LL-37
Cathelicidin fragment
LL-37 is the active 37-amino-acid fragment of human cathelicidin, a host-defence peptide the body produces itself as part of innate immunity.
Regulatory status: A naturally occurring human peptide, not an approved drug and not a lawful dietary supplement. Synthetic LL-37 is used in laboratory and preclinical research.
Default vial
5 mg
Default mix
2 mL
Reported range
100–500 mcg
Draw (U-100)
4 u
Antimicrobial peptide; start very low — injection-site reactions and flu-like effects are common at higher doses. Short courses only.
What it is
- A 37-amino-acid peptide cleaved from the precursor protein hCAP18, the only cathelicidin in humans.
- Produced naturally by neutrophils, epithelial cells and other immune cells at sites of infection or injury.
- Described in reviews as pleiotropic: antimicrobial, immunomodulatory and wound-healing activity have all been reported.
- Studied topically, in cell culture and systemically in animal models; it is not an established human injectable therapeutic.
How it is described to act
- 1
Released naturally from its stored precursor when cleaved at sites of infection or injury; in experiments it is applied topically or added to cell cultures.
- 2
Reported to interact directly with bacterial and host cell membranes and to be present in skin, mucosal and immune tissue.
- 3
Pharmacology reviews propose signalling through receptors including formyl peptide receptor 2 and modulation of Toll-like receptor pathways.
- 4
Observed across a wide range of in vitro and animal contexts; more recent papers propose relevance to COVID-19 inflammation as a hypothesis.
What the research has looked at
Mechanism and pharmacology
- A 2016 review in Pharmacological Reports reported that LL-37 shows pleiotropic antimicrobial and immunomodulatory activity acting through several receptor pathways, including FPR2.
COVID-19 hypothesis work
- Researchers writing in Frontiers in Immunology (2022) proposed that upregulating LL-37 expression may help limit severe COVID-19 inflammatory responses and microthrombosis. The authors present this as a mechanistic hypothesis, not a tested treatment.
Strength of evidence: Preclinical evidence only
LL-37's role in normal human immunity is well established, but its use as an administered therapeutic remains preclinical and hypothesis-driven.
What is published comes from cell and animal studies. Findings in those models frequently do not carry over to people.
Reported cautions and unknowns
- Because it is endogenous, LL-37 is already present in the body; safety data for exogenous administered dosing are limited.
- Pharmacology reviews link excess or dysregulated LL-37 to autoimmune conditions including psoriasis and lupus, describing a double-edged immunomodulatory role.
- The COVID-19 proposal in the cited paper is explicitly hypothesis-generating rather than an established clinical intervention.
References
Handling this vial
- Lyophilized vials are generally stored at 2–8 °C and kept out of light; once reconstituted with bacteriostatic water they are refrigerated and commonly discarded after 28 days.
- Mix by aiming water down the vial wall and rolling gently — do not shake — and never re-freeze a reconstituted vial.
- Pep-Tidy cannot verify what is in your vial. Ask your supplier for a current Certificate of Analysis (HPLC/MS).
LL-37 questions people ask
How do you reconstitute LL-37?
A common starting point for a 5 mg vial of LL-37 is 2 mL of bacteriostatic water, which gives 2.5 mg per mL. Aim the water down the inside wall of the vial, let it dissolve on its own, and roll gently instead of shaking. Pep-Tidy's reconstitution calculator will recalculate the numbers for any other vial size or water volume you use.
How many units of LL-37 is one dose?
At 2.5 mg per mL, that works out to about 4 units on a U-100 insulin syringe for a 100 mcg dose. Change the vial size, water volume, or target dose in the calculator and the syringe reading updates with it. This is arithmetic, not a dosing recommendation.
What dosing schedule is reported for LL-37?
Published and community sources describe 100–500 mcg, subcutaneous, every other day, typically run 4 weeks on and 4 weeks off. These figures describe what has been reported, not what anyone should take — talk to a licensed clinician first.
How should LL-37 be stored?
Lyophilized LL-37 vials are generally kept at 2–8 °C and out of light. Once reconstituted with bacteriostatic water they are refrigerated and commonly discarded after about 28 days. Never re-freeze a reconstituted vial and never shake it.
Read this before you act on anything above
Everything on this page is a summary of what other people have published — it is not medical advice, not a recommendation, and not a dosing instruction. Reported dose ranges describe what appears in the literature or in community protocols, not what anyone should take. Talk to a licensed clinician before using any peptide.