LL-37 Peptide: The Human Cathelicidin in Antimicrobial and Immune Research
LL-37 is the only human cathelicidin antimicrobial peptide, a 37-residue cationic peptide that both punctures microbial membranes and signals to the immune system. This research-use-only reference explains how LL-37 kills microbes, recruits immune cells through the FPR2 receptor, neutralizes bacterial endotoxin, and behaves differently at low versus high concentrations.
Research-use-only disclaimer: LL-37 supplied as a research chemical is intended strictly for in-vitro and laboratory research use and is not intended for human or veterinary use in that context. Every finding below is drawn from cell-culture or animal models and is described in hedged, mechanistic terms. Nothing here is medical advice.
TL;DR
LL-37 is the human cathelicidin, a 37-amino-acid cationic peptide cleaved from hCAP18 (the CAMP gene). It kills bacteria by disrupting their membranes, and it also acts as an immune signal: it recruits neutrophils, monocytes, and T cells through the FPR2 receptor, drives angiogenesis via VEGF, and binds bacterial LPS to blunt TLR4-driven inflammation. Its effect flips with concentration (anti-inflammatory low, pro-inflammatory high). Research use only.
Identity: only human cathelicidin; 37 residues; cleaved from hCAP18 (CAMP gene).
Antimicrobial: cationic, membrane-disrupting; broad activity in research models.
Immune: chemotaxis of neutrophils, monocytes, T cells via FPR2; VEGF-linked angiogenesis.
Endotoxin: binds LPS, blunting TLR4-driven cytokine release.
Concentration-dependent: anti-inflammatory at low levels, pro-inflammatory at high levels.
What Is LL-37?
LL-37 is the single human member of the cathelicidin family of antimicrobial peptides. It is a 37-amino-acid cationic peptide (its name comes from the two leucines at the start and its length) released by proteolytic cleavage from the C-terminus of the hCAP18 protein, the product of the CAMP gene. It is produced by neutrophils, epithelial cells of skin and mucosa, and other immune cells, placing it at the front line of innate defense.[1]
How Does LL-37 Kill Microbes?
LL-37 is cationic and amphipathic, so it is drawn to the negatively charged surface of bacterial membranes and inserts into them, breaking membrane integrity. Because this is a physical, membrane-level mechanism rather than a single enzyme target, classical resistance is harder for microbes to develop.[2] In research models it shows activity against Gram-positive and Gram-negative bacteria and some fungi and viruses.
Why it draws interest: a host-derived, membrane-active peptide is studied as a template for antimicrobial approaches where conventional antibiotics are losing ground.[3]
How Does LL-37 Modulate the Immune System?
LL-37 does more than kill. It recruits neutrophils, monocytes, and CD4+ T cells to sites of infection and injury by acting on the formyl peptide receptor FPR2 (also called FPRL1), and it promotes angiogenesis through FPR2-linked VEGF signaling.[1] That dual identity, direct antimicrobial plus immune messenger, is why LL-37 is studied as a "host defense peptide" rather than only an antibiotic.
How Does LL-37 Neutralize LPS (Endotoxin)?
LL-37 binds bacterial lipopolysaccharide (LPS, the endotoxin on Gram-negative bacteria) with high affinity. By sequestering LPS, it reduces LPS activation of TLR4 on macrophages and blunts the pro-inflammatory cytokine cascade that can drive sepsis in models.[1] This endotoxin-neutralizing property is a distinct research angle from its direct microbial killing.
Is LL-37 Anti-Inflammatory or Pro-Inflammatory?
Both, depending on concentration, which is the honest and important nuance. At low concentrations LL-37 tends to be anti-inflammatory, suppressing TNF-alpha release from LPS-stimulated macrophages. At high concentrations it can become pro-inflammatory.[1] Context (cell type, local level, other signals) shapes the outcome, so results do not reduce to a single "LL-37 is anti-inflammatory" claim.
What Does LL-37 Do in Wound-Healing Models?
In tissue-repair research, LL-37 is linked to faster wound closure through several routes at once: it promotes angiogenesis, stimulates the migration of keratinocytes and other cells, and is associated with collagen deposition.[3] These are model-based observations, and how they translate to controlled human outcomes remains an open, actively studied question.
| Function | Mechanism | Main model |
|---|---|---|
| Direct antimicrobial | Cationic membrane disruption | Bacterial/fungal cultures |
| Immune-cell recruitment | FPR2 (FPRL1) chemotaxis | Neutrophil/monocyte assays |
| Angiogenesis | FPR2-linked VEGF signaling | Endothelial cells |
| Endotoxin neutralization | LPS binding, reduced TLR4 activation | Macrophage assays |
| Wound repair | Migration, angiogenesis, collagen | Cell and animal wounds |
How is research-grade LL-37 characterized?
LL-37 is a long, cationic peptide, so identity and purity verification matter for reproducible immunology and antimicrobial work. Research-grade LL-37 is typically confirmed by reversed-phase HPLC for purity and mass spectrometry for identity, handled cold, and supplied for laboratory use only. At PrymaLab, research peptides are characterized with HPLC/MS verification and independent third-party testing. No specific lot data are asserted in this general reference.
Frequently Asked Questions
What is LL-37?
The only human cathelicidin antimicrobial peptide, a 37-residue cationic peptide cleaved from hCAP18 (CAMP gene), produced by epithelial and immune cells.
How does LL-37 work?
It disrupts microbial membranes directly and, separately, signals through FPR2 to recruit immune cells, drives angiogenesis, and binds LPS to reduce TLR4-driven inflammation.
Is LL-37 anti-inflammatory?
At low concentrations it tends to be anti-inflammatory; at high concentrations it can be pro-inflammatory. The effect is concentration- and context-dependent.
Is LL-37 approved for human use?
No. LL-37 reference material is for laboratory research only and is not a drug or treatment.
References
- Vandamme D, Landuyt B, Luyten W, Schoofs L. A comprehensive summary of LL-37, the factotum human cathelicidin peptide. Cell Immunol. 2012;280(1):22–35.
- Dürr UHN, 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.
- The human cathelicidin antimicrobial peptide LL-37 as a potential treatment for polymicrobial infected wounds. PMC. PMC3699762
- Decoding LL-37: structure and antimicrobial mechanisms. ScienceDirect. 2025. Journal
Final disclaimer: This article is an educational research reference. LL-37 is sold and studied for laboratory research use only and is not approved by any regulatory authority for human or veterinary use. Statements have not been evaluated by the FDA. Nothing here should be interpreted as medical advice.
Mechanistic descriptions are observations from cell and animal models that may not generalize. Always verify the legal status of any research compound in your jurisdiction before purchase or use.
