The only human cathelicidin, fighting infection and rebuilding tissue at once
Injection, Topical · 503A Compounding
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.
Researched and maintained by the PepHookup team. Regulatory status last verified April 17, 2026.
LL-37 is strongly expressed along the migrating keratinocyte edge of healing wounds and is nearly absent in chronic venous ulcer epithelium. In the only published human efficacy trial, topical LL-37 reduced ulcer area in stalled venous leg ulcers, supporting a real role in closing wounds that otherwise fail to progress.[1][2]
LL-37 activates endothelial FPR2/ALX signaling to promote new vessel formation, an effect that has been demonstrated in cell and animal models including rabbit hindlimb ischemia. Rebuilding the vascular bed beneath a wound is part of why it supports repair rather than acting only as an antimicrobial.[5]
LL-37 chemotactically recruits neutrophils, monocytes, and T cells through formyl peptide receptor 2 (FPR2/ALX, also called FPRL1). It also binds and neutralizes bacterial LPS endotoxin, dampening the LPS-driven inflammatory cascade in macrophages rather than amplifying it.[6][7]
As the only human cathelicidin, LL-37 disrupts bacterial, fungal, and enveloped viral membranes through carpet and toroidal-pore mechanisms. Because the action is physical rather than aimed at a single molecular target, classical single-target antibiotic resistance pathways are less effective against it.[8]
The CAMP gene that encodes LL-37 is a direct transcriptional target of the vitamin D receptor, linking serum vitamin D to cathelicidin output in keratinocytes and myeloid cells. This connection underlies part of vitamin D's documented role in skin and respiratory antimicrobial immunity.[9][10]
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 C-terminal fragment of the 18 kDa precursor hCAP-18, which is encoded by the single human cathelicidin gene, CAMP. In neutrophils, the enzyme proteinase 3 cleaves hCAP-18 during degranulation to release LL-37, which folds into its bioactive helix on contact with membranes or anionic surfaces.
LL-37 is the only cathelicidin found in the human genome. It is produced by neutrophils, which hold its largest reservoir in secondary granules, and by keratinocytes, epithelial cells lining the respiratory, gastrointestinal, and genitourinary tracts, mast cells, monocytes, macrophages, and natural killer cells. Expression rises sharply with inflammation and wounding, and it is induced by 1,25-dihydroxyvitamin D3 acting through a vitamin D response element in the CAMP promoter. First characterized in the mid-1990s, LL-37 is now understood as an alarmin that bridges antimicrobial defense and tissue repair.
Despite being a natural human peptide, LL-37 has limited clinical development. Human evidence is essentially confined to topical use on chronic wounds in two small randomized trials. There is no approved drug product, and the same biology that makes it useful in wound healing makes it a documented autoantigen in psoriasis and lupus, which is central to how it should be evaluated.
LL-37's cationic amphipathic helix binds the anionic outer membrane of gram-positive and gram-negative bacteria, many fungi, and enveloped viruses. It first lies parallel to the bilayer in the carpet model, then at threshold concentrations organizes into transient toroidal pores that collapse the membrane potential and lyse the cell. Because the mechanism is physical, bacteria adapt mainly by altering outer-surface charge rather than by the target mutations that defeat conventional antibiotics.
Beyond killing pathogens, LL-37 is chemotactic for neutrophils, monocytes, mast cells, and T cells through the G-protein-coupled receptor FPR2/ALX. It binds and neutralizes bacterial LPS, and in macrophages it has been shown to inhibit LPS- and ATP-driven inflammatory pyroptosis, blunting a sepsis-like inflammatory response. At lower concentrations it shapes dendritic cell differentiation and tunes cytokine output. This combination of direct killing and immune signaling is why it is classified as an alarmin rather than a simple antibiotic.
In skin, LL-37 is upregulated at the migrating edge of re-epithelializing wounds yet is nearly absent from the edges of chronic venous ulcers. Blocking endogenous LL-37 with neutralizing antibodies arrests re-epithelialization in ex vivo human wound cultures, which suggests its deficiency is part of the failure to heal rather than a bystander finding. LL-37 drives keratinocyte migration by transactivating the EGF receptor and signals through FPR2/ALX, while inducing endothelial proliferation and new vessel formation in cell and animal models.
An honest counterpoint runs through the same biology. When LL-37 binds self-DNA or self-RNA released from dying cells, it forms complexes that activate plasmacytoid dendritic cells and drive type-I interferon. This makes it a documented autoantigen in psoriasis, including a direct T-cell target, and a driver of self-DNA-peptide complexes in systemic lupus. Its cancer behavior is context-dependent, with pro-tumor signals reported in melanoma and ovarian models and tumor-suppressing or pro-apoptotic effects reported in gastric and colon cancer cells.
The only human cathelicidin, fighting infection and rebuilding tissue at once
LL-37 disrupts pathogen membranes, recruits immune cells through FPR2/ALX, neutralizes LPS endotoxin, and drives keratinocyte migration and angiogenesis. A single endogenous peptide that fights infection and rebuilds tissue in parallel, with the same biology underlying its autoimmune cautions.
LL-37 protein was strongly expressed along migrating keratinocyte tongues in acute healing wounds but was absent or markedly reduced at chronic ulcer edges. Blocking LL-37 with neutralizing antibodies inhibited re-epithelialization in ex vivo wound cultures, establishing LL-37 deficiency as a feature of non-healing wounds rather than a correlate.
Heilborn JD, Nilsson MF, Kratz G, et al. · J Invest Dermatol, 120(3):379-389 (2003) · PubMed
The 1.6 mg/mL arm reduced mean ulcer area by roughly half and showed a healing rate constant about three times placebo, with a 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, an inverted-U dose response. No safety concerns were identified. This is the pivotal published human efficacy trial.
Gronberg A, Mahlapuu M, Stahle M, Whately-Smith C, Rollman O · Wound Repair Regen, 22(5):613-621 (2014) · PubMed
A larger follow-up trial of topical LL-37 in venous leg ulcers. The peptide was well tolerated, but the efficacy signal seen in the earlier Phase I/IIa study did not reach the same level of statistical significance in this cohort, underscoring that human efficacy evidence remains limited and not yet definitive.
Mahlapuu M, Bjorn C, Ekblom J · Wound Repair Regen, 29(6):938-950 (2021) · PubMed
Circulating LL-37-specific T cells were detected in a majority of patients with moderate-to-severe plaque psoriasis and correlated with disease activity. LL-37 acted as a genuine T-cell autoantigen driving both interferon-gamma and Th17 responses, building on the earlier finding that LL-37 bound to self-DNA activates plasmacytoid dendritic cells. This establishes a concrete prescribing caution rather than a theoretical one.
Lande R, Botti E, Jandus C, et al. · Nat Commun, 5:5621 (2014) · PubMed
In ovarian cancer, LL-37 promoted tumor progression by recruiting mesenchymal stromal cells through FPR2/ALX. In gastric cancer cells, by contrast, LL-37 activated tumor-suppressing bone morphogenetic protein signaling and inhibited proliferation. These opposing findings show the cancer effect is tissue-specific, which is why patients with active or recent malignancy warrant caution.
Coffelt SB, Marini FC, Watson K, et al. · Proc Natl Acad Sci U S A, 106(10):3806-3811 (2009) · PubMed
start low, go slow
Topical (evidence-based)
Subcutaneous / systemic (NOT established)
Topical (evidence-based): Follows the Gronberg 2014 Phase I/IIa venous leg ulcer protocol under standard compression and moist-wound-care dressings. The 1.6 mg/mL concentration showed the strongest signal; 0.5 mg/mL appeared under-dosed and 3.2 mg/mL did not outperform 1.6 mg/mL. Actual dosing is determined by a licensed provider.
Subcutaneous / systemic (NOT established): No published Phase I human safety trials of subcutaneous or injectable LL-37 exist. Any systemic protocol circulating in wellness or compounding literature is unvalidated, lacks human pharmacokinetic data, and should be treated as research-only.
Dosing is determined by a licensed provider based on the specific condition and treatment goals. Human efficacy evidence is limited to topical use on chronic wound beds, and extrapolation to systemic dosing is not supported by published human data.
The topical dose response is non-monotonic, following an inverted-U. Higher concentrations did not produce better healing in the Gronberg trial, consistent with cytotoxicity thresholds becoming relevant at the wound surface.
LL-37 is a peptide and is therefore heat- and protease-sensitive. It requires sterile compounding, refrigerated storage, and use within a short window after reconstitution.
The FDA has cited immunogenicity and aggregation as specific concerns for LL-37 as a compounded bulk substance, which is directly relevant to the safety profile of any injectable formulation.
LL-37 complexed with self-DNA or self-RNA activates plasmacytoid dendritic cells and drives type-I interferon. It is a documented T-cell autoantigen in psoriasis and a driver of self-DNA-peptide complexes in systemic lupus, where it is also associated with neutrophil extracellular traps and inflammasome activation. This is an established prescribing consideration, not a theoretical one.
Published human exposure is essentially limited to topical application on wounds in two small randomized trials. There is no Phase III data, no long-term safety data, and no published Phase I systemic pharmacokinetic or tolerability study.
Cancer biology is context-dependent. Pro-tumor signals in cutaneous melanoma and ovarian models contrast with tumor-suppressing and pro-apoptotic effects reported in gastric and colon cancer cells. The literature is mixed, so patients with active or recent malignancy warrant a cautious approach.
The FDA placed LL-37 in 503A Category 2 citing immunogenicity and aggregation concerns. Category 2 means enforcement risk rather than prohibition, so most compounding pharmacies decline to prepare it and many physicians are hesitant to prescribe it while its regulatory status is unsettled.
| 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, balanced against documented autoimmune cautions. |
| GHK-Cu | Anti-Aging & Skin Regeneration | Topical, Injection | 8-12 weeks | A naturally occurring copper-carrier peptide that rebuilds the skin matrix and, per gene-expression analysis, shifts expression of about a third of human genes toward repair |
| Glutathione | Antioxidant & Detoxification | IV, Oral, Sublingual, Topical | Ongoing supplementation | The body's own master antioxidant, with controlled human data showing oral and sublingual forms can raise body stores and immune markers |
| BPC-157 | Recovery & Healing | Injection, Oral | 4–8 weeks | Unusually stable in gastric acid; broad multi-system healing signal, though evidence is largely preclinical |
| Thymosin Alpha-1 | Immune Support | Injection | 6-12 months (chronic) / short courses (acute) | Bidirectional immunomodulation that can strengthen suppressed immunity while helping temper hyperinflammation; approved as a pharmaceutical in 35+ countries |
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.
Looking into Cathelicidin LL-37? Find a provider who knows this peptide and can walk you through your options.
Find a ProviderA tripeptide antioxidant central to cellular redox, detoxification, and immune function.
Produced endogenously and supplemented via IV, injection, or oral routes; clinical evidence remains mixed.
A 28-residue peptide that modulates T-cell maturation and innate immune signaling.
Approved outside the U.S. for chronic hepatitis; domestic compounding remains ineligible after PCAC review.
A 3-residue α-MSH fragment with selective anti-inflammatory activity.
Studied for IBD, colitis, and wound healing; acts independently of melanocortin receptor binding.
“Advanced peptide therapies and personalized luxury care for optimal health, vitality, and longevity.”
Vetted providers offering Cathelicidin LL-37.