The human body's endogenous antimicrobial peptide with broad antibacterial, antiviral, and immune-modulating effects.
LL-37 is the only cathelicidin produced in humans — a class of antimicrobial peptides that form part of the innate immune system's first-line defense. It is a 37-amino acid peptide produced by neutrophils, epithelial cells, macrophages, mast cells, and NK cells in response to infection and inflammation.
The name 'LL-37' comes from its N-terminal di-leucine (LL) and its 37 amino acids in length. It is derived from the larger precursor protein hCAP18 (human cationic antimicrobial protein-18) through cleavage by proteases. Its primary role is disrupting bacterial cell membranes — it can kill bacteria rapidly without inducing resistance the way conventional antibiotics do.
Beyond antimicrobial activity, LL-37 has increasingly recognized roles in immune regulation: it modulates the inflammatory response, promotes wound healing, attracts immune cells to sites of infection, and may have antiviral and antifungal properties. This broad immune-modulating profile has generated interest for therapeutic applications beyond infection.
Preclinical research demonstrates LL-37's efficacy against antibiotic-resistant bacteria (MRSA, VRE), viruses (including influenza and HIV in cell culture), and certain fungi. It promotes wound healing by stimulating angiogenesis and re-epithelialization. Research in inflammatory skin conditions (rosacea, psoriasis, atopic dermatitis) shows LL-37 plays complex roles — elevated in some conditions where it may contribute to inflammation.
Human clinical trials of LL-37 are limited. A Phase 1/2a trial showed possible benefit in venous leg ulcers when applied topically. The systemic therapeutic use of LL-37 is largely investigational. The complex role of LL-37 in inflammatory conditions means it may have both pro- and anti-inflammatory effects depending on context.
📚 Key Reference: PMID: 12089319 (LL-37 antimicrobial), PMID: 20053756 (LL-37 wound healing)
As an endogenous human peptide, LL-37 is generally tolerated. However, therapeutic administration of exogenous LL-37 is investigational. In some inflammatory conditions (like rosacea), elevated LL-37 contributes to pathology — careful patient selection is essential. Potential for allergic reactions. Quality of source material is critical — only from licensed compounding pharmacies. Consult your provider.
NOT FDA-approved for any therapeutic indication. Research use only. Available through some compounding pharmacies. Emerging clinical interest but very limited human trial data.