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Terminus Peptides
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Research profile · Peptide

LL-37

Also known as Cathelicidin antimicrobial peptide

Early human — evidence level 3 of 4: Early human evidenceExperimental — UK regulatory status: Experimental — not authorised for human use in the UK

Overview

The only cathelicidin-derived antimicrobial peptide found in humans, and a genuine component of innate immunity.

Category
Peptide
Highest evidence level identified
Early human evidence
Last scientifically reviewed
20 August 2026
Last regulatory review
20 August 2026

Mechanism under investigation

LL-37 is the only cathelicidin-derived antimicrobial peptide found in humans, cleaved from a precursor protein and expressed in neutrophils, monocytes, epithelial cells and keratinocytes. It is a genuine component of human innate immunity rather than a foreign compound: it disrupts microbial membranes, neutralises bacterial endotoxin and acts as a signal recruiting immune cells. Its effects are strongly context-dependent — the same peptide is reported to be both anti-inflammatory and pro-inflammatory depending on concentration and cell type.

Research areas

  • Innate immunity
  • Wound repair models

These are fields in which the compound has been investigated. Listing a field is not a statement that anything was demonstrated within it.

Current evidence

In-vitro evidence

Cells, tissues or biochemical systems outside a living organism.

Extensive and high quality — the best-developed layer for this peptide. Membrane permeabilisation, biofilm dispersal, endotoxin neutralisation and receptor interactions are all well characterised.

Animal evidence

Studies in living non-human animals.

Present, including murine sepsis and inflammation models.

Human observational evidence

Studies observing people without assigning an intervention.

Present. Expression correlates with vitamin D status, and altered levels are described in psoriasis, rosacea and atopic disease — notably, sometimes as a driver of pathology rather than a benefit.

Clinical-trial evidence

Studies assigning an intervention to human participants.

Better than commonly assumed, but ultimately negative on its primary endpoint. A first-in-human trial in hard-to-heal venous leg ulcers reported accelerated healing at lower concentrations. The subsequent phase 2b trial in 148 patients across fifteen sites failed to meet its primary endpoint: complete wound closure was 26.5, 24.7 and 25.3 per cent across the two active arms and placebo. A post hoc subgroup of large wounds showed a nominal benefit, which is hypothesis-generating only.

Study limitations

  • The pivotal phase 2b trial was negative on its primary endpoint. The only favourable signal is a post hoc subgroup analysis, which carries a high risk of false positives.
  • Both clinical trials tested topical application to leg ulcers only. There is no clinical trial evidence supporting systemic administration for immune, antimicrobial or general wellness purposes.
  • Direct bactericidal activity requires relatively high concentrations, and its physiological importance at achievable tissue levels is actively debated.
  • The peptide is cytotoxic to many human cell types at concentrations within the physiologically relevant range, which complicates any assumption that more is better.
  • Much mechanistic work uses simplified membrane or single-cell-type systems that may not reflect integrated human physiology.

UK regulatory context

Experimental — not authorised for human use in the UK

A compound appearing in research literature that holds no UK authorisation for human use in any indication.

Source: The Human Medicines Regulations 2012, regulation 46 — prohibition on sale or supply of an unauthorised medicinal product (opens legislation.gov.uk in a new tab) (legislation.gov.uk)

Regulatory classification is jurisdiction-specific. A compound authorised elsewhere is not thereby authorised in the UK, and a supplier’s description of a substance does not determine how it is classified in law. See safety and regulation for the framework and the authoritative sources.

Safety and interpretation

In the two topical wound-healing trials the peptide was well tolerated, with mostly mild to moderate local reactions. That reassurance is confined to topical use on ulcers. The wider literature describes cytotoxicity to human cells at physiologically relevant concentrations and roles in driving inflammation in psoriasis and rosacea, so systemic exposure cannot be assumed benign on the basis of the topical data. That the body produces this peptide naturally says nothing about the safety of administering it.

References