LL-37
The only known human cathelicidin antimicrobial peptide, studied for antimicrobial activity, immune modulation, and wound healing in research.
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What is LL-37?
LL-37 is the only known human cathelicidin, a family of host defense peptides found across vertebrate species. The peptide is produced from the precursor protein hCAP-18 (human cationic antimicrobial protein, 18 kDa) through enzymatic cleavage by proteinase 3 in neutrophils, kallikrein-5 in skin, and other tissue-specific proteases. The name LL-37 refers to its 37-amino-acid length beginning with the dipeptide leucine-leucine. The peptide is constitutively expressed in many epithelial tissues and stored in neutrophil granules for release at sites of infection or inflammation.
LL-37 is notable in research as a critical component of the innate immune system, providing rapid first-line defense against bacterial, viral, and fungal pathogens while also serving immunomodulatory roles that bridge innate and adaptive immunity. Beyond direct antimicrobial activity, the peptide has been investigated for roles in wound healing, angiogenesis, chemotaxis of immune cells, and modulation of inflammatory responses. Dysregulated LL-37 expression has been implicated in conditions including chronic wound healing failure, psoriasis, rosacea, and certain inflammatory skin disorders.
Mechanism of action
LL-37’s mechanisms of action have been investigated across multiple pathways:
- Direct antimicrobial activity: The peptide’s amphipathic α-helical structure allows it to interact with negatively charged microbial membranes, causing membrane permeabilization and microbial cell death across gram-positive and gram-negative bacteria, enveloped viruses, and fungi.
- Immunomodulation: Research has documented effects on neutrophils, monocytes, macrophages, and dendritic cells, including chemotaxis promotion, cytokine production modulation, and influence on adaptive immune response development.
- Wound healing and tissue repair: Studies have shown effects on keratinocyte and endothelial cell migration, angiogenesis, and growth factor signaling, with reduced LL-37 levels associated with chronic wound healing failure.
- LPS neutralization: The peptide binds and neutralizes bacterial lipopolysaccharide, reducing inflammatory responses to gram-negative bacterial infections.
- Resistance-evasion mechanism: The broad membrane disruption mechanism makes microbial resistance development difficult, distinguishing the peptide from conventional small-molecule antibiotics.
These pathways are characterized in both preclinical models and human research contexts.
Research applications
LL-37 has been investigated across several research domains, with the most active areas including:
- Antimicrobial research: Studies have examined LL-37 against numerous pathogens including methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Mycobacterium tuberculosis, herpes simplex virus, influenza virus, and Candida species. The compound and its analogs have been investigated as potential alternatives to conventional antibiotics.
- Chronic wound research: Reduced LL-37 levels are associated with chronic wound healing failure, particularly in diabetic ulcers and pressure ulcers. Research has examined supplementation with LL-37 or its analogs to support wound healing in these contexts.
- Inflammatory skin disease research: LL-37 expression is dysregulated in psoriasis (elevated, contributing to autoimmunity) and rosacea (post-translational modifications producing pro-inflammatory fragments). Research has examined therapeutic modulation of LL-37 pathways for these conditions.
- Respiratory and gut research: LL-37 plays critical roles in maintaining barrier function and microbial defense in respiratory and gastrointestinal tissues. Research has examined applications in cystic fibrosis, inflammatory bowel disease, and other conditions with epithelial barrier dysfunction.
- Cancer immunotherapy research: Studies have examined LL-37’s effects on tumor immune microenvironment and its potential roles in modulating anti-tumor immune responses across various cancer models.
This compound is intended for laboratory research use only. It has not been approved for human therapeutic use by any regulatory agency.
Storage & reconstitution
In its lyophilized form, LL-37 tolerates ambient temperatures during shipping but should be stored long-term at -20°C, protected from light. Properly stored lyophilized peptide remains stable for 24 months or longer.
Once reconstituted with bacteriostatic water for injection, LL-37 solutions should be stored refrigerated at 2-8°C and used within 28 days. The peptide can adhere to standard glass and some plastic surfaces, so low-binding containers are preferred. Avoid repeated freeze-thaw cycles, which can degrade peptide structure and reduce activity.
Visual inspection should be performed before each use. The reconstituted solution should be clear and colorless. Reject any solution that appears cloudy, discolored, or contains visible particulate matter.
For step-by-step reconstitution calculations, see our reconstitution calculator.
For laboratory research use only. The compound described on this page is intended exclusively for in vitro research and laboratory experimentation by qualified researchers and is not for human or veterinary use. It is not a drug, food, dietary supplement, or cosmetic, and has not been approved by the FDA, Health Canada, EMA, or any other regulatory authority for the diagnosis, treatment, cure, mitigation, or prevention of any disease or medical condition. The information provided on this page is for educational and reference purposes only and does not constitute medical advice. By accessing this content you confirm that you are a qualified researcher purchasing for legitimate laboratory purposes.