LL-37

LL-37 is the only cathelicidin antimicrobial peptide made by the human body, and it sits at the crossroads of infection defense and immune signaling. Released from a larger precursor protein called hCAP-18 by neutrophils and at skin and mucosal surfaces, this 37-residue peptide both punches holes in microbes and tells the immune system where to go. That dual nature has made LL-37 one of the most-studied host-defense peptides, and also one of the most cautionary: the same molecule that protects can, when dysregulated, drive inflammatory disease.

What is LL-37?

LL-37 is a cationic, amphipathic, alpha-helical peptide and the sole human member of the cathelicidin family. Its name comes from its two leading leucine residues (“LL”) followed by its 37-amino-acid length. The CAMP gene encodes a 170-residue precursor (hCAP-18); enzymes such as proteinase 3 cleave off a “cathelin” pro-domain to release the active C-terminal peptide. You will see it referred to by several names, including cathelicidin, CAP-18, hCAP18, and FALL-39 (an earlier designation reflecting a 39-residue form). It is a naturally occurring human peptide — not a designed drug — which is part of why it draws so much research interest.

How LL-37 is studied to work

LL-37 carries a strong positive charge and folds into a helix that is water-loving on one face and oil-loving on the other. That amphipathic shape lets it stick to the negatively charged surfaces of bacteria and to receptors on human immune cells. Researchers describe two broad modes of action — direct microbial killing and immune signaling:

• Membrane disruption: binds bacterial lipopolysaccharide (LPS) and anionic membranes, then permeabilizes the microbial membrane.
• FPR2 receptor: acts as a chemoattractant for neutrophils, monocytes, and T cells through formyl peptide receptor 2.
• Endotoxin neutralization: binds and dampens LPS, modulating inflammation.
• Angiogenesis: promotes endothelial cell proliferation and new blood-vessel formation.
• Wound healing: stimulates keratinocyte and epithelial cell migration.
• Nucleic-acid sensing: forms complexes with self-DNA/RNA that can activate plasmacytoid dendritic cells.

Reported effects and benefits in the research literature

Across laboratory and preclinical studies, LL-37 has been reported to show:

• Broad-spectrum antimicrobial activity against Gram-negative and Gram-positive bacteria.
• Antiviral and antifungal activity in various models.
• Anti-biofilm activity, interfering with biofilm formation and disrupting established biofilms.
• Wound-healing support, including in chronic-wound models and small human ulcer trials.
• Immune modulation — chemotaxis, endotoxin neutralization, and cytokine tuning.
• Context-dependent anti-cancer signals in some tumor models.

LL-37 is often called “double-edged” for good reason. Elevated or dysregulated LL-37 is implicated in psoriasis (self-DNA–LL-37 complexes activating immune cells), rosacea (abnormal cathelicidin processing), and a pro-tumor role in certain cancers, while it is often reduced in atopic dermatitis.

What this does not mean: these findings are predominantly in-vitro, animal, and early or small human studies. They do not establish that exogenous LL-37 is a safe or effective treatment for any infection, wound, immune condition, or cancer in people. Because dysregulated LL-37 is itself linked to disease, “more” is not necessarily better.

What the human evidence shows

LL-37 is not FDA-approved for any indication; it is used as a research and investigational compound. The human data that does exist is limited to small, early-phase trials. A randomized, placebo-controlled study reported that LL-37 was safe and enhanced healing of hard-to-heal venous leg ulcers, and a later multicenter trial continued to evaluate it. A randomized controlled trial of an LL-37-containing cream for diabetic foot ulcers reported improved granulation and healing. In oncology, a completed Phase 1 trial of intratumoral LL-37 injections in melanoma reported safety and immune stimulation — though a published report also documented dermatologic toxicity from the therapy. In short: encouraging early signals exist, but there is no pivotal efficacy data and no approval.

Handling, storage and reconstitution (research context)

• Lyophilized powder: the most stable form; typically stored desiccated and protected from light, with long-term storage at -20 °C or colder. Let the vial reach room temperature before opening to limit condensation.
• Reconstituted: far less stable — LL-37 is protease-sensitive. Commonly reconstituted in sterile water or buffer, kept refrigerated (about 2–8 °C) for short-term use, and aliquoted/frozen to avoid repeated freeze–thaw cycles.
• General: cationic amphipathic peptides can adsorb to surfaces and are prone to oxidation; follow the certificate-of-analysis instructions for the specific lot. Our reconstitution calculator and the units explainer cover the lab math.

Cautions and considerations

• LL-37 is a research compound, not an approved medicine; human safety and efficacy are not established.
• Its double-edged biology means the same peptide is implicated in inflammatory and some malignant disease when dysregulated.
• Unregulated “research” material varies in purity and endotoxin — a meaningful certificate of analysis matters.
• This page is informational only and not medical advice; intended for an audience 21+.

Frequently asked questions

Is LL-37 a natural human peptide?

Yes. It is the only human cathelicidin, produced from the CAMP gene as the hCAP-18 precursor and cleaved into the mature 37-residue LL-37 by neutrophils and at epithelial surfaces.

Is LL-37 FDA-approved or proven to treat infections?

No. It is not approved for any use. Human evidence is limited to small early-phase trials, mainly in wound healing plus one Phase 1 melanoma study.

Why is LL-37 called “double-edged”?

Because the same peptide can be protective (antimicrobial, wound-healing) or harmful — implicated in psoriasis, rosacea, and invasion in some cancers — depending on tissue, concentration, and how it is processed.

How does LL-37 both kill microbes and signal to the immune system?

Its cationic, amphipathic helix disrupts microbial membranes and neutralizes bacterial LPS, while also recruiting immune cells through the FPR2 receptor and influencing cytokine release.

Related compounds and further reading

• How to reconstitute peptides — step-by-step handling guide.
• Sterile technique — clean handling fundamentals.
• KPV — a small anti-inflammatory peptide also studied in host defense.
• BPC-157 and TB-500 — tissue-repair research peptides.
• GHK-Cu — copper peptide studied in skin and wound research.
• Browse the full peptide library and our handling guides.

For informational use only. Not medical advice; consult a qualified healthcare professional. 21+.