What is the dosing range for LL-37?

LL-37 is typically dosed at 100mcg (low), 300mcg (moderate), or 500mcg (high) mcg, administered Daily or 3–5x weekly. These ranges are aggregated from preclinical research and community protocols — not medical dosing guidance.

What are the reported side effects of LL-37?

Reported side effects of LL-37 include: Injection site redness and irritation (common — pro-inflammatory at injection site), Transient flu-like symptoms (immune activation), Local induration, High doses may be cytotoxic — dose-response curve is non-linear.

Healing

LL-37

Also known as: Cathelicidin LL-37, hCAP-18 C-terminal fragment, CRAMP (murine equivalent)

LL-37 is a research compound not approved for human use. For informational purposes only.

📚 Content aggregated from:3 peer-reviewed sources·r/Peptides community·PubMed / NCBI

Overview

LL-37 is the only human cathelicidin — a host defense peptide produced by neutrophils, epithelial cells, and macrophages in response to infection and inflammation. It functions simultaneously as a broad-spectrum antimicrobial agent and an immune-modulatory signaling molecule. Research interest has expanded dramatically since COVID-19 studies linked low LL-37 levels to severe outcomes, and gut health research identified it as a key regulator of intestinal barrier integrity.

Research Summary

LL-37 exerts antimicrobial activity by disrupting bacterial membranes via electrostatic interaction with negatively charged lipopolysaccharide — effective against gram-positive and gram-negative bacteria, fungi, and enveloped viruses including SARS-CoV-2 in vitro. Beyond direct antimicrobial action, LL-37 modulates innate immunity through TLR4 signaling, promotes wound healing via EGFR and FPRL1 receptor activation, and has demonstrated anti-biofilm activity against P. aeruginosa and S. aureus. Vitamin D is the primary driver of endogenous LL-37 production.

Dosing Range

low

100mcg

moderate

300mcg

high

500mcg

Units: mcg · Frequency: Daily or 3–5x weekly

Dosing ranges are aggregated from preclinical research and community protocols. Not medical dosing guidance.

Administration Routes

Subcutaneous injectionIntranasal (for respiratory applications)Topical (wound care)

Reconstitution Notes

Reconstitute with sterile water or bacteriostatic water. Sensitive to aggregation at high concentrations — use 0.5mg/mL or lower. Vortex gently. Stable 14 days refrigerated; minimize freeze-thaw cycles.

Step-by-step reconstitution guide →

Supplies you'll need

Insulin Syringes (U-100)Reconstitution Needles Lambda BAC Water Alcohol Prep Pads

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Reported Side Effects

Injection site redness and irritation (common — pro-inflammatory at injection site)
Transient flu-like symptoms (immune activation)
Local induration
High doses may be cytotoxic — dose-response curve is non-linear

Research Papers

3 peer-reviewed sources

LL-37: The Only Human Member of the Cathelicidin Family of Antimicrobial Peptides

Biochimica et Biophysica Acta2005

Vitamin D Induces Innate Antibacterial Responses in Human Monocytes/Macrophages by Upregulating Cathelicidin Antimicrobial Peptide

Journal of Immunology2006

LL-37 and SARS-CoV-2: Vitamin D and COVID-19 Severity

Nutrients2020

Community Experiences

Aggregated from public forums. Anecdotal — not clinical evidence.

r/Peptides

Community reports on LL-37 for chronic infections, gut permeability, and immune support protocols.

View original thread

Overview

LL-37 sits at the intersection of antimicrobial defense and immune regulation — it is not simply an antibiotic peptide, but a multifunctional signaling molecule that bridges innate and adaptive immunity. Named for its 37-amino acid length beginning with two leucines, it is the C-terminal fragment of the precursor protein hCAP-18.

Mechanism of Action

Antimicrobial Activity

LL-37 disrupts microbial membranes through electrostatic interaction. Its amphipathic alpha-helix structure inserts into negatively charged bacterial membranes (rich in phosphatidylglycerol and cardiolipin), forming pores that cause osmotic lysis. This mechanism is:

Broad-spectrum (gram+ and gram−)
Effective against biofilms (penetrates the extracellular matrix)
Difficult for bacteria to develop resistance against (membrane composition changes slowly)

Immune Modulation

Beyond killing pathogens, LL-37:

Neutralizes LPS (lipopolysaccharide) — prevents gram-negative endotoxin-driven sepsis cascade
Activates dendritic cells via TLR4 and FPR2 — bridges innate to adaptive immunity
Promotes wound healing — activates EGFR on keratinocytes to drive re-epithelialization
Anti-inflammatory at physiological concentrations — modulates cytokine balance

Vitamin D Connection

1,25-dihydroxyvitamin D3 (the active form) directly upregulates LL-37 gene transcription in epithelial cells, macrophages, and neutrophils. This explains the epidemiological link between vitamin D deficiency and susceptibility to respiratory infections — low D → low LL-37 → reduced innate defense.

Gut Health Applications

LL-37 is secreted by intestinal epithelial cells and maintains barrier integrity by:

Killing pathogenic bacteria preferentially over commensal flora
Promoting tight junction protein expression
Suppressing local NF-κB-driven inflammation in the gut mucosa

Research interest in LL-37 for IBD, SIBO, and post-antibiotic gut repair is growing, though no clinical trials are complete.

COVID-19 Research Context

Multiple studies (2020–2022) noted that severe COVID-19 outcomes correlated with low vitamin D and low LL-37 levels. In vitro, LL-37 disrupts SARS-CoV-2 envelope membranes and reduces viral entry. While this doesn't constitute clinical evidence for prophylaxis, it reactivated research interest in the peptide.