Library / Peptides / Immune Support / LL-37
Emerging evidence · Grade B

LL-37

LL-37 (Human Cathelicidin Antimicrobial Peptide)
Evidence
Emerging
Route
Subcutaneous injection
Frequency
Once daily
Category
Immune Support
TL;DR
LL-37 is the only cathelicidin-derived antimicrobial peptide found in humans. It is a 37-amino-acid peptide (beginning with two leucines, hence 'LL') cleaved from the precursor protein hCAP18 and is produced by immune cells, epithelial cells, and other tissues.
Part 01 · How it works

Mechanism.

LL-37 is the only cathelicidin-derived antimicrobial peptide found in humans. It is a 37-amino-acid peptide (beginning with two leucines, hence 'LL') cleaved from the precursor protein hCAP18 and is produced by immune cells, epithelial cells, and other tissues. LL-37 has broad-spectrum antimicrobial activity against bacteria, viruses, and fungi, and also functions as an immune modulator, wound healing promoter, and anti-biofilm agent.

LL-37 is like a special forces soldier in your immune system — it directly punches holes in bacterial armor (membrane disruption), calls in backup troops (immune cell recruitment), breaks down enemy fortifications (biofilm disruption), and helps rebuild the town after the battle (wound healing).

Mechanism · technical
LL-37 disrupts microbial membranes through electrostatic interaction with negatively charged bacterial surfaces, forming pores that lyse the pathogen. Beyond direct killing, it modulates the innate immune response by acting as a chemoattractant for immune cells, stimulating angiogenesis, and promoting wound healing through activation of formyl peptide receptor-like 1 (FPRL1) and P2X7 receptors. It neutralizes lipopolysaccharide (LPS) endotoxin, reducing septic inflammatory responses. LL-37 also disrupts bacterial biofilms, making it relevant for chronic and resistant infections.
Part 02 · Dosing & administration

How it's taken.

Values below describe how LL-37 has been administered in published trials and labeling. Provided for educational purposes only — this is not medical advice and not instructions for self-administration. Consult your healthcare provider before making any health decision.

Standard dose
50-100 mcg
Subcutaneous injection · Once daily
Duration
2-4 weeks typical cycle

Human cathelicidin antimicrobial peptide. Research compound. Used off-label for immune support and biofilm-associated infections. Endogenous production is vitamin D-dependent. No FDA-approved indication.

Need help with reconstitution?

Use the free peptide calculator for dilution, unit conversion, and injection volume.

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Part 03 · Safety

Side effects, rare serious events, who shouldn't.

Reported side effects
Limited human safety data exists for exogenous LL-37 administration. Potential side effects include injection site reactions, localized inflammation, and theoretical risk of exacerbating certain inflammatory skin conditions (endogenous LL-37 overexpression is implicated in rosacea and psoriasis pathology). Systemic effects at therapeutic doses are not well characterized.
Absolute · do not use
×
Active autoimmune disease (LL-37 is a potent immune activator and may exacerbate autoimmunity)
×
Pregnancy or breastfeeding
×
Children under 18
×
Known hypersensitivity to LL-37 or any component
×
Rosacea or psoriasis (LL-37 is elevated in these conditions and may worsen symptoms)
Interactions
Immunosuppressants
LL-37 strongly activates innate immunity; may counteract immunosuppressive therapy
Major
Biologic therapies (TNF inhibitors, IL-17 inhibitors)
LL-37 activates inflammatory pathways that biologics aim to suppress; potential for opposing effects
Moderate
Anticoagulants
LL-37 has been shown to affect platelet activation and coagulation pathways
Moderate
Labs to monitor
CBC with Differential
Baseline and monthly
Monitor immune cell counts with antimicrobial peptide use
CMP (Comprehensive Metabolic Panel)
Baseline and every 3 months
Liver and kidney function
CRP / ESR
Baseline and monthly
Track inflammatory markers
Vitamin D, 25-OH
Baseline
Vitamin D regulates LL-37 expression; deficiency reduces endogenous production
Part 04 · Research log

Every study we cite.

Each study with its published finding and a plain-language note on limitations or funding.

01
2013
0
LL-37 as a multifunctional peptide in human host defense
LL-37 has direct antimicrobial, immunomodulatory, and wound healing properties
Comprehensive review; well-cited
PMID 23446442 ↗
02
2011
0
Vitamin D and cathelicidin in infection defense
Vitamin D supplementation upregulated LL-37 expression and improved antimicrobial defense
Clinical and mechanistic studies supporting vitamin D–LL-37 axis
PMID 21527855 ↗
Part 05 · Cost & access

Where you can get it.

Regulatory status
LL-37 is not FDA-approved for any indication. It is available through some compounding pharmacies and as a research peptide. Clinical trials have been conducted for topical LL-37 in wound healing (venous leg ulcers). It remains primarily investigational.
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Part 06 · Your appointment

Questions to bring.

01
Is LL-37 appropriate for my specific infection or immune condition?
02
What is the delivery method — injectable, topical, or nasal?
03
How does LL-37 compare to conventional antibiotics for my situation?
04
Are there any autoimmune concerns with using an immune-stimulating peptide?
05
What is the evidence level for LL-37 in humans versus animal models?
06
Could LL-37 worsen inflammatory conditions like rosacea or psoriasis?