What Is LL-37? A Cathelicidin Antimicrobial Peptide Overview

LL-37 is the only human cathelicidin-derived antimicrobial peptide — a 37-amino-acid cationic, amphipathic peptide cleaved from the hCAP18 precursor protein. It is one of the most extensively studied host-defense peptides in laboratory research, where it is investigated for antimicrobial, immunomodulatory, and innate-immunity signaling activity.

Research-use-only (RUO) note: LL-37 is referenced here strictly as a subject of preclinical, in-vitro, and animal research. It is not a drug, supplement, or therapy, and nothing below describes effects in humans.

Quick facts

• Class: cathelicidin antimicrobial peptide (host-defense peptide)
• Length: 37 amino acids; cationic (net charge ~+6), amphipathic α-helix in membrane environments
• Precursor: hCAP18 (human cationic antimicrobial protein, 18 kDa)
• Origin: the only cathelicidin family member found in humans
• Research focus: antimicrobial activity & immunomodulation / innate-immune signaling

What is LL-37?

LL-37 is a small cationic peptide and the sole human member of the cathelicidin family of antimicrobial peptides. Its name comes from its 37-residue length and the two leucine (“LL”) residues at its N-terminus. The peptide is generated by enzymatic cleavage of the C-terminal domain of its precursor protein, hCAP18, which also contains an N-terminal signal sequence and a conserved cathelin-like pro-domain. In laboratory characterization, LL-37 is unstructured in water but folds into an amphipathic α-helix when it contacts lipid membranes — an arrangement central to how researchers study its interactions with microbial structures.

What does the research show?

Across the published literature, LL-37 is frequently described as the best-studied human antimicrobial peptide, valued in research for its multifunctional behavior within innate immunity (Zeth & Sancho-Vaello, 2021). In in-vitro models, investigators report activity against a broad range of bacterial and other microbial targets, alongside an apparent capacity to interact with bacterial endotoxin (lipopolysaccharide) and to influence immune-cell signaling in cultured systems. A 2025 review summarizing the experimental record notes that LL-37 has been studied for multiple, parallel mechanisms by which it may limit microbial spread in laboratory and animal models (Svensson & Nilsson, 2025). These are preclinical research observations only.

Mechanisms studied in the lab

• Microbial membrane disruption: biophysical studies (solid-state NMR, molecular-dynamics simulations) indicate LL-37 binds microbial membrane surfaces and perturbs them, with evidence favoring a toroidal-pore / carpet-like mode of disruption over a barrel-stave pore (Bhattacharjya, Zhang & Ramamoorthy, 2024).
• Structural plasticity: its secondary structure and oligomeric state shift with lipid, pH, salt, and ion conditions, which researchers correlate with adaptation to different bacterial target structures.
• Immunomodulatory signaling: in cell-based assays, LL-37 is studied for endotoxin (LPS) binding and for effects on immune-cell chemotaxis and activation.

Research status

LL-37 is supplied and discussed for research use only (RUO). It is not approved by the FDA for the diagnosis, treatment, cure, or prevention of any disease, and is not intended for human or veterinary use, consumption, or administration. All findings referenced here come from controlled laboratory and animal studies.

Related research peptides

If you are exploring host-defense and signaling peptides for laboratory work, browse the full research peptide catalog. You may also find these overviews useful: What is KPV? (a tripeptide studied in anti-inflammatory research) and What is BPC-157? (a peptide studied in tissue-repair and gut-related preclinical research).

FAQ

Is LL-37 the same as cathelicidin? LL-37 is the active antimicrobial peptide derived from the human cathelicidin precursor hCAP18. It is the only cathelicidin-family peptide identified in humans, so the terms are often used interchangeably, though “cathelicidin” technically refers to the broader precursor/family.

What is hCAP18? hCAP18 is the 18-kDa precursor protein that LL-37 is cleaved from. It includes a signal peptide, a cathelin-like pro-domain, and the C-terminal LL-37 sequence released by enzymatic processing.

Can I use LL-37 for health or infection purposes? No. LL-37 is a research-use-only material. It is not a medicine or supplement, has no approved human use, and the laboratory findings described here do not translate into any human benefit or application.

References

1. Svensson D, Nilsson BO. Human antimicrobial/host-defense peptide LL-37 may prevent the spread of a local infection through multiple mechanisms: an update. Inflamm Res. 2025.
2. Bhattacharjya S, Zhang Z, Ramamoorthy A. LL-37: Structures, Antimicrobial Activity, and Influence on Amyloid-Related Diseases. Biomolecules. 2024.
3. Zeth K, Sancho-Vaello E. Structural Plasticity of LL-37 Indicates Functional Adaptation to Bacterial Target Structures. Int J Mol Sci. 2021.

For research use only. Not for human or veterinary use; not a drug, supplement, food, or cosmetic. Statements have not been evaluated by the FDA.