LL-37: Complete Guide
LL-37 is the only human cathelicidin antimicrobial peptide, consisting of 37 amino acids beginning with two leucine residues (hence 'LL'). It is produced by immune cells (neutrophils, macrophages, epithelial cells) as part of the innate immune response and plays a critical role in first-line defense against bacterial, viral, and fungal infections. Beyond direct antimicrobial activity, LL-37 modulates inflammation, promotes wound healing, and influences adaptive immune responses.
Last updated: 2026-01-28
Quick Facts
- Category
- immune
- Also Known As
- Cathelicidin
- Related Goals
- inflammation, healing
Who Researches LL-37?
LL-37 is researched by people focused on immune defense — particularly those dealing with recurring infections, chronic wounds, or biofilm-related conditions (like certain gut or sinus issues). It's the body's own antimicrobial peptide, so research interest often comes from people looking for alternatives or complements to conventional antibiotics. If you're interested in immune modulation or wound healing, LL-37 offers a unique mechanism. It's typically used in short cycles during acute immune challenges rather than as ongoing supplementation.
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What Is LL-37?
LL-37 is the active form of human cathelicidin antimicrobial peptide (hCAP18). It is cleaved from the precursor protein by proteinase 3 in neutrophil granules, producing the mature 37-amino-acid peptide that is released at sites of infection and inflammation.
LL-37 represents the body's first-line chemical defense against invading pathogens. It is expressed in the skin, respiratory tract, gastrointestinal tract, and urogenital tract — the body's primary interfaces with the external environment. Its expression is upregulated by vitamin D (which is why vitamin D deficiency is associated with increased infection susceptibility).
Mechanism of Action
- Membrane disruption: LL-37 is an amphipathic α-helical peptide that inserts into bacterial membranes, forming pores that cause cell lysis
- Biofilm disruption: Penetrates and disrupts bacterial biofilms — a critical capability since biofilms are resistant to conventional antibiotics
- LPS neutralization: Binds and neutralizes lipopolysaccharide (bacterial endotoxin), reducing the inflammatory response to gram-negative bacteria
- Immune cell recruitment: Acts as a chemoattractant for neutrophils, monocytes, and T cells
- Wound healing: Promotes keratinocyte migration, angiogenesis, and re-epithelialization
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Dosage Overview
LL-37 dosing in research:
- Subcutaneous: 50–100 mcg daily
- Topical: Applied to wounds or infection sites
- Research cycles: Typically short courses (7–14 days) aligned with infection or healing timelines
LL-37 is a larger peptide (37 amino acids) and more expensive than smaller peptides. Use the peptide calculator for reconstitution.
Side Effects & Safety
- Injection site reactions: Can be more pronounced than with smaller peptides due to LL-37's immunostimulatory properties
- Pro-inflammatory at high concentrations: While LL-37 modulates inflammation at physiological doses, high concentrations can be pro-inflammatory — dose selection is important
- Mast cell activation: LL-37 can activate mast cells, potentially causing histamine-related effects (redness, itching, swelling)
- Autoimmune considerations: LL-37 has been implicated in the pathogenesis of psoriasis and rosacea — it may not be appropriate for individuals with these conditions