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The Peptide Effect
preclinicalImmune & Antimicrobial

LL-37

Also known as: Cathelicidin, hCAP18 C-terminal peptide, CAMP, Human Cathelicidin Antimicrobial Peptide

LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino acid fragment cleaved from the C-terminus of the precursor protein hCAP18. It serves as a critical first-line defense against infections, capable of directly killing bacteria, viruses, and fungi. Beyond its antimicrobial role, LL-37 modulates immune responses, promotes wound healing, and disrupts biofilms.

Key Facts

Mechanism
LL-37 kills pathogens primarily through membrane disruption — its amphipathic alpha-helical structure allows it to insert into and destabilize microbial membranes. It also neutralizes bacterial endotoxins (LPS), disrupts established biofilms by interfering with quorum sensing, acts as a chemoattractant for neutrophils and monocytes via formyl peptide receptor-like 1 (FPRL1), modulates TLR signaling to balance pro- and anti-inflammatory responses, and promotes wound healing through stimulation of keratinocyte and endothelial cell migration.
Research Status
preclinical
Half-Life
~15 minutes in serum
Molecular Formula
C₂₀₅H₃₄₀N₆₀O₅₃
Primary Use
Immune & Antimicrobial
Table of Contents

Benefits

  • Broad-spectrum antimicrobial activity — kills gram-positive and gram-negative bacteria, viruses, and fungistrong
  • Disrupts established biofilms that are resistant to conventional antibioticsmoderate
  • Promotes wound healing through keratinocyte migration and angiogenesismoderate
  • Modulates innate and adaptive immune responses without excessive inflammationmoderate
  • Potential adjunct for chronic Lyme disease and tick-borne infections (biofilm penetration)anecdotal
  • Neutralizes bacterial endotoxins (LPS), reducing sepsis-associated inflammationmoderate

Dosage Protocols

RouteDosage RangeFrequencyNotes
Subcutaneous injection50–100 mcgDaily or 3× weeklyMost common protocol for systemic immune support and chronic infection adjunct
Topical application50–100 mcg in carrierDailyApplied directly to wounds or skin infections for localized antimicrobial and healing effects
Subcutaneous injection (intensive)100–200 mcgDaily for 4–8 weeksHigher-dose protocol used by some practitioners for chronic infections; requires monitoring

Medical disclaimer

Dosage information is provided for educational reference only. Always follow your prescriber's instructions and consult a qualified healthcare provider before starting any peptide protocol.

Side Effects

  • Injection site pain, redness, or swellingcommon
  • Transient flu-like symptoms from immune activationcommon
  • Skin irritation or redness with topical applicationrare
  • Potential for autoimmune activation or exacerbation at high doses (LL-37 is elevated in psoriasis and lupus)serious
  • Headache or mild fatiguerare

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Frequently Asked Questions

Does LL-37 help with Lyme disease?
LL-37 has gained popularity in the Lyme disease community because of its ability to disrupt biofilms, which Borrelia burgdorferi (the Lyme-causing bacterium) uses to evade antibiotics and the immune system. While there is strong laboratory evidence that LL-37 can penetrate biofilms and kill bacteria within them, clinical data specifically for Lyme disease is limited to case reports and practitioner anecdotes. It is used as an adjunct to antibiotic therapy, not a standalone treatment.
Can LL-37 cause autoimmune problems?
LL-37 is naturally produced by the body, but elevated levels have been associated with autoimmune conditions like psoriasis (where it triggers plasmacytoid dendritic cell activation) and lupus. Exogenous LL-37 at therapeutic doses has not been shown to trigger autoimmune disease in otherwise healthy individuals, but caution is warranted for those with existing autoimmune conditions. Start with lower doses and monitor for any flare-ups.
How does LL-37 penetrate biofilms?
LL-37 disrupts biofilms through multiple mechanisms: it interferes with bacterial quorum sensing (the communication system bacteria use to coordinate biofilm formation), directly degrades the extracellular polymeric substance (EPS) matrix that holds biofilms together, and kills the bacteria exposed after biofilm disruption. This multi-pronged approach makes it more effective than antibiotics alone, which often cannot penetrate intact biofilm structures.
Does vitamin D increase natural LL-37 production?
Yes. Vitamin D is one of the primary regulators of LL-37 expression. The cathelicidin gene (CAMP) contains a vitamin D response element (VDRE) in its promoter region. When vitamin D levels are sufficient, the body produces more LL-37 naturally. This is one reason why vitamin D deficiency is associated with increased infection susceptibility. Many practitioners recommend optimizing vitamin D levels (50–80 ng/mL) alongside or before supplementing with exogenous LL-37.
Where can I get LL-37?
LL-37 is not FDA-approved for any medical condition. It is available through compounding pharmacies with a practitioner's prescription and as a research chemical. Quality and purity vary significantly between sources. Because it is a relatively complex peptide (37 amino acids), proper synthesis and purification are critical. Work with a reputable compounding pharmacy or research supplier that provides third-party purity testing (HPLC/MS).

References

  1. 1
    The human cationic antimicrobial protein (hCAP-18) is expressed in the bone marrow and myeloid cells(2003)PubMed ↗
  2. 2
    Antimicrobial peptides: an emerging category of therapeutic agents(2005)PubMed ↗
  3. 3
    LL-37, the only human member of the cathelicidin family of antimicrobial peptides(2003)PubMed ↗
  4. 4
    Cathelicidin antimicrobial peptide LL-37 in psoriasis enables keratinocyte reactivity against TLR9 ligands(2007)PubMed ↗

Last updated: 2026-02-14