LL-37

Mechanism

Your body's own natural antibiotic peptide. It fights bacteria, viruses, and fungi by poking holes in their outer membranes. Beyond killing microbes, it also calms inflammation and helps wounds heal. Used as an injection or topically for infections, biofilms, and chronic inflammatory conditions.

Effects

**Innate Immune System (Tier 1 — Extensively Studied):** LL-37 is the only cathelicidin antimicrobial peptide in humans — a 37-amino acid peptide cleaved from its precursor hCAP18 by proteinase 3. It is a first-line innate immune defense molecule with DIRECT antimicrobial activity against bacteria (Gram-positive and Gram-negative), fungi (Candida spp.), enveloped viruses, and mycobacteria. Mechanism: LL-37 is cationic and amphipathic — it inserts into microbial membranes, forming pores that cause osmotic lysis. At sub-bactericidal concentrations, it disrupts biofilms by preventing initial bacterial attachment and degrading established biofilm matrix. **Biofilm Disruption (Tier 1-2 — Critical for Functional Medicine):** LL-37 is one of the most potent known natural biofilm disruptors. It prevents Pseudomonas aeruginosa biofilm formation at 0.5mcg/mL (sub-MIC). Degrades established Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas biofilms. Disrupts polymicrobial biofilms in chronic wound, sinus, and gut environments. This biofilm activity is why it is heavily used in functional medicine for Lyme disease (Borrelia burgdorferi forms biofilms), SIBO, and chronic sinusitis. **Immunomodulatory (Tier 1):** Beyond direct killing, LL-37 is a potent immune modulator. It recruits immune cells (chemotactic for neutrophils, monocytes, and T cells), promotes wound healing (stimulates keratinocyte migration and angiogenesis), modulates dendritic cell differentiation, suppresses LPS-induced TNF-alpha (anti-endotoxin), and activates the FPRL1/FPR2 receptor for chemotaxis. It bridges innate and adaptive immunity. **Respiratory System (Tier 2):** LL-37 is produced by airway epithelial cells and is a key component of airway surface liquid defense. Deficiency of LL-37 (low vitamin D → low cathelicidin expression) is associated with increased respiratory infection susceptibility. This is the mechanistic basis for vitamin D's role in respiratory immune defense. Nebulized LL-37 has been explored for respiratory infections and cystic fibrosis airway colonization. **Gut/GI System (Tier 2):** LL-37 is expressed by colonic epithelial cells and Paneth cells. It maintains gut barrier integrity by killing invasive bacteria while sparing commensal species (selectivity based on membrane composition). Deficiency associated with increased gut permeability and dysbiosis. Modulates gut inflammation through NF-kB pathway regulation. **Anti-inflammatory Paradox (Tier 2):** Despite being an "antimicrobial" peptide, LL-37 has potent anti-inflammatory effects in certain contexts — it neutralizes LPS (endotoxin), reduces sepsis-related cytokine storm, and inhibits pyroptosis. However, in autoimmune contexts (psoriasis, lupus), LL-37 can act as an autoantigen and AMPLIFY inflammation by forming complexes with self-DNA that activate TLR9 in plasmacytoid dendritic cells. This dual nature requires clinical awareness.

Practitioner Guide

**Lyme Disease / Tick-Borne Illness Protocol:** - LL-37 is a cornerstone of integrative Lyme protocols due to its biofilm-disrupting and direct borreliacidal activity - Dose: 50-100mcg SC daily during active treatment phase (4-8 weeks) - Often combined with: BPC-157 (gut/tissue repair), thymosin alpha-1 (immune support), and antimicrobial herbs or antibiotics - Biofilm disruption protocol: LL-37 100mcg SC daily for 2 weeks before starting or alongside antibiotic therapy — "break the biofilm first, then kill the exposed organisms" - Some practitioners pulse LL-37: 2 weeks on, 1 week off, for 2-3 cycles - Herxheimer reactions are common when biofilms are disrupted — start low (25-50mcg) and titrate up **Mold Illness / CIRS Protocol:** - LL-37 for CIRS: addresses the chronic innate immune activation and biofilm colonization (nasal MARCoNS — Multiple Antibiotic Resistant Coagulase Negative Staphylococci) - Dose: 50-100mcg SC daily for 2-4 weeks - Nasal use for MARCoNS: some practitioners compound LL-37 into nasal spray (concentration varies, typically 50-100mcg/mL, 1-2 sprays each nostril BID) - Sequence in Shoemaker protocol: LL-37 can be used to help eradicate MARCoNS (Step 6 in Shoemaker protocol), often alongside BEG spray (Bactroban/EDTA/Gentamicin) - Often combined with VIP (vasoactive intestinal peptide) — LL-37 addresses infection/biofilm while VIP addresses the inflammatory cascade **Gut Dysbiosis / SIBO / Leaky Gut Protocol:** - Oral LL-37: 50-100mcg oral daily (sublingual or in capsule on empty stomach) - Some practitioners use both SC (systemic) and oral (local gut effect) simultaneously - Targets biofilm-forming gut pathogens while preserving commensal bacteria - Combined with: BPC-157 (gut healing), KPV (anti-inflammatory), larazotide (tight junction support) - Duration: 4-8 weeks as part of comprehensive gut restoration protocol **Nebulized Use for Respiratory Infections:** - Nebulized LL-37: 25-50mcg in 2-3mL sterile saline, nebulized 1-2x daily - Used for: chronic sinusitis, recurrent respiratory infections, post-COVID respiratory symptoms, biofilm-associated respiratory colonization - Often combined with nebulized glutathione (200-400mg) for synergistic mucolytic/antimicrobial effect - Caution: some patients report transient airway irritation — start with lower concentration - NOT FDA-approved for nebulized use — practitioner discretion / compounding pharmacy **Important Clinical Considerations:** - Vitamin D status directly regulates LL-37 expression — always optimize vitamin D (target 60-80 ng/mL) alongside LL-37 therapy - In psoriasis or lupus patients: LL-37 may WORSEN autoimmune flares (acts as autoantigen in these conditions) — relative contraindication - LL-37 is degraded by bacterial proteases — in heavily infected environments, higher doses may be needed - Store reconstituted peptide refrigerated; avoid repeated freeze-thaw; use within 30 days

Dosing Protocols

Contraindications & Cautions

• hard stop — Pregnancy
  No human safety data for exogenous LL-37 during pregnancy. Immunomodulatory peptide could affect maternal-fetal immune tolerance and placental function.
  Action: Do not use during pregnancy.
• hard stop — Breastfeeding
  No data on safety of exogenous LL-37 during lactation. While LL-37 is naturally present in breast milk, supraphysiologic doses have unknown effects.
  Action: Do not use while breastfeeding.
• hard stop — Under 18 years of age
  Research peptide. Not for pediatric use.
  Action: Do not provide to individuals under 18.
• requires physician — Autoimmune disease (lupus, psoriasis, rosacea)
  LL-37 (cathelicidin) is endogenously elevated in psoriasis, rosacea, and lupus, where it acts as an autoantigen driving inflammatory pathology. Exogenous LL-37 administration may worsen these conditions by amplifying the existing pathological immune response, promoting neutrophil extracellular trap (NET) formation, and activating plasmacytoid dendritic cells.
  Action: Requires specialist evaluation by dermatologist or rheumatologist. Avoid in active psoriasis, rosacea, or lupus flares. Monitor for disease worsening.
• caution — Sepsis or systemic infection
  LL-37 has complex immunomodulatory effects. While antimicrobial, it can also promote excessive inflammation and cytokine release in the setting of severe systemic infection, potentially worsening sepsis-associated organ damage.
  Action: Use with caution. Monitor inflammatory markers. Physician supervision required in acute infection settings.

Evidence

• Little peptide, big effects: the role of LL-37 in inflammation and autoimmune disease

  Kahlenberg JM, Kaplan MJ (2013) — Journal of Immunology — PMID: 23913958

  Comprehensive review of LL-37 (human cathelicidin) biology covering antimicrobial activity against bacteria, viruses, and fungi; immunomodulatory functions including chemotaxis, cytokine modulation, and dendritic cell activation; and roles in autoimmune diseases (psoriasis, lupus). LL-37 serves as a critical bridge between innate and adaptive immunity.

  moderate

• Wound healing activity of the human antimicrobial peptide LL37

  Ramos R, Silva JP, Rodrigues AC, Costa R, Guardao L, Schmitt F, Soares R, Vilanova M, Domingues L, Gama M (2011) — Peptides — PMID: 21262303

  LL-37 accelerated wound closure in a murine excisional wound model, demonstrating dual antimicrobial and wound healing properties. The peptide promoted re-epithelialization, angiogenesis, and reduced bacterial colonization at wound sites. Mechanism involves activation of formyl peptide receptor-like 1 (FPRL1) and promotion of keratinocyte migration.

  moderate

Stacks featuring this peptide

Research Summary

**Tier 1 — Extensively Published Basic and Translational Science:** - Thousands of peer-reviewed publications on LL-37/cathelicidin (one of the most-studied antimicrobial peptides) - Direct antimicrobial activity demonstrated against: S. aureus, MRSA, P. aeruginosa, E. coli, K. pneumoniae, Candida albicans, M. tuberculosis, and Borrelia burgdorferi - Biofilm disruption: in vitro studies showing LL-37 prevents and disrupts Pseudomonas and Staphylococcus biofilms (Overhage et al., Infect Immun 2008) - Vitamin D-cathelicidin axis: landmark studies by Liu et al. (Science 2006) showing vitamin D induces LL-37 expression in macrophages — mechanistic basis for vitamin D's immune role - Wound healing: LL-37 promotes re-epithelialization and angiogenesis (Heilborn et al., J Invest Dermatol 2003) **Tier 2 — Clinical Evidence:** - Phase I/II clinical trial: topical LL-37 for chronic venous leg ulcers showed improved healing rates (Groenink et al., 2014) - Observational studies: low serum LL-37 levels associated with increased infection susceptibility, especially in ICU patients and neonates - Cystic fibrosis: LL-37 levels in airway fluid correlate with bacterial colonization resistance - COVID-19: multiple studies showing low LL-37/cathelicidin levels associated with severe COVID outcomes **Tier 3 — Emerging/Functional Medicine:** - Nebulized LL-37 for respiratory infections: preclinical data promising, no completed human RCTs - LL-37 for Lyme biofilms: in vitro data showing activity against Borrelia biofilms; clinical use is practitioner-level evidence - Oral/sublingual LL-37 for gut dysbiosis: pharmacokinetic data on gut stability is limited; clinical use is empirical - Synthetic LL-37 analogs with improved protease resistance in development - Combination protocols (LL-37 + conventional antibiotics): synergy demonstrated in vitro against MRSA and Pseudomonas