LL-37.
LL-37 is the only human cathelicidin-derived antimicrobial peptide, a 37-residue cationic, amphipathic alpha-helical peptide (named for its two leading leucine residues) cleaved from the C-terminus of the precursor protein hCAP18 (gene CAMP).
LL-37 is the only human cathelicidin-derived antimicrobial peptide, a 37-residue cationic, amphipathic alpha-helical peptide (named for its two leading leucine residues) cleaved from the C-terminus of the precursor protein hCAP18 (gene CAMP). LL-37 is research / preclinical, and PepCue grades its published evidence F tier (34/100). This is a research reference, not medical or dosing advice.
What it is
LL-37 is the only human cathelicidin-derived antimicrobial peptide, a 37-residue cationic, amphipathic alpha-helical peptide (named for its two leading leucine residues) cleaved from the C-terminus of the precursor protein hCAP18 (gene CAMP). It is an endogenous component of innate immunity, produced by neutrophils, epithelial cells, keratinocytes, and other tissues, where it acts as both a broad-spectrum antimicrobial and a host-defense signaling molecule.
How it works
As a cationic amphipathic peptide, LL-37 binds anionic microbial membranes and disrupts them (a detergent-like/toroidal-pore mechanism), giving broad activity against Gram-positive and Gram-negative bacteria, some fungi, and enveloped viruses, plus the ability to neutralize LPS and disrupt biofilms. Beyond direct killing, it is strongly immunomodulatory: it is chemotactic for neutrophils, monocytes, and T cells (acting partly via the FPR2/FPRL1 receptor), promotes angiogenesis and keratinocyte migration and proliferation (relevant to wound re-epithelialization), and modulates Toll-like-receptor and inflammatory signaling. A double-edged feature is that LL-37 can bind self-DNA/RNA and convert it into a potent activator of plasmacytoid dendritic cells via TLR9/TLR7, a pathway implicated in psoriasis and other autoimmunity.
Mechanism pathways
Host-defense peptides that disrupt microbial membranes and steer immune responses.
Antimicrobial peptides are an ancient arm of innate immunity, found across essentially all multicellular life. They work on a physical principle rather than a receptor one. The peptides are cationic, carrying a net positive charge, and amphipathic, meaning they have distinct hydrophobic and hydrophilic faces. Bacterial membranes are rich in anionic phospholipids and lipopolysaccharide, giving them a strongly negative surface charge, whereas mammalian cell membranes present mostly neutral phospholipids on their outer leaflet and contain cholesterol. The charge difference is what provides selectivity. On contact with a microbial membrane the peptide binds electrostatically, then inserts its hydrophobic face into the lipid bilayer. At sufficient local concentration this produces either detergent-like disruption of the membrane or organised pores, and the cell loses its ability to maintain an electrochemical gradient. Because the target is the membrane's basic physical composition rather than a specific protein, resistance is harder for bacteria to acquire than resistance to conventional antibiotics, though it is not impossible. Activity extends across Gram-positive and Gram-negative bacteria, some fungi, and enveloped viruses, and these peptides can also neutralise lipopolysaccharide and disrupt biofilms. Direct killing is only part of the story, and arguably not the most important part at physiological concentrations. The human cathelicidin in this group is strongly immunomodulatory: it is chemotactic for neutrophils, monocytes, and T cells, acting partly through a formyl peptide receptor, and it promotes angiogenesis, keratinocyte migration, and wound closure. Its expression is induced by vitamin D, which is one of the more concrete mechanistic links between vitamin D status and innate immune function. The same properties that make these peptides useful also make them difficult drugs. Selectivity for microbial over host membranes is relative rather than absolute, so systemic administration risks damaging host cells, and the peptides are rapidly degraded by proteases and inactivated by physiological salt concentrations and serum proteins. This is the central reason that decades of interest have produced few approved systemic antimicrobial peptides. Honest summary: the membrane-disruption mechanism is well established biophysically and is not in dispute. The immunomodulatory roles are also well documented in laboratory systems. What has not been established is that administering these peptides to people produces clinical benefit, and this cathelicidin has also been implicated in driving inflammation in certain skin conditions, meaning more is not straightforwardly better.
The evidence
Direct human interventional evidence is limited and centers on chronic wounds. A multicentric, prospective, randomized, placebo-controlled trial evaluated topical LL-37 in hard-to-heal venous leg ulcers (Gronberg et al., Wound Repair Regen, 2021, PMID 34687253), building on an earlier safety/efficacy study reporting improved healing of venous leg ulcers (PMID 25041740); these are small, wound-specific studies rather than large confirmatory trials. The great majority of the LL-37 literature is mechanistic, in vitro, or animal-based: for example, cathelicidin's protective role against urinary-tract infection was shown in mice and human cells (Chromek et al., Nat Med, 2006, PMID 16751768). Much of the peptide's purported breadth (antiviral, anticancer, antibiofilm, metabolic effects) remains preclinical, and endogenous LL-37 biology should not be conflated with proven benefit from administering exogenous LL-37 in humans. Honest summary: human efficacy data exist mainly for topical chronic-wound healing and remain early-stage; systemic therapeutic use is not established.
The evidence, in brief
The active form of the human cathelicidin antimicrobial peptide, an endogenous host-defence molecule with antimicrobial, immunomodulatory and wound-healing activity. The evidence base is predominantly preclinical with only early-stage human research; not an approved drug.
- The Human Cathelicidin LL-37 as a Potential Treatment for Polymicrobial Infected Wounds (review)Front Immunol, 2013 (PMID 23840194)
Evidence maturity
An evidence-only reading: approval status, human vs preclinical data, mechanism and safety. Popularity never raises it. Research file #038
Mostly preclinical or mechanistic; little human data.
Findings come mainly from animal models, not people.
Claim receipts
Popular claims about LL-37, checked against the state of the evidence. The verdict describes evidence maturity, never an invented study result.
The membrane-disrupting activity is well characterized in laboratory systems, but that is not the same as demonstrated antimicrobial benefit from giving it to people.
Small randomized placebo-controlled topical studies in hard-to-heal venous leg ulcers exist, and they are early-stage rather than confirmatory.
Human data is confined to localized topical wound use; systemic administration has not been established as therapeutic.
The same self-nucleic-acid-binding activity is implicated in psoriasis and other autoimmune conditions, and the peptide can be cytotoxic and hemolytic at higher concentrations.
Safety profile
LL-37 has a genuinely double-edged profile: the same self-nucleic-acid-binding and dendritic-cell-activating activity that aids host defense is mechanistically implicated in autoimmune and inflammatory disease, and LL-37 is recognized as an autoantigen targeted by T cells in psoriasis. Elevated or dysregulated cathelicidin has also been linked to rosacea, lupus, atherosclerosis, and a context-dependent (pro- or anti-) role in cancer, so effects are highly tissue- and concentration-dependent. At higher concentrations the peptide can be cytotoxic and hemolytic to host cells, and it can be degraded or inactivated by serum and proteases, complicating systemic delivery. Human safety data are essentially confined to localized topical wound use; the safety of exogenous systemic administration in humans is not established.
Compound notes
- LL-37 is the active fragment of human cathelicidin, a host-defense (antimicrobial) peptide of the innate immune system.
- It is studied for antimicrobial activity, immune modulation, and wound healing.
- It has context-dependent effects: it can be pro- or anti-inflammatory depending on setting.
- Not FDA-approved; research-only.
- Dysregulated LL-37 is implicated in some inflammatory skin conditions; more is not simply better.
Regulatory status
LL-37 is not an FDA-approved drug; it is an endogenous human peptide studied as an investigational and research-use agent. Clinical work has been early-phase and indication-specific (notably topical chronic-wound trials), and no LL-37 product holds general marketing approval.
Sold research-use-only; human evidence is limited or preclinical.
By the numbers
- 01The only cathelicidin antimicrobial peptide in humans, derived from the hCAP18/CAMP gene product
- 0237 amino acids long; named for two N-terminal leucines (LL) plus its length (37)
- 03Produced by neutrophils, keratinocytes, and epithelial surfaces as part of innate immunity
- 04Pleiotropic: direct microbe-membrane disruption plus chemotaxis, angiogenesis, and wound-healing signaling
- 05Acts in part through the formyl-peptide receptor FPR2/FPRL1
- 06Implicated as a psoriasis autoantigen via self-DNA/RNA binding and TLR-mediated dendritic-cell activation
LL-37: research formats
Choose the format you are researching to see route-specific notes.
Cationic antimicrobial peptide; requires acetic acid reconstitution.
LL-37 is a highly cationic peptide with a pI that causes aggregation in BAC water. Reconstitution follows the standard acid-first protocol: dissolve in 0.01–0.6% acetic acid, then dilute with BAC water. Sold as 5–10 mg vials.
LL-37 reconstitution: add 0.2 mL of 0.6% acetic acid first, swirl until fully clear, then add BAC water to total 2.0 mL. Do not add all BAC water directly, or precipitation occurs.
Sources
Every factual claim above resolves to a real, published source.
- Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: A multicentric prospective randomized placebo-controlled clinical trialWound Repair and Regeneration, 2021, PMID 34687253
- Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcersWound Repair and Regeneration, 2014, PMID 25041740
- LL-37: Cathelicidin-related antimicrobial peptide with pleiotropic activityPharmacological Reports, 2016, PMID 27117377
- The antimicrobial peptide cathelicidin protects the urinary tract against invasive bacterial infectionNature Medicine, 2006, PMID 16751768
Cite this page
PepCue. “LL-37: the evidence.” PepCue, reviewed June 1, 2026. https://www.pepcue.app/p/ll-37.
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