LL-37: The Body’s Own Antimicrobial Peptide

LL-37 is a 37-amino-acid peptide your body produces as part of innate immunity. It is the only human cathelicidin — released by neutrophils and epithelial cells, and one of the first-line defences against microbes.

Being endogenous is what makes it interesting as a therapeutic candidate. It is also why "more of it" is not a straightforwardly good idea.

What it does

LL-37 is amphipathic — one face attracts water, the other repels it — which lets it insert into and disrupt bacterial membranes directly. That is a physical mechanism rather than a biochemical one, and it is why resistance to it develops less readily than to conventional antibiotics.

It also does more than kill microbes:

• Immune signalling. Recruits immune cells and modulates inflammatory response.

• Wound healing. Involved in re-epithelialisation and angiogenesis, which drives much of the therapeutic interest.

• Biofilm disruption. Reported activity against bacterial biofilms, which resist conventional antibiotics.

Why it is double-edged

The same properties that make LL-37 useful make it a problem in excess. It is implicated in inflammatory conditions where its activity contributes to disease rather than resolving it — psoriasis and rosacea are the most cited examples, where elevated cathelicidin activity is part of the pathology rather than the defence.

Membrane disruption is also not perfectly selective. At sufficient concentration, the mechanism that lyses bacterial membranes acts on host cells too.

Where development has gone

LL-37 and derived peptides have been investigated clinically, most substantially for wound healing — hard-to-heal ulcers, where both the antimicrobial and the repair-promoting properties are relevant at once.

The delivery route is central. Topical application to a wound puts the peptide where both mechanisms are wanted; systemic injection distributes an immunomodulatory, membrane-active peptide everywhere. Most of the clinical work is topical, and that is not incidental.

It shares that pattern with GHK-Cu, where the evidence is likewise concentrated on topical use while vials are sold for injection.

The vial math

LL-37 is supplied lyophilised, commonly in 5 mg vials, with figures discussed in micrograms to low milligrams.

The peptide calculator converts any vial and target into units.

Storage

Storage is the same as any reconstituted vial: 2–8 °C, protected from light, never frozen, and bounded by the shorter of peptide stability and the 28-day limit on bacteriostatic water. The bacteriostatic water guide covers the detail.

Frequently asked questions

Is LL-37 an antibiotic?

It is an antimicrobial peptide with a membrane-disruption mechanism, which differs from how conventional antibiotics work. That mechanism is why resistance develops less readily.

If the body makes it, is it safe?

Endogenous does not mean safe at any level. LL-37 is implicated in inflammatory skin conditions where excess activity is part of the problem.

Why is most research topical?

Because wound healing puts both the antimicrobial and repair properties exactly where they are wanted. Systemic delivery distributes a membrane-active immunomodulator throughout the body instead.