Editorial note: this article summarises published research on LL-37 and KPV. Baclabs does not sell LL-37, KPV or any peptide; we supply bacteriostatic water and reconstitution consumables. Nothing here is medical advice.
LL-37 and KPV are usually sold side by side as “immune” or “gut” peptides, but they are very different molecules with very different evidence. LL-37 is the only cathelicidin antimicrobial peptide humans make, a 37-residue chain released from the precursor hCAP18 by neutrophils and epithelial cells, and it has been tested topically in placebo-controlled trials for leg ulcers [1][2][3]. KPV is a three-amino-acid fragment (lysine-proline-valine) of alpha-melanocyte-stimulating hormone (α-MSH) with anti-inflammatory activity in mouse models of colitis and no published human trials [4][5].
This article explains how each works, what the studies actually measured, what is known about adverse effects, and how the reconstitution arithmetic applies to the vials they are sold in. Both sit under the regenerative peptides hub.
LL-37: the human cathelicidin
What it does in the body
Cathelicidins are a family of host-defence peptides found across vertebrates. Humans have one, encoded by the CAMP gene, stored as the inactive precursor hCAP18 and cleaved to the active LL-37 (so named because it begins with two leucines and is 37 residues long) [1][6]. It is produced mainly by neutrophils and by epithelial cells of the skin, gut and airway [6].
Its best-characterised action is direct killing of bacteria, fungi and some enveloped viruses: the amphipathic helix inserts into microbial membranes and forms pores [3]. It also acts as an “alarmin”, a signal that recruits and activates neutrophils, monocytes and T cells, binds and neutralises bacterial lipopolysaccharide, promotes angiogenesis, and stimulates keratinocyte migration and re-epithelialisation in wounds [1][2][3]. The same immune-activating properties are implicated in disease: LL-37 complexes with self-DNA drive plasmacytoid dendritic cell activation in psoriasis, and it contributes to the pathophysiology of systemic lupus erythematosus [7].
ll 37 antimicrobial peptide benefits: what the trials show
LL-37 is unusual among peptides in this cluster because a pharmaceutical version has been through placebo-controlled human trials, all topical, all in chronic wounds.
- First-in-man trial, 2014. Thirty-four patients with hard-to-heal venous leg ulcers had a 3-week placebo run-in, then 4 weeks of twice-weekly topical LL-37 at 0.5, 1.6 or 3.2 mg/mL or placebo. Healing rate constants for 0.5 and 1.6 mg/mL were roughly six- and three-fold those of placebo (p = 0.003 and p = 0.088), and the treatment was described as safe [8].
- HEAL LL-37 phase 2b, 2021. A double-blind, randomised, placebo-controlled multicentre study of topical LL-37 with compression therapy in 148 patients with venous leg ulcers [9]. This is the largest LL-37 trial published.
- Diabetic foot ulcer, 2023. A randomised double-blind trial of LL-37 cream measured wound healing rate, IL-1α and TNF-α levels and aerobic bacterial colonisation in mildly infected ulcers (NCT04098562) [10].
Three points matter. The doses were applied to an open wound and cannot be converted into a subcutaneous dose. The benefit was wound closure, not “immune support”. And the highest dose in the first trial did not outperform the lowest. No trial has tested injected LL-37 in humans, and there is no human evidence for the systemic uses (chronic infection, biofilm, “immune enhancement”) that vendor listings describe.
Adverse effects and unknowns
Topical LL-37 was well tolerated in the trials above. Systemic dosing is a different question. LL-37 is reported to be cytotoxic to host cells at higher concentrations, it is pro-inflammatory in several autoimmune settings, and elevated levels are associated with psoriasis and lupus [3][7]. Injecting a peptide whose job is to activate neutrophils and dendritic cells, in the absence of any dose-finding data, carries an inflammatory and immunogenicity risk that the trials do not address.
KPV: the α-MSH tripeptide
Mechanism
α-MSH is a 13-residue melanocortin hormone with well-documented anti-inflammatory effects. Its C-terminal tripeptide, Lys-Pro-Val (KPV), retains that anti-inflammatory activity. In intestinal epithelial and immune cells, KPV is transported into the cell by PepT1, an oligopeptide transporter that is expressed at low levels in the healthy colon and upregulated in inflammatory bowel disease [4][11]. Once inside, nanomolar concentrations inhibit activation of NF-κB and MAP kinase signalling and reduce pro-inflammatory cytokine expression [4].
kpv peptide gut health: the mouse data
The evidence is small, consistent and entirely animal.
- A 2008 study in Inflammatory Bowel Diseases tested KPV in two murine models of inflammatory bowel disease, including dextran sodium sulfate (DSS) colitis, and reported significant anti-inflammatory activity [5].
- A 2008 Gastroenterology study gave KPV in drinking water in DSS colitis and a T-cell transfer model; KPV reduced histological inflammation and pro-inflammatory cytokine mRNA, and the effect was shown to depend on PepT1-mediated uptake [4].
- Later work used KPV to prevent colitis-associated cancer in mice [11] and to reduce TNBS-induced colitis in rats via a rectal hydrogel [12], and exploited its PepT1 affinity to target nanoparticles to inflamed colon [13].
The picture that emerges is of a peptide acting locally on inflamed gut epithelium, which fits oral or rectal delivery and says little about injection. Doses in the mouse work were delivered in drinking water; there is no human pharmacokinetic study, no human dose, and no human trial of any kind for KPV, oral or injected. Vendor claims for KPV in skin, allergy or “systemic inflammation” have no published basis.
Safety
KPV has not been tested in humans, so its adverse effect profile is unknown. The mouse studies did not report toxicity. A tripeptide is unlikely to be strongly immunogenic on its own, but impurities and aggregation in an unregulated product remain a concern for any injected peptide, as the FDA noted when it placed both KPV and LL-37 in Category 2 of its compounding list in 2023 [14].
Regulatory status
Neither LL-37 nor KPV is a licensed medicine in the UK, EU or US. Both were placed in Category 2 (substances raising significant safety risks) of the FDA’s 503A bulk substances list on 29 September 2023 [14]. In July 2026 an FDA advisory committee voted 8–6 to recommend allowing KPV to be compounded; LL-37 was not on the agenda, and the vote is non-binding [15]. In the UK, selling or supplying either as a medicine breaches regulation 46 of the Human Medicines Regulations 2012, and the MHRA has said it disregards “research use” labelling used to avoid that [16][17]. Neither is specifically named on the WADA list, but S0 covers any non-approved pharmacological substance.
Reconstitution for LL-37 and KPV vials
Both are sold as lyophilised powder in multi-dose vials, and the arithmetic is the same as for any peptide: concentration = mass ÷ diluent volume, and each U-100 insulin syringe unit is 0.01 mL.
| Vial | Bacteriostatic water | Concentration | mcg per unit |
|---|---|---|---|
| LL-37 5 mg | 2 mL | 2,500 mcg/mL | 25 mcg |
| LL-37 5 mg | 2.5 mL | 2,000 mcg/mL | 20 mcg |
| KPV 10 mg | 2 mL | 5,000 mcg/mL | 50 mcg |
| KPV 10 mg | 5 mL | 2,000 mcg/mL | 20 mcg |
LL-37 is cationic and amphipathic, which makes it prone to sticking to surfaces and aggregating; gentle swirling rather than shaking matters more than usual. A vial drawn from repeatedly needs a preserved diluent, which is the difference between bacteriostatic water and sterile water explained in this comparison. Baclabs supplies UK-stocked bacteriostatic water in 30 mL vials; the reconstitution guide covers technique and storage and shelf life explains the 28-day limit after first puncture. The BPC-157 protocol guide has a fuller worked example.
Frequently asked questions
What are the benefits of LL-37 antimicrobial peptide?
In the body, LL-37 kills microbes by disrupting their membranes, neutralises bacterial endotoxin, recruits immune cells and promotes wound re-epithelialisation. As a treatment, the only human evidence is topical: placebo-controlled trials in venous leg ulcers showed faster healing at 0.5–1.6 mg/mL applied to the wound. No injected use has been tested in people.
Is KPV peptide good for gut health?
In mice, yes: KPV in drinking water reduced colitis severity and inflammatory cytokines in several models, acting through the PepT1 transporter on gut epithelium. In humans, unknown: there are no published trials, no pharmacokinetic data and no established dose. The mouse data support a local effect in the gut, which does not justify injection.
What is the difference between LL-37 and KPV?
LL-37 is a 37-residue antimicrobial and immune-signalling peptide with direct microbe-killing activity; KPV is a three-residue anti-inflammatory fragment of α-MSH with no antimicrobial action. LL-37 has topical human trial data; KPV has mouse data only. Both are unlicensed and both were restricted from US compounding in 2023.
Are there side effects of LL-37?
Topical LL-37 was well tolerated in leg ulcer trials. Systemic effects are unknown because it has never been injected in a controlled human study. LL-37 is cytotoxic to human cells at high concentrations and is implicated in psoriasis and lupus, so unregulated systemic use carries an inflammatory and immunogenicity risk.
Is KPV legal in the UK?
Possession for personal use is not an offence. Selling or supplying it as a medicine without a marketing authorisation breaches the Human Medicines Regulations 2012 regardless of “research use” labelling, according to the MHRA. It is not a licensed product anywhere and cannot be prescribed as one.
References
- Cathelicidin LL-37: a multitask antimicrobial peptide. 2010 (PMID 20049649)
- The roles of cathelicidin LL-37 in immune defences and novel clinical applications. 2009 (PMID 19068548)
- The human cathelicidin LL-37 – a pore-forming antibacterial peptide and host-cell modulator. 2016 (PMID 26556394)
- PepT1-mediated tripeptide KPV uptake reduces intestinal inflammation. Gastroenterology, 2008 (PMC2431115)
- Melanocortin-derived tripeptide KPV has anti-inflammatory potential in murine models of inflammatory bowel disease. Inflammatory Bowel Diseases, 2008 (PMID 18092346)
- Tissue-specific Regulation of Innate Immune Responses by Human Cathelicidin LL-37. 2018 (PMID 29589544)
- Cathelicidin LL-37: A new important molecule in the pathophysiology of systemic lupus erythematosus. 2020 (PMC7388365)
- Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial. Grönberg A et al., Wound Repair and Regeneration, 2014 (PMID 25041740)
- Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: A multicentric prospective randomized placebo-controlled clinical trial. Mahlapuu M et al., Wound Repair and Regeneration, 2021 (PMC9298190)
- Efficacy of LL-37 cream in enhancing healing of diabetic foot ulcer: a randomized double-blind controlled trial. 2023 (PMC10514151; NCT04098562)
- Critical role of PepT1 in promoting colitis-associated cancer and therapeutic benefits of the anti-inflammatory PepT1-mediated tripeptide KPV in a murine model. 2016 (PMC4957955)
- Self-Cross-Linked Hydrogel of Cysteamine-Grafted γ-Polyglutamic Acid Stabilized Tripeptide KPV for Alleviating TNBS-Induced Ulcerative Colitis in Rats. 2021 (PMID 34547895)
- A PepT1 mediated medicinal nano-system for targeted delivery of cyclosporine A to alleviate acute severe ulcerative colitis. 2019 (PMID 31408067)
- 503A Bulk Drug Substances Categories Update, September 29 2023. Alliance for Pharmacy Compounding, 2023
- FDA Panel Backs 6 Peptides for Compounding. AJMC, July 2026
- The Human Medicines Regulations 2012, Regulation 46. legislation.gov.uk
- Grey-market peptides: what pharmacists need to know. The Pharmacist, April 2026
Disclaimer: This content is for educational purposes only and does not constitute medical advice. Bacteriostatic water is supplied for reconstitution of substances intended for research and for use as directed by a healthcare professional. Peptides and medicines discussed here may be unlicensed in the UK or prescription-only; consult a qualified clinician before using any medicine. Baclabs does not sell peptides.