The only human cathelicidin, doing two jobs at once
A 37-residue antimicrobial peptide from the human cathelicidin family.
Educational content. This page describes Cathelicidin LL-37 for informational purposes only and is not medical advice, diagnosis, or treatment. Consult a licensed provider before starting, stopping, or modifying any therapy.
As the only human cathelicidin, LL-37 disrupts bacterial, fungal, and enveloped viral membranes via carpet and toroidal pore mechanisms. The physical mechanism sidesteps classical single-target resistance pathways.[4]
The CAMP gene is a direct transcriptional target of the vitamin D receptor, linking serum 25-OH vitamin D to cathelicidin output in keratinocytes and myeloid cells. This is one of the mechanistic bases for vitamin D's role in skin and respiratory immunity.[7]
Cathelicidin LL-37 is a 37-amino-acid cationic, amphipathic alpha-helical host-defense peptide with the sequence LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES and a molecular weight near 4.5 kDa. It is the mature active fragment of the 18 kDa precursor hCAP-18, encoded by the single human cathelicidin gene, CAMP. In neutrophils, proteinase 3 cleaves hCAP-18 during or after degranulation to release LL-37, which folds into its bioactive helix upon contact with membranes or anionic surfaces.
LL-37 is the only cathelicidin encoded in the human genome. It is produced by neutrophils (its largest reservoir, stored in secondary granules), keratinocytes, epithelial cells of the respiratory, GI, and genitourinary tracts, mast cells, monocytes and macrophages, and NK cells. Expression is sharply upregulated by inflammation, wounding, and by 1,25-dihydroxyvitamin D3 acting through a vitamin D response element in the CAMP promoter. First characterized in the mid-1990s, it is now recognized as a multifunctional alarmin bridging antimicrobial defense and tissue repair.
LL-37's cationic amphipathic helix binds the anionic outer membrane of gram-positive and gram-negative bacteria, many fungi, and enveloped viruses. It inserts parallel to the bilayer (the carpet model) and, at threshold concentrations, organizes into transient toroidal pores that collapse membrane potential and cause lysis. Because the mechanism is physical rather than target-specific, classical resistance pathways are less effective against it.
Beyond killing pathogens, LL-37 is chemotactic for neutrophils, monocytes, mast cells, and T cells via the G-protein coupled receptor FPR2/ALX (also called FPRL1). It binds and neutralizes bacterial LPS to dampen TLR4-driven sepsis-like cytokine storms. At lower concentrations it shapes dendritic cell differentiation and tunes IL-6, IL-8, and TNF-alpha output. This dual kill-and-signal role is why it is classified as an alarmin rather than a pure antibiotic.
In skin, LL-37 is upregulated at the migrating edge of re-epithelializing wounds but nearly absent in the edges of chronic venous ulcers. Antibody blockade of endogenous LL-37 arrests re-epithelialization in ex vivo wound models. It drives keratinocyte migration through heparin-binding EGF-mediated transactivation of EGFR and through FPR2/ALX, and it induces endothelial proliferation and vessel-like tube formation in vitro, with angiogenesis confirmed in chorioallantoic-membrane and rabbit hindlimb ischemia models in vivo.
An honest counterpoint: the same peptide, when bound to self-DNA or self-RNA released from dying cells, activates plasmacytoid dendritic cells through TLR9/TLR7 and is a documented autoantigen in psoriasis and a T-cell target in SLE. Its cancer biology is context-dependent, with pro-proliferative signals in melanoma and ovarian models and NK-cell-dependent anti-tumor effects in colon and gastric contexts.
The only human cathelicidin, doing two jobs at once
LL-37 simultaneously disrupts pathogen membranes, recruits immune cells through FPR2/ALX, and drives keratinocyte migration plus VEGF-like angiogenesis. A single peptide that fights infection and rebuilds tissue in parallel.
Key studies supporting the therapeutic use of this peptide.
The 1.6 mg/mL arm reduced mean ulcer area by approximately 50% and showed a healing-rate constant roughly 3x placebo, with significant reduction from baseline on square-root-transformed wound area (p = 0.011). The 0.5 and 3.2 mg/mL doses were less effective (inverted-U dose response). No safety concerns. Remains the pivotal published human efficacy trial.
Grönberg A, Mahlapuu M, Ståhle M, Whately-Smith C, Rollman O — Wound Repair Regen, 22(5):613-621 (2014) · PubMed
LL-37 protein was strongly expressed along migrating keratinocyte tongues in acute healing wounds but was absent or markedly reduced in chronic ulcer edges. Blocking LL-37 with neutralizing antibodies inhibited re-epithelialization in ex vivo wound cultures, establishing that LL-37 deficiency is a feature, not just a correlate, of non-healing wounds.
Heilborn JD, Nilsson MF, Kratz G, et al. — J Invest Dermatol, 120(3):379-389 (2003) · PubMed
LL-37 binds extracellular self-DNA released from dying cells, forming condensed aggregates that are retained in pDC endosomes where they activate TLR9 and drive type-I interferon production. This pathway is implicated in psoriasis pathogenesis. The finding establishes a real prescribing caution: the same peptide that heals wounds can sustain autoimmune skin inflammation in susceptible patients.
Lande R, Gregorio J, Facchinetti V, et al. — Nature, 449(7162):564-569 (2007) · PubMed
hCAP-18/LL-37 was overexpressed in melanoma versus normal melanocytes. Exogenous LL-37 enhanced melanoma cell migration and proliferation. One of several studies supporting context-dependent, pro-tumor activity in cutaneous melanoma.
Kim JE, Kim HJ, Choi JM, et al. — Br J Dermatol, 163(5):959-967 (2010) · PubMed
Typical protocols used in clinical practice. Always consult a licensed provider for personalized dosing.
Topical (evidence-based)
Subcutaneous / systemic (NOT established)
Topical (evidence-based): Follows the Grönberg 2014 Phase I/IIa venous leg ulcer protocol under standard compression and moist-wound-care dressings. The 1.6 mg/mL dose showed the strongest signal; 0.5 mg/mL was under-dosed and 3.2 mg/mL did not outperform 1.6 mg/mL.
Subcutaneous / systemic (NOT established): No published Phase I human safety trials of subcutaneous or injectable LL-37 exist. Any systemic protocol circulating in compounding or wellness literature is unvalidated, lacks human pharmacokinetic data, and should be treated as research-only.
Clinical efficacy evidence is limited to topical use on chronic wound beds. Extrapolation to systemic dosing is not supported by published human data.
The topical dose response is non-monotonic (inverted-U). Higher concentrations did not produce better healing in Grönberg 2014, suggesting that in vitro cytotoxicity thresholds may matter at the wound surface.
LL-37 is a peptide, so it is heat and protease sensitive and requires sterile compounding, refrigerated storage, and use within a short window after reconstitution.
LL-37 complexed with self-DNA or self-RNA activates plasmacytoid dendritic cells via TLR9 or TLR7 and drives type-I interferon in psoriasis. It is also targeted by autoreactive T cells and associated with neutrophil extracellular traps in lupus. This is a documented prescribing consideration, not theoretical.
Published human exposure is essentially limited to topical application on wounds in one small Phase I/IIa cohort. There is no Phase III, no long-term safety data, and no published Phase I systemic PK/tolerability study.
Cancer biology is context-dependent. Pro-tumor signals in cutaneous melanoma and ovarian cancer models are offset by anti-tumor roles via NK-cell dependence in colon and gastric cancer. The literature is mixed, and patients with active or recent malignancy should be approached cautiously.
See how Cathelicidin LL-37 compares to peptides with overlapping benefits.
| Peptide | Primary Use | Administration | Cycle Length | Key Differentiator |
|---|---|---|---|---|
| Cathelicidin LL-37 | Chronic Wound Healing & Antimicrobial | Topical | 4 weeks (twice weekly application) | The only human cathelicidin. A single endogenous peptide that combines wound-healing, angiogenic, and broad-spectrum antimicrobial activity through overlapping FPR2/ALX and EGFR pathways. |
| GHK-Cu | Anti-Aging & Recovery | Topical, Injection | 8–12 weeks | Only peptide demonstrated to modulate ~31% of human genes, epigenetically resetting cellular function toward a younger phenotype |
| Glutathione | Antioxidant & Detoxification | IV, Oral, Sublingual | Ongoing supplementation | The body's own master antioxidant, with clinical data supporting oral bioavailability (challenging earlier assumptions) and dramatic immune cell activation at high doses |
| BPC-157 | Recovery & Healing | Injection, Oral | 4–8 weeks | Uniquely stable in gastric acid; broad multi-system healing with human IBD trial data |
| Thymosin Alpha-1 | Immune Support | Injection | 6–12 months (chronic) / 1–4 weeks (acute) | Only peptide with bidirectional immunomodulation, enhancing suppressed immunity while regulating hyperinflammation, approved in 35+ countries |
Current FDA classification and compounding eligibility.
The FDA placed this substance in Category 2 of the 503A bulk drug substances evaluation, flagging significant safety risks. 503A compounding carries FDA enforcement risk, so most pharmacies decline to prepare it and many physicians hesitate to prescribe it.
In April 2026, HHS Secretary Robert F. Kennedy Jr. announced that nominators withdrew 12 peptides from Category 2 of the FDA's 503A bulk drug substances evaluation, including this one. The FDA referred them to its Pharmacy Compounding Advisory Committee (PCAC) for re-evaluation at meetings beginning July 2026. If PCAC recommends Category 1 status and the FDA agrees, licensed 503A pharmacies could compound it under FDA enforcement discretion again. The outcome is not final.
Endogenous antimicrobial peptide studied for antimicrobial, wound-healing, and anti-inflammatory applications. Listed in Category 2 with FDA-cited immunogenicity and aggregation concerns. Named by HHS in April 2026 among 12 peptides withdrawn from Category 2 for PCAC re-evaluation.
FDA PCAC re-evaluation following April 2026 withdrawal from Category 2. Expected Q3 2026 onward.
Listed as 'Cathelicidin LL-37' in 503A Category 2
Last verified April 17, 2026. PepHookup tracks public FDA actions. This is not legal or medical advice.
Koczulla R, von Degenfeld G, Kupatt C, et al. “An angiogenic role for the human peptide antibiotic LL-37/hCAP-18.” J Clin Invest, 111(11):1665-1672 (2003)
Tokumaru S, Sayama K, Shirakata Y, et al. “Induction of keratinocyte migration via transactivation of the epidermal growth factor receptor by the antimicrobial peptide LL-37.” J Immunol, 175(7):4662-4668 (2005)
Kahlenberg JM, Carmona-Rivera C, Smith CK, Kaplan MJ “Neutrophil extracellular trap-associated protein activation of the NLRP3 inflammasome is enhanced in lupus macrophages.” J Immunol, 190(3):1217-1226 (2013)
Kim JE, Kim HJ, Choi JM, et al. “The antimicrobial peptide human cationic antimicrobial protein-18/cathelicidin LL-37 as a putative growth factor for malignant melanoma.” Br J Dermatol, 163(5):959-967 (2010)
Mahlapuu M, Björn C, Ekblom J “Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: a multicentric prospective randomized placebo-controlled clinical trial.” Wound Repair Regen (2021)
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