LL-37 Cathelicidin Peptide Guide: Antimicrobial Mechanism, Vitamin D Axis, and Wound-Healing Research

✓ Medically reviewed by  ·  Last reviewed: May 2026

Morgan Ellis

Pharmacy Researcher · 8 years experience

Pharmacy researcher with 8 years reviewing clinical drug information, generic formulation equivalence, and international pharmaceutical standards. Focuses on patient-facing accuracy in medication education.

What is LL-37 and where does it come from?

LL-37 is the only member of the cathelicidin family of antimicrobial peptides expressed in humans. It is a 37-residue amphipathic peptide with the sequence LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES. The two leading leucines give it its name; the molecular weight is 4493 Da; the isoelectric point is 10.6 (strongly cationic at physiological pH); and the CAS identifier is 154947-66-7.

In structural terms, LL-37 is unstructured in dilute aqueous solution but folds into an amphipathic alpha-helix when it contacts a membrane interface — with hydrophobic residues clustered on one face of the helix and positively charged residues on the other. This amphipathic structure is the basis of its antimicrobial activity: it inserts into negatively charged bacterial membranes via electrostatic attraction, then disrupts membrane integrity via hydrophobic insertion of the lipophilic face.

LL-37 is produced and stored by neutrophils, keratinocytes, sweat-gland epithelium, gut epithelium, lung epithelium, and oral epithelium. The expression pattern matches the body’s antimicrobial frontline: where pathogens encounter epithelial barriers, LL-37 is present at constitutive or induced levels. The other major cellular source — activated neutrophils — releases it from secondary granules during phagocytosis.

LL-37 sits in the cationic antimicrobial peptide (CAMP) family alongside defensins, dermcidin and histatin. It is structurally and pharmacologically distinct from peptide families such as the KPV anti-inflammatory tripeptide, the gut-healing BPC-157, or the copper-binding cosmetic peptides such as GHK-Cu. The complete peptide-research map is at the MedsBase peptides hub.

The CAMP gene, hCAP-18 and proteinase-3 cleavage

LL-37 is not transcribed directly. The CAMP gene encodes the 18 kDa precursor protein hCAP-18 (human cationic antimicrobial protein, 18 kDa) consisting of two regions: an N-terminal “cathelin” domain that is highly conserved across the cathelicidin family, and a C-terminal active domain that varies between species and contains the eventual mature peptide.

In humans, the precursor hCAP-18 is biologically inactive. It must be cleaved by proteinase 3 (a serine protease released from neutrophil azurophilic granules during activation) to release the active 37-residue C-terminal peptide. This cleavage is the rate-limiting step in LL-37 generation at infection sites and was demonstrated by Sørensen and colleagues (Sørensen OE et al., Blood 2001, PMID 11389039).

The CAMP gene promoter has a number of regulatory elements with practical importance for research. The most studied is the vitamin D response element (VDRE) bound by the ligand-activated vitamin D receptor (covered in detail below). Other documented regulators include butyrate (via histone deacetylase inhibition), retinoic acid, and STAT3-driven inflammatory signals.

Antimicrobial mechanism — membrane disruption

LL-37’s direct antimicrobial activity is driven by membrane disruption. Three sub-mechanisms have been described in the published literature, and which one dominates depends on the target organism, the peptide concentration, and the lipid composition of the target membrane:

1. Carpet model — LL-37 accumulates parallel to the membrane surface above a threshold density, then disintegrates the bilayer through detergent-like solubilisation. Dominant at high local concentrations.
2. Toroidal-pore model — LL-37 inserts into the bilayer in a perpendicular orientation and induces lipid-headgroup curvature, forming transient water-permeable pores. Dominant at intermediate concentrations.
3. Translocation model — LL-37 crosses the membrane without permanent disruption, then engages intracellular targets including DNA, ribosomes, and cell-wall synthesis machinery. Dominant at sub-membrane-disrupting concentrations.

Activity spectrum is broad: Gram-positive (Staphylococcus aureus, including some methicillin-resistant strains; Streptococcus species; Enterococcus species), Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Klebsiella); mycobacteria (covered separately below); selected fungi; and selected enveloped viruses (the lipid envelope provides the same target as a bacterial membrane).

An important practical limit: LL-37 is inactivated by physiological salt concentrations and by serum proteins. The peptide is most active in low-ionic-strength environments at epithelial surfaces; in blood, it binds apolipoprotein A-I and other carrier proteins that reduce free-peptide concentration. This is one of the central design constraints in LL-37-based research formulations — topical and mucosal applications work better than systemic.

The most current mechanistic overview is the 2026 review by Tan and colleagues on LL-37 in intestinal disease (PMID 42095322, Immunity, Inflammation and Disease).

Immunomodulation — the “second job”

Direct antimicrobial activity is only half of LL-37’s biology. The peptide has a parallel role as an immunomodulator, and in many physiological settings the immunomodulatory effects may be more important than direct microbe-killing. Documented immunomodulatory activities include:

• Chemotaxis — LL-37 is a chemoattractant for neutrophils, monocytes, T cells and mast cells via formyl peptide receptor-like 1 (FPRL1) / FPR2.
• Dendritic-cell priming — LL-37 modulates dendritic-cell function and antigen-presentation, with downstream effects on adaptive immune polarisation.
• Keratinocyte migration — LL-37 induces keratinocyte migration through epidermal growth factor receptor (EGFR) transactivation, which is central to its wound-healing role.
• Angiogenesis — LL-37 induces endothelial-cell proliferation and tube formation, again contributing to wound-healing biology.
• LPS neutralisation — the cationic LL-37 binds anionic bacterial lipopolysaccharide (LPS) and reduces TLR4-mediated sepsis-like cytokine responses. This is the basis for sepsis-research interest.
• Apoptosis modulation — LL-37 has cell-type-specific effects on apoptosis: pro-apoptotic in some cancer cells, anti-apoptotic in keratinocytes and neutrophils.

The vitamin D – LL-37 axis

The single most important molecular link between LL-37 and human health is the vitamin-D-driven transcriptional regulation of the CAMP gene. The landmark paper was Liu and colleagues in Science 2006 (Liu PT et al., Science 2006, PMID 16497887), which demonstrated that:

1. Toll-like receptor 2/1 (TLR2/1) activation on human macrophages by Mycobacterium tuberculosis lipoprotein upregulates the vitamin D receptor (VDR) and the activating enzyme CYP27B1.
2. This converts 25-hydroxyvitamin D (the storage form circulating in serum) into the active 1,25-dihydroxyvitamin D within the macrophage.
3. The active vitamin D then binds the VDR which translocates to the nucleus and binds the VDRE in the CAMP gene promoter.
4. This drives transcription of hCAP-18, processing to LL-37, and direct anti-mycobacterial activity.

The chain is intracellular and autocrine: the same macrophage detects the pathogen, makes the active vitamin D, drives LL-37 expression, and kills the intracellular organism. Vitamin D deficiency interrupts the chain at step 2 — the macrophage has functional VDR and CYP27B1 but no 25-hydroxyvitamin D substrate to convert.

This is why vitamin D status correlates with TB outcomes, with skin-barrier antimicrobial defence, and with respiratory-infection risk. The 2009 follow-up paper by Edfeldt and colleagues (PMID 19299728, Journal of Immunology) and the 2010 paper by Liu and colleagues (PMID 21149724, PNAS) explored T-cell cytokine modulation of the same pathway.

Wound-healing research — diabetic foot ulcers and beyond

Endogenous LL-37 is upregulated at wound margins as part of the normal healing response, and its three-arm activity (antimicrobial, chemotactic, keratinocyte-migration) is well matched to wound-healing biology. Topical or wound-deposited LL-37 has therefore been one of the most active clinical-research areas.

The single most important published study to date is the 2023 randomised placebo-controlled trial of topical LL-37 cream for diabetic foot ulcer (PMID 37480520, Archives of Dermatological Research 2023), which reported significantly enhanced healing rates in the LL-37 arm versus placebo over 8–12 weeks. The mechanistic basis was elaborated in a 2024 mouse study by Lu and colleagues that identified TFEB-dependent autophagy as the molecular driver of LL-37’s enhanced diabetic-wound effect (PMID 38423213, Peptides).

The broader 2026 review by Iwasaki and colleagues on cathelicidin LL-37 and ceragenins in wound healing (PMID 41791569, European Journal of Pharmacology) covers the current state of the wound-healing field. Diabetic ulcers, chronic venous ulcers, pressure ulcers, and post-surgical wounds with infection risk are the four most active sub-areas.

Background on chronic skin conditions and wound care is maintained at MedlinePlus Skin Conditions.

Skin-disease research — acne, rosacea, atopic dermatitis

The skin is the largest LL-37-expressing organ and LL-37 disorders are a major area of dermatology research. The same peptide that drives healthy antimicrobial defence in normal skin contributes to pathology when dysregulated:

• Rosacea — chronically over-expressed LL-37 and abnormal proteolytic processing in rosacea lesions generates pro-inflammatory peptide fragments that drive the flushing, erythema and papulopustular phenotype.
• Atopic dermatitis — reduced LL-37 expression contributes to the increased Staphylococcus aureus colonisation rates seen in atopic-dermatitis skin. The defect is partly downstream of Th2 cytokines (IL-4, IL-13) which suppress LL-37 production.
• Acne vulgaris — LL-37 activity against Cutibacterium acnes contributes to the antimicrobial limb of acne pathology. LL-37 is induced by retinoid signalling, which may be one mechanism of action of topical retinoids.
• Psoriasis — LL-37 in complex with self-DNA activates plasmacytoid dendritic cells via TLR9 and is one of the key amplifiers of psoriatic inflammation. This is a context where reducing LL-37 activity could be therapeutic.

The complexity is significant: LL-37 is the right intervention in atopic dermatitis (boost it) and a target to inhibit in rosacea and psoriasis (reduce it). The same peptide, the same molecular activity, opposite therapeutic directions in different diseases.

Oral biofilm and dental research

The oral cavity is one of the body’s most biofilm-dense environments — an estimated 700 microbial species coexist in dental plaque. LL-37 is constitutively expressed by oral epithelium and is present in saliva and gingival crevicular fluid.

A 2026 paper on LL-37 and bacterial DNA complexes in dental plaque (PMID 41862276, Journal of Oral Biosciences) describes how LL-37 binds bacterial DNA within biofilms and modulates both biofilm structural integrity and host innate-immune sensing. The biofilm-disruption arm of LL-37 activity is mechanistically distinct from planktonic-bacteria killing — it acts on the extracellular matrix structure rather than on individual cells — and is an active research target for periodontal-disease and dental-implant-infection research.

Anti-mycobacterial research and TB

The 2006 Liu Science paper that established the vitamin-D-CAMP axis was driven by the observation that vitamin D deficiency correlates with tuberculosis susceptibility. The subsequent two decades have refined the picture: LL-37 has direct anti-mycobacterial activity against M. tuberculosis, M. bovis BCG, and non-tuberculous mycobacteria, with mechanistic action including disruption of the mycobacterial outer cell envelope and modulation of intracellular phagosome maturation.

A 2026 review (PMID 42003198, Current Protein and Peptide Science) covers the current state of antimicrobial-peptide approaches against drug-resistant TB — LL-37 is one of several candidate peptides with documented activity but limited progression to clinical-research stages, largely because of the salt-sensitivity and proteolysis problems mentioned above.

Broader background on antimicrobial resistance and antibiotic stewardship is maintained by the CDC Antibiotic Use resource. The full body of LL-37 research is browsable at the PubMed search for “LL-37 cathelicidin”.

Cancer research — the dual-role complication

The same dual-function biology that makes LL-37 valuable in wound healing creates a complicated picture in cancer research. The 2026 paper by Yu and colleagues on cancer-cell migration under LL-37 control (PMID 41916132, Biomedicine & Pharmacotherapy) is one of many that documents the bidirectional activity:

• Pro-apoptotic in some cancers — LL-37 induces apoptosis in colon-cancer, gastric-cancer and oral-cancer cell lines via mitochondrial membrane disruption. The mechanism overlaps with its bacterial-membrane mechanism (cancer-cell membranes have abnormally negative surface charge from exposed phosphatidylserine).
• Pro-tumorigenic in others — LL-37 promotes proliferation, migration and invasion in lung-cancer, ovarian-cancer and breast-cancer models. The mechanism involves EGFR transactivation (the same mechanism as in keratinocytes during wound healing).

The published research consensus is that LL-37’s role in cancer is highly context-dependent: tumour type, microenvironmental pH, local proteolytic activity, and host genetics all affect which arm dominates. It is one of the active research questions that any responsible research-grade use of LL-37 should be aware of.

Stability, routes and research formulations

LL-37 is challenging to formulate, and most research uses one of three approaches to work around the stability and bioavailability problems:

The cathelicidin family also includes a number of analogue peptides (ceragenins, IDR-1018, and others) designed to retain LL-37’s antimicrobial activity while improving salt-tolerance and proteolytic stability. These are usually compared head-to-head against parent LL-37 in published research. For broader context on selecting and comparing peptide administration routes see our Peptide Injection Routes guide.

Reconstitution, storage and laboratory handling

LL-37 is supplied as a sterile lyophilised TFA or acetate salt powder. Standard laboratory reconstitution practice:

• Diluent: sterile water for injection or 0.01% acetic acid in water (improves dissolution of the cationic peptide). Bacteriostatic water (0.9% benzyl alcohol) is also commonly used for multi-use applications.
• Concentration: typically 0.5–2 mg/mL. Higher concentrations risk peptide self-aggregation and reduced activity.
• pH: reconstituted solution should be slightly acidic (pH 4–6); LL-37 aggregates at neutral or alkaline pH. Do not reconstitute in PBS or other neutral buffers for long-term storage.
• Storage of lyophilised powder: −20°C protected from light; stable 24+ months unopened. The peptide is hygroscopic — minimise air exposure during dispensing.
• Storage of reconstituted solution: 2–8°C in acidified buffer; use within 7–14 days. For longer-term storage, aliquot and freeze at −20°C; avoid repeated freeze–thaw cycles.
• Avoid: contact with anionic surfactants (SDS, etc.) — complete loss of activity; metal cation surfaces during dispensing — partial activity loss; vortexing — aggregation, use gentle inversion.

The full laboratory cold-chain handling protocol is set out in the Peptide Storage & Cold-Chain guide, and reconstitution-volume mathematics in How to Reconstitute Peptides.

Research-grade sourcing — what to look for on a COA

A defensible research-grade Certificate of Analysis (COA) for LL-37 will document at minimum:

1. Identity — mass spectrometry confirmation of the molecular ion. Theoretical monoisotopic mass for LL-37: 4490.3 Da; observed [M+H]⁺ ~4491; commonly reported as multi-charged ions [M+3H]³⁺ (m/z ~1498) or [M+4H]⁴⁺ (m/z ~1124) due to instrument range.
2. Purity — RP-HPLC purity ≥99% at 220 nm absorbance, with the chromatogram included in the COA. Single significant impurity peak <0.5%. The most common synthesis impurity is the deletion peptide LL-36 (missing one residue) — should be specifically called out and quantified.
3. Counter-ion — either TFA (trifluoroacetate) or acetate. TFA is the standard from RP-HPLC purification; acetate exchange is preferred for biological research to avoid TFA toxicity at higher concentrations.
4. Net peptide content — the actual peptide mass per vial after counter-ion correction. A 1 mg vial of TFA-salt LL-37 typically contains 0.85–0.90 mg of net peptide; this affects dosing calculations significantly.
5. Water content — Karl Fischer titration <8%.
6. Endotoxin — LAL test <1 EU/mg for products intended for in-vivo research use.
7. Bacterial bioburden — <100 CFU/g.
8. CAS number — 154947-66-7. Anything else is mislabelled.

The methodology for reading and verifying any peptide COA is set out in our dedicated How to Read a Peptide COA guide. LL-37 in particular benefits from explicit net-peptide-content disclosure because the TFA counter-ion is a significant fraction of the vial mass.

MedsBase supplies LL-37 (Cathelicidin Antimicrobial Peptide) as a research-grade laboratory reagent from a WHO-GMP-certified manufacturer, with HPLC purity ≥99%, full batch COA on file, mass-spec confirmation, and CAS-keyed labelling. Worldwide Shipping. The compound is supplied for laboratory and research use only.

Frequently Asked Questions

Is LL-37 the same as cathelicidin?

Almost — with one important nuance. “Cathelicidin” is a family name covering many species’ antimicrobial peptides; what humans have is the single family member CAMP-encoded hCAP-18 / LL-37 system. In informal scientific usage “the human cathelicidin” and “LL-37” are interchangeable. Strictly, hCAP-18 is the inactive precursor and LL-37 is the active mature peptide released after proteinase-3 cleavage.

Why is vitamin D status so important for LL-37?

Because the CAMP gene promoter contains a vitamin D response element (VDRE) and is transcriptionally driven by the ligand-activated vitamin D receptor. In vitamin D deficiency, even cells with intact CAMP genes, intact VDR, and intact processing machinery cannot produce adequate LL-37 because the upstream activating signal is missing. The 2006 Liu Science paper (PMID 16497887) established this chain experimentally; it is the most well-characterised single-gene molecular link between vitamin D status and any aspect of human immune function.

Does LL-37 work against viruses?

Against enveloped viruses, partially yes — the lipid envelope provides the same membrane target as a bacterial membrane. Direct antiviral activity has been documented in vitro against influenza, herpes simplex virus, respiratory syncytial virus, and several others. Against non-enveloped viruses the direct activity is minimal. The immunomodulatory arm of LL-37 (chemotaxis, dendritic-cell priming) may still affect non-enveloped-virus infections indirectly through host-immune modulation.

Why is LL-37 used as a topical rather than systemic intervention?

Three reasons. First, LL-37 is inactivated by physiological salt concentrations — activity drops significantly between low-ionic-strength wound exudate and serum. Second, serum proteins (apolipoprotein A-I and others) bind cationic peptides and reduce free-peptide concentration in plasma. Third, LL-37 is susceptible to proteolysis by plasma proteases. Topical or mucosal-surface administration sidesteps all three problems. Systemic administration is studied but is research-niche.

How does LL-37 differ from KPV?

Different molecular weight, different mechanism, different research applications. KPV is a 3-amino-acid C-terminal fragment of alpha-MSH that acts as a direct anti-inflammatory at the cellular level. LL-37 is a 37-amino-acid cathelicidin with dual antimicrobial and immunomodulatory functions. They share research interest in mucosal-barrier biology and wound healing but operate through entirely different molecular targets and are not interchangeable.

Can LL-37 be combined with other peptides?

Some combinations have published rationale — particularly LL-37 with GHK-Cu and similar copper-binding peptides in cosmetic / hair-loss research where the antimicrobial limb of LL-37 complements the regenerative limb of GHK-Cu. LL-37 also features in the broader cosmetic peptides comparison hub as one of the antimicrobial layer of an integrated skin-research approach. The general principle — combine compounds with complementary, not overlapping, mechanisms — is set out in our Peptide Blends Explained guide.

Does LL-37 cause inflammation?

It depends on context and concentration. At physiological concentrations in healthy skin, LL-37 is one of the regulators of well-controlled antimicrobial defence and does not produce visible inflammation. At pathologically elevated concentrations (rosacea, psoriasis) or with aberrant proteolytic processing (rosacea), it amplifies inflammatory cascades and contributes to disease pathology. In research formulations applied topically to wounds, the net effect is healing-promoting rather than inflammation-promoting because the timing and local concentration are matched to the wound-healing cascade.

Where do I find the foundational mechanism papers?

Three papers anchor the field. Sørensen 2001 (PMID 11389039) established the proteinase-3 cleavage that releases mature LL-37 from hCAP-18. Liu 2006 in Science (PMID 16497887) established the TLR2/1-driven vitamin-D-VDR-CAMP axis. Tan 2026 (PMID 42095322) provides the most current comprehensive mechanism review. The complete published literature is browsable at the PubMed search for “LL-37 cathelicidin”.

Does LL-37 need cycling?

No. Unlike receptor-agonist peptide families (GHRPs, GLP-1 analogues), LL-37 acts via direct membrane interaction and via multiple chemokine receptors with no documented receptor down-regulation on chronic exposure. Cycling is not required for tolerance. The general framework for which peptide classes need cycling (and which don’t) is covered in our Peptide Cycling Protocols guide.

Outbound research references in this guide: PMID 11389039 — Sørensen 2001 proteinase-3 cleavage · PMID 16497887 — Liu 2006 vit-D-CAMP axis (Science) · PMID 19299728 — Edfeldt 2009 vit-D rheostat · PMID 21149724 — Liu 2010 T-cell-vit-D · PMID 37480520 — 2023 LL-37 cream DFU RCT · PMID 38423213 — 2024 LL-37 TFEB autophagy diabetic wound · PMID 41791569 — 2026 cathelicidin + ceragenins wound · PMID 41862276 — 2026 LL-37 + bacterial DNA in dental biofilm · PMID 41916132 — 2026 LL-37 cancer cell migration · PMID 42003198 — 2026 AMPs in drug-resistant TB · PMID 42095322 — 2026 LL-37 intestinal disease mechanism · PubMed: all LL-37 papers · MedlinePlus — Skin conditions · CDC — Antibiotic use.

Written by

Sophie Chen

Pharmaceutical Content Researcher · 8 years experience

Sophie Chen is a pharmaceutical content researcher with 8 years covering generic medication access and clinical pharmacology. She specialises in international regulatory frameworks, bioequivalence standards, and patient-facing education on therapeutic drug classes. She is not a clinician.