LL-37

1. Quick Facts

2. Summary

LL-37 is the only known human cathelicidin antimicrobial peptide and serves as an important component of the innate immune system. Produced by neutrophils, epithelial cells, macrophages, and numerous other tissues, LL-37 helps protect the body against bacterial, viral, and fungal pathogens while also participating in wound healing, immune cell recruitment, angiogenesis, and regulation of inflammatory signaling.

Unlike conventional antibiotics that primarily kill microorganisms, LL-37 demonstrates a diverse range of biologic activities. Research has shown that it can directly disrupt microbial membranes, modulate cytokine production, recruit immune cells to sites of injury, promote tissue regeneration, and influence both innate and adaptive immune responses. These broad physiologic effects have made LL-37 an active area of investigation in infectious disease, regenerative medicine, chronic wounds, autoimmune disorders, and inflammatory conditions.

What People Commonly Claim

• Supports wound healing and tissue repair
• Enhances innate immune function
• Possesses broad antimicrobial activity
• May improve recovery following injury
• May reduce chronic inflammation

What the Literature Actually Shows

• LL-37 is a naturally occurring human antimicrobial peptide central to innate immunity.
• It demonstrates broad antibacterial, antiviral, antifungal, and immunomodulatory properties in laboratory studies.
• Research supports important roles in wound healing, angiogenesis, and immune cell signaling.
• Most therapeutic applications remain investigational despite extensive preclinical research.
• Human clinical evidence continues to expand but remains substantially smaller than the preclinical literature.

3. Reconstitution Guide

At this concentration:
• 500 mcg = 0.250 mL (25 units)
• 1,000 mcg = 0.500 mL (50 units)

*Different vial sizes may limit reconstitution volume. If your product differs from the specifications listed here, please use the Peptide Calculator to calculate custom concentrations and dosing protocols.

4. Route of Administration

LL-37 is most commonly administered by subcutaneous injection in research settings, although topical, intradermal, and localized administration have also been investigated depending upon the intended application.

5. Common Research Protocols

6. Mechanism of Action

LL-37 is the only naturally occurring human cathelicidin antimicrobial peptide and is generated through proteolytic cleavage of the precursor protein hCAP-18. It functions as a key component of the innate immune system by providing rapid, nonspecific defense against invading microorganisms while simultaneously regulating numerous aspects of the inflammatory response.

Unlike conventional antimicrobial agents that act through a single mechanism, LL-37 exhibits broad biologic activity. It can directly disrupt bacterial, fungal, and viral membranes while also acting as an immunomodulatory signaling molecule. Research has demonstrated that LL-37 influences leukocyte recruitment, cytokine production, angiogenesis, epithelial repair, and extracellular matrix remodeling, making it an important mediator of both host defense and tissue regeneration.

Potential downstream effects discussed in research include:

• Direct antimicrobial membrane disruption
• Recruitment of neutrophils, monocytes, and other immune cells
• Modulation of pro-inflammatory and anti-inflammatory cytokines
• Promotion of angiogenesis and vascular remodeling
• Stimulation of epithelial cell migration and wound closure
• Support of extracellular matrix remodeling during tissue repair

7. Potential Benefits

• Broad-spectrum antimicrobial activity
• Support for wound healing and tissue regeneration
• Modulation of innate immune responses
• Promotion of angiogenesis during tissue repair
• Recruitment and regulation of immune cell activity
• Potential support for chronic wound healing under investigational conditions
• Extensive preclinical evidence supporting multiple regenerative mechanisms

8. Potential Risks / Side Effects

Moderate / High

• Injection-site irritation
• Localized redness or swelling
• Flu-like symptoms
• Transient inflammatory responses
• Possible worsening of autoimmune or inflammatory conditions through immune activation
• Theoretical risk of excessive inflammation in susceptible individuals
• Limited long-term human safety data for investigational use

9. Half-Life

LL-37 has a relatively short circulating half-life, generally estimated to be approximately one hour due to rapid degradation by endogenous proteases present throughout blood and tissues. Despite this brief plasma persistence, biologic effects may continue beyond measurable circulating concentrations because LL-37 initiates complex immune signaling pathways and cellular responses.

In healthy physiology, LL-37 is produced locally at sites of infection or tissue injury where concentrations may remain substantially higher than those measured in systemic circulation. Consequently, many research studies focus on localized biologic activity rather than plasma pharmacokinetics alone.

Its short half-life, combined with broad immunomodulatory activity, has prompted ongoing investigation into modified analogs and delivery systems designed to improve peptide stability while preserving its antimicrobial and regenerative properties.

10. Storage Information

• Store lyophilized peptide according to the manufacturer’s recommendations until reconstitution.
• After reconstitution with bacteriostatic water, refrigerate at 2–8°C (36–46°F).
• Do not freeze after reconstitution.
• Protect from excessive heat and direct light.
• Discard the solution if it becomes cloudy, develops particulate matter, or changes color.
• When prepared using appropriate sterile technique and bacteriostatic water, many researchers limit refrigerated use to approximately 28–30 days.

11. Contraindications / Warnings

• Known hypersensitivity to LL-37 or formulation components.
• Use caution in individuals with autoimmune or chronic inflammatory disorders due to its immunomodulatory activity.
• May provoke transient inflammatory responses following administration.
• Long-term human safety data remain limited for investigational use.
• The effects of prolonged administration on immune homeostasis have not been fully established.
• Pregnancy and breastfeeding have not been adequately studied.
• Because LL-37 influences multiple immune signaling pathways, research protocols should be interpreted within the context of the specific disease model under investigation.

12. Further Study

Tier 1 – Essential Reading

• Human Antimicrobial/Host Defense Peptide LL-37 May Prevent the Spread of a Local Infection Through Multiple Mechanisms: An Update
  A comprehensive modern review describing LL-37 biology, production, antimicrobial mechanisms, immune modulation, inflammatory signaling, and host defense. An excellent introduction to the peptide and its diverse physiologic roles.
• The Human Cathelicidin Antimicrobial Peptide LL-37 as a Potential Treatment for Polymicrobial Infected Wounds
  Frontiers in Immunology
  A landmark review discussing LL-37’s antimicrobial activity, biofilm disruption, wound healing, immunomodulation, and regenerative potential in chronic wound physiology.

Tier 2 – Mechanisms & Regenerative Biology

• A Systematic Review of the Design and Applications of Antimicrobial Peptides in Wound Healing
  A modern systematic review examining antimicrobial peptides in regenerative medicine, including LL-37’s role in angiogenesis, fibroblast activity, epithelial migration, collagen deposition, and chronic wound repair.
• The Potential of Human Peptide LL-37 as an Antimicrobial and Anti-Biofilm Agent
  Antibiotics
  An open-access review focused on antimicrobial resistance, biofilm disruption, therapeutic development, and peptide engineering, highlighting LL-37’s potential against persistent infections.

Tier 3 – Advanced Reading

• LL-37, a Multi-Faceted Amphipathic Peptide Involved in NETosis
  An advanced review exploring LL-37’s role in neutrophil extracellular trap (NET) formation, innate immunity, inflammatory signaling, autoimmune disease, and emerging therapeutic applications.

CKF Note: Unlike many research peptides that exert a single primary mechanism of action, LL-37 functions as both a direct antimicrobial peptide and a complex immune signaling molecule. Its ability to simultaneously influence host defense, inflammation, angiogenesis, and tissue repair has made it one of the most extensively studied endogenous peptides in innate immunity.

13. Research References

1. Human Antimicrobial/Host Defense Peptide LL-37 May Prevent the Spread of a Local Infection Through Multiple Mechanisms: An Update. PMCID: PMC11893641.
2. The Human Cathelicidin Antimicrobial Peptide LL-37 as a Potential Treatment for Polymicrobial Infected Wounds. Frontiers in Immunology. PMCID: PMC3699762.
3. A Systematic Review of the Design and Applications of Antimicrobial Peptides in Wound Healing. PMCID: PMC11089580.
4. The Potential of Human Peptide LL-37 as an Antimicrobial and Anti-Biofilm Agent. Antibiotics. 2021.
5. LL-37, a Multi-Faceted Amphipathic Peptide Involved in NETosis. PMCID: PMC9368159.

14. Last Reviewed

Last Reviewed: July 2026