LL-37 Peptide: Research, Purity Data and Sourcing

LL-37 is not a synthetic invention, and it is not a designer molecule built in a medicinal chemistry lab. It is a 37-residue fragment the human body cleaves out of a larger precursor protein, and it is the only cathelicidin that humans produce. That single fact explains most of the confusion surrounding LL-37 in the research-peptide market.

What is LL-37?

LL-37 is the only human cathelicidin antimicrobial peptide: a 37-amino-acid, alpha-helical fragment released from the precursor protein hCAP18 by proteolytic cleavage. The published literature describes it as both directly antimicrobial and immunomodulatory. LL-37 is a research compound rather than an approved medicine, and identity should be confirmed by HPLC and mass spectrometry before laboratory work begins.

The common oversimplification is that LL-37 is simply a natural antibiotic. Reviews of cathelicidin biology describe something far more conditional: direct membrane killing weakens sharply in physiological salt and serum, while immune signalling and biofilm interference persist at lower concentrations. This page covers the molecular mechanism, what the peer-reviewed LL-37 literature actually reports, the adverse findings and open questions researchers have flagged, what is and is not known about LL-37 half-life, and how to read a certificate of analysis before accepting a vial.

Where does LL-37 come from inside the human body?

LL-37 is encoded by the CAMP gene (cathelicidin antimicrobial peptide gene) on human chromosome 3, which produces an inactive precursor called hCAP18 with a molecular weight near 18 kDa. The active peptide is liberated when proteases cut away the conserved cathelin domain: proteinase 3 performs this cleavage in neutrophil granules, while kallikrein-family serine proteases handle it in skin. What remains is a roughly 4.5 kDa peptide of 37 residues, named for the two leucines at its N-terminus.

Cathelicidins exist across mammals, and a structural review of the family describes the pattern clearly: a highly conserved cathelin pro-region attached to a wildly variable C-terminal effector peptide. Humans ended up with exactly one. Pigs have several. That is why cross-species extrapolation in cathelicidin work is so unreliable.

Expression is not constant. The CAMP promoter carries a vitamin D response element, and research on vitamin D, infections and immunity describes 1,25-dihydroxyvitamin D as a direct transcriptional driver of cathelicidin expression in monocytes and epithelial cells. Work on vitamin D and tuberculosis immunity traces the same axis in macrophage antimicrobial responses.

In our experience fielding questions from research buyers, the single most common point of confusion is naming. LL-37, hCAP18 and 'human cathelicidin' are not interchangeable terms, which we unpack in detail on whether cathelicidin and LL-37 are the same thing and in our broader overview of antimicrobial peptides as natural defence molecules.

How does LL-37 work at the membrane and receptor level?

LL-37 carries a net positive charge near +6 at physiological pH and folds into an amphipathic alpha helix, meaning hydrophobic and cationic residues segregate onto opposite faces of the helix. That architecture is the entire mechanism. The cationic face is drawn electrostatically to anionic bacterial surfaces, lipopolysaccharide in Gram-negative outer membranes and lipoteichoic acid in Gram-positive walls, while the hydrophobic face inserts into the lipid bilayer. Mammalian cell membranes are comparatively zwitterionic and cholesterol-rich, which is the basis of its selectivity.

Membrane disruption is only half the story. A review of cathelicidins as immunomodulatory antimicrobials describes LL-37 neutralising lipopolysaccharide before it engages TLR4, recruiting neutrophils and monocytes through the formyl peptide receptor FPR2, and influencing epithelial repair signalling. These immune effects occur at concentrations well below those needed for outright bacterial lysis.

Biofilms behave differently again. An in-depth review of the antibiofilm properties of LL-37 reports interference with bacterial attachment, twitching motility and quorum-sensing systems at sub-inhibitory concentrations, which is mechanistically distinct from killing planktonic cells. Fungal targets have their own literature, summarised in a review of the antifungal properties of cathelicidin LL-37.

Those two mechanisms are why researchers approach the compound from different angles, which is the dividing line between our pages on LL-37 in antimicrobial research and LL-37 in biofilm disruption research.

What does the peer-reviewed LL-37 literature actually cover?

The LL-37 evidence base clusters into four areas, and almost all of it is in vitro or animal work. First, antibacterial and antibiofilm activity against both Gram-positive and Gram-negative organisms. Second, antifungal activity. Third, mucosal and epithelial biology: a detailed review of cathelicidin LL-37 in health and diseases of the oral cavity covers its presence in saliva and gingival tissue and its relationship to periodontal inflammation. Fourth, the vitamin D axis, including a review of vitamin D in the context of COVID-19 that examines cathelicidin induction as one proposed link between vitamin D status and respiratory immunity.

Here is what the literature does not contain: a completed human therapeutic programme. There is no approved LL-37 medicine, and the compound is studied in laboratory models rather than clinical practice.

Search demand runs well ahead of evidence on certain applications. Questions about LL-37 and tick-borne illness arrive constantly, and the honest position is that no controlled clinical evidence supports it in that setting, which is exactly how we frame our page on LL-37 and Lyme-related research questions. The same discipline applies to our overviews of LL-37 in immune research, LL-37 in infection-defence research and LL-37 in wound-repair research. Research suggests mechanisms. It has not established outcomes.

What does the research say about LL-37 side effects and open questions?

Because LL-37 has not been approved by the FDA for any indication, there is no regulatory adverse-event database for it, and anyone presenting a tidy side-effect list is inventing one. What the laboratory literature does report is concentration-dependent loss of selectivity: above a certain threshold in vitro, the same amphipathic helix that permeabilises bacterial membranes begins to permeabilise mammalian cells, with haemolysis and cytotoxicity as the measured endpoints.

The more interesting finding is that LL-37 is not uniformly protective. Rosacea research has made that unambiguous. Work on rosacea pathogenesis identifies abnormally processed cathelicidin fragments, generated by elevated kallikrein-5 activity, as drivers of inflammation and vascular change rather than bystanders. Later reviews of rosacea pathogenesis and therapeutic correlates, signalling pathways in rosacea and current and future rosacea targets all keep the cathelicidin pathway at the centre of the model.

So the honest framing of LL-37 side effects is this: the peptide is context-dependent, and how it is cut matters as much as how much is present. Open questions include immunogenicity, the behaviour of exogenous peptide in a system that already regulates its own cathelicidin output, and proteolytic fragment profiles. Researchers comparing inflammation-focused compounds often read this alongside our breakdown of how KPV and LL-37 differ.

What is reported — and what is not — about LL-37 half-life and pharmacokinetics?

There is no single canonical LL-37 half-life figure, and any page that quotes one with confidence is extrapolating from one model system to all of them. We would rather say that plainly than invent a number.

What the literature does describe are the mechanisms that shorten the lifetime of free peptide. LL-37 is a substrate for host proteases and for bacterial proteases, which cleave it into fragments with altered activity profiles. In plasma it associates with apolipoprotein A-I, which lowers the free, biologically available fraction. In the gastrointestinal tract it faces pepsin and pancreatic proteases, which is the straightforward reason it does not survive intact passage, a point we expand on in our page covering why LL-37 is degraded in the gut.

Stability in vitro is also matrix-dependent. Ionic strength, serum content and the presence of competing polyanions all change apparent activity in a buffer-versus-media comparison, and a result obtained in dilute phosphate buffer will not reproduce in full serum.

That is also why the field has nothing useful to say about timing. Searchers ask about frequency and time of day constantly, and our pages on frequency questions around LL-37 and morning-versus-night circadian questions exist to explain why the literature does not answer them rather than to pretend it does.

How do researchers verify an LL-37 vial before using it?

A certificate of analysis is the only document that connects the label on a vial to the molecule inside it. For LL-37, a usable COA shows four things: a reverse-phase HPLC chromatogram with a stated purity figure, where 98% or higher is the common benchmark for synthetic peptide of this length; a mass spectrometry trace, ESI or MALDI-TOF, confirming an average mass near 4,493 Da; the specific batch number matching the vial in hand; and the analysis date.

Two details separate people who read COAs from people who collect them.

First, net peptide content. A lyophilised peptide vial also contains counterion, commonly trifluoroacetate from purification, plus residual water. Gross vial mass and peptide mass are not the same figure, and a COA that reports only gross mass has left out the number that matters for concentration calculations.

Second, and this is the one most guides miss entirely: mass spectrometry confirms mass, not sequence. Two peptides with the same amino acid composition in a different order are isobaric and produce the same parent ion. Only MS/MS fragmentation or amino acid analysis distinguishes them. For a 37-residue peptide synthesised stepwise, that distinction is not academic.

Real Peptides supplies LL-37 for laboratory research with a published certificate of analysis. What to demand from any supplier is covered in our guides to third-party-tested LL-37 suppliers and buying LL-37 safely online.

How is a cationic peptide stored and handled in the laboratory?

Lyophilised LL-37 is stored at minus 20 degrees Celsius or colder, desiccated and protected from light. Once in solution, short-term refrigeration at 2 to 8 degrees Celsius is standard practice, with single-use aliquots held at minus 80 degrees Celsius for longer intervals. Repeated freeze-thaw cycling is the most common avoidable cause of lost activity, because each cycle promotes aggregation and partial unfolding of the alpha helix.

Here is the handling problem specific to LL-37 that almost no general peptide guide mentions: it is strongly cationic, and cationic peptides adsorb onto glass and onto standard polypropylene surfaces. Prepare a dilute aqueous working solution in an ordinary tube and a meaningful fraction of the peptide can end up on the tube wall rather than in solution. The assay then reports low activity, and the vial gets blamed.

Low-binding tubes, siliconised glassware, carrier protein in the working buffer and avoiding unnecessarily dilute intermediate solutions are the standard mitigations. Our team has seen this pattern enough times to flag it first whenever someone reports an LL-37 preparation that appears inert.

The second handling variable is the assay medium itself. Cation-adjusted Mueller-Hinton broth, with its defined magnesium and calcium content, suppresses the activity of cationic antimicrobial peptides relative to low-salt buffer. That is a real and reproducible effect, not a quality problem with the peptide.

What is the legal status and research-use-only framing for LL-37?

LL-37 is sold and handled as a research chemical. It has not been approved by the FDA as a drug product for any indication, it is not a dietary supplement ingredient, and it is not an over-the-counter antimicrobial. All compounds discussed on this page are sold for research use only and are not for human consumption.

In practice, that means LL-37 belongs in a laboratory with institutional oversight. Work involving animals runs through institutional animal care and use committee review, and any question that involves a specific animal belongs with a licensed veterinarian who can examine that animal directly, not with a peptide supplier. Work involving live pathogens runs through biosafety review.

The information on this page is educational and describes published research literature and laboratory documentation practice. It is not guidance for use in people.

How does LL-37 compare with BPC-157, thymosin alpha-1 and KPV?

Researchers usually arrive at LL-37 after reading about one of three other peptides, and the comparison that matters is molecule class and target, not popularity. The table below sets out what each compound is and how developed its evidence base is.

Deeper side-by-side treatments live on our pages comparing BPC-157 and LL-37, LL-37 and thymosin alpha-1 and LL-37 and VIP.

What are the key takeaways?

• LL-37 is the only cathelicidin peptide humans produce, released from the 18 kDa precursor hCAP18 by proteolytic cleavage into a 37-residue, roughly 4.5 kDa alpha helix.
• The CAMP gene that encodes LL-37 carries a vitamin D response element, which is why cathelicidin expression appears repeatedly in vitamin D and immunity research.
• LL-37 activity is strongly conditional: direct antimicrobial killing drops in physiological salt and serum, while biofilm interference and immune signalling continue at sub-inhibitory concentrations.
• Rosacea research identifies abnormally processed LL-37 fragments, generated by elevated kallikrein-5 activity, as inflammatory drivers, so the peptide is not uniformly beneficial.
• No canonical LL-37 half-life figure exists in the literature, because proteolysis, apolipoprotein A-I binding and matrix composition all change the free peptide fraction.
• A usable LL-37 certificate of analysis shows batch-matched HPLC purity, mass spectrometry confirming roughly 4,493 Da, and net peptide content rather than gross vial mass.

What If: LL-37 Laboratory Scenarios

What if a vial of LL-37 arrives warm?

Record the condition on receipt, photograph the packaging and contact the supplier before opening anything. Lyophilised peptide is considerably more tolerant of short ambient excursions than peptide in solution, because the dry powder restricts the molecular mobility that drives hydrolysis and aggregation. The variable that cannot be assessed by eye is cumulative time at temperature, which is why documentation at the point of receipt matters more than appearance.

What if the mass spectrometry figure on the COA does not match 4,493 Da?

Treat any unexplained mass discrepancy as an identity failure until the supplier accounts for it. Small positive offsets can reflect adducts or oxidation of specific residues, while larger deviations suggest a deletion sequence or an entirely different peptide. Ask whether the reported figure is average or monoisotopic mass, since those are not the same number, and request the raw trace rather than a summary line.

What if LL-37 shows no activity in a standard broth assay?

Check the buffer and the plasticware before concluding the peptide is degraded. Cation-adjusted media suppress cationic peptide activity, serum proteins sequester free peptide, and adsorption onto untreated polypropylene removes material from solution silently. Re-running the same preparation in low-salt buffer with low-binding consumables resolves a large share of apparent LL-37 failures.

What if a supplier cannot produce a batch-specific COA?

Decline the batch. A generic certificate showing a historical analysis of a different lot verifies nothing about the vial in hand, since synthesis of a 37-residue peptide varies batch to batch in purity and in impurity profile. Batch traceability is the minimum standard, not a premium feature.

What is the uncomfortable truth about cathelicidin research?

Let's be direct about this: most of what circulates about LL-37 online is petri-dish data wearing a lab coat. Micromolar activity in low-salt buffer against a reference strain is a real finding, and it tells you almost nothing about behaviour in a complex biological matrix where salt, serum proteins, host proteases and competing polyanions all push in the opposite direction. The rosacea literature cuts the other way too. The same peptide that reads as a defence molecule in one tissue reads as an inflammatory driver in another, depending entirely on how it is processed. Anyone selling LL-37 as simply a natural antibiotic has not read the dermatology papers.

How we researched this page

Everything on this page is drawn from peer-reviewed literature indexed on PubMed, and every study claim carries an inline link to the source record so it can be checked directly. The source set includes reviews of cathelicidin structure and evolution, cathelicidin immunomodulation, antibiofilm and antifungal activity, oral cavity biology, the vitamin D and cathelicidin axis, and four separate rosacea pathogenesis reviews.

We make no first-party testing claims here. Real Peptides has not run clinical trials on LL-37, and nothing in this article reports internal experimental results. Where published evidence is thin or absent, including pharmacokinetics and tick-borne illness, we have said so rather than filling the gap with a plausible-sounding figure.

For readers working through sourcing and comparison questions, the related material on this site includes our guides to choosing an LL-37 supplier, buying LL-37 peptide, ordering LL-37 online and shipping logistics for research orders, alongside comparison and combination-research pages covering BPC-157 versus LL-37 in detail, the structural differences between BPC-157 and LL-37, BPC-157 and LL-37 in chronic infection research, combination study designs involving both peptides and combination questions involving thymosin alpha-1.

LL-37 is one of the few research peptides where the human body itself has already run the experiment, and the result is more ambiguous than the marketing suggests: the same 37 residues that help clear pathogens at a mucosal surface help sustain inflammation in rosacea skin, depending entirely on which protease got to the precursor first. That is not a flaw in the peptide. It is the actual biology, and it is the reason serious LL-37 work starts with a chromatogram and a mass spectrum rather than with a conclusion.

References

Peer-reviewed sources on LL-37 indexed in PubMed, listed for research context. Real Peptides supplies LL-37 for laboratory research use only.

1. Cathelicidin LL-37-ApoB-100 interaction promotes LDL clearance and attenuates cholesterol accumulation in the liver. Science China. Life sciences, 2026. PMID 40971038. doi:10.1007/s11427-025-3006-2
2. Cancer cell migration under control of human cathelicidin LL-37. Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie, 2026. PMID 41916132. doi:10.1016/j.biopha.2026.119241
3. Cathelicidin LL-37-Induced Transcriptome of Human Keratinocyte Identifies Chemokine CXCL10 Link to T-Cell-Mediated Rosacea Pathogenesis through Jak1/STAT1 Pathway. The Journal of investigative dermatology, 2026. PMID 40835085. doi:10.1016/j.jid.2025.08.003
4. Antimicrobial peptide LL-37 increases rhinovirus-induced interferon β expression in human airway epithelial cells through a Ca(2+)-dependent mechanism. Biochemistry and biophysics reports, 2025. PMID 40612001. doi:10.1016/j.bbrep.2025.102105
5. Study of cathelicidin (LL-37) immunoexpression in the skin of vitiligo patients. Archives of dermatological research, 2025. PMID 39873762. doi:10.1007/s00403-025-03801-2
6. Human cathelicidin LL-37 rapidly disrupted colonic epithelial integrity. Biochimica et biophysica acta. Biomembranes, 2025. PMID 39837472. doi:10.1016/j.bbamem.2025.184410
7. LL-37 as a biomarker for therapeutic response to scaling and root planing. Journal of Indian Society of Periodontology, 2025. PMID 41438788. doi:10.4103/jisp.jisp_405_24
8. Vitamin D triggers hCAP18/LL-37 production: Implications for LL-37-induced human osteoblast cytotoxicity. Biochemical and biophysical research communications, 2024. PMID 38642493. doi:10.1016/j.bbrc.2024.149962