LL-37

LL-37 is the only cathelicidin-derived antimicrobial peptide produced by the human immune system. It is a 37-amino-acid peptide (beginning with two leucine residues, hence the name) cleaved from its precursor protein hCAP18 by proteinase 3. LL-37 is constitutively expressed in neutrophils, macrophages, epithelial cells of the skin, respiratory tract, and gastrointestinal tract, and its expression is upregulated by vitamin D signaling — the mechanistic link behind vitamin D's well-documented immune-supportive effects. It belongs to the cathelicidin family, one of the two major classes of human antimicrobial peptides.

LL-37's mechanism of action is multifaceted. As an antimicrobial, it disrupts bacterial membranes through electrostatic interaction with negatively charged lipopolysaccharides (gram-negative) and lipoteichoic acids (gram-positive), creating pores that cause osmotic lysis. Critically, LL-37 is also active against bacterial biofilms — the protective polysaccharide matrices that make chronic infections resistant to conventional antibiotics. It penetrates established biofilm structures and prevents new biofilm formation. Beyond direct antimicrobial activity, LL-37 functions as an immune modulator: it acts as a chemoattractant for neutrophils, monocytes, and T-cells; stimulates angiogenesis and wound healing; modulates dendritic cell differentiation; and promotes the clearance of cellular debris through enhanced phagocytosis.

Research applications for LL-37 span antimicrobial defense, wound healing, immune modulation, and anti-biofilm strategies. Studies have demonstrated efficacy against methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa biofilms, Candida species, and various respiratory pathogens. Its wound-healing properties have been documented in chronic wound models, where it promotes re-epithelialization, angiogenesis, and inflammatory resolution simultaneously. Researchers investigating upper respiratory defense, chronic wound management, and immune system optimization have found LL-37 to be a compound of significant interest.

LL-37 is best suited for researchers investigating immune defense enhancement, biofilm-associated infections, chronic wound healing, and mucosal immunity. It is particularly relevant for protocols involving compromised immune function or environments with elevated infection risk.

Reconstitute the 5mg vial with 1-2ml bacteriostatic water. LL-37 is administered via subcutaneous injection, with typical research dosing of 50-100mcg per day. Due to its antimicrobial nature, reconstituted LL-37 is relatively resistant to bacterial contamination, but standard sterile handling and refrigeration at 2-8C remain essential. Use reconstituted solution within 21-28 days. LL-37 has a plasma half-life of approximately 1-2 hours and is susceptible to proteolytic degradation, so consistent daily dosing is standard in research protocols. Store lyophilized powder at -20C for long-term preservation.

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