Overview
Overview
LL-37 (also known as CAP-18) is a 37-amino-acid cationic antimicrobial peptide derived from the C-terminal of human cathelicidin (hCAP18)[1]. It is the only known human cathelicidin, exhibiting broad-spectrum antibacterial activity and immune-modulating properties[2][3]. This educational protocol presents a once-daily subcutaneous approach using a practical dilution for clear insulin-syringe measurements. Reconstitute: Add 3.0 mL bacteriostatic water → ~1.67 mg/mL concentration. Typical daily r
- Category
- Healing
- Routes
- subcutaneous
Mechanism
LL-37
Mechanism of action
Mechanism of action
LL-37 exerts both direct and indirect antimicrobial effects. Its amphipathic, cationic α-helical structure (net +6 charge) allows it to preferentially bind and disrupt negatively charged microbial membranes [2] . Beyond direct killing, LL-37 modulates host immunity: in murine sepsis models, it induced neutrophils to release microvesicles rich in antimicrobial proteins, lowering bacterial burden and improving survival [3] . LL-37 can also bind bacterial lipopolysaccharide (LPS) and block its interaction with CD14/TLR4, reducing endotoxin-triggered TNF release and neutrophil apoptosis [2] . These combined mechanisms help explain its potential in infection control and tissue-repair contexts.
Key research findings
- 01
Identity: LL-37 is the only human cathelicidin-derived antimicrobial peptide (37 residues beginning with two leucines), processed from the hCAP18 precursor; it is an endogenous component of innate immunity.
- 02
In vitro: broad antimicrobial activity (bacteria, some fungi and viruses) is reported, attributed largely to disruption of microbial membranes.
- 03
In vitro / animal model: well-documented immunomodulatory roles, including chemotaxis of immune cells, modulation of inflammatory signaling, and wound-related angiogenesis.
- 04
In vitro / animal model: wound studies report involvement in re-epithelialization and tissue-repair processes.
- 05
In vitro / observational research: context-dependent roles are described, with elevated LL-37 associated with certain inflammatory skin conditions, illustrating that effects are concentration- and context-dependent.
Primary source: LL-37 has a large, well-established preclinical research base (extensive in vitro and animal studies) as an endogenous human host-defense peptide with antimicrobial and immunomodulatory roles. Synthetic LL-37 and analogs are studied as research materials, but clinical translation of administered LL-37 remains early.
Researched Effects
Researched benefits
Areas of active research and investigation. Results may vary and are based on preclinical or early clinical data.
In chronic venous leg ulcers (which often lack endogenous LL-37), topical treatment with synthetic LL-37 significantly accelerated healing rates compared to placebo[4].
In diabetic foot ulcer trials, LL-37 cream improved granulation tissue formation and wound closure[5].
Broad-spectrum antimicrobial action helps clear infections; in experimental sepsis models, LL-37 treatment reduced bacterial loads and mortality[3].
Protocol Reference
Protocol reference
Commonly cited research range: 50–400 mcg, daily.
Reference figures reported in the research literature — not a dosing recommendation. For interactive vial math and scheduling, see the Calculator and Schedule tabs.
Cited protocol & reconstitution guide
Source-backed reference fields by phase, including any volume fields authored in the cited guide.
Starting range (community subQ)
100-200 mcg/day
Commonly reported cluster (community subQ)
100-250 mcg per day
Upper range cited (community subQ)
Up to 500 mcg/day
| Phase | Reference amount | Units / volume |
|---|---|---|
| Starting range (community subQ) | 100-200 mcg/day | 4–8 units (0.04–0.08 mL) |
| Commonly reported cluster (community subQ) | 100-250 mcg per day | 4–10 units (0.04–0.10 mL) |
| Upper range cited (community subQ) | Up to 500 mcg/day | 20 units (0.20 mL) |
Titration protocol
- StartStart100-200 mcg/day
Once daily, often 5 days/week
- 2-4 week blockBuild100-250 mcg per day
Once daily, often 5 days on with 2 days off, for a 2-4 week block
- Upper rangeBuildUp to 500 mcg/day
Once daily
- CycleMaintenance-
2-4 weeks on, then a break. Short block: 2-3 weeks on / 2+ weeks off (most common); standard block: 4 weeks on / 2-4 weeks off
Storage & Handling
Storage requirements(typical for most peptides)
Can be stored for extended periods. Protect from moisture.
Store in refrigerator door. Never freeze after reconstitution.
Label vials with reconstitution date. Discard if cloudy.
Reconstitution steps
- 01🌡️Sanitize: wipe the vial stopper and BAC water stopper with an alcohol swab
- 02🧴Draw 2 mL bacteriostatic water into a sterile syringe — this 5 mg vial yields 2.5 mg/mL.
- 03💉Add slowly: let the water run down the inside wall of the vial, not straight onto the powder
- 04💧Dissolve gently: swirl, do not shake; wait until the solution is clear
- 05🔄Inspect: solution should be clear and colorless; discard if cloudy or particulate
- 06🏷️Store cold: refrigerate the reconstituted vial at 2-8 °C (35.6-46.4 °F) and keep it out of light
- 07❄️Use promptly: LL-37 degrades in solution, so use within its refrigerated window rather than storing for weeks
- 08💉Important: This guide is for educational purposes only and is not medical advice. For research use only. Not for human consumption.
Additional storage notes
Store at −20 °C (−4 °F) in dry, dark conditions; stable ~24 months.
Refrigerate at 2–8 °C (35.6–46.4 °F) for up to 4 weeks; frozen at −20 °C (−4 °F) for up to 6 months.
Allow vials to reach room temperature before opening to reduce condensation uptake.
Clinical Evidence
Clinical evidence
Extensively researched in innate-immunity and wound-healing models for both antimicrobial and immunomodulatory activity.
LL-37 has a large, well-established preclinical research base (extensive in vitro and animal studies) as an endogenous human host-defense peptide with antimicrobial and immunomodulatory roles. Synthetic LL-37 and analogs are studied as research materials, but clinical translation of administered LL-37 remains early.
- 01Identity: LL-37 is the only human cathelicidin-derived antimicrobial peptide (37 residues beginning with two leucines), processed from the hCAP18 precursor; it is an endogenous component of innate immunity.
- 02In vitro: broad antimicrobial activity (bacteria, some fungi and viruses) is reported, attributed largely to disruption of microbial membranes.
- 03In vitro / animal model: well-documented immunomodulatory roles, including chemotaxis of immune cells, modulation of inflammatory signaling, and wound-related angiogenesis.
- 04In vitro / animal model: wound studies report involvement in re-epithelialization and tissue-repair processes.
- 05In vitro / observational research: context-dependent roles are described, with elevated LL-37 associated with certain inflammatory skin conditions, illustrating that effects are concentration- and context-dependent.
Evidence maturity varies by compound; much peptide research is preclinical (in vitro or animal-model). Where human data are limited, findings should be read as research observations, not clinical conclusions.
References
Literature references
Published research articles and sources related to LL-37.
- 01DiVA Portal / Wound Repair and Regeneration — Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: multicentric RCT View Source
- 02Journal of Immunology (PMC) — Little peptide, big effects: the role of LL-37 in inflammation and autoimmune disease View Source
- 03Innate Immunity (PMC) — Antimicrobial peptide LL-37 ameliorates a murine sepsis model via microvesicle release from neutrophils View Source
- 04Wound Repair and Regeneration (PMC) — Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: a multicentric prospective RCT View Source
- 05Archives of Dermatological Research (PMC) — Efficacy of LL-37 cream in enhancing healing of diabetic foot ulcer: a randomized double-blind controlled trial View Source
- 06Pure Lab Peptides — LL-37 (CAP-18) 5 mg product page (purity, storage, and batch documentation) View Source
- 07Bachem Knowledge Center — Handling and storage guidelines for peptides View Source
- 08CDC One & Only Campaign — One needle, one syringe, only one time (injection safety) View Source
- 09Johns Hopkins Arthritis Center — How to give a subcutaneous injection (site selection, rotation) View Source
- 10PubMed / Journal of Steroid Biochemistry — Vitamin D and the antimicrobial peptide cathelicidin (LL-37) View Source
- 11MedlinePlus (NIH) — Subcutaneous (SQ) injections: patient instructions View Source
- 12CDC — Vaccine administration: subcutaneous injection (angle/site; no aspiration) View Source
- 13NCBI Bookshelf — Best practices for injection (asepsis, preparation, and administration) View Source
- 14Clinical Pharmacology & Therapeutics (PMC) — Subcutaneous drug injection review: pharmacologic considerations View Source
Observed Effects
Observed effects in cited research
Reported
- Generally well tolerated; occasional mild injection-site reactions (redness, itch) may occur with subcutaneous administration.
Research Considerations
Research considerations
Research Use Only - not for human or veterinary therapeutic use. Current evidence is limited to in vitro and/or animal-model research; human data are minimal or absent. Consult a licensed healthcare professional for any clinical decisions.
Factors noted in the research literature; not patient-specific medical advice.
Regulatory Status
Regulatory status
RUO
Comparisons
Comparisons
| Compound | Mechanism | Route | Status |
|---|---|---|---|
| LL-37this | The sole human cathelicidin-derived cationic antimicrobial peptide (37 residues), studied for broad-spectrum antimicrobial activity, immune modulation, and roles in wound healing and angiogenesis. | subcutaneous | Investigational / RUO |
| MGF | A splice variant of IGF-1 (IGF-1Ec) produced in response to mechanical stress; its unique C-terminal E-peptide is studied for activation of muscle satellite cells and tissue repair. | subcutaneous | Investigational / RUO |
| PEG MGF | A pegylated form of mechano growth factor designed for extended stability and systemic half-life; the C-terminal E-peptide is studied for satellite-cell activation and muscle repair. | subcutaneous | Investigational / RUO |
| PNC-27 | A synthetic peptide combining an HDM-2-binding domain with a membrane-penetrating sequence, studied for selective membrane disruption of cancer cells displaying surface HDM-2. | subcutaneous | Investigational / RUO |
| TB-500 | Upregulates actin, promotes cell migration, reduces inflammation, and stimulates wound healing and tissue repair. | subcutaneous, intramuscular | Investigational / RUO |
| Mazdutide | A long-acting dual agonist of GLP-1 and glucagon receptors, combining GLP-1 appetite/glycemic signaling with glucagon-mediated energy expenditure. | subcutaneous | Investigational / RUO |
| Melanotan II | A synthetic non-selective melanocortin receptor agonist (including MC1R and MC4R) studied for stimulation of melanogenesis (skin pigmentation) and central melanocortin-mediated activity. | subcutaneous | Investigational / RUO |
Attributes shown for research comparison only; not a statement of efficacy or therapeutic equivalence.
FAQ
Frequently asked questions
It is the active antimicrobial peptide derived from human cathelicidin (hCAP18) u2014 the only cathelicidin found in humans. It is a naturally occurring part of innate immunity and is also studied as a synthetic research peptide.
In vitro work describes direct antimicrobial activity through disruption of microbial membranes, plus immunomodulatory roles such as recruiting immune cells and influencing inflammatory signaling and wound-related processes.
Research shows context-dependent roles. While it contributes to host defense and tissue-repair processes, elevated levels have also been associated with certain inflammatory skin conditions in research, so its effects depend on concentration and context.
LL-37 is naturally present in the human body, but synthetic LL-37 as an administered agent is still at an early research stage, and robust clinical evidence for it is limited.
Synthetic LL-37 is not an FDA-approved drug and is not a dietary supplement; it is handled as a research-use-only material.
Research-grade lyophilized peptide is generally stored frozen and protected from light; reconstituted solution is typically refrigerated and used promptly, as longer peptides can be susceptible to degradation. Follow the supplier's certificate of analysis and protocol reference.
Research-reported concentrations vary widely across in vitro and animal studies and are not standardized for human administration. This platform does not provide dosing instructions; see the protocol reference. This is not medical advice.
Research-use notice
Research Use Only. This educational content and calculation support is intended for private research documentation. It does not provide medical advice, human-use directions, or claims of safety or effectiveness.