LL-37 (Cathelicidin Antimicrobial Peptide)

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What Is LL-37?

LL-37 is the active C-terminal 37-amino-acid peptide released by proteolytic cleavage of human cathelicidin antimicrobial peptide hCAP-18 — the only cathelicidin gene product in humans, encoded by the CAMP gene on chromosome 3. The peptide takes its name from its first two residues (Leu-Leu) and its length (37 residues). It belongs to the cathelicidin family of innate-immunity host-defense peptides found across most vertebrate lineages and represents the central effector molecule in the human cathelicidin arm of innate immunity, alongside the defensin family.

Inactive hCAP-18 proform is produced in neutrophil granules, in epithelial surfaces (skin keratinocytes, respiratory and gut epithelium), and in lower amounts by macrophages, NK cells, mast cells, B-cells, and γδ T-cells. Activation occurs by proteinase-3 cleavage (in neutrophils) or by kallikrein-5/kallikrein-7 (in skin), liberating the bioactive 37-mer that adopts a strongly amphipathic α-helical conformation in membrane-mimetic environments. The peptide carries a +6 net positive charge at neutral pH, with cationic lysine and arginine residues concentrated on one face of the helix and hydrophobic leucine, phenylalanine, isoleucine, and valine residues on the opposing face — the canonical “amphipathic α-helix” architecture that enables selective interaction with negatively-charged microbial membranes.

LL-37 combines two distinct host-defense modalities in a single peptide. Its direct antimicrobial activity spans Gram-positive bacteria (including methicillin-resistant S. aureus, MRSA), Gram-negative bacteria (including E. coli, K. pneumoniae, P. aeruginosa), enveloped viruses (HSV-1, influenza, RSV), fungi (Candida), and microbial biofilms. Its immunomodulatory activity includes binding and neutralisation of bacterial lipopolysaccharide (LPS) and lipoteichoic acid, chemotaxis of neutrophils / monocytes / T-cells / mast cells via formyl peptide receptor like-1 (FPRL1/FPR2), modulation of TLR signalling, suppression of LPS-induced cytokine storms, induction of angiogenesis through FPRL1 signalling on endothelial cells, and stimulation of keratinocyte migration in wound repair. Dysregulation of LL-37 is implicated in the pathogenesis of psoriasis (where excess LL-37 complexes with self-DNA to activate plasmacytoid dendritic cells), atherosclerosis, and certain cancers. LL-37 is not approved by the FDA, EMA, MHRA, or any other major regulator for human therapeutic use. The research-grade LL-37 sold here is supplied tylko do użytku laboratoryjnego and is not intended for human or veterinary administration.

Mechanism of Action — Membrane Disruption + Immunomodulation

LL-37 acts through three principal mechanisms documented in published research:

• Selective microbial membrane disruption via amphipathic α-helix insertion — In bulk aqueous solution LL-37 is largely unstructured, but on contact with a negatively-charged microbial membrane (rich in phosphatidylglycerol, cardiolipin, lipoteichoic acid, or LPS) it folds rapidly into an amphipathic α-helix. The cationic face engages with the anionic membrane surface; the hydrophobic face inserts into the lipid bilayer. At threshold peptide-to-lipid ratios, this drives formation of toroidal pores or “carpet”-style membrane disintegration, depolarising the microbial cell and disrupting essential transmembrane gradients. Mammalian cell membranes are protected by their zwitterionic outer leaflet (phosphatidylcholine, sphingomyelin) and the presence of cholesterol — providing a degree of microbial selectivity that distinguishes AMPs from broadly cytotoxic detergents.
• LPS neutralisation and TLR4 pathway modulation — LL-37 binds directly to bacterial lipopolysaccharide (LPS) with high affinity, sequestering it from the TLR4 / MD-2 / CD14 receptor complex. This blocks LPS-driven NF-κB activation, reduces downstream TNF-α / IL-6 / IL-1β release, and protects host tissue from sepsis-like cytokine storms during severe Gram-negative infections. The same property makes LL-37 a research tool for dissecting LPS-driven signalling.
• Immunomodulation via FPRL1 (formyl peptide receptor-like 1) and downstream signalling — LL-37 acts as a chemoattractant for neutrophils, monocytes, and T-cells through binding to FPRL1 (FPR2), a G-protein-coupled receptor expressed broadly on innate-immunity effector cells. The same receptor on endothelial cells mediates LL-37’s pro-angiogenic effect — stimulating endothelial-cell proliferation, migration, and tube formation. Keratinocyte migration during wound re-epithelialisation is also FPRL1-dependent. The peptide additionally engages purinergic P2X7 receptors on macrophages, contributing to inflammasome modulation.

A distinctive feature of LL-37 biology is the “sword vs shield” balance: at low concentrations the peptide is dominantly immunomodulatory and tissue-protective, while at high local concentrations the direct membrane-disruptive activity dominates. This concentration-dependent functional switching is one reason why LL-37 has therapeutic-research interest across both antimicrobial and wound-healing indications, and why detailed dose-response characterisation is critical in any in-vitro or in-vivo protocol.

Opublikowane zastosowania badawcze

LL-37 is used in laboratory research contexts that investigate:

• Antimicrobial-resistance research — broad-spectrum minimum-inhibitory-concentration (MIC) panels against MRSA, ESBL-producing Enterobacteriaceae, carbapenem-resistant strains, and biofilm-associated pathogens; AMP-development pipeline benchmarking
• Biofilm research — biofilm-prevention assays, established-biofilm disruption assays against P. aeruginosa, S. aureus, oraz K. pneumoniae — important in cystic-fibrosis and chronic-wound research contexts
• LPS / sepsis research — LPS-neutralisation assays, TLR4 signalling dissection, septic-shock cytokine-storm models
• Wound-healing and skin research — keratinocyte migration assays, dermal-fibroblast and endothelial wound-closure models; one of the primary research peptides in cutaneous wound-healing research
• Psoriasis pathogenesis research — LL-37 / self-DNA / plasmacytoid-dendritic-cell axis dissection (LL-37 is overexpressed in psoriatic skin and complexes with self-DNA to break tolerance via TLR9 in pDCs)
• Atherosclerosis research — LL-37 in plaque macrophages, oxidised LDL interaction, vascular-inflammation models
• Oncology research — paradoxical pro- and anti-tumour effects depending on tumour type (LL-37 is pro-proliferative in some cancers via FPRL1, anti-tumour in others through direct membrane disruption of tumour cells)
• Innate-immunity mechanistic research — FPRL1 signalling, P2X7 modulation, neutrophil extracellular trap (NET) biology, vitamin-D-mediated CAMP induction

For broader context on innate-immunity and host-defense peptide research, see KPV (α-MSH-derived anti-inflammatory tripeptide), BPC-157 (multi-pathway tissue-repair pentadecapeptide), and TB-500 (Thymosin Beta-4 fragment, broad tissue repair). Browse the full katalog peptydów badawczych w poszukiwaniu powiązanych związków.

Dostępne mocowania i stężenia

MedsBase stocks LL-37 in 5 mg lyophilized vials. Available in 10-vial or 20-vial pack formats with full reconstitution guidance:

LL-37 is supplied as the unmodified linear 37-mer free-acid form (no acylation, no PEGylation, no disulfide bridge). The peptide is sensitive to plastic adsorption — researchers should use low-binding tubes for stock storage and dilution. Working concentrations in published assays range from ~0.5 µg/mL in chemotaxis assays up to ~50 µg/mL in direct-killing antimicrobial assays.

How It Compares — LL-37 vs KPV

LL-37 and KPV are both used in innate-immunity research but operate at completely different scales and target different machinery. LL-37 is a full 37-residue host-defense peptide combining direct antimicrobial membrane disruption with FPRL1-mediated immunomodulation. KPV (Lysine-Proline-Valine) is a 3-residue C-terminal fragment of α-melanocyte-stimulating hormone (α-MSH) that acts as a focused anti-inflammatory and modest antimicrobial peptide through melanocortin-receptor pathway modulation.

For research focused on broad-spectrum antimicrobial activity, biofilm disruption, or membrane-pore mechanisms, LL-37 is the canonical reference peptide. For research focused on melanocortin-pathway anti-inflammatory signalling at the cellular level, KPV is the more selective tool. See also BPC-157 for tissue-repair-focused anti-inflammatory research and TB-500 for broad tissue-repair benchmarking.

Przechowywanie i rekonstytucja

Przed rekonstytucją: store lyophilized vials refrigerated at 2–8 °C in original packaging for short-term working stock. For long-term storage, freeze unopened vials at −20 °C. Lyophilized LL-37 is stable under refrigeration for up to 24 months and at −20 °C for up to 36 months. Avoid freeze-thaw cycles of the lyophilized powder. Like all cationic AMPs, LL-37 is prone to plastic adsorption — even small losses to standard polypropylene tubes can confound dose-response data. Use low-binding tubes (siliconised glass, Protein LoBind, or polypropylene pre-coated with bovine serum albumin) for stock storage and serial dilutions in low-protein assay buffers.

Procedura rekonstytucji: inject bacteriostatic water down the side wall of the vial (not directly onto the lyophilized cake). For a 5 mg vial, 1.0 mL of bacteriostatic water yields a 5 mg/mL working concentration; 2.0 mL yields a 2.5 mg/mL working stock. Swirl gently — do not vortex aggressively, as foaming entrains air and can disrupt helix folding. Allow the powder to dissolve fully (typically 1–2 minutes) before withdrawing. For applications sensitive to bacteriostatic agents (cell-culture experiments), reconstitute in sterile water or 0.01% acetic acid. Once reconstituted, store the vial at 2–8 °C and use within 14–28 days. Protect from light. Discard if cloudiness, particulates, or colour change appears.

Najczęściej zadawane pytania

Is LL-37 the same as cathelicidin?

LL-37 is the active C-terminal 37-amino-acid peptide released from human cathelicidin (the inactive proform hCAP-18, encoded by the CAMP gene). Cathelicidin is the family name and refers across many vertebrate species; LL-37 is the specific name of the active human cathelicidin peptide. Other names you may see in the literature — CAP-18 and FALL-39 — refer to the same molecule from different historical naming conventions.

How is LL-37 different from defensins?

LL-37 and the defensins (α- and β-defensins) are the two main families of mammalian antimicrobial peptides. Defensins are smaller, cysteine-rich, and adopt β-sheet structures stabilised by 3 disulfide bonds. LL-37 is a longer linear cationic peptide that adopts an amphipathic α-helix in membrane environments — with no disulfide bridge. Both classes share broad antimicrobial activity and immunomodulatory roles but operate through structurally distinct mechanisms.

What is the typical effective concentration of LL-37 in antimicrobial assays?

Published minimum inhibitory concentrations (MICs) for LL-37 against susceptible Gram-positive and Gram-negative pathogens generally range from 1 to 32 µg/mL depending on strain, assay buffer ionic strength, and biofilm vs planktonic format. Higher concentrations (50–100 µg/mL) are commonly used for direct membrane-disruption studies and biofilm-eradication assays. Immunomodulatory readouts (chemotaxis, LPS neutralisation, keratinocyte migration) typically use much lower concentrations (0.5–10 µg/mL). Determine dose ranges from peer-reviewed literature appropriate to your specific protocol.

Why does plastic adsorption matter for LL-37?

Cationic AMPs like LL-37 can adsorb significantly to standard polypropylene and polystyrene labware surfaces, especially in low-protein buffers. Losses of 30–80% to a single tube transfer have been documented in the literature for cationic peptides at low concentrations. This can produce systematic under-estimation of activity, particularly in dilution series for MIC determination. Use low-binding tubes, pre-coat tubes with BSA, or include carrier protein in dilution buffers as appropriate to the assay readout.

How does LL-37 distinguish microbial from mammalian membranes?

The selectivity arises from membrane composition. Microbial membranes (especially Gram-negative outer membranes and Gram-positive cytoplasmic membranes) are rich in negatively-charged lipids (phosphatidylglycerol, cardiolipin, LPS, lipoteichoic acid). Mammalian cytoplasmic membranes carry a zwitterionic outer leaflet (phosphatidylcholine, sphingomyelin) and a high cholesterol content that stabilises the bilayer. The cationic face of LL-37 preferentially engages the negatively-charged microbial surface; the cholesterol-stabilised mammalian membrane is much less susceptible to insertion. Selectivity is concentration-dependent — at very high local concentrations LL-37 can become cytotoxic to mammalian cells as well.

What is the “sword vs shield” model of LL-37 function?

The model describes the concentration-dependent functional switching of LL-37: at low concentrations (<5 µg/mL) the peptide is dominantly immunomodulatory and tissue-protective — chemotactic, pro-angiogenic, LPS-neutralising. At high concentrations (>20 µg/mL) the direct membrane-disruptive antimicrobial activity dominates. This dual nature underlies LL-37’s diverse roles in host defense and is one of the reasons careful dose-response characterisation is essential in any in-vitro or in-vivo research context.

What is the link between LL-37 and psoriasis?

LL-37 is markedly overexpressed in psoriatic skin lesions and binds avidly to self-DNA and self-RNA released from damaged keratinocytes. These LL-37 / self-nucleic-acid complexes activate plasmacytoid dendritic cells via TLR9 (DNA) and TLR7 (RNA), driving the IFN-α-rich autoimmune-like inflammation that characterises psoriasis. Targeting the LL-37 / pDC / TLR axis is an active area of psoriasis pharmacology research.

Why are some cancer studies pro-tumour while others are anti-tumour?

LL-37 has documented context-dependent effects on cancer. In some tumour types (ovarian, breast, lung, colorectal) elevated LL-37 expression correlates with worse outcome — likely through FPRL1-mediated pro-proliferative and pro-angiogenic signalling. In others (gastric, melanoma in some models) LL-37 has direct membrane-disruptive cytotoxic effect on tumour cells with weaker anti-tumour activity. The net effect depends on tumour type, local concentration, FPRL1 expression, and tumour-microenvironment composition.

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