Cathelicidin LL-37

Cathelicidin LL-37 is a 37-amino-acid human antimicrobial peptide from the cathelicidin family that defends against bacterial, viral, and fungal infections by disrupting microbial membranes, while also promoting wound healing and modulating immunity.

Brief glance

The primary outcome is Immune Support, but it's also used for Recovery & Repair. This compound is considered a Peptide. It is also known as LL-37, CAP-18. It is not currently indicated as compoundable in 503A pharmacies. It is not listed under a DEA schedule.

Overview

LL-37 is a powerful cationic antimicrobial peptide derived from the precursor protein cathelicidin that exhibits broad-spectrum activity against bacteria, viruses, fungi, and biofilms. Naturally produced by immune cells including epithelial cells, neutrophils, and macrophages in response to pathogens or injury, LL-37 extends its effects beyond antimicrobial action to support immune modulation, inflammation resolution, and tissue regeneration. The peptide's unique mechanism involves disrupting microbial cell membranes while simultaneously enhancing wound healing and endothelial cell proliferation, making it a candidate for treating infections and promoting recovery.

Cathelicidin LL-37 is the active 37-amino-acid form of the human cathelicidin antimicrobial peptide (CAMP), derived from the precursor protein CAP-18 through proteolytic cleavage by enzymes such as proteinase 3 or skin serine proteases like kallikrein 5 and 7. Produced by innate immune cells including neutrophils, macrophages, and epithelial cells, particularly in response to infection, injury, or inflammation, it exhibits broad-spectrum antimicrobial activity against bacteria, viruses, fungi, and biofilms by disrupting microbial membranes and inhibiting processes like quorum sensing. Beyond direct pathogen killing, LL-37 modulates immune responses, promotes wound healing through cell proliferation, migration, and angiogenesis, and acts as an alarmin by influencing receptors such as formyl peptide receptor-like 1 and Toll-like receptors. Dysregulated levels contribute to skin disorders like rosacea and psoriasis, where excess LL-37 drives inflammation, highlighting its dual role in host defense and pathology.

Benefits

Cathelicidin LL-37 exhibits direct antimicrobial activity against bacteria, promotes chemotaxis and chemokine induction, and supports wound healing and angiogenesis, positioning it as a candidate for topical treatment of polymicrobially infected wounds such as diabetic ulcers.¹,² In preclinical sepsis models, intravenous administration of LL-37 improves survival by suppressing pro-inflammatory macrophage pyroptosis, enhancing neutrophil extracellular trap (NET) release for bactericidal effects, and stimulating antimicrobial ectosome production, while reducing bacterial loads in blood and peritoneal fluids.³ Its anti-biofilm properties at sub-inhibitory concentrations further support potential utility against chronic biofilm-associated infections.²

Side effects

Common side effects of Cathelicidin LL-37 include mild injection site reactions such as temporary redness, swelling, or discomfort, along with transient fatigue, mild flu-like symptoms, or gastrointestinal upset, which typically resolve quickly.⁴,⁵ Less common effects may involve a Herxheimer reaction (die-off symptoms) occurring in more than 10% of cases.⁶ Serious adverse effects are rare but can include allergic reactions, immune activation symptoms, or cytotoxicity at high concentrations, with potential toxicity to human leukocytes, T-lymphocytes, and hemolytic effects due to interactions with eukaryotic cell membranes.⁴,⁶,⁷ LL-37 may drive inflammation, making it contraindicated in certain inflammatory conditions, and it exhibits dual immunomodulatory effects that can promote or inhibit inflammation depending on context.⁶,⁸,⁹ Physicians should monitor patient response closely, adjusting dosing to minimize risks, and consultation with a healthcare provider is essential prior to use.⁴,⁵

Mechanisms of action

Cathelicidin LL-37 exerts its antimicrobial effects through direct interactions with pathogenic membranes, utilizing its cationic and lipophilic properties to interact with the anionic lipopolysaccharide components of bacterial cell membranes and disrupt membrane integrity². The peptide accomplishes this by forming pores in bacterial cell walls at sufficient concentrations, allowing translocation of monomers into the periplasmic space and enabling leakage of cytoplasmic material, while also perturbing membrane homeostasis through interactions with electron transport proteins¹⁰. Beyond direct antimicrobial activity, LL-37 operates through activation of multiple cell surface receptors—including G protein-coupled receptors, receptor tyrosine kinases, ligand-gated ion channels, and toll-like receptors—which trigger downstream signaling pathways that modulate immune responses¹¹. At the cellular level, LL-37 enhances antimicrobial host defense by reducing epithelial cell permeability to prevent pathogen entry, modulating chemokine and cytokine production through monocytes and lymphocytes, and regulating both pro-inflammatory and anti-inflammatory responses¹⁰. The peptide demonstrates broad-spectrum activity against both gram-positive and gram-negative bacteria as well as fungal organisms such as Candida albicans through membrane permeabilization mechanisms that are largely independent of conventional antibiotic resistance pathways²,¹².