Independent peptide research, reference & news No clinic, pharmacy, or telehealth affiliation
Subscribe
Immune Preliminary evidence

LL-37

LL-37 (human cathelicidin antimicrobial peptide)

Also known as: Cathelicidin LL-37, CAP-18 fragment, hCAP18

Written and reviewed by the Peptide.it editorial team Last reviewed June 2026 · Every claim is tier-rated and sourced

In plain language

LL-37 is the body's main cathelicidin, a natural antimicrobial peptide that is part of innate immunity. It is heavily studied in immunology for fighting microbes and modulating inflammation. Despite a large research base, it is not an approved therapy, and its biology in disease is complex (sometimes protective, sometimes harmful).

What it is explored for

LL-37 is one of the body's own first-line defenders, and that natural role makes it a rich subject for immunology research. It is studied for its broad antimicrobial activity and tissue-repair links, with the honest caveat that its biology is complex and it is not an approved therapy.

  • Immune system support and modulation
  • Broad antimicrobial defense
  • Wound and tissue repair support
  • Biofilm disruption in persistent conditions
  • Immune and inflammatory balance
  • Recovery in post-infectious protocols

These are areas of active interest and reported use, not proven outcomes. This peptide carries a preliminary evidence rating, see the evidence summary below for how strong the science actually is.

How it works

LL-37 is produced from the cathelicidin precursor and acts as both a direct antimicrobial and an immune-signaling molecule. Its roles are well studied at the laboratory level.

  • Direct antimicrobial action. Disrupts bacterial membranes and shows activity against bacteria, fungi, and some viruses in lab studies.
  • Immune modulation. Influences immune-cell recruitment, inflammation, and wound healing as part of innate immunity.
  • Context-dependent effects. In some conditions LL-37 appears protective, while in others (such as certain autoimmune and inflammatory diseases) it may contribute to pathology.

Most data are from cell and animal immunology research. There is no approved LL-37 therapy and its net effect depends heavily on context.

Evidence summary

LL-37 is one of the most studied human antimicrobial peptides, with a deep mechanistic and immunological literature. However, that research has not translated into an approved human therapy, and its dual protective/harmful roles complicate any therapeutic use, so it stays preliminary.

Reported safety & side effects

There is no established safety profile for LL-37 as a therapy. Because it can drive inflammation and has been linked to some autoimmune processes, therapeutic use is not straightforward.

Human safety dataNot established as a therapy
Inflammatory riskCan promote inflammation and is implicated in some autoimmune conditions
Long-term effectsUnknown

Frequently asked

Is LL-37 naturally in the body?

Yes. It is the main human cathelicidin and a normal part of innate immune defense, produced by skin and immune cells.

If it is natural and antimicrobial, why is it not a drug?

Its effects are context-dependent, and it can also drive inflammation and autoimmunity. That complexity, plus a lack of approved formulations and trials, keeps it experimental.