LL-37 Research: The Human Cathelicidin Peptide and What Studies Have Investigated

What is LL-37?

What is LL-37? It is a 37-residue linear peptide and the only member of the cathelicidin family found in humans. Its sequence, recorded in UniProt entry P49913 as residues 134–170 of the cathelicidin antimicrobial peptide precursor, is LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES. The name is descriptive rather than coded: two leucines, thirty-seven residues.

Its defining chemical property is charge. The sequence is dense in lysine and arginine and carries a strong net positive charge at physiological pH, while hydrophobic residues line up along one face when the chain folds into a helix. That combination — cationic and amphipathic — is the canonical architecture of the antimicrobial peptides and the structural basis of every mechanism below. The same UniProt entry catalogues shorter fragments from the same precursor region (FALL-39, LL-29, LL-23, FF-33, RK-31, KS-30, KR-20); several appear in the literature under similar names, and an analytical certificate reporting mass is what distinguishes them.

Discovery and origin in the literature

From gene to peptide

LL-37 was identified in the mid-1990s as the mature product of a human gene originally designated FALL39, now the CAMP gene, encoding the precursor protein hCAP18. Gudmundsson, Agerberth and colleagues reported in the European Journal of Biochemistry in 1996 (PMID 8681941) how the cathelin precursor is processed in granulocytes to release the antibacterial peptide. The architecture is shared across the family: a conserved N-terminal cathelin-like domain that is not itself the antimicrobial agent, and a variable C-terminal segment that is, held inactive until proteolysis frees it.

The vitamin D link

Liu and colleagues reported in Science in 2006 (PMID 16497887) that Toll-like receptor triggering in human macrophages induced expression of the vitamin D receptor and the vitamin-D-1-hydroxylase gene, leading to induction of the cathelicidin antimicrobial peptide. It is cited here as a study of gene regulation in a defined cell system — how expression of the endogenous peptide is controlled — and not as a statement about any supplement, nutrient or intervention.

Reference data

The molecule facts below are drawn from the public record (UniProt P49913 and PubChem CID 16198951). They describe identity and physical form only.

The secondary-structure row is stated as conditional deliberately, because that is exactly what the primary literature reports. No reconstitution procedure, quantity or route is given or implied.

Mechanisms researchers have examined

The LL-37 mechanism literature spans biophysics, microbiology and immunology. Each point below is what studies characterise in model systems:

• Conditional helix formation — Johansson et al. (1998, J Biol Chem, PMID 9452503) showed by circular dichroism that LL-37 is disordered at micromolar concentration in water, that 15 mM bicarbonate, sulfate or trifluoroacetate drives helix formation while 160 mM chloride is less efficient, and that a cooperative concentration-dependent transition consistent with oligomer formation occurs. Helicity was retained above pH 13 and lost below pH 5.
• Helicity as the activity correlate — in the same study, α-helicity correlated with antibacterial activity against both Gram-positive and Gram-negative organisms, and two N-terminally truncated homologues needing higher anion concentrations to form a helix were correspondingly less active against E. coli. The cationic amphipathic helix is described across this literature as associating with anionic bacterial membranes and disrupting their integrity — a physicochemical mechanism rather than a receptor-mediated one, which is why resistance to this class is discussed differently from resistance to conventional antibiotics.
• Lipopolysaccharide neutralization — Nagaoka and colleagues (2002, Clin Diagn Lab Immunol, PMID 12204946) studied the LPS-neutralizing activities of CAP18/LL-37-derived peptides and how sequence modification augments them. Binding endotoxin is a distinct activity from killing the organism that carries it.
• Chemotaxis through FPRL1 — Yang and colleagues (2000, J Exp Med, PMID 11015447) reported that LL-37 uses formyl peptide receptor-like 1 as a receptor to chemoattract human peripheral blood neutrophils, monocytes and T cells — the receptor-mediated arm of its biology.
• Wound-repair models — Heilborn and colleagues (2003, J Invest Dermatol, PMID 12603850) examined the peptide’s involvement in re-epithelialization of human skin wounds and reported that it was lacking in chronic ulcer epithelium.

Research areas in the literature

Vandamme and colleagues (2012, Cell Immunol, PMID 23246832) provide the standard review, describing the human cathelicidin as pleiotropic across antibacterial, antifungal and antiviral activity, chemotactic and immunomodulatory effects, wound healing, angiogenesis, apoptosis modulation, and a role investigated in cancer biology. That breadth is itself the honest headline of this field. Grouped by what investigators examined: direct antimicrobial work, in which minimal inhibitory concentrations are measured against defined strains in defined buffers with the ionic composition of the medium treated as an experimental variable rather than a background detail; innate-immune signalling, covering receptor-mediated leukocyte recruitment, endotoxin binding and regulation of the peptide’s own expression; tissue-repair models with re-epithelialization and angiogenesis endpoints; and comparative peptide chemistry across truncated fragments and engineered variants, where the relationship between charge, helicity and activity was mapped.

Research models and evidence status

LL-37 is well characterised as a molecule and as a biophysical object, and the innate-immunity literature around it is substantial. Two things in that literature are genuinely unresolved, and both belong on this page rather than being smoothed over.

The dual pro- and anti-inflammatory behaviour is not reconciled

The same peptide neutralizes lipopolysaccharide (Nagaoka 2002) and recruits neutrophils, monocytes and T cells through a chemotactic receptor (Yang 2000) — one action dampens an inflammatory stimulus, the other amplifies cellular recruitment. Vandamme et al. treat this pleiotropy as a defining feature rather than a contradiction to be resolved, and no established framework predicts which behaviour will dominate in an arbitrary system; concentration, ionic environment, cell type and serum proteins all appear to matter. Any summary presenting LL-37 as simply “anti-inflammatory” or simply “antimicrobial” is selecting from the literature rather than reporting it.

The concentration window is narrow, and cytotoxicity is documented

Johansson et al. (1998) reported a minimal inhibitory concentration against E. coli of 5 µM and cytotoxicity against several eukaryotic cell types at 13–25 µM — a separation of roughly three to five fold in their system. The same authors noted that in solutions matching the ionic composition of plasma, intracellular fluid or interstitial fluid the peptide is helical, and wrote that it “could pose a danger to human cells upon release”; they also reported that human serum inhibited both activities. These are findings of a specific in-vitro study, and they are why the peptide’s selectivity is treated as an open problem in its own field.

What is not established, and is deliberately not claimed here, is any property of the supplied research material in a person. The work above is in-vitro biophysics, bacterial culture, isolated primary cells and skin-model systems. This page makes no efficacy, therapeutic, antimicrobial, cosmetic or other use claim of any kind, and the material is supplied for laboratory research use only — not for human or veterinary use.

How to verify this compound yourself

At 37 residues LL-37 is a demanding synthesis, and that changes what its Certificate of Analysis has to carry:

• HPLC purity — solid-phase synthesis of a long, highly cationic sequence produces deletion sequences (chains missing one or more residues) at a higher rate than a short peptide does, and separating those from full-length product is what reversed-phase chromatography is for. For LL-37 the HPLC trace carries more diagnostic weight than it would for a tripeptide.
• Mass-spec identity — mass spectrometry confirms the measured mass against the expected ≈ 4493 Da, which also distinguishes full-length LL-37 from the shorter cathelicidin fragments catalogued alongside it in UniProt.
• Counter-ion and net peptide content — a strongly cationic peptide is normally isolated with a counter-ion, commonly trifluoroacetate. That is a documentation question rather than a purity question, and it matters here for a second reason: Johansson et al. reported trifluoroacetate as one of the anions that drives helix formation, so the counter-ion is not inert with respect to this molecule’s conformation.
• Endotoxin — especially meaningful for a peptide studied specifically for its interaction with lipopolysaccharide, since endotoxin contamination is a confounder in exactly the assays this compound is used in. Reported in EU/mL where tested, independent of chemical purity.

See how to read a COA for what each certificate line means, and how to verify peptide purity for how the methods fit together. The exact batch received can be checked on the self-serve verify tool.

Research-grade sourcing and verification

LL-37 is not held in stock. It is listed on our sourcing catalogue as available to order — our supplier lists it, we have not bought it, and material of this kind typically takes about two to three weeks to reach us. For laboratory research use only, it is supplied with a per-batch Certificate of Analysis reporting HPLC purity (%) and mass-spec identity confirmation, verifiable at the lot level. For the adjacent immune-signalling compound in this library, see KPV research — the C-terminal α-MSH tripeptide studied against NF-κB-linked inflammatory pathways, a different molecule and a different literature, handed off rather than merged with this one. This is sourcing and quality-assurance framing only.

Frequently asked questions

Literature cited

1. Gudmundsson GH, Agerberth B, Odeberg J, Bergman T, Olsson B, Salcedo R. “The human gene FALL39 and processing of the cathelin precursor to the antibacterial peptide LL-37 in granulocytes.” Eur J Biochem. 1996;238(2):325–332. PMID 8681941. pubmed.ncbi.nlm.nih.gov/8681941.
2. Johansson J, Gudmundsson GH, Rottenberg ME, Berndt KD, Agerberth B. “Conformation-dependent antibacterial activity of the naturally occurring human peptide LL-37.” J Biol Chem. 1998;273(6):3718–3724. PMID 9452503. pubmed.ncbi.nlm.nih.gov/9452503.
3. Yang D, Chen Q, Schmidt AP, et al. “LL-37, the neutrophil granule- and epithelial cell-derived cathelicidin, utilizes formyl peptide receptor-like 1 (FPRL1) as a receptor to chemoattract human peripheral blood neutrophils, monocytes, and T cells.” J Exp Med. 2000;192(7):1069–1074. PMID 11015447. pubmed.ncbi.nlm.nih.gov/11015447.
4. Nagaoka I, Hirota S, Niyonsaba F, et al. “Augmentation of the lipopolysaccharide-neutralizing activities of human cathelicidin CAP18/LL-37-derived antimicrobial peptides.” Clin Diagn Lab Immunol. 2002;9(5):972–982. PMID 12204946. pubmed.ncbi.nlm.nih.gov/12204946.
5. Heilborn JD, Nilsson MF, Kratz G, et al. “The cathelicidin anti-microbial peptide LL-37 is involved in re-epithelialization of human skin wounds and is lacking in chronic ulcer epithelium.” J Invest Dermatol. 2003;120(3):379–389. PMID 12603850. pubmed.ncbi.nlm.nih.gov/12603850.
6. Liu PT, Stenger S, Li H, et al. “Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response.” Science. 2006;311(5768):1770–1773. PMID 16497887. pubmed.ncbi.nlm.nih.gov/16497887.
7. Vandamme D, Landuyt B, Luyten W, Schoofs L. “A comprehensive summary of LL-37, the factotum human cathelicidin peptide.” Cell Immunol. 2012;280(1):22–35. PMID 23246832. pubmed.ncbi.nlm.nih.gov/23246832.
8. UniProt Consortium. “P49913 (CAMP_HUMAN), Cathelicidin antimicrobial peptide.” uniprot.org/uniprotkb/P49913 (sequence, precursor residue boundaries, fragment family).
9. National Center for Biotechnology Information. “PubChem Compound Summary for CID 16198951, LL-37.” pubchem.ncbi.nlm.nih.gov/compound/16198951 (formula, mass, CAS 154947-66-7).