LL-37
Also known as: Cathelicidin · Human cathelicidin antimicrobial peptide · hCAP18
Contents
MW
4493.37 Da
Amino Acids
37 AA
Half-Life
4 hours
Route
SubQ, Topical
Formula
C205H340N60O53
Amino Acid Sequence
LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES
Mechanism of Action
LL-37 is the sole human cathelicidin — a 37-amino acid antimicrobial peptide naturally produced by neutrophils, epithelial cells, macrophages, and keratinocytes in response to infection and tissue injury.
DIRECT ANTIMICROBIAL: LL-37's amphipathic α-helical structure inserts into bacterial cell membranes, forming pores that cause rapid cell lysis. Effective against gram-positive and gram-negative bacteria, fungi, and enveloped viruses. Kills pathogens within minutes — faster than adaptive immunity.
ENDOTOXIN NEUTRALIZATION: Binds lipopolysaccharide (LPS) with high affinity, neutralizing bacterial endotoxin and preventing septic cascade activation.
IMMUNE CELL RECRUITMENT: Chemotactic — recruits neutrophils, monocytes, and T-cells to infection sites via FPR2 (formyl peptide receptor 2).
WOUND HEALING: Promotes keratinocyte migration and proliferation via EGFR transactivation. Stimulates angiogenesis at wound sites.
ADAPTIVE IMMUNITY: Activates dendritic cells → enhanced antigen presentation → bridges innate and adaptive immunity.
Vitamin D directly upregulates LL-37 expression — this is a key mechanism by which vitamin D supports immune function.
Dosing Protocol
Low Dose
███ – ███ mcg/day
Standard Dose
███ mcg/day
High Dose
███ – ███ mcg/day
Dosing protocols are for paid members
Get exact dosing ranges, injection frequency, timing rationale, and reconstitution math.
Get Clinical Access — $79/moFrequency
Daily or every other day during infection/immune challenge.
Half-Life
4 hours
Reconstitution Guide
Full reconstitution protocol with BAC water volumes, concentration math, and units-to-draw per dose is available on the Clinical plan.
Unlock reconstitution guide →Clinical Warnings
Pro-inflammatory at high doses (excessive neutrophil activation).
Potential autoimmune exacerbation.
Antimicrobial resistance theoretical concern.
Not FDA approved for therapeutic use.
Quality from compounding variable.
Contraindications
Absolute
Pregnancy
Relative Cautions
Autoimmune disease
Psoriasis (may worsen)
Rosacea
Side Effect Profile
Mild
- ●Injection site reaction
- ●Mild redness
Moderate
- ●Localized inflammation
- ●Headache
Severe (Rare)
- ●Autoimmune flare
- ●Excessive inflammation
Synergistic Peptides
Common Stacks
Thymosin Alpha-1
KPV
BPC-157
Research Status
Well-characterized biochemistry. PMID 11278193 (Agerberth 1995): Human cathelicidin characterization. PMID 22474249 (Heilborn 2003): Wound healing promotion. Extensive mechanistic data, limited therapeutic human RCTs.
Frequently Asked Questions
How does LL-37 work?
LL-37 is the sole human cathelicidin — a 37-amino acid antimicrobial peptide naturally produced by neutrophils, epithelial cells, macrophages, and keratinocytes in response to infection and tissue injury. DIRECT ANTIMICROBIAL: LL-37's amphipathic α-helical structure inserts into bacterial cell membranes, forming pores that cause rapid cell lysis. Effective against gram-positive and gram-negative bacteria, fungi, and enveloped viruses. Kills pathogens within minutes — faster than adaptive immuni
What is the standard dose of LL-37?
LL-37 dosing protocols are available with a ClinPep Clinical subscription. Dosing varies by indication and patient factors — consult a licensed healthcare provider. General frequency: Daily or every other day during infection/immune challenge.
What is the half-life of LL-37?
The half-life of LL-37 is 4 hours. This determines optimal dosing frequency and timing.
Who should not use LL-37?
LL-37 is absolutely contraindicated in: Pregnancy. Use with caution in: Autoimmune disease; Psoriasis (may worsen); Rosacea.
What are the side effects of LL-37?
Common mild side effects include: Injection site reaction, Mild redness. Moderate effects: Localized inflammation, Headache.
What peptides stack well with LL-37?
LL-37 is commonly stacked with: Thymosin Alpha-1, KPV, BPC-157.
How do you reconstitute LL-37?
LL-37 is reconstituted with bacteriostatic water. Exact volumes, concentrations, and units-to-draw calculations are available in the ClinPep Clinical plan. Always follow your compounding pharmacy's instructions.
How long should you cycle LL-37?
LL-37 cycle protocols vary by indication. Detailed cycle length, on/off schedules, and monitoring guidelines are available with ClinPep Clinical access. Consult your healthcare provider for personalized cycling guidance.
References & Citations
10 PubMed studies · 3 clinical trials
The dysregulation of innate immunity by Porphyromonas gingivalis in the etiology of Alzheimer's disease.
Barron Annelise E, Lin Jennifer S, Ryder Mark I, Bergman Peter. Journal of internal medicine. 2026
The etiology of Alzheimer's disease (AD) remains under active debate. In this perspective, we explore the hypothesis that a primarily infection-caused chronic dysregulation and weakening of human inna
Functional characterization of Cr-CATHs: Novel antimicrobial peptides from the coastal bird Chroicocephalus ridibundus.
Dou Haoran, Li Shuangyu, Zhang Pingchuan, Ye Zifan et al.. Biochimie. 2026
The escalating global threat of antimicrobial resistance (AMR) and chronic biofilm-associated infections underscores the urgent need for novel therapeutic agents. Antimicrobial peptides (AMPs) offer a
LL37-induced mitochondrial stress activates the mtDNA/cGAS/STING pathway to promote mast cell-mediated rosacea inflammation.
Sun Rui, Fan Huiping, Ma Qingsong, Li Xiaojin et al.. Free radical biology & medicine. 2026
Rosacea is a chronic inflammatory skin disease characterized by persistent facial erythema and telangiectasia. The antimicrobial peptide LL37 is a key initiator in rosacea, with mast cells serving as
Pneumococcal S protein coordinates cell wall modification and repair to resist host antimicrobials.
Burnier Jessica, Gallay Clement, Bruce Kevin E, Bjånes Elisabet et al.. Nature microbiology. 2026
S protein is conserved among streptococci and contributes to group A Streptococcus virulence, but the mechanisms involved are unclear. Here we used genetic, biochemical, single-molecule, in vitro and
Synthetic antimicrobial peptide LD4-PP protects the host against E. coli-induced cell death.
Mohanty Soumitra, White John Kerr, Yin Yundi, Muhammad Taj et al.. Frontiers in immunology. 2025
With antibiotic resistance being a major global concern, there is a huge need of new treatment options to fight bacterial infections. In this study, we highlight the antibacterial and host-protective
Immunomodulatory effects of QsCATH on macrophages: transcriptomic insights and molecular docking analysis.
Qiao Fen, Qian Xin-Yi, Wu Jia-Le, Wang Zi-Xuan et al.. Scientific reports. 2025
The molecular mechanisms underlying the immunomodulatory effects of cathelicidins on macrophages remain poorly characterized. This study aimed to elucidate the immunomodulatory mechanisms of QsCATH, a
Novel integrated approach modeling proanthocyanidins and bacteriophages to combat multidrug Salmonella Typhimurium in challenged broilers.
Al-Khalaifah Hanan S, Ibrahim Doaa, Abdelfattah-Hassan Ahmed, Ibrahim Dina et al.. Frontiers in veterinary science. 2025
The emergence of multidrug bacterial isolates, including Salmonella (S.) Typhimurium, which primarily spreads to humans through chicken products, is correlated with a rising prevalence of antimicrobia
Host defense peptides in malaria infection: their contributions, significance and constraints.
Alfaki Dia Aldeen, Elbasheir Mohamed Mubarak. Malaria journal. 2025
Plasmodium-induced malaria infection remains a leading global health threat. Host defense peptides (HDPs), key components of innate immunity, target multiple stages of Plasmodium development through d
Registered Clinical Trials
Cellular Immunotherapy for Septic Shock
The Effects of Vitamin D Supplementation on Aerobic Fitness in Athletes
The Role of Anti-inflammatory Cytokines and Antimicrobial Peptide LL-37 Biomarkers in the Treatment of Periodontal Disease.
Symptom Indications
Full Clinical Access
Complete LL-37 Protocol
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This information is for educational and research reference purposes only. ClinPep does not provide medical advice, diagnosis, or treatment recommendations. All protocols should be reviewed by a licensed healthcare provider.