LL-37
Cathelicidin / Human Cathelicidin / hCAP-18
LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino acid cationic peptide cleaved from its precursor protein hCAP-18 by proteinase 3 in neutrophils and various epithelial cells. It serves as a critical component of the innate immune system, providing broad-spectrum antimicrobial activity against bacteria, viruses, and fungi while also modulating inflammation and promoting wound healing. LL-37 expression is upregulated by vitamin D3, which mechanistically explains many of vitamin D's documented immune-enhancing effects.
Mechanism of Action
Endogenous human antimicrobial peptide cleaved from cathelicidin precursor hCAP-18. Disrupts microbial membranes, neutralizes endotoxin (LPS), modulates TLR signaling, promotes wound healing via angiogenesis, and recruits immune cells through chemotactic activity.
Research Protocols
For research purposes only. Not medical advice.
Research protocols use 50-100mcg subcutaneously daily. Topical applications for wound healing at 10-50mcg/ml. Intranasal protocols studied for upper respiratory infections. Cycles of 1-4 weeks.
Research Notes
Clinical Research Status
LL-37 is actively being investigated in clinical trials for chronic wound healing, with a Phase I/II trial (by Promore Pharma, now Lipigon) demonstrating safety and efficacy in venous leg ulcers. Research applications span chronic infections, biofilm-associated conditions, diabetic wound healing, and as a topical antimicrobial agent. No systemic injectable formulation has reached clinical trials due to challenges with peptide stability and potential hemolytic activity at high systemic concentrations. The connection between vitamin D deficiency and susceptibility to infections has driven research into LL-37 as the mechanistic link.
Key Published Findings
LL-37 demonstrates broad-spectrum antimicrobial activity against gram-positive and gram-negative bacteria, including MRSA and Pseudomonas aeruginosa, through membrane disruption mechanisms. A landmark 2006 Science paper showed LL-37 disrupts bacterial biofilms at sub-MIC concentrations by interfering with biofilm attachment and stimulating twitching motility. Research in the Journal of Immunology demonstrated LL-37 acts as a chemoattractant for neutrophils, monocytes, and T-cells through formyl peptide receptor-like 1 (FPRL1) activation. Studies show vitamin D supplementation increases LL-37 expression 3-5 fold in human macrophages, establishing a direct molecular link between vitamin D status and innate immunity.
Safety Profile
Topical application of LL-37 has been well-tolerated in clinical wound healing trials with no serious adverse events reported. At high systemic concentrations, LL-37 can exhibit cytotoxicity to mammalian cells and hemolytic activity, limiting its use as a systemic injectable. Local injection site reactions including redness and transient pain have been reported but resolve within hours. The peptide is rapidly degraded by serum proteases, which provides a natural safety mechanism against systemic accumulation but limits bioavailability.
Drug Interactions & Contraindications
High-dose vitamin D supplementation increases endogenous LL-37 production and may have additive effects when combined with exogenous LL-37 administration. Concurrent use with other membrane-active antimicrobials (daptomycin, polymyxins) could theoretically produce synergistic cytotoxicity requiring dose adjustment. Patients with rosacea or psoriasis may have elevated endogenous LL-37 levels contributing to their pathology, and exogenous administration could exacerbate these conditions. Not recommended for patients with systemic lupus erythematosus as LL-37-DNA complexes may activate plasmacytoid dendritic cells and worsen autoimmune responses.
Comparison to Related Compounds
Unlike conventional antibiotics, LL-37 kills bacteria through physical membrane disruption, making resistance development extremely difficult compared to target-specific drugs. Compared to other antimicrobial peptides (defensins, magainins), LL-37 is unique in its additional immunomodulatory, angiogenic, and wound-healing properties beyond direct microbial killing. Relative to KPV (another immune peptide), LL-37 is primarily antimicrobial and pro-healing while KPV is primarily anti-inflammatory. Its biofilm-disrupting properties distinguish it from virtually all conventional antibiotics, which are ineffective against established biofilms.
Community Observations
Users primarily employ LL-37 topically or via local subcutaneous injection near chronic wounds, infections, or biofilm-associated conditions at doses ranging from 50-200 mcg. Reports suggest benefit for chronic sinusitis, Lyme disease co-infections, and recurrent skin infections where biofilm involvement is suspected. Many users supplement with vitamin D3 (5,000-10,000 IU daily) to simultaneously boost endogenous LL-37 production alongside exogenous administration. The peptide is considered poorly suited for systemic injection due to rapid degradation and is most often used in targeted, localized applications.
Half-Life
~4-6 hours
Reconstitution
Sterile water or bacteriostatic water
Storage
Lyophilized
Store at -20C for long term.
Reconstituted
Refrigerate 2-8C. Use within 7 days.
US Legal Status
Also Known As
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