LL-37: What Researchers Need to Know About the Human Cathelicidin Peptide
Research overview of LL-37, the human cathelicidin: origin, mechanisms, wound healing and antimicrobial RCT data, reconstitution notes, and EU shipping.
LL-37 occupies an unusual position among research peptides. It is not a foreign synthetic construct but a genuinely human molecule, released from the hCAP18 precursor and present in neutrophils, epithelia and mucosal surfaces throughout the body. What makes LL-37 particularly interesting for researchers in 2026 is that, unlike many peptides discussed on this blog, it has actually been tested in controlled human trials (Grönberg 2014, a 2023 diabetic foot ulcer RCT, the 2023 oral COVID-19 trial by Zhao), which sets it apart from the predominantly preclinical data available for most peptides of this size.
Cathelicidin-derived antimicrobial peptide (37 amino acids). Researched for innate immunity, antimicrobial activity, and wound-healing pathways. ≥98% HPLC purity with Janoshik CoA.
Background: Origin and Sequence
LL-37 is the sole human cathelicidin, a 37-amino-acid peptide starting with two leucines (hence the name "LL"). It is cleaved by proteinase 3 from the 18 kDa cationic antimicrobial protein hCAP18, encoded by the CAMP gene on chromosome 3. The mature sequence is:
LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES
This amphipathic alpha-helix is highly cationic at physiological pH, which underlies both its membrane activity and its secondary immunomodulatory functions. Unlike BPC-157 or Thymosin Beta-4, LL-37 exists natively in the human body, constitutively expressed in keratinocytes, macrophages and neutrophil granules. Its expression is strongly induced by vitamin D via the VDR response element in the CAMP promoter, a link established in the mid-2000s that remains clinically relevant for interpreting LL-37 research.
Why Is LL-37 So Intensively Researched?
Three threads dominate the LL-37 literature: wound healing, antimicrobial resistance (AMR), and, more recently, viral inhibition including SARS-CoV-2.
On wound healing, Heilborn and colleagues showed in 2003 (J Invest Dermatol, PMID 12603850) that LL-37 is required for re-epithelialisation of human skin wounds. Low LL-37 expression was documented in chronic venous ulcers, providing a biological rationale for substitution. This line culminated in a Phase II randomised controlled trial by Grönberg and colleagues (Wound Repair Regen 2014;22:613-621, PMID 25041740) showing a roughly sixfold higher healing rate in venous leg ulcers with topical LL-37. A 2023 RCT in Archives of Dermatological Research extended this evidence to diabetic foot ulcers, again reporting enhanced healing versus placebo.
On the AMR axis, LL-37 is active against MRSA, VRE and the full ESKAPE pathogen panel, which has made it a reference molecule for antimicrobial peptide development. Keshri and colleagues review the field comprehensively in their 2025 Int J Antimicrob Agents paper (PMID 39643165), and a 2025 IJMS review (26(16):8103) discusses engineered LL-37 derivatives with improved therapeutic index.
Mechanisms of Action
Membrane Disruption Plus Immunomodulation
LL-37 acts through at least two distinct modes. At higher concentrations, the cationic amphipathic helix directly permeabilises bacterial membranes ("carpet" or toroidal-pore models). At sub-lethal concentrations, it functions as an immunomodulator, activating the STING pathway, recruiting neutrophils, shaping dendritic cell responses and influencing wound epithelial cell migration. Its transcription is tightly coupled to vitamin D status, which is why serum 25(OH)D is routinely reported in cathelicidin studies.
A 2023 J Med Virol report (Zhao et al., DOI 10.1002/jmv.29035) added a viral dimension: in a randomised oral LL-37 trial during the Omicron BA.5.1.3 wave, treatment shortened nucleic-acid clearance time, with mechanistic support for STING activation and direct interference with spike/ACE2 binding. A separate 2024 study documented TMPRSS2 inhibition by LL-37 in non-Omicron lineages.
The 2025 sepsis and acute lung injury literature has added yet another layer: Gao and colleagues (Toxins 2025;17(6):306, PMID 40559884) describe a ZBP1-autophagy axis through which LL-37 mitigates lung injury in animal sepsis models. This remains preclinical, but the mechanism is novel.
Quality Criteria
LL-37 is a long peptide (37 residues), and synthesis artefacts are a real issue. Researchers should insist on published analytical data rather than relying on a generic assurance.
Purity Testing
Research-grade LL-37 should reach at least 98% HPLC purity. A full Certificate of Analysis includes HPLC chromatogram, mass spectrometry to confirm the expected mass (4493.3 Da for the free acid form), peptide content corrected for counterions, and residual solvent data. At PeptidesDirect, LL-37 batches are independently tested by Janoshik Analytical, with the COA provided on request.
Storage Notes
LL-37 is more labile than small peptides like GHK-Cu or BPC-157. Lyophilised powder should be stored at -20 degC, ideally -80 degC for long-term archiving. After reconstitution, LL-37 is light-sensitive and prone to oxidation at the methionine residue; use amber or foil-wrapped vials, keep refrigerated (2-8 degC), and use within two to three weeks. Repeated freeze-thaw cycles should be avoided, so aliquoting is advisable.
EU shipping: For researchers in Europe, PeptidesDirect ships LL-37 from within the EU, which avoids customs, import duties and the degradation risk associated with prolonged uncooled transit from non-EU suppliers. Delivery typically takes two to three working days with tracking.
Reconstituting LL-37
The long sequence and methionine residue make careful reconstitution more important than with shorter peptides. For general background, see our peptide storage guide.
USP-grade sterile water with 0.9% benzyl alcohol - the standard solvent for reconstituting lyophilized peptides. Essential accessory for any peptide research. Each vial is sealed and ready to use.
Current Evidence (2023-2026)
Four papers are worth pointing to for anyone orienting themselves in the current LL-37 landscape.
Grönberg 2014 (Wound Repair Regen, PMID 25041740) remains the strongest controlled human data point. A Phase II RCT with 34 patients showed a sixfold higher healing rate in venous leg ulcers treated with topical LL-37 versus placebo, with a clear dose-response relationship.
Diabetic foot ulcer RCT 2023 (Arch Dermatol Res, DOI 10.1007/s00403-023-02657-8) replicated the wound-healing signal in a different chronic-wound population. The double-blind design and placebo control place this trial above most peptide literature methodologically.
Zhao 2023 (J Med Virol, DOI 10.1002/jmv.29035) is the only randomised human trial of oral LL-37 against SARS-CoV-2. The shortening of NAT clearance time and the proposed dual mechanism (STING plus S-protein/ACE2 interference) make it a reference study for the antiviral line.
Keshri 2025 (Int J Antimicrob Agents, PMID 39643165) provides the most up-to-date review of LL-37 against MRSA, VRE and ESKAPE pathogens, and should be the starting point for researchers framing LL-37 in the AMR context.
On the cautious side, the dual role of LL-37 in cancer biology (Zhang et al., PMC11000334) is worth noting. LL-37 is pro-angiogenic and can be tumour-promoting in some contexts while suppressing tumours in others. This duality means that extrapolation from a wound-healing or antimicrobial setting to oncology contexts is not straightforward.
Ordering LL-37
For a long and moderately labile peptide like LL-37, three things matter when choosing a supplier: an independent HPLC purity report (not just an internal claim), cold-chain handling documented end-to-end, and EU-based dispatch to minimise transit time. PeptidesDirect addresses all three.
Cathelicidin-derived antimicrobial peptide (37 amino acids). Researched for innate immunity, antimicrobial activity, and wound-healing pathways. ≥98% HPLC purity with Janoshik CoA.