LL-37: the body's own antibiotic, with two faces

The same molecule that clears intruders can also keep inflammation burning, and that is exactly where the scientific question sits.

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The same molecule that clears intruders can also keep inflammation burning. That is exactly where the scientific question sits.

MVMichel van der VeenRegistered Nurse · Science Editor, Peptalis Sources checked via PubMed · 7 referencesReviewed August 2026 · 8 MIN READ In short
  • LL-37 is cut out of a larger precursor protein, hCAP-18, and counts 37 amino acids.
  • The best-understood mechanism is physical: the two-sided coil opens holes in the outer layer of microbes.
  • The same peptide also signals to the body's own cells: during wound healing, and during inflammation that persists.
  • What stays scarce: controlled human studies that separate those roles.

LL-37 is the body's own antibiotic in humans. Skin cells and immune cells make it, but not as a finished molecule. It first sits hidden inside a larger precursor protein, hCAP-18. A stretch of 37 amino acids is cut out of it; that loose stretch is the active peptide. It starts with two leucines, L and L, and counts 37 building blocks. Hence the name.

37amino acids in the active peptidehCAP-18precursor protein2,518PubMed publications · as of Aug 2026

The shape explains almost everything

In water LL-37 folds into a coil with two sides: one side that attracts water and one side that attracts fat. That two-sided shape fits precisely into the fatty outer layer of a bacterium. There the peptide wedges itself inward and opens holes in the bacterial wall. The bacterium leaks empty and dies. That is the best-understood mechanism of action: LL-37 punctures microbes and clears them directly (Xhindoli et al., 2016, PMID 26556394).

Two-sided coil · three functional routes · outcome depends on context In human skin present in a healing wound and absent in chronic wounds that fail to close (observational, Heilborn et al., 2003).No controlled human studies with administered LL-37. Raised presence has also been described in rosacea and psoriasis.

More than killing bacteria

It does more than kill bacteria. It also sends signals to the body's own cells. At a wound it draws immune cells in, prompts cells to divide so the wound closes sooner, and helps new blood vessels form. Because it arranges so many different things at once, a well-known review calls LL-37 a “factotum”, a jack of all trades (Vandamme et al., 2012, PMID 23246832). In human skin that role is clearly visible: in a healing wound LL-37 is present, and in chronic wounds that will not close it is missing (Heilborn et al., 2003, PMID 12603850; human observational).

Two faces

And here the interesting part begins: the same molecule has two faces. In the right amount and at the right place LL-37 is a helper: it clears intruders and supports tissue repair. But when there is too much of it, or when it turns up where it does not belong, it flips. It then keeps the immune response switched on and drives inflammation. In skin conditions such as rosacea and psoriasis exactly that pattern is described: an excess of, or badly processed, LL-37 that keeps prodding the immune system (Schiffmann et al., 2021, PMID 34163212; human observational). The same signals that call for help at a wound stoke, in these conditions, a fire that no longer goes out.

So LL-37 is not simply “good”. It balances on the edge between defence and damage, and which way it tips depends on the amount, the shape and the context. That balance is what makes it a compelling starting point for research: the open question is what decides for one face or the other.

Where the research is heading

More recent work tries to steer those functions, for instance by packaging LL-37 into engineered exosomes, the minute vesicles cells use to transport substances (Su et al., 2022, PMID 35930707; in vitro). That is early laboratory work; it shows where curiosity is moving, not where an application already sits.

What is missing

The literature is large (search yield 2,518 PubMed-indexed publications, as of August 2026), but the curated picture leans heavily on reviews, laboratory work and observations in people. What stays scarce are controlled human studies that separate the many roles of LL-37, and that show, above all, when it protects and when it drives inflammation. For laboratories working on innate defence and on membrane biology, that is a natural next path.

About the authorMVMichel van der VeenRegistered Nurse · Science Editor, Peptalis

Registered nurse with eleven years in psychiatry and founder of Peptalis. Writes the platform's knowledge layer: compound profiles, evidence reviews and the quality methodology. Works from primary literature (PubChem for chemistry, PubMed for studies) and states where evidence is absent.

Sources checked via PubMed · 7 references

Compound profilesEvidence reviewsQualityIN THIS ARTICLE
  • The shape explains almost everything
  • More than killing bacteria
  • Two faces
  • Where the research is heading
  • What is missing
SCIENTIFIC REFERENCESView all references →RELATED COMPOUNDLL-37 →RELATED ARTICLES

Compounds in this article

For laboratory research use only. Not for human use.

SCIENTIFIC REFERENCES

These references are provided for informational and research purposes only. They do not constitute medical advice.

  1. 01ReviewEpithelial antimicrobial peptides in host defense against infection.Bals R. Respir Res. 2000;1(3):141–150.View on PubMed →
  2. 02Human observationalThe cathelicidin anti-microbial peptide LL-37 is involved in re-epithelialization of human skin wounds.Heilborn JD, Nilsson MF, Kratz G, et al. J Invest Dermatol. 2003;120(3):379–389.Present in healing wounds, absent in chronic wounds that fail to close: an observed association, not a demonstrated cause.View on PubMed →
  3. 03ReviewAntimicrobial peptides: update on classifications and databases.Izadpanah A, Gallo RL. J Am Acad Dermatol. 2005;52(3 Pt 1):381–390.View on PubMed →
  4. 04ReviewA comprehensive summary of LL-37, the factotum human cathelicidin peptide.Vandamme D, Landuyt B, Luyten W, Schoofs L. Cell Immunol. 2012;280(1):22–35.The review that calls LL-37 a “factotum”: many jobs in one molecule.View on PubMed →
  5. 05ReviewThe human cathelicidin LL-37 — a pore-forming antibacterial peptide and host-cell modulator.Xhindoli D, Pacor S, Benincasa M, et al. Biochim Biophys Acta. 2016;1858(3):546–566.The membrane mechanism in detail: how the two-sided coil opens holes in a bacterial wall.View on PubMed →
  6. 06Human observationalCathelicidin LL-37 in inflammatory skin disease.Schiffmann S, et al. J Inflamm Res. 2021;14:2811–2823.Observations in rosacea and psoriasis: the same peptide occurs alongside inflammation that does not settle.View on PubMed →
  7. 07In vitroEngineered exosomes carrying LL-37 for antimicrobial and wound-related research.Su Y, et al. Adv Healthc Mater. 2022;11(19):e2201397.Early laboratory work; it shows where curiosity is heading, not where an application sits.View on PubMed →

Peptalis is a knowledge platform. All content on this page is provided for scientific and educational reference purposes only and does not constitute medical advice. Compounds discussed are research compounds and are not intended for human or veterinary use.