Quick summary
LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino acid fragment of hCAP-18 with broad-spectrum activity against bacteria, viruses, and fungi. It modulates innate immunity, promotes wound healing, and is closely linked to vitamin D status.
Overview
LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino-acid peptide cleaved from the precursor protein hCAP-18. It is produced by immune cells (neutrophils, macrophages), epithelial cells, and keratinocytes as part of the innate immune response. It has broad-spectrum antimicrobial activity against bacteria, viruses, and fungi, and plays a role in wound healing and immune modulation.
Mechanism of action
LL-37 has a helical amphipathic structure that allows it to insert into and disrupt microbial cell membranes, creating pores and causing lysis. Beyond direct antimicrobial action, it modulates the immune response by recruiting immune cells (chemotaxis), promoting wound healing, inhibiting biofilm formation, neutralizing bacterial endotoxins (LPS), and modulating TLR signaling. Vitamin D regulates LL-37 expression, linking vitamin D deficiency to increased infection susceptibility.
Dosing protocols
| Purpose | Route | Dosage | Frequency | Notes |
|---|---|---|---|---|
| immune support | subcutaneous | 50–100 mcg | daily | Low doses used for systemic immune support. Higher doses used in clinical settings for wound healing. 2-4 week cycles. |
Dosing information is for educational purposes only. Consult a qualified healthcare professional before using any peptide.
Research summary
Extensive research on innate immunity. Studies show broad-spectrum activity against MRSA, E. coli, Pseudomonas, Candida, and enveloped viruses including influenza and HIV. Anti-biofilm activity demonstrated against surgical implant infections. Wound healing promotion through angiogenesis and re-epithelialization. Phase I/II clinical trials for chronic leg ulcers showed improved healing. Vitamin D supplementation increases LL-37 levels — a key finding linking vitamin D to immune function.[1][2][3][4][5]
Evidence grading
Each claimed benefit is graded by the strength of available evidence. Grades reflect study quality, not effect size.
Strong = multiple RCTs · Moderate = limited trials or observational · Preliminary = animal or in vitro only · Insufficient = anecdotal or no published data
Side effects
Side effects vary by individual. This is not an exhaustive list. Report unusual symptoms to a healthcare professional.
Common stacks
Peptides commonly paired with LL-37 for synergistic effects.
Legal status
Not FDA-approved. Available as a research peptide. In clinical development for wound healing and infection applications.
Sourcing & access
Research compound
LL-37 is classified as a research compound. Regulatory status varies by jurisdiction. Always verify current legal status and source from vendors providing third-party certificates of analysis (COA).
Frequently asked questions
LL-37 is a 37-amino acid antimicrobial peptide cleaved from the precursor protein hCAP-18. It is produced by immune cells and epithelial cells as part of the innate immune response and has broad-spectrum activity against bacteria (including MRSA), viruses, and fungi.
LL-37 has an amphipathic helical structure that inserts into and disrupts microbial cell membranes. Beyond direct antimicrobial action, it recruits immune cells, promotes wound healing through angiogenesis, inhibits biofilm formation, and neutralizes bacterial endotoxins.
Reported side effects include injection site reactions, redness or swelling, and rare mild fever attributed to immune activation. LL-37 is not FDA-approved and is available only as a research peptide, so its long-term safety profile in humans is not formally characterized outside small Phase I and II chronic wound healing trials.
Vitamin D directly regulates LL-37 gene expression through the vitamin D receptor, which binds response elements in the cathelicidin gene promoter. Supplementation measurably increases endogenous LL-37 levels, and this pathway is the core mechanism linking vitamin D deficiency to increased susceptibility to bacterial, viral, and fungal infections.
Research references
- LL-37, the only human member of the cathelicidin family of antimicrobial peptidesPubMed
- Cathelicidin LL-37: a multitask antimicrobial peptideReview
- Therapeutic Potential of Cathelicidin Peptide LL-37, an Antimicrobial Agent, in a Murine Sepsis ModelPubMed
- The Human Cathelicidin Antimicrobial Peptide LL-37 and Mimics are Potential Anticancer DrugsPubMed
- Antimicrobial peptide LL-37 promotes bacterial phagocytosis by human macrophagesPubMed