Description
LL-37 is the only human cathelicidin — a 37-amino acid amphipathic alpha-helical peptide cleaved from its 18-kDa precursor protein hCAP18 by proteinase 3. Its name reflects both its length and the two leucine residues at its N-terminus. Produced by neutrophils, macrophages, mast cells, and epithelial cells as part of the first-line innate immune response, LL-37 operates through direct membrane disruption of microbial lipid bilayers via electrostatic interaction with negatively charged phospholipid head groups. Beyond direct antimicrobial activity, it modulates innate immune signaling through LPS endotoxin neutralization, immune cell chemotaxis, and biofilm disruption — a multi-functional profile that makes it a central research tool in specialty research peptide innate immunity models.
Key Characteristics
- Only human cathelicidin identified — while defensins represent a multi-member family of human antimicrobial peptides, LL-37 is the sole cathelicidin, giving it a unique position in human innate immunity research and making it the reference compound for studying cathelicidin biology across species
- Direct membrane disruption operates through amphipathic helix formation — in contact with negatively charged bacterial membranes, LL-37 adopts an alpha-helical conformation that embeds into the lipid bilayer; it demonstrates two distinct interaction pathways depending on membrane lipid composition, producing either pore formation or nanofibre-mediated membrane extraction
- Dual pro- and anti-inflammatory activity is a distinctive and mechanistically complex feature — LL-37 can both amplify and suppress inflammatory signaling depending on concentration and cellular context, which requires careful experimental design when used in inflammation research models
- Unlike Thymosin Alpha 1, which activates innate immunity through Toll-like receptor signaling on dendritic cells, LL-37 acts through direct membrane interaction and endotoxin neutralization — two compounds that probe innate immune defense through mechanistically independent routes
- Cell-penetrating properties allow LL-37 to cross eukaryotic plasma membranes through lipid raft domains, enabling intracellular signaling that extends its research relevance beyond extracellular antimicrobial activity into intracellular TLR activation and immune modulation contexts
Handling and Storage
Store as lyophilized powder at -20°C, away from heat, moisture, and light. LL-37 is susceptible to proteolytic degradation once reconstituted. Reconstitute in sterile water immediately before use, store reconstituted peptide at 2–8°C, and use within the same experimental session where possible. Avoid repeated freeze-thaw cycles.
FAQs
What is LL-37?
LL-37 is the only human cathelicidin antimicrobial peptide — a 37-amino acid amphipathic alpha-helix cleaved from the hCAP18 precursor by proteinase 3. It is produced by multiple innate immune cell types and acts through direct disruption of microbial lipid bilayers, LPS endotoxin neutralization, biofilm dissolution, and immune cell chemotaxis recruitment. Its dual role as a direct antimicrobial agent and an immunomodulator makes it a central research tool in innate immunity studies.
How does LL-37’s membrane disruption mechanism work?
LL-37 carries a net positive charge that enables electrostatic attraction to negatively charged bacterial membrane phospholipids. Upon contact, it adopts an amphipathic alpha-helical structure that embeds into the lipid bilayer. The mode of disruption depends on membrane lipid composition — unsaturated phospholipid bilayers trigger pore formation, while saturated phospholipid membranes produce nanofibre-mediated lipid extraction. This mechanistic duality reflects LL-37’s capacity to disrupt structurally diverse bacterial membranes through different physical interaction pathways.
Why does LL-37’s dual pro- and anti-inflammatory activity matter for research design?
LL-37 does not have a fixed inflammatory signaling direction — it can amplify or suppress inflammatory responses depending on concentration, cell type, and the specific signaling context. At the sites of infection, high local concentrations produce a strong pro-inflammatory response that recruits immune cells. At lower concentrations, anti-inflammatory effects predominate. Researchers designing LL-37 experiments must account for this concentration-dependent duality when interpreting cytokine output data, as the same compound can produce opposing downstream effects under different experimental conditions.
