Educational reference only. Informational material drawn from peer-reviewed literature. Not medical advice and not a recommendation to use, dose, or modify any therapy. Decisions about hormone therapy should be made with a qualified healthcare provider.
Overview
Overview
LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino acid endogenous peptide that represents a fundamental component of the innate immune system. The compound is named for its first two amino acids (LL) and total length (37): the sequence begins L-L (leucine-leucine) and contains exactly 37 residues. LL-37 is produced from a 170-amino acid precursor protein called hCAP-18 (human cationic antimicrobial protein, 18 kDa) which contains an N-terminal cathelin domain and a C-terminal antimicrobial domain. LL-37 is liberated from this precursor by proteolytic cleavage, primarily by neutrophil-derived proteinase 3.
LL-37 occupies a fundamentally different position in this library than the Russian peptide bioregulator or the mitochondrial-derived peptide compounds: it represents the Western research tradition focused on innate immunity and antimicrobial peptides. The compound was identified in 1995 by three independent groups (Cowland, Agerberth, Larrick) almost simultaneously. It was initially called FALL-39 after the first four amino acid residues, then renamed LL-37 when the proteolytic processing was better characterized.
LL-37 has broad-spectrum biological activity that extends far beyond antimicrobial effects:
- Antimicrobial activity: Broad-spectrum against Gram-positive and Gram-negative bacteria (including MRSA, Pseudomonas), fungi, and enveloped viruses
- Anti-biofilm activity: Disrupts bacterial biofilms (resistant to conventional antibiotics)
- Wound healing: Promotes re-epithelialization, granulation tissue, angiogenesis
- Immunomodulation: Modulates inflammation, immune cell recruitment, cytokine production
- Anti-apoptotic effects: Protects keratinocytes from apoptosis
- Anti-cancer activity: Studied in various malignancies
Forms
Available forms & half-lives
| Form | Approximate half-life |
|---|---|
| Topical LL-37 | Local; depends on formulation |
| Subcutaneous LL-37 | Several hours |
| Inhaled LL-37 | Local |
| Sublingual / oral LL-37 | Limited bioavailability |
| Recombinant LL-37 | Variable |
What it does
Main effects
- Broad-spectrum antimicrobial activity: Gram-positive (including MRSA), Gram-negative (including Pseudomonas), fungi (including Candida), enveloped viruses (HIV, influenza, herpes), mycobacteria (including TB), some parasites
- Anti-biofilm activity: Disrupts biofilm structure; reduces extracellular polymeric substance production; inhibits quorum sensing; particularly relevant for chronic wound infections where conventional antibiotics fail
- Wound healing: Keratinocyte migration, re-epithelialization, granulation tissue formation, angiogenesis stimulation, matrix metalloproteinase activation; mechanisms documented PMID: 17805349
- Immunomodulation: Modulates neutrophil, macrophage, dendritic cell, and T-cell function; immune cell recruitment; cytokine production effects
- Anti-apoptotic effects on keratinocytes: Protects against camptothecin-induced apoptosis; reduces caspase-3 activity PMID: 18923446
- Anti-LPS activity: Neutralizes lipopolysaccharide (endotoxin); modulates innate immune signaling; protective in sepsis contexts
- EGFR transactivation and FPRL-1 activation: Multi-receptor wound healing signaling; MAPK and PI3K/Akt pathway activation
- Vitamin D-regulated expression: 1,25-dihydroxyvitamin D₃ strongly induces LL-37 via CAMP gene vitamin D response element; connects vitamin D status to innate immunity
What to watch for
Common side effects
- Generally well-tolerated: No major adverse events at therapeutic doses; acceptable safety in wound healing trials
- Injection site reactions: Mild; standard for subcutaneous peptide administration
- Theoretical psoriasis activation: LL-37 implicated in psoriasis pathogenesis; LL-37 + DNA complexes activate plasmacytoid dendritic cells; caution in psoriasis or family history
- Theoretical autoimmune concern: LL-37-DNA complexes can be autoantigens; generally low clinical risk but not zero
- Limited long-term controlled data: Endogenous peptide nature reduces some concerns; no major chronic toxicity signals
- Quality concerns (research chemical): Identity verification important (37 aa peptide); sterility for injection required; synthesis quality variable across vendors
- Not WADA-prohibited as of current information (verify before use in tested sport)
Key facts
Key facts worth knowing
- LL-37 is a 37-amino acid peptide with sequence LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES. Molecular weight 4493.34 Da. The compound is the only human cathelicidin. Most mammals have multiple cathelicidins, but humans have just this one.
- Encoded by the CAMP gene (cathelicidin antimicrobial peptide gene) on chromosome 3. Precursor: hCAP-18 (170 aa protein, 18 kDa) containing N-terminal cathelin domain and C-terminal LL-37 sequence. Proteolytic activation: Primarily by neutrophil proteinase 3 at the granulocyte level; also by kallikreins in skin.
- Independent discovery 1995 by three groups: Cowland et al. (FEBS 1995); Agerberth et al. (PNAS 1995); Larrick et al. (FEBS Letters 1996). Originally named FALL-39 (first four amino acids of predicted sequence; 39 total amino acids predicted). Renamed LL-37 after exact cleavage characterization.
- Vitamin D regulation: Expression strongly induced by 1,25-dihydroxyvitamin D₃ through vitamin D response element in the CAMP gene promoter. This connects vitamin D status to innate immunity and explains some historically observed tuberculosis-vitamin D connections. Vitamin D deficiency reduces LL-37 production.
- Multi-target mechanism: Direct membrane disruption (antimicrobial); biofilm disruption; immune cell recruitment; EGFR transactivation (wound healing); FPRL-1 activation; anti-LPS activity (neutralizes endotoxin); MAPK and PI3K/Akt signaling activation; pro-angiogenic effects.
- Anti-biofilm activity is particularly notable: Biofilm-mediated infections are problematic clinically; conventional antibiotics often fail against biofilms; LL-37 disrupts biofilm structure; particularly relevant for chronic wound infections. PMC: 3699762 PMC: 3699762
- Wound healing mechanisms documented: Keratinocyte migration; re-epithelialization; granulation tissue formation; angiogenesis stimulation; matrix metalloproteinase activation. Demonstrated in vitro and in vivo (ob/ob mice excisional wounds). PMID: 17805349 PMID: 17805349
- Psoriasis complexity: Elevated LL-37 in psoriatic skin; LL-37 + DNA complexes activate plasmacytoid dendritic cells; triggers psoriasis-related inflammation; bidirectional relationship: protective in some contexts, pathogenic in others. Autoreactive T-cell responses to LL-37 in some psoriasis patients.
- Phase 1/2 clinical trials for wound healing (diabetic ulcers, venous ulcers); cystic fibrosis research (inhaled formulations); topical antimicrobial applications. No Phase 3 development; no FDA approval.
- Resistance considerations: Membrane-disruption mechanism inherently more resistant to bacterial adaptation than conventional antibiotic targets; no specific protein target to mutate; resistance is possible but harder to develop. Some bacteria have developed LL-37 resistance through membrane charge modifications, efflux pumps, and proteolytic degradation.
Legal status
Legal status
No FDA approval. Phase 1/2 clinical trials conducted. Some compounded formulations available. Not WADA prohibited.