LL-37
The body's main antimicrobial peptide — a natural part of the immune system that fights bacteria, viruses, and fungi. Beyond fighting germs, it promotes wound healing, helps regulate inflammation, and stimulates new blood vessel growth at injury sites. The body makes it in response to infection or tissue damage. People use it for wound healing and immune support.
Dosage
50-200 mcg subcutaneous once daily
Dosages shown are for research reference only. Always consult a qualified healthcare provider.
Administration
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Effects
Antimicrobial
Broad-spectrum activity against bacteria, viruses, and fungi through membrane disruption.
Immune Modulation
Recruits immune cells, enhances phagocytosis, and neutralizes endotoxin.
Wound Healing
Promotes angiogenesis and re-epithelialization at injury sites.
Mechanism of Action
LL-37 is the only cathelicidin-derived antimicrobial peptide in humans, cleaved from the precursor protein hCAP-18 by proteinase 3 in neutrophil granules. It functions as a critical component of the innate immune system's first line of defense, with both direct antimicrobial activity and sophisticated immunomodulatory signaling.
The direct antimicrobial mechanism relies on LL-37's amphipathic alpha-helical structure — one face is positively charged (cationic) while the other is hydrophobic. The cationic face electrostatically attracts the negatively charged phospholipid headgroups of bacterial membranes (which differ from mammalian membranes in their lipid composition and charge distribution). Once bound, the hydrophobic face inserts into the lipid bilayer, creating pores or disrupting membrane integrity through a 'carpet' or 'toroidal pore' mechanism. This physical membrane disruption kills bacteria, fungi, and enveloped viruses rapidly and is difficult for microbes to develop resistance against, unlike conventional antibiotics that target specific enzymes.
The immunomodulatory functions are equally important. LL-37 acts as a chemoattractant for neutrophils, monocytes, and T cells through formyl peptide receptor-like 1 (FPRL1) activation, recruiting immune cells to infection sites. It promotes macrophage phagocytosis and enhances the killing capacity of neutrophil extracellular traps (NETs). Critically, LL-37 neutralizes bacterial lipopolysaccharide (LPS/endotoxin), preventing the cytokine storm that leads to sepsis. It also stimulates angiogenesis through VEGF upregulation and promotes wound re-epithelialization by activating epidermal growth factor receptor (EGFR) transactivation. LL-37 production is upregulated by vitamin D (which is why vitamin D status affects innate immunity), and its expression is found in skin, airways, the gastrointestinal tract, and virtually all epithelial barrier tissues.
Regulatory Status
Not FDA approved. Research peptide. Clinical trials underway for wound healing and chronic infections. Endogenous production can be boosted by vitamin D supplementation.
Risks & Safety
Common
injection site inflammation, local redness and swelling.
Serious
at high doses it can worsen inflammation instead of calming it; may trigger or worsen autoimmune conditions like psoriasis, lupus, or atherosclerosis.
Rare
body-wide inflammatory response, allergic reactions. Effects depend on dose — low doses calm inflammation, high doses can increase it.
Compare LL-37 With
Research Papers
30Published: February 19, 2026
AI Summary
Low-power fractional microneedle radiofrequency can treat stubborn rosacea, but the best treatment settings still need to be confirmed.
Published: January 21, 2026
AI Summary
Three antimicrobial peptides from dromedary camels kill drug-resistant bacteria and damage bacterial membranes with minimal harm to red blood cells. These findings open new paths for fighting antibiotic-resistant infections.
Published: January 20, 2025
AI Summary
The review ties together genes, nerve and blood vessel dysfunction, the TLR2/LL-37/mTORC1 pathway, and gut-skin microbes as drivers of rosacea. A clearer picture of causes could support better, more personalized treatments.
Published: February 3, 2026
AI Summary
Chinese skullcap, self-heal, and LL-37 each reduce Pseudomonas virulence by dampening quorum sensing genes. Combining plant extracts with LL-37 may offer new ways to treat resistant infections.
Published: January 30, 2026
AI Summary
Genome mining revealed 287 cathelicidin genes in reptiles, with 219 full sequences and six structural types per order. This catalog supports future work on reptile immunity and peptide-based drugs.
Published: January 26, 2026
AI Summary
A subset of neutrophils uses cathelicidin in NETs to kill anti-tumor T cells and help breast cancer spread to the lungs. Blocking this pathway could restore immunity and limit metastasis.
Published: January 7, 2026
AI Summary
Antimicrobial peptides are promising alternatives to antibiotics for gut infections because they act broadly and bacteria develop resistance slowly. The review summarizes current evidence for their use in intestinal disease.
Published: December 20, 2025
AI Summary
LL-37 levels rise in colorectal cancer and track with advanced stage and spread. It likely acts through FPR2 and TLR3, suggesting it could be a biomarker or treatment target.
Published: January 18, 2026
AI Summary
The review covers mammalian antimicrobial factors such as lysozymes, defensins, and cathelicidins. Understanding these systems may lead to new ways to treat resistant infections in people and animals.
Published: October 2, 2025
AI Summary
Heparan sulfate on the eye surface binds and blocks cathelicidins, helping Staphylococcus infect the cornea. Reducing 2-O-sulfation made mice more resistant, pointing to a new target for eye infections.
Published: March 9, 2026
AI Summary
LL-37, the main human cathelicidin, fights microbes and shapes immunity in the mouth. The review outlines its roles in oral health and disease.
Published: January 15, 2026
AI Summary
A frog-derived peptide (Cath-Ka) activates TLR2 and TLR4, boosts macrophage activity, and promotes inflammation. It may be useful for infections and other TLR-related conditions.
Published: January 26, 2026
AI Summary
A single amino acid at the defensin N-terminus controls how well LL-37 and defensins work together to kill bacteria while sparing host cells. HNP2 lacks this cooperation, unlike HNP1, HNP3, HNP4, and hBD1.
Published: January 13, 2026
AI Summary
Five bovine host defense peptides alter immune and inflammatory responses in blood and airway cells in different ways. Their effects depend on context and could inform new treatments for livestock infections.
Published: June 5, 2026
AI Summary
LL37 binds cell-free DNA and blocks DNase, worsening inflammation in autoimmune disease. Giving heparin first to release the DNA, then a long-acting DNase nanoparticle, reduced joint inflammation in a rheumatoid arthritis model.
Published: March 5, 2026
AI Summary
Three cathelicidins from pygmy sperm whales kill bacteria, disrupt biofilms, and clear persisters. Kb5 was most effective and improved survival in mice with peritonitis.
Published: January 5, 2026
AI Summary
Cathelicidins link gut immunity to brain inflammation: they protect the gut barrier and shape microbes, but in the brain their effects depend on where they come from. They may be useful targets for gut–brain disorders.
Published: February 14, 2026
AI Summary
A peptide built from cathelicidin and LL-37 fragments (KF-22) kills drug-resistant bacteria, disrupts biofilms, and is safe in mice. It is a strong candidate for further development against resistant infections.
Published: March 21, 2026
AI Summary
Gum disease bacteria may weaken innate immunity and degrade LL-37, allowing herpesviruses to spread and contribute to Alzheimer’s. Treating the infection or blocking its enzymes could reduce risk.
Published: December 17, 2025
AI Summary
Three cathelicidin-like peptides from a coastal bird were identified; Cr1 was most potent, safe, and effective in a mouse infection model. Cr1 is a promising lead for new antimicrobials.
Published: February 15, 2026
AI Summary
LL37 triggers mitochondrial stress in mast cells, which activates the mtDNA/cGAS/STING pathway and drives rosacea inflammation. Understanding this chain could lead to new treatments for the condition.
Published: January 18, 2026
AI Summary
Pneumococcal S protein helps bacteria resist LL-37 and lysozyme by coordinating cell wall repair. Blocking this pathway could make antibiotics more effective.
Published: December 2, 2025
AI Summary
LD4-PP, derived from LL-37, kills drug-resistant E. coli, disrupts biofilms, and protects bladder cells from infection-induced death. It is a promising candidate for urinary tract infections.
Published: December 11, 2025
AI Summary
A frog cathelicidin (QsCATH) reduces inflammation in macrophages by dampening NF-κB and related pathways. It may inform new peptide-based treatments for infection and inflammation.
Published: November 25, 2025
AI Summary
Bacteriophages plus grape seed proanthocyanidins improved growth, gut barrier, and immunity in Salmonella-challenged broilers. The combo boosted cathelicidin and defensin expression and cut harmful bacteria.
Published: November 25, 2025
AI Summary
LL37 drives mast cell activation and rosacea inflammation through the TLR2/JAK2/STAT3 pathway. Targeting this axis could offer new therapeutic options for the disease.
Published: December 4, 2025
AI Summary
Host defense peptides such as defensins and cathelicidins act against malaria at several stages. The review summarizes their roles and the limits of current knowledge.
Published: December 1, 2025
AI Summary
Packaging LL-37 into bacterial vesicles improved antibacterial and wound-healing effects while lowering toxicity. The approach could be a useful delivery system for antimicrobial peptides.
Published: November 30, 2025
AI Summary
The peptide bac7 (1-35) disrupts bacterial membranes and ribosomes, breaks down Klebsiella biofilms, and blocks organ spread in mice. It shows promise against drug-resistant Klebsiella infections.
Published: October 21, 2025
AI Summary
Cathelicidins and defensins fused to phage capsids keep antimicrobial activity. The system can produce vaccine and antimicrobial particles without complex genetic engineering.
Frequently Asked Questions
What is LL-37?
The body's main antimicrobial peptide — a natural part of the immune system that fights bacteria, viruses, and fungi. Beyond fighting germs, it promotes wound healing, helps regulate inflammation, and stimulates new blood vessel growth at injury sites. The body makes it in response to infection or tissue damage. People use it for wound healing and immune support.
What is LL-37 used for?
The body's main antimicrobial peptide — a natural part of the immune system that fights bacteria, viruses, and fungi. Beyond fighting germs, it promotes wound healing, helps regulate inflammation, and stimulates new blood vessel growth at injury sites. The body makes it in response to infection or tissue damage. People use it for wound healing and immune support.
What is the dosage for LL-37?
Research: 50-200 mcg subcutaneous once daily. Topical formulations also used for wound healing applications. No standardized clinical dosing established.
What are the side effects of LL-37?
Common: injection site inflammation, local redness and swelling. Serious: at high doses it can worsen inflammation instead of calming it; may trigger or worsen autoimmune conditions like psoriasis, lupus, or atherosclerosis. Rare: body-wide inflammatory response, allergic reactions. Effects depend on dose — low doses calm inflammation, high doses can increase it.
How does LL-37 work?
LL-37 is the only cathelicidin-derived antimicrobial peptide in humans, cleaved from the precursor protein hCAP-18 by proteinase 3 in neutrophil granules. It functions as a critical component of the innate immune system's first line of defense, with both direct antimicrobial activity and sophisticated immunomodulatory signaling. The direct antimicrobial mechanism relies on LL-37's amphipathic alpha-helical structure — one face is positively charged (cationic) while the other is hydrophobic. The cationic face electrostatically attracts the negatively charged phospholipid headgroups of bacterial membranes (which differ from mammalian membranes in their lipid composition and charge distribution). Once bound, the hydrophobic face inserts into the lipid bilayer, creating pores or disrupting membrane integrity through a 'carpet' or 'toroidal pore' mechanism. This physical membrane disruption kills bacteria, fungi, and enveloped viruses rapidly and is difficult for microbes to develop resistance against, unlike conventional antibiotics that target specific enzymes. The immunomodulatory functions are equally important. LL-37 acts as a chemoattractant for neutrophils, monocytes, and T cells through formyl peptide receptor-like 1 (FPRL1) activation, recruiting immune cells to infection sites. It promotes macrophage phagocytosis and enhances the killing capacity of neutrophil extracellular traps (NETs). Critically, LL-37 neutralizes bacterial lipopolysaccharide (LPS/endotoxin), preventing the cytokine storm that leads to sepsis. It also stimulates angiogenesis through VEGF upregulation and promotes wound re-epithelialization by activating epidermal growth factor receptor (EGFR) transactivation. LL-37 production is upregulated by vitamin D (which is why vitamin D status affects innate immunity), and its expression is found in skin, airways, the gastrointestinal tract, and virtually all epithelial barrier tissues.
How is LL-37 administered?
LL-37 is administered via subcutaneous injection or topical.
What is the half-life of LL-37?
The half-life of LL-37 is 4-6 hours (varies by tissue environment).
Is LL-37 legal?
Not FDA approved. Research peptide. Clinical trials underway for wound healing and chronic infections. Endogenous production can be boosted by vitamin D supplementation.
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