At a glance
| Length | 37 amino acids |
|---|---|
| Precursor | hCAP18 |
| Functions studied | Antimicrobial defense and immune-cell signaling |
| Clinical formulation | Topical ropocamptide research |
| Phase IIb result | No significant overall ulcer-healing improvement |
Overview
LL-37 forms part of innate defense at epithelial surfaces and in immune cells. Its name reflects two starting leucines and a 37-residue sequence. Biological studies show actions extending beyond direct microbial membrane effects, including recruitment of immune cells and effects on wound-related signaling. These activities motivated development of topical ropocamptide for hard-to-heal venous ulcers. The clinical record is mixed: an early small study was encouraging, whereas the later phase IIb trial did not establish benefit across the full treated population. Evidence from local wound application does not validate injected LL-37 for chronic infections, inflammatory disorders, or nonspecific immune support.
How it works
LL-37 is generated from hCAP18 by proteolytic processing and interacts with microbial membranes and host signaling systems. Primary experiments showed recruitment of leukocytes through formyl peptide receptor-related signaling. Such pleiotropic activity can contribute to defense and repair but can also intensify inflammation in the wrong setting. Antimicrobial activity in a laboratory assay does not define a safe systemic concentration or clinical effectiveness against an infection.
What the venous-ulcer trial found
The HEAL LL-37 phase IIb trial studied topical LL-37 with compression care in 148 treated participants. The overall population did not show significantly improved healing compared with placebo. A post hoc large-ulcer subgroup suggested possible benefit, but that finding requires a prospectively designed confirmatory study rather than being presented as established efficacy.
Supporting sources [1]
Human defense biology is not a dosing study
Experiments identified LL-37 as a cleavage product of hCAP18 and showed its ability to attract human immune cells. These findings explain why researchers study it, but endogenous regulated release differs from administering a manufactured peptide. Local concentration, tissue context, and inflammatory state may change the direction and magnitude of its effects.
Systemic safety remains unresolved
FDA highlights possible immune reactions and impurity-characterization problems in compounded LL-37, along with insufficient human safety information for proposed uses. It also notes concerning nonclinical findings involving reproduction and tumor-related behavior in some tissues. These findings should not be converted into a precise human risk estimate, but they rule out casual reassurance.
Supporting sources [4]
Can topical results justify injections for infection?
No. The clinical trial used application to venous ulcers alongside compression, not systemic treatment of an infection. Different routes create different exposure and safety questions. Neither a favorable cell-culture antimicrobial result nor the peptide’s natural presence establishes an approved or proven injected treatment.
Reading this profile
Jurisdiction: United States: no FDA-approved LL-37 medicine; topical clinical research does not establish systemic use.. Molecular class: Endogenous 37-amino-acid host-defense peptide.
This profile was written with AI-assisted research and checked against the linked sources. It has not been represented as a clinician’s review. Evidence summaries describe the cited studies and products; they do not establish that a separately purchased preparation is equivalent.
Sources & references
Follow the original material. Product labels define specific formulations and uses; trial registration describes a study and does not by itself establish benefit.
- HEAL LL-37 randomized phase IIb venous-ulcer trial ↗Original research · Checked 2026-10-27
- LL-37, the neutrophil granule- and epithelial cell-derived cathelicidin, utilizes formyl peptide receptor-like 1 (FPRL1) as a receptor to chemoattract human peripheral blood neutrophils, monocytes, and T cells. ↗Original research · Checked 2026-10-27
- Human cathelicidin, hCAP-18, is processed to the antimicrobial peptide LL-37 by extracellular cleavage with proteinase 3. ↗Original research · Checked 2026-10-27
- FDA — bulk substances with potential significant safety risks ↗Regulatory source · Checked 2026-10-27