinical studies on LL-37. See all Immune System peptides for comparison.
Side Effects & Risks
Adverse effects reported in the research literature. All data sourced from preclinical and clinical study reports. View all peptides' side effects →
Dosing Data from the Literature
Doses referenced below are sourced from published preclinical and clinical studies. Use the peptide dose calculator to convert these values to injection volume.
LL-37 research dosing is poorly standardised and highly route-dependent. Clinical studies have used primarily topical and local applications rather than systemic administration, given the cytotoxicity concerns at high systemic concentrations.
Topical application for wound healing: solutions of 0.1–1 mg/ml applied directly to wound beds, 1–2 times daily. This is the best-characterised application route.
Subcutaneous injection for systemic immune modulation: 0.5–2 mg per injection, 2–3 times weekly. This is less well-characterised and carries a higher side-effect risk.
Intranasal: 0.5–1 mg/ml solution applied intranasally for respiratory infection resistance - an emerging application given LL-37's expression in the respiratory epithelium.
Given the limited human data for systemic administration, conservative starting doses and careful monitoring are essential.
Administration in Research Settings
Standard reconstitution and administration methodology for laboratory research use.
LL-37 can be administered topically, subcutaneously, or intranasally depending on the research objective. For topical wound healing applications, prepare a solution in sterile saline (0.1–1 mg/ml) and apply directly to wound surfaces under appropriate dressing.
For subcutaneous injection, reconstitute with bacteriostatic water and administer via insulin syringe. Given the cytotoxicity concerns at high concentrations, start with 0.5 mg and assess tolerance before escalating.
LL-37 is sensitive to proteolytic degradation - both in solution and in wound environments. Some researchers use modified formulations (fatty acid conjugations, polymer encapsulation) to extend its local stability. Store lyophilised at -20°C; reconstituted solutions should be used within 7–14 days and stored at 2–8°C.
What the research doesn't show
LL-37 is pro-inflammatory at higher concentrations and is elevated in inflammatory conditions like psoriasis, rosacea, and lupus -- meaning it's not simply anti-inflammatory. Its relationship with cancer is complex: it kills some cancer cells in vitro but promotes tumor angiogenesis in other contexts. The therapeutic window is real but context-dependent.
Research Video
Medical Expert Videos
Physicians, researchers, and pharmacologists explain LL-37, covering mechanisms of action, clinical context, and study findings.
Videos sourced from YouTube search. KnowYourPeptide does not endorse any individual creator. For research education only.
The Bottom Line
LL-37 has a growing body of preclinical evidence and a well-characterised safety profile in research settings. The most-studied application is: the only human cathelicidin antimicrobial peptide - part of the innate immune first line of defence against bacteria and viruses.
The most commonly reported side effect in research subjects is cytotoxic to mammalian cells at high concentrations - the antimicrobial mechanism (membrane disruption) also affects host cells above therapeutic concentrations. It is a research chemical, not approved for human use.
Frequently Asked Questions
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Quick Reference
How It Compares
Thymosin alpha-1 is another peptide with broad immune-modulating effects but works primarily through T cell and dendritic cell pathways rather than direct antimicrobial activity. BPC-157 also promotes wound healing but through angiogenesis and growth factor upregulation rather than direct pathogen killing. LL-37's combination of direct antimicrobial + immune-signaling + wound healing activity in a single peptide is genuinely unusual.
Compare LL-37 side-by-sideResearch Use Only
This information is for educational research purposes only. This is not medical advice. Consult a qualified healthcare professional.