Research guides

LL-37 cathelicidin: what the research says

The only cathelicidin humans make, with a physical antimicrobial mechanism and a published randomised trial in venous leg ulcers. Also genuinely double-edged.

Available in the catalogue

Supplied as research material. Sizes and pricing are on the product page. Availability is not a statement about what a compound does.

  • LL-37

    Immune & Anti-Inflammatory

LL-37 is not a designed compound. It is a peptide the human immune system already makes, which changes the shape of its literature: there is a large body of work on what it does physiologically, and a much smaller body on what happens when it is supplied as a therapeutic.

What the molecule is

A 37-amino-acid peptide produced by human immune and epithelial cells — the only cathelicidin found in humans, cleaved from the precursor hCAP-18.

A physical mechanism, and what follows from it

It kills bacteria by disrupting their membranes. That is a physical mechanism rather than a biochemical one aimed at a specific protein target, and the practical consequence is that resistance develops slowly — there is no single enzyme a bacterium can modify to escape it. That property is the reason host defence peptides attract interest as an antimicrobial strategy at all.

It is also a signalling molecule in its own right, recruiting immune cells and influencing wound closure, which is why the literature generally calls it a host defence peptide rather than simply an antibiotic.

The human trial

A randomised placebo-controlled clinical trial published in 2014 examined treatment of hard-to-heal venous leg ulcers and reported that it was safe and effective at enhancing healing in that population. For a compound in this catalogue, a randomised placebo-controlled trial with a clinical endpoint is a strong piece of evidence, and it is worth knowing it exists.

The other half of the literature

Cathelicidin biology is not uniformly benign. The same peptide has been implicated in inflammatory pathology as well as in host defence, which is why review articles describe it as pleiotropic rather than protective. A molecule that recruits immune cells does so whether or not the recruitment is wanted, and the published work on its role in inflammatory conditions is part of its evidence base rather than a caveat to it.

What studies reported

Each entry states what a study examined and the model it used. Nothing below describes an outcome for a person.

Everything below is drawn from published research, and each entry names the model the study used. Approval status varies by compound and by country, and nothing described here is supplied as a medicine or for use in a person.

  1. Grönberg et al. (2014)Wound Repair and Regeneration · 22(5):613–21

    Tested treatment of hard-to-heal venous leg ulcers, reporting that it was safe and effective in enhancing healing against placebo.

    human, randomised placebo-controlled clinical trial Source

  2. Fabisiak et al. (2016)Pharmacological Reports · 68(4):802–8

    A review of the peptide's antimicrobial activity and its wider immunological roles, describing it as pleiotropic rather than single-purpose.

    review of in vitro and in vivo work Source

Adverse and null findings reported

No dedicated safety study has been published for this compound. That is not a finding that none exists — it means the question has not been asked in print, and the gaps below say so.

What the research does not establish

An absence cannot be cited, so these are stated plainly. They are the part of the picture that silence would otherwise hide.

  • The `adverse` list is empty in the sense of dedicated safety publications. That is not the same as an absence of concern: the review literature describes this peptide as pleiotropic and implicates cathelicidin biology in inflammatory pathology as well as host defence, and those reports sit in the mechanism literature rather than in a safety study.
  • The randomised evidence is one trial, in one indication, applied to a wound. Nothing published supports reading it across to any other route or context.
  • It holds no marketing authorisation in any jurisdiction despite the positive trial, and no phase 3 programme has been published.
  • Host defence peptides in general have struggled to translate from laboratory antimicrobial activity into approved medicines, and the reasons — stability, toxicity to host cells at higher concentrations, cost — are class problems that apply here.
  • Its physiological role means that supplying more of it is a different intervention from most compounds in this catalogue, and the consequences of doing so systemically have not been characterised in published human work.

Common questions

What does LL-37 do?
It kills bacteria by physically disrupting their membranes, and it acts as an immune signalling molecule that recruits cells and influences wound closure. It is the only cathelicidin humans produce.
Has LL-37 been tested in humans?
Yes. A randomised placebo-controlled trial published in 2014 examined hard-to-heal venous leg ulcers and reported it was safe and effective at enhancing healing in that population.
Why is resistance said to develop slowly?
Because the mechanism is physical rather than biochemical. Disrupting a membrane is not a specific protein target a bacterium can modify its way around, which is the general argument for host defence peptides as an antimicrobial strategy.
Is LL-37 purely protective?
No, and the review literature is explicit about it. Cathelicidin biology has been implicated in inflammatory pathology as well as in host defence, which is why the peptide is described as pleiotropic.
Is LL-37 an approved medicine?
No, in any jurisdiction. It is supplied here as a laboratory reagent for in-vitro research and not for human or veterinary use.

Compounds covered

The reference page for each compound this article discusses.

Related articles

All guides