LL-37 is the only cathelicidin peptide the human body makes, a 37-residue host-defence peptide of the innate immune system. Searches for "LL-37 peptide benefits" usually blur two very different things: what LL-37 does as a natural molecule inside us, and what happens when researchers apply synthetic LL-37 in the lab. This overview separates the two, summarises the benefits reported in peer-reviewed studies, and lays out the doses actually used in research, strictly as reference material. For the full chemistry and reference data, see our LL-37 monograph.
What is LL-37?
LL-37 is the mature, active fragment of the human cathelicidin protein hCAP18, the product of the single human cathelicidin gene CAMP on chromosome 3. Neutrophils and epithelial cells store hCAP18 and cleave off its C-terminal 37-amino-acid peptide, named "LL-37" for its two leading leucine residues, when host defence calls for it [2]. It is the only cathelicidin humans produce, which is exactly why it draws so much attention as a model host-defence peptide [1][3].
Processing happens extracellularly: in neutrophils the serine protease proteinase 3 cleaves hCAP18 to liberate the active LL-37 fragment, and in skin kallikrein-family proteases do the equivalent job [14]. Because both release and breakdown are enzyme-driven, LL-37 activity is gated by the local protease balance rather than by any fixed circulating level, a point that matters when interpreting "dose" for an endogenous peptide.
The molecule is short (about 4.5 kDa), strongly cationic (net charge ≈ +6) and amphipathic. In water it is largely disordered, but on contact with anionic (microbial) membranes it folds into an α-helix, a structural switch tightly coupled to its activity [1][4].
How LL-37 works: two modes
Direct antimicrobial action
The classic function is membrane disruption. LL-37's positive charge draws it to the negatively charged surfaces of bacteria; the folded helix then accumulates on the membrane and destabilises it in a "carpet"-like fashion, forming transient pores and causing detergent-like breakdown [4]. This yields broad activity against Gram-positive and Gram-negative bacteria, some fungi and enveloped viruses [1][3]. The effect is conformation-dependent, the killing correlates with the peptide's ability to adopt its α-helix, and it extends beyond free-floating bacteria to established biofilms, with additive or synergistic behaviour alongside other innate factors such as lysozyme and lactoferrin [3]. A caveat that recurs across studies: LL-37's antimicrobial potency is highly sensitive to the surrounding ionic environment, physiological salt and divalent cations can blunt it, one reason lab results do not translate straightforwardly to the body [5].
Immunomodulation
Beyond killing microbes, LL-37 is a signalling molecule. It acts through the formyl peptide receptor FPR2 (FPRL1) to chemoattract neutrophils, monocytes and T cells, bridging innate and adaptive immunity [6]. It also binds and neutralises bacterial lipopolysaccharide (LPS), damping the hyper-inflammatory response to endotoxin [3][12]. These host-defence functions, recruiting immune cells and tuning inflammation, are now regarded as at least as important as the direct antibiotic effect [12].
Researched benefits of LL-37
The table below summarises the activities most consistently reported in the primary literature. Each is a study finding under defined conditions, not a claimed human effect.
Wound healing and angiogenesis
Some of the most cited "benefit" data are in tissue repair. LL-37 promotes angiogenesis: Koczulla and colleagues showed it drives endothelial cell proliferation and migration and stimulates new-vessel formation, identifying an angiogenic role independent of its antibiotic activity [7]. In wound models, Carretero and colleagues reported that LL-37 accelerates re-epithelialisation of skin both in vitro and in vivo, and that blocking endogenous LL-37 impairs healing [8]. Together these give a mechanistic basis for the clinical wound-healing work described below.
The vitamin D connection
The CAMP gene carries a vitamin D response element, so 1,25-dihydroxyvitamin D3 (the active hormone) directly switches on LL-37 production in myeloid and epithelial cells [10]. This is the molecular link behind the long-standing observation that vitamin D status influences innate antimicrobial defence, and one reason LL-37 is studied in the context of infection susceptibility.
The other side: LL-37 as an autoantigen
LL-37's benefits come with a documented downside any honest overview must include. Because it is cationic, LL-37 binds the body's own DNA and RNA; these complexes are carried into plasmacytoid dendritic cells and trigger a type I interferon response through TLR9/TLR7 [11]. In psoriasis, LL-37 itself becomes a target of autoreactive T cells, an autoantigen, and increased cathelicidin is implicated in psoriasis and rosacea [11][12]. So more LL-37 is not simply "better": its role is context-dependent, protective in host defence yet pro-inflammatory when dysregulated.
LL-37 in studies: where to find the dosing data
Across studies LL-37 and its derivatives were used in lab and animal models; the exact concentrations and schedules depended on the model and the question. We deliberately leave them out of this article as instruction, the study data are collected in the reference LL-37: dosing schedule.
KR-12 and other derivatives
Because full-length LL-37 can be cytotoxic to host cells, much research focuses on shorter fragments. The best known is KR-12 (residues 18–29), the smallest segment that retains antibacterial activity while shedding much of the toxicity toward human cells, which is why it serves as a scaffold for engineered analogues. Structural work in lipid micelles mapped how both LL-37 and KR-12 fold and engage membranes, and pinpointed the residues that drive membrane binding [13]. That structure-activity map is what lets researchers design shorter, more selective, more protease-stable analogues, trying to keep the antimicrobial and immunomodulatory upsides while trimming the host-cell toxicity and the autoantigen behaviour that make the full-length peptide a double-edged tool.
Form, storage and reconstitution
Research-grade LL-37 ships as a lyophilised (freeze-dried) powder. Our LL-37 is supplied as a 5 mg vial, HPLC (high-performance liquid chromatography, a purity-testing method)-tested for purity and accompanied by a batch certificate of analysis. Lyophilised cathelicidin is stored sealed at −20 °C or below, protected from moisture, and allowed to reach room temperature before opening to avoid condensation. It dissolves in water or dilute aqueous buffers; high-phosphate and divalent-cation buffers are avoided because they promote aggregation, and the peptide can adsorb to plastic and glass surfaces. To work out concentrations from a given vial and diluent volume, use our reconstitution calculator.
Research use only
This article is compiled from publicly available, peer-reviewed sources and is provided for reference and informational purposes only. It is not medical advice and not a recommendation for use. LL-37 offered on this site is supplied strictly for laboratory research; it is not intended for human consumption, nor for diagnostic or therapeutic use. All doses and effects described above were observed under controlled research conditions and must not be read as instructions for application.
The full list of sources with links, is in the monograph: LL-37.
