LL-37 Research Guide: The Human Cathelicidin
By UK Peptide Lab Research Team•19 September 2026•8 min read
Key Takeaways
- LL-37 is the 37-residue, cationic, amphipathic C-terminal fragment of human cathelicidin hCAP-18, and the only human member of the cathelicidin family of antimicrobial peptides (Dürr et al., Biochim Biophys Acta, 2006).
- The peptide was first predicted as FALL-39 (Agerberth et al., Proc Natl Acad Sci USA, 1995), isolated from granulocytes (Gudmundsson et al., Eur J Biochem, 1996) and shown to be released from hCAP-18 by proteinase 3 (Sorensen et al., Blood, 2001).
- Research has examined broad-spectrum antimicrobial activity (Turner et al., Antimicrob Agents Chemother, 1998), wound healing and angiogenesis (Koczulla et al., J Clin Invest, 2003; Carretero et al., J Invest Dermatol, 2008) and epithelial immunomodulation, including self-DNA sensing (Lande et al., Nature, 2007).
- Human data are thin: one randomised trial of topical LL-37 in hard-to-heal venous leg ulcers reported safety but no difference from placebo at the highest concentration tested (Grönberg et al., Wound Repair Regen, 2014). No marketing authorisation exists anywhere. Supplied for in-vitro laboratory research only.
What is LL-37?
LL-37 is a 37-residue, cationic, amphipathic antimicrobial peptide that forms the C-terminal portion of human cathelicidin, hCAP-18. Its sequence is Leu-Leu-Gly-Asp-Phe-Phe-Arg-Lys-Ser-Lys-Glu-Lys-Ile-Gly-Lys-Glu-Phe-Lys-Arg-Ile-Val-Gln-Arg-Ile-Lys-Asp-Phe-Leu-Arg-Asn-Leu-Val-Pro-Arg-Thr-Glu-Ser, written LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES, with a molecular formula of C₂₀₅H₃₄₀N₆₀O₅₃, a molecular weight of 4493.3 g/mol and CAS number 154947-66-7. Eleven basic residues (six lysines, five arginines) against five acidic residues give a net charge of +6 at neutral pH, and the sequence contains no cysteine, methionine or tryptophan. We supply LL-37 5mg as lyophilised powder for in-vitro laboratory research only.
Discovery: from FALL-39 to LL-37
LL-37 was first predicted from a human bone-marrow cDNA library by Agerberth and colleagues (Proc Natl Acad Sci USA, 1995), who named the putative peptide FALL-39, reflecting its N-terminal Phe-Ala-Leu-Leu motif, its 39 residues and its conspicuous lack of cysteine residues. Gudmundsson and colleagues (Eur J Biochem, 1996) then isolated the mature peptide from human granulocytes and characterised the full gene, showing that the 39-residue precursor is trimmed to the 37-residue peptide now named for its two N-terminal leucines. Sorensen and colleagues (Blood, 2001) later identified proteinase 3 as the neutrophil enzyme that cleaves the inactive precursor hCAP-18 to release active LL-37 during degranulation.
Structure and Membrane Chemistry
In aqueous buffer LL-37 is largely disordered and prone to self-association, but in membrane-mimetic environments it folds into an amphipathic alpha-helix, with hydrophobic residues clustered on one face of the helix and basic residues on the other. The solution structures of LL-37 and its smallest antimicrobial fragment KR-12 in lipid micelles were reported by Wang (J Biol Chem, 2008). The +6 charge is the functional centre of gravity: it drives the peptide's association with the anionic phospholipid-rich membranes of bacteria over the zwitterionic membranes of mammalian cells, although that selectivity is relative rather than absolute. The absence of cysteine means there are no disulfide constraints, and the absence of methionine removes the oxidation liability that dominates handling guidance for many research peptides. The review by Dürr and colleagues (Biochim Biophys Acta, 2006) remains the standard reference for the field.
Antimicrobial Activity
The foundational activity study is Turner and colleagues (Antimicrob Agents Chemother, 1998), who reported that LL-37 from human neutrophils showed activity against Pseudomonas aeruginosa, including mucoid and antibiotic-resistant strains, Salmonella typhimurium, Escherichia coli, Listeria monocytogenes, Staphylococcus aureus and vancomycin-resistant enterococci. The proposed mechanism is membrane disruption: the amphipathic helix accumulates on the bacterial surface, permeabilises the cytoplasmic membrane and kills the cell. Later work extended the picture to anti-biofilm activity against established bacterial communities and to activity against certain enveloped viruses. Two honest qualifications matter for experimental design. Activity is attenuated in the presence of serum, a point discussed in the Dürr review (Biochim Biophys Acta, 2006), and most findings derive from in-vitro assays with standard laboratory strains.
Wound Healing and Angiogenesis
The wound-healing literature runs through three complementary studies. Koczulla and colleagues (J Clin Invest, 2003) reported that LL-37 promoted endothelial cell proliferation and, in model systems, new blood-vessel formation, establishing an angiogenic role for the peptide alongside its antimicrobial one. Shaykhiev and colleagues (Am J Physiol Lung Cell Mol Physiol, 2005) reported that LL-37 stimulated proliferation and wound closure in airway epithelial cells. Carretero and colleagues (J Invest Dermatol, 2008) examined skin: LL-37 promoted keratinocyte migration in vitro, and adenovirus-mediated LL-37 gene transfer improved wound healing in diabetic mice by increasing re-epithelialisation and granulation tissue formation. Across these studies the peptide appears to act on multiple cell types, epithelial, endothelial and immune, rather than through a single receptor. All are preclinical or cell-culture findings.
Epithelial Immunomodulation
A further literature positions LL-37 as an immunomodulator of epithelial and immune tissues rather than a simple antibiotic. The peptide is chemotactic for several immune cell types and modulates cytokine release from epithelial cells. The most mechanistically striking finding is from Lande and colleagues (Nature, 2007): in psoriasis, LL-37 forms complexes with self-DNA that deliver the DNA into plasmacytoid dendritic cells, activating Toll-like receptor 9 and driving type I interferon production. That study illustrates the double-edged character of the peptide, contributing to host defence in one context and, in another, to autoimmune inflammation. It also underlines how much of LL-37 biology is context-dependent rather than intrinsic.
The Human Evidence: Honest Limits
Honesty about the human evidence matters here, because the in-vitro literature is large and the human literature is not. The only randomised, placebo-controlled trial to date tested topical LL-37 in hard-to-heal venous leg ulcers (Grönberg et al., Wound Repair Regen, 2014). Treatment was safe and well tolerated, but the highest concentration tested showed no difference from placebo on the primary outcome, and the effects on healing-related predictors seen at the two lower concentrations were framed by the authors as warranting further investigation rather than as proof of efficacy. Beyond that single trial, human data consist of observational and correlational studies, many of them measuring endogenous LL-37 levels rather than administered peptide. LL-37 holds no marketing authorisation in any jurisdiction, no therapeutic claim can be made for it, and this guide therefore carries no dosing information and no human-use recommendations. The material is supplied for in-vitro laboratory research only.
Laboratory Handling
Store the lyophilised vial at -20°C, protected from light and moisture. Reconstitute by slowly injecting Bacteriostatic Water down the inner wall of the vial and swirling gently until dissolved; never shake or vortex. Two cautions are specific to LL-37: it adsorbs readily to plastic surfaces, so minimise dilution steps in plastic vessels, and it aggregates in solution, so work with cold diluents and prepare fresh working dilutions rather than storing them. Store the reconstituted solution at 2-8°C and use within 4 weeks. See the peptide reconstitution guide and the peptide storage guide for full methodology.
Sourcing in the UK
UK Peptide Lab supplies research-grade LL-37 5mg as lyophilised powder, supplier-tested, batch UKPL-9509 at 99.97% purity by HPLC, with the supplier certificate of analysis published on the product page and independent third-party verification pending. Same-day UK dispatch on orders placed before 2pm GMT, free Royal Mail Tracked shipping over £45. For in-vitro laboratory research use only, not for human consumption; purchasers must be 18 or over.
Related Products
Disclaimer: This article is for research and educational purposes only. All information provided is not intended as medical advice. UK Peptide Lab products are not for human consumption and are sold strictly for laboratory research use only.
Frequently Asked Questions
What is LL-37?
LL-37 is a 37-residue, cationic, amphipathic antimicrobial peptide that forms the C-terminal region of human cathelicidin hCAP-18. Its sequence is LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES, with a molecular formula of C₂₀₅H₃₄₀N₆₀O₅₃, a molecular weight of 4493.3 g/mol and CAS number 154947-66-7. It is the only human member of the cathelicidin family of antimicrobial peptides, and it holds no marketing authorisation in any jurisdiction. Supplied as lyophilised powder for in-vitro laboratory research only.
Does LL-37 have any human clinical data?
Very little. The only randomised, placebo-controlled trial to date tested topical LL-37 in hard-to-heal venous leg ulcers (Grönberg et al., Wound Repair Regen, 2014). Treatment was safe and well tolerated, but the highest concentration tested showed no difference from placebo on the primary outcome, and effects on healing-related predictors at the two lower concentrations were framed by the authors as warranting further investigation. Most human studies are observational and measure endogenous LL-37 levels rather than administered peptide.
How should LL-37 be reconstituted and stored?
Reconstitute by slowly injecting bacteriostatic water down the inner glass wall, then swirl gently until dissolved; never shake or vortex. The peptide adsorbs to plastic surfaces and aggregates in solution, so work with cold diluent and minimise plastic handling steps. Store lyophilised vials at -20°C protected from light and moisture, and hold reconstituted solution at 2-8°C, using within 4 weeks. LL-37 is supplied for in-vitro laboratory research use only.
References
- [1] FALL-39, a putative human peptide antibiotic, is cysteine-free and expressed in bone marrow and testis. Proc Natl Acad Sci USA (1995). View →
- [2] LL-37, the only human member of the cathelicidin family of antimicrobial peptides. Biochim Biophys Acta (2006). View →
- [3] An angiogenic role for the human peptide antibiotic LL-37/hCAP-18. J Clin Invest (2003). View →
- [4] Structures of human host defense cathelicidin LL-37 and its smallest antimicrobial peptide KR-12 in lipid micelles. J Biol Chem (2008). View →
- [5] Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial. Wound Repair Regen (2014). View →