LL-37
Human Cathelicidin · Antimicrobial Peptide
LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino acid cationic peptide derived from hCAP18 that exhibits broad-spectrum antimicrobial activity against bacteria, viruses, and fungi while modulating immune responses.
Overview
LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino acid cationic peptide derived from hCAP18 that exhibits broad-spectrum antimicrobial activity against bacteria, viruses, and fungi while modulating immune responses.
Provides direct antimicrobial activity through membrane disruption, promotes wound healing by enhancing keratinocyte migration and angiogenesis, and modulates immune responses without systemic exposure when used topically.
Research indications
What the compound has been studied for, grouped by body system. Effect size is the reported magnitude where it was measured — not a recommendation.
68% ulcer area reduction demonstrated with 0.5mg/mL concentration in clinical trials.
Enhanced granulation tissue formation and wound closure.
Accelerated healing demonstrated in animal models.
Boosts natural immune defenses against pathogens.
Active against MRSA and multi-drug resistant bacteria with >4 log reduction in biofilms.
Balances immune responses without causing immunosuppression.
Stimulates skin cell growth and regeneration.
Promotes new blood vessel formation for tissue repair.
Supports collagen production for wound healing.
A large effect in a weak study and a small effect in a strong one are different things. Effect size is never evidence of use in people.
- Class
- Cationic antimicrobial peptide
- Chain length
- 37 residues
- Typical dose
- 0.5-1.6 mg/mL topical gel or 100-150 mcg injectable
- Frequency
- Topical: Daily to twice weekly on wounds. Injectable: Once daily subcutaneous
- Cycle length
- 2-8 weeks depending on wound healing progress
- Storage
- Lyophilized: 2-8°C. Reconstituted: 2-8°C, maintain sterility
Molecular data
- Type
- Cationic antimicrobial peptide
- Chain length
- 37 residues
Dosing reference
Doses reported in the literature and by suppliers. These are a record of what has been used in research — reference, never instruction.
| Context | Route | Amount | Frequency |
|---|---|---|---|
| Wound healing - Standard | Direct wound application | 0.5mg/mL gel/cream | Daily to twice weekly |
| Wound healing - Intensive | Direct wound application | 1.6mg/mL gel/cream | Daily |
| Systemic immune support | SubQ | 100-150mcg | Once daily |
Interactions
Enhanced wound healing through complementary mechanisms.
Combined anti-inflammatory and healing effects.
FICI values 0.25-0.5 against resistant bacteria when combined.
Acts as cofactor for endogenous LL-37 production.
Safe combined use with no negative interactions.
High salt concentrations may reduce antimicrobial activity.
Physical incompatibility, especially with IV formulations.
Quality checklist
- ✓Sterile, clear formulation
- ✓≥98% purity by HPLC
- ✓White to off-white lyophilized powder
- ✓Proper cold chain maintenance (2-8°C)
- ✓Appropriate gel base compatible with peptide activity
- ✓Clinical-grade concentrations (0.5-1.6mg/mL)
- !Brief room temperature exposure acceptable if promptly refrigerated
- !Homemade topical formulations may lack sterility
- ×Discolored or cloudy solutions
- ×Yellow discoloration or visible particles
- ×Pre-mixed liquid formulations (LL-37 unstable long-term)
- ×Non-sterile preparations
- ×Microbial contamination
What to expect
Safety
- Generally well-tolerated
- Mild injection site reactions (injectable)
- Local irritation at application site (topical)
- Severe injection site reactions with spreading inflammation
- Allergic reaction signs (rash, difficulty breathing, swelling)
- Persistent flu-like symptoms
- Signs of wound infection (increased redness, warmth, drainage)
- Worsening wound condition or delayed healing
- Unusual pain or irritation at application site
- Pre-existing hypersensitivity to peptides
- Compromised immune status (relative contraindication)
- Non-sterile wound environments
FAQ
How much faster does LL-37 heal wounds compared to standard care?
LL-37 at 0.5mg/mL concentration reduced chronic venous leg ulcer area by 68% in clinical trials. Healing acceleration is most dramatic in weeks 2-4, with granulation tissue formation and epithelial migration visibly increasing compared to untreated wounds.
Is LL-37 effective against antibiotic-resistant bacteria?
Yes. LL-37 showed >4 log reduction in MRSA biofilms compared to conventional antibiotics. Its broad-spectrum antimicrobial activity works through membrane disruption, bypassing resistance mechanisms. It's effective against resistant gram-positive and gram-negative bacteria.
Can LL-37 be combined with antibiotics?
Yes, synergistically. LL-37 combined with conventional antibiotics shows FICI values of 0.25-0.5, indicating synergistic antimicrobial activity. Using them together may enhance efficacy against resistant organisms.
Does topical LL-37 cause systemic effects?
No. Topical LL-37 has minimal systemic absorption when applied to wounds. Effects are localized to the wound site with direct antimicrobial and healing benefits. This makes it safe for wound-specific application without systemic side effects.