LL-37 (LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES) is the only cathelicidin-derived antimicrobial peptide (AMP) found in humans. It is a 37-amino acid cationic, amphipathic peptide named after its N-terminal leucine-leucine motif. LL-37 is encoded by the CAMP (cathelicidin antimicrobial peptide) gene and is produced as the C-terminal fragment of an inactive 18 kDa precursor protein called hCAP-18. Activation occurs via proteolytic cleavage by neutrophil elastase, serine proteinase 3, or other enzymes at sites of infection or tissue injury.
LL-37 is expressed by neutrophils, macrophages, monocytes, epithelial cells of the skin, gut, lungs, and urinary tract, and is found in wound fluid, sweat, breast milk, and mucosal secretions. It serves as a critical first-line defense molecule of the innate immune system, with activity against Gram-positive bacteria, Gram-negative bacteria, fungi, viruses, and biofilms.
What makes LL-37 exceptional among antimicrobial peptides is its multifunctionality. Beyond directly killing pathogens through membrane disruption, LL-37 acts as a chemotactic agent (recruiting immune cells to infection sites), an immunomodulator (regulating cytokine production), an angiogenesis promoter (stimulating new blood vessel growth), and a wound healing accelerator (driving re-epithelialization through EGFR transactivation). This combination of antimicrobial and host-defense properties has generated intense interest in LL-37 as a potential therapeutic for chronic wounds, biofilm-associated infections, and antibiotic-resistant pathogens.
Critical dual nature: LL-37's effects are concentration-dependent. At low concentrations it is anti-inflammatory and promotes healing. At high concentrations it can amplify inflammatory responses and has been implicated in the pathogenesis of autoimmune conditions including psoriasis, lupus, and atherosclerosis. This dose-dependent duality is a key consideration for any therapeutic application.
| Weeks | Dosage | Syringe units (U-100) |
|---|---|---|
| Week 1 | 0.05 mg | 3 units0.03 mL |
| Week 2 | 0.1 mg | 6 units0.06 mL |
| Week 3 | 0.15 mg | 9 units0.09 mL |
| Week 4 | 0.2 mg | 12 units0.12 mL |
| Week 5 | 0.25 mg | 15 units0.15 mL |
| Week 6 | 0.3 mg | 18 units0.18 mL |
| Week 7 | 0.35 mg | 21 units0.21 mL |
| Week 8 | 0.4 mg | 24 units0.24 mL |
FrequencyOnce daily, subcutaneous.
For review — no systemic human dosing exists. The few human trials injected LL-37 directly into the wound or lesion being treated; the systemic weekly ladder in the chart follows a circulated research protocol. The concentration strip above the chart is calculated from the vial and water volume and is correct.
Unverified — no cited trial establishes a systemic frequency for LL-37.
LL-37 has been injected into humans, but only into the lesion being treated — a local application at the site, which says nothing about a systemic amount — and no dose-ranging work supports the eight-step ladder charted here, so it is flagged for review. The reason its clinical development stayed local is a safety one: LL-37 is directly cytotoxic to human cells at concentrations not far above the range where it kills bacteria, so the margin between the two is narrow. The ladder is charted one week at a time because that is how the protocol sets it out; the steps have not been condensed into ranges, since grouping them would state a schedule the source does not. Athena lists one strength: a 5 mg vial made up with 3 mL gives about 1.67 mg/mL, so the ladder runs from 3 units at the 0.05 mg first step to 24 units at the 0.4 mg top step, and every row fits inside one 50-unit syringe.
What this evidence establishes. No systemic human dosing exists for LL-37. A small number of trials have injected it directly into wounds or lesions at the site being treated, which is a different question from a systemic dose, and no dose-ranging work supports a general protocol. LL-37 is also directly cytotoxic at concentrations not far above its antimicrobial range, which is why its clinical development has stayed local rather than systemic. The table below is reconstitution arithmetic only.
For educational and laboratory research purposes only. It does not provide medical advice, dosing recommendations, or instructions for human or veterinary use. Syringe units assume a U-100 syringe, on which 1 mL is 100 units and a 50-unit syringe holds 0.5 mL.
LL-37 operates through multiple parallel mechanisms, functioning as both a direct antimicrobial agent and a sophisticated immune signaling molecule:
Amphipathic alpha-helical structure inserts into and perforates bacterial cell membranes. Forms tetrameric channels causing ion leakage and bacterial lysis. Effective against Gram+ and Gram- bacteria.
Disrupts and eradicates preformed biofilms at sub-MIC concentrations. Critical for chronic wound infections where biofilm is the primary barrier to healing (Pseudomonas, Staphylococcus).
Acts as chemoattractant for neutrophils, monocytes, and T-cells via FPRL1 (formyl peptide receptor-like 1) signaling. Enhances phagocytosis and neutralizes endotoxin (LPS).
Promotes keratinocyte migration via EGFR transactivation. Stimulates angiogenesis at injury sites. hCAP-18 is strongly expressed in healing skin; absent in chronic ulcer epithelium.
Demonstrated activity against enveloped viruses including RSV, influenza, HIV, and HSV. Disrupts viral envelopes and interferes with viral attachment to host cells.
Low concentrations: anti-inflammatory, healing. High concentrations: pro-inflammatory, potentially pathogenic. Implicated in psoriasis (DNA-LL-37 complexes activate pDCs), lupus, and atherosclerosis.
LL-37 has been studied extensively in preclinical models. Limited human data exists primarily from wound healing and dermatological contexts:
| Concern | Risk Level | Rationale |
|---|---|---|
| Dose-dependent inflammatory effects | HIGH (critical) | Low doses are anti-inflammatory and promote healing. High doses amplify inflammation and can trigger autoimmune pathways. Dose optimization is essential and poorly defined for exogenous administration. |
| Autoimmune conditions (psoriasis, lupus) | CONTRAINDICATED | LL-37-DNA complexes drive psoriatic inflammation via pDC activation. Elevated LL-37 is implicated in lupus and atherosclerosis pathogenesis. Exogenous LL-37 could worsen autoimmune conditions. |
| Host cell cytotoxicity at high concentrations | MODERATE | At concentrations needed for robust antimicrobial activity, LL-37 can damage host cell membranes. Therapeutic window is narrow. Nanoparticle and analog strategies aim to address this. |
| Injection site inflammation | MODERATE (expected) | Local redness, swelling, and inflammation reported. Consistent with LL-37's immune-activating properties. Generally mild at low doses. |
| Pregnancy / breastfeeding | MODERATE (complex) | LL-37 is naturally present in breast milk and is part of normal neonatal immune defense. Effects of supraphysiological exogenous doses during pregnancy are unstudied. |
| Cancer (context-dependent) | COMPLEX | LL-37 can induce apoptosis in some cancer cells (lung, breast). But may promote angiogenesis and tumor growth in other contexts. Effects are highly cancer-type-specific. |
| Drug interactions | LOW (limited data) | No significant drug interactions identified. May synergize with conventional antibiotics against biofilm-associated infections. Formal interaction studies are limited. |
| Topical tolerability | FAVORABLE | Topical LL-37 formulations (creams, hydrogels) generally well-tolerated in wound healing contexts. Localized delivery reduces systemic exposure concerns. |
| Human therapeutic trial data | LIMITED | No LL-37-based drug has reached the pharmaceutical market. Clinical data is primarily from academic wound healing studies and analog testing. Full therapeutic safety profile is unestablished. |
FDA: LL-37 is not FDA-approved for any therapeutic indication. No LL-37-based drug has completed the clinical development pipeline. Several LL-37-derived analogs and peptide-based antimicrobials are in various stages of preclinical and early clinical development.
Availability: Synthetic LL-37 is available from peptide suppliers for research and is used in integrative medicine practices, primarily for immune support and wound healing applications.
Antibiotic Resistance Context: Antimicrobial resistance gives LL-37 research urgency that extends beyond the peptide community. With multidrug-resistant infections projected to affect 10 million people a year by 2050, endogenous antimicrobial peptides and their engineered derivatives represent one of the most critical frontiers in infectious disease research.
Key distinction: LL-37 is fundamentally different from most peptides on this site because it is a core component of your own immune system. Every human produces it. The research question is not "does this foreign molecule do something?" but "can we harness and enhance an endogenous defense system?" The dose-dependent duality (healer at low doses, pathogen at high doses) means therapeutic development requires precision that simple supplementation cannot provide.
Test your understanding of LL-37 innate immunity, antimicrobial mechanism, wound healing role, and dose-dependent duality.
This profile is for educational and research purposes only. It is not medical advice, and nothing on it is a protocol, a recommendation, or an instruction for use in a person or an animal.
Athena Peptides Education does not prescribe, sell, or recommend any compound. Compounds discussed here are for laboratory research only and are not for human consumption. Always consult a qualified physician before making any decision about your health.