LL-37
The body's native antimicrobial peptide — kills bacteria, viruses, fungi, and biofilms while modulating immune signalling.
Research facts
| Half-life | ~2–4h |
|---|---|
| Route | SubQ / Topical / Nasal |
| Typical dose | 25–100 mcg/day |
| Frequency | Once or twice daily |
| Solvent | Bacteriostatic water |
| pH | 5.5–7.5 |
| Stability | 30 days at +4°C |
Mechanism of action
LL-37 is the C-terminal active fragment of the human cathelicidin hCAP18 — the only member of the cathelicidin family in humans. It is an amphipathic alpha-helical peptide that disrupts microbial membranes via electrostatic interaction and insertion into lipid bilayers, causing membrane permeabilisation and death. Its antimicrobial spectrum includes gram-positive bacteria (MRSA, Streptococcus), gram-negative bacteria (E. coli, Pseudomonas), fungi, and enveloped viruses. Beyond direct killing, LL-37 activates TLR signalling, recruits neutrophils and macrophages, induces dendritic cell maturation, and has documented anti-biofilm activity against chronic biofilm-forming pathogens (a major limitation of conventional antibiotics). It also promotes wound healing, angiogenesis, and re-epithelialisation via EGF receptor transactivation.
Documented effects (research-model)
- Broad-spectrum antimicrobial (bacteria, fungi, viruses)
- Anti-biofilm activity against antibiotic-resistant pathogens
- Immune cell recruitment and activation
- Wound healing via EGF receptor transactivation
- Anti-inflammatory dual role (context-dependent)
- Topical and systemic infection defence research
Research protocols
| Protocol | Dose | Frequency | Cycle | Vial |
|---|---|---|---|---|
| Standard | 50 mcg/day SubQ | Once daily | 4–8 weeks | 5mg / 5mL BAC water |
Research context only. Not medical advice. Consult a qualified healthcare professional before any protocol decision.
Synergies
- Thymosin Alpha-1 MODERATE
LL-37 provides innate antimicrobial killing; TA-1 enhances adaptive immune response. Complementary immune defence.
Myths & misconceptions
Evidence gaps
- No completed human RCTs for LL-37 as an antimicrobial therapeutic.
- Optimal delivery route for different infection types is not established.
- Pro-inflammatory effects at high concentrations (LL-37 can worsen inflammatory conditions like psoriasis) vs. anti-inflammatory at physiological levels — dose-response not characterised in humans.
Safety notes
Generally well-tolerated topically. Injectable use has limited human safety data. High concentrations may exacerbate inflammatory conditions (psoriasis, atopic dermatitis). Research use only.
Biomarkers to monitor
Primary-source citations
- PMID 16091480 — Antimicrobial peptides and innate immunity (Nat Rev Immunol. 2005)
Frequently asked
What is LL-37?
LL-37 (Human Cathelicidin Antimicrobial Peptide — hCAP18 Active Fragment) is a research compound classified in our library as Tier D — Animal or in-vitro data only.. The body's native antimicrobial peptide — kills bacteria, viruses, fungi, and biofilms while modulating immune signalling.
What is the evidence tier for LL-37?
We classify LL-37 as Tier D: Animal or in-vitro data only. See our full peptide evidence tiers explainer for how we assign S/A/B/C/D.
What is the research dose of LL-37?
For LL-37, typical research dose is 25–100 mcg/day, route is SubQ / Topical / Nasal, half-life is ~2–4h. Protocols vary by research goal — see the protocols section on this page for standard and advanced dosing schedules. Research use only, not medical advice.
Is LL-37 safe?
Generally well-tolerated topically. Injectable use has limited human safety data. Research context only — no compound on this site is approved for human therapeutic use unless explicitly noted.