Introduction to LL-37

LL-37 is the sole human cathelicidin, a family of host defence peptides that form a critical component of innate immune defence. It is derived through proteolytic cleavage of the 18 kDa protein hCAP18 (human Cationic Antimicrobial Protein 18), which is stored in neutrophil secondary granules and secreted by epithelial cells in response to infection or injury.

The name LL-37 reflects its first two leucine residues and its 37-amino acid length. Its sequence, LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES, encodes an amphipathic alpha-helical structure that enables both microbial membrane disruption and immune cell signalling through G-protein coupled receptors, including FPRL-1/FPR2.

For research use only. Not intended for human consumption. All findings referenced here derive from in vitro cell-based or animal pre-clinical models.

Antimicrobial Mechanism in Cell Models

Membrane Disruption

LL-37 exerts its antimicrobial activity primarily through disruption of bacterial membrane integrity. At sub-micromolar concentrations, LL-37 inserts into negatively charged bacterial membranes (rich in phosphatidylglycerol and cardiolipin) via its cationic face, forming toroidal pores or carpet-like defects that depolarise the membrane and allow ion leakage.

In Staphylococcus aureus biofilm models, LL-37 at 2–8 μg/mL concentrations has been shown to reduce colony-forming units by 2–4 log10 and disrupt established biofilm structure through destabilisation of the biofilm matrix. Similar biofilm dispersal activity has been documented against Pseudomonas aeruginosa in CF airway epithelial models.

Endotoxin Neutralisation

Beyond direct bacterial killing, LL-37 binds lipopolysaccharide (LPS) and lipoteichoic acid (LTA) with nanomolar affinity, sequestering these inflammatory ligands before they can engage Toll-like receptors (TLR4/TLR2). In macrophage cell cultures stimulated with LPS, LL-37 pre-treatment (5 μg/mL) reduced TNF-α and IL-6 secretion by approximately 60–70%, demonstrating an anti-inflammatory effect independent of its direct antimicrobial action.

Immunomodulatory Properties

Dendritic Cell Maturation

LL-37 enhances dendritic cell (DC) maturation and antigen presentation capacity in vitro. In monocyte-derived DC cultures, LL-37 (10 μg/mL) upregulated CD80, CD86, and HLA-DR expression and promoted IL-12p70 secretion, shifting the DC phenotype toward a Th1-polarising profile. This may help explain the role of cathelicidins in bridging innate and adaptive immunity.

Macrophage Polarisation

In THP-1 macrophage cultures, LL-37 modulated M1/M2 polarisation dynamics: at low concentrations (1–5 μg/mL), it promoted phagocytic activity and M1 markers (iNOS, IL-12); at higher concentrations (10–20 μg/mL), it suppressed excessive inflammation by reducing NLRP3 inflammasome activation and IL-1β secretion. This dose-dependent bidirectional immunomodulation positions LL-37 as a context-sensitive immune regulator rather than a simple pro-inflammatory signal.

Mast Cell and Neutrophil Activation

LL-37 activates mast cells via FPRL-1 receptor engagement, triggering chemokine release and supporting neutrophil recruitment to sites of infection. In human neutrophil cultures, LL-37 enhanced FcγR-mediated phagocytosis and NET (neutrophil extracellular trap) formation, two mechanisms important in bacterial clearance.

Wound Healing and Tissue Repair Models

Keratinocyte Migration and Proliferation

In scratch assay models using human HaCaT keratinocytes, LL-37 at 1–10 μg/mL significantly accelerated wound closure through EGFR transactivation and PI3K-Akt pathway stimulation. LL-37 also promoted keratinocyte proliferation in a concentration-dependent manner and enhanced E-cadherin expression, supporting epithelial sheet formation.

Angiogenesis in Endothelial Models

HUVEC (Human Umbilical Vein Endothelial Cell) tube formation assays demonstrate that LL-37 (2–10 μg/mL) promotes angiogenesis through FPRL-1/Akt/ERK pathway activation. LL-37 also induces VEGF secretion from fibroblasts, creating a paracrine loop that may contribute to improved vascularisation in wound beds.

Stability and Storage

LL-37 is a 37-residue linear peptide with no disulfide bridges, making it structurally simpler than many folded proteins. Key stability considerations for research programmes:

  • Protease sensitivity: LL-37 is susceptible to serine proteases (including chymotrypsin and thermolysin) present in serum; experiments in serum-containing media may require high-serum controls or use of protease inhibitor cocktails
  • Aggregation at high concentrations: Above 50 μg/mL in low-salt buffers, LL-37 can self-aggregate into amyloid-like fibrils; use phosphate-buffered saline (150 mM NaCl) for stock preparation
  • Storage: Lyophilised LL-37 at -20°C for up to 24 months; reconstituted solutions at -80°C in aliquots to prevent freeze-thaw degradation
  • Purity verification: HPLC ≥99% and MALDI-TOF or ESI-MS to confirm MW of 4493.3 Da

Research Formats at Stackpure

Stackpure offers LL-37 in three research-grade formats:

All Stackpure LL-37 is verified by HPLC (+99% purity) and mass spectrometry confirmation, with an independent Certificate of Analysis accompanying every batch.

Key References

  • Vandamme D et al. (2012). A comprehensive summary of LL-37, the factotum human cathelicidin peptide. Cellular Immunology, 280(1):22–35.
  • Braff MH et al. (2005). Structure and function of human defensins. Biochemistry, 44(44):14609–14619.
  • Heilborn JD et al. (2003). The cathelicidin anti-microbial peptide LL-37 is involved in re-epithelialization of human skin wounds and is lacking in chronic ulcer epithelium. Journal of Investigative Dermatology, 120(3):379–389.
  • Wang G. (2014). Human antimicrobial peptides and proteins. Pharmaceuticals, 7(5):545–594.

All content is for in vitro research reference only. Not for human or veterinary use. Not evaluated by FDA or any regulatory authority.