LL-37 (Cathelicidin / hCAP18 fragment)
The principal human cathelicidin antimicrobial peptide — a key effector of innate immunity.
At a glance
What it is: The principal human cathelicidin antimicrobial peptide — a key effector of innate immunity..
Primary research applications:
- Antimicrobial / wound healing research
- Inflammatory and immune signaling research
- Topical wound and skin applications
Editorial summary: LL-37 is a foundational antimicrobial peptide of human innate immunity with extensive basic-science literature. Its translational profile is most established in topical wound and skin contexts; broader systemic use remains an active research frontier rather than an established clinical tool.
- Class / structure
- 37-amino-acid cationic alpha-helical peptide (cleaved from hCAP18)
- Half-life
- Tissue-context dependent; minutes in plasma
- First described
- 1995 (cloning of human CAP18 cDNA)
- Regulatory status
- Not FDA-approved; topical analogs in development
What is LL-37?
LL-37 is a 37-amino-acid cationic alpha-helical peptide derived from hCAP18 by proteinase 3 cleavage. Its name derives from the leucine-leucine residues at the N-terminus and its 37-amino-acid length.
Discovery and development
LL-37 is the C-terminal active fragment cleaved from the precursor protein hCAP18 (human cathelicidin antimicrobial protein, 18 kDa), the only cathelicidin in the human genome. It was first cloned in 1995 (Cowland et al.) and has since become one of the most studied antimicrobial peptides in mammalian biology, expressed by neutrophils, epithelial cells, and several other cell types as part of the innate immune barrier.
Mechanism of action
LL-37 has multiple, partly overlapping activities:
- Direct antimicrobial action — disrupts microbial membranes, especially bacteria and enveloped viruses.
- Immunomodulation — modulates dendritic cell function, neutrophil recruitment, and cytokine signaling.
- Wound healing — promotes keratinocyte migration, angiogenesis, and re-epithelialization.
The dual antimicrobial / immunomodulatory profile is part of why cathelicidins have attracted such broad translational interest.[1]
Pharmacokinetics
LL-37 is generated locally at sites of infection or injury, with rapid plasma turnover that reflects its role as a tissue-resident effector rather than a circulating hormone. Therapeutic interest centers on local delivery — topical, inhaled, or wound-bed application — rather than systemic dosing.
What the research shows
The peer-reviewed literature on LL-37 is summarized below across two tiers: human research (the highest standard), and preclinical / emerging research (animal models and early-stage human work).
Claims and the evidence behind them
This table summarizes commonly discussed claims and how the published evidence weighs in. The aim is clarity — supported claims, claims that look promising but need more data, and claims that outrun the science.
| Claim | What the evidence shows | Verdict |
|---|---|---|
| Has direct antimicrobial activity in vitro | Extensive literature | Supported |
| Promotes wound healing in topical applications | Animal models and small human trials | Supported |
| Is a generally safe systemic therapy | Systemic toxicity profile is incompletely characterized | Uncertain |
| Replaces antibiotics | Adjunctive in research; not a clinical substitute | Unsupported |
Reported user experiences
How the research describes administration
Most published research uses topical or local formulations. Systemic peptide formulations are limited by short plasma half-life and the molecule's potent immunomodulatory profile.
Editorial note
Administration details above describe how the peptide is given in published studies. We summarize this for educational completeness — these descriptions are not protocols, dosing recommendations, or instructions for personal use. Decisions about treatment require an appropriately licensed clinician.
Safety considerations and open questions
The takeaway
LL-37 sits at the heart of modern antimicrobial-peptide research — a foundational human innate-immune effector with rich biology and a credible if incomplete translational pathway. Its near-term clinical relevance is most likely in topical wound and skin applications; a broader systemic role remains an active research question.
Frequently asked questions
Is LL-37 the same thing as cathelicidin?
LL-37 is the active fragment cleaved from hCAP18, the human cathelicidin precursor. "Cathelicidin" can refer to the broader gene family or, in human contexts, specifically to LL-37.
Does vitamin D affect LL-37?
Yes. The vitamin D receptor regulates cathelicidin expression in monocytes and keratinocytes — one mechanism by which vitamin D status connects to innate immunity.
References
- Dürr UH, Sudheendra US, Ramamoorthy A. LL-37, the only human member of the cathelicidin family of antimicrobial peptides. Biochim Biophys Acta. 2006;1758(9):1408-1425. https://pubmed.ncbi.nlm.nih.gov/16716248/
- Gronberg A, et al. 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;22(5):613-621. https://pubmed.ncbi.nlm.nih.gov/25041618/