Immune
LL-37 is a research-use product carried by vendors we track, grouped under Immune. For research use only; an editorial review is pending.
LL-37 is offered by one or more vendors we track. We have not yet written a detailed editorial summary for this compound. The offerings below reflect what vendors currently carry. For research use only — verify dosing, handling, and safety against primary sources.
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Best $/mg
Evidence level
Preclinical only
The C-terminal active fragment of human cathelicidin (hCAP18), and the only cathelicidin in humans. A 37-amino-acid amphipathic antimicrobial peptide with broad activity against bacteria, viruses, and fungi, plus immunomodulatory effects. Heavily studied preclinically; clinical translation is constrained by toxicity and cost.
Mechanism
Mechanism not yet documented.
Researched benefits
Broad-spectrum antimicrobial activity
Disrupts microbial membranes via amphipathic alpha-helix insertion. Active against gram-positive and gram-negative bacteria, including some resistant strains, plus enveloped viruses and several fungi. MIC values vary by organism and assay conditions.
Innate immune modulation
Acts on neutrophils, monocytes, and epithelial cells via FPR2 and other receptors. Modulates chemotaxis, cytokine production, and resolution of inflammation. The net immunomodulatory effect is context-dependent — pro-inflammatory in acute infection, sometimes pro-resolution later.
Wound healing and skin barrier
Endogenous LL-37 is upregulated in healing skin. Topical or local administration in animal wound models promotes re-epithelialization. Deficiency is implicated in chronic wound failure.
Vitamin D-induced expression
Endogenous LL-37 is one of the major effectors of vitamin D's antimicrobial action in macrophages. This is part of the rationale for vitamin D's effect on tuberculosis and respiratory infection susceptibility.
Risks & cautions
Cytotoxicity at higher doses
LL-37 is membrane-active and can damage host cells at concentrations not far above its antimicrobial concentration. Systemic dosing has a narrow therapeutic window in animal studies.
Autoimmunity association
Elevated LL-37 is implicated in psoriasis and lupus pathophysiology — it complexes with self-DNA/RNA and triggers TLR-mediated interferon responses. Chronic systemic elevation may not be benign.
Pro-tumor effects in some cancers
LL-37 has been shown to promote growth and metastasis in certain cancers (lung, breast, ovarian in preclinical models) while being anti-tumor in others. Net oncologic effect is unsettled.
Limited human safety data
No approved indication. Clinical trials have largely focused on topical or local administration. Systemic SC use in healthy adults is not well characterized.
Injection-site reactions
The peptide is membrane-active and can produce more local irritation than typical peptides.
Dosing
No standardized human protocol. Commonly reported research-peptide use is in the range of 100–500 mcg subcutaneously, often for short courses.
Vial sizes
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Half-life
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Route
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Half-life is short. Susceptible to proteolysis. The narrow therapeutic index relative to other peptides argues for conservative dosing. Topical formulations have a different risk profile than systemic administration.
Contraindications
In depth
LL-37 is the C-terminal 37-amino-acid fragment cleaved from human cathelicidin (hCAP18), the only cathelicidin in the human genome. It was characterized in the mid-1990s as part of the broader discovery of mammalian host defense peptides. It is expressed by neutrophils, epithelial cells (especially skin and respiratory tract), and macrophages.
The name "LL-37" reflects the two N-terminal leucine residues and the peptide length.
LL-37 has dual identity as antimicrobial and immunomodulator:
Direct microbial killing: LL-37 adopts an amphipathic alpha-helical structure on contact with negatively charged microbial membranes, inserts into the lipid bilayer, and disrupts membrane integrity (carpet model). Effective against many gram-positive and gram-negative bacteria, mycobacteria, some fungi, and enveloped viruses (including influenza, RSV, and several others in vitro).
Chemotaxis: Recruits neutrophils, monocytes, and T cells through FPR2 (formyl peptide receptor 2) and other receptors.
Inflammation modulation: Effects on cytokine production are context-dependent — can suppress LPS-induced TNF-α (anti-inflammatory) but also potentiate IL-6/IL-8 in other contexts.
Nucleic acid complexation: Binds bacterial DNA/RNA and self-DNA/RNA. The latter is implicated in autoimmunity — LL-37–self-DNA complexes activate TLR9 in plasmacytoid dendritic cells and drive type I interferon production (Lande 2007). This is part of psoriasis and lupus pathophysiology.
Wound healing: Promotes keratinocyte migration and angiogenesis at the wound edge.
Extensive. LL-37 is one of the most studied antimicrobial peptides. Mouse and rat studies confirm:
References
