LL-37
Cathelicidin, hCAP-18, CAMP
The body's own broad-spectrum antimicrobial peptide, with real antibiofilm activity in the laboratory and a fundamental delivery problem in a live wound.
Preclinical only
Not approved anywhere. Studied topically for infected wounds and never approved for any indication. Sold as research material for injection, a route with no supporting evidence.
What it is
LL-37 is the only cathelicidin in humans, a 37 amino acid peptide cleaved from a precursor protein and released by neutrophils and epithelial cells. It is part of innate immunity, and it does several things at once: it kills bacteria by disrupting membranes, it disperses biofilms, it neutralises endotoxin, and it recruits immune cells to a site.
Membrane disruption is a mechanism bacteria find hard to develop resistance against, which is why antimicrobial peptides attract interest as antibiotic resistance worsens.
The evidence is laboratory evidence
LL-37 has demonstrated activity against a broad range of Gram-positive and Gram-negative pathogens and against biofilms, and in animal wound models it improves re-epithelialisation and granulation tissue formation.
None of that is a human trial. The research programme has been topical, aimed at infected wounds, and it has not produced an approved product.
The problem that has stalled it
LL-37 is destroyed at the site where it is needed.
Chronic and infected wounds are proteolytically hostile environments. Pseudomonas aeruginosa produces elastase that degrades LL-37 directly, and stability studies in non-healing wound environments have found the peptide does not persist. A drug that is consumed before it can act is a delivery problem, and solving it is where most of the field's effort has gone.
That has direct bearing on injecting it. If LL-37 struggles to survive in the wound it is applied to, its fate in circulation after a subcutaneous injection is not more favourable.
The autoimmune complication
LL-37 is not a straightforwardly protective molecule. When it binds self-DNA, the complex activates plasmacytoid dendritic cells through TLR9 and drives interferon production. This is an established mechanism in psoriasis, where LL-37 is a recognised autoantigen, and it has been implicated in lupus.
Deliberately raising LL-37 exposure in someone with or predisposed to an interferon-driven autoimmune condition is pushing on the mechanism that drives it.
Practical notes
- Injection-site reactions are the most consistently reported effect. A membrane-disrupting peptide injected under the skin does to local tissue some of what it does to bacteria.
- The topical research does not license systemic use. The two are different interventions with different exposures, and only one has any supporting data.
- This is an interesting antibiotic candidate, not an immune supplement. Its appeal in the literature is in resistant infection, which is not what it is being sold for.
Side effects and warning signs
Commonly reported
- Injection-site pain and irritation, frequently reported and often marked
- Flu-like symptoms after dosing, self-reported
- Histamine release, since LL-37 degranulates mast cells
Stop and get medical help
- Autoimmune conditions, particularly psoriasis and lupus. LL-37 bound to self-DNA is a recognised autoantigen in both, and this is a mechanistic concern rather than a theoretical one
- Any systemic inflammatory reaction after dosing
Sources
From the community
Discussion for this compound concentrates in r/Peptides.
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