Skip to content
Peptide Atlas
All peptides

LL-37

Tier 2 · Preclinical
Also known as Cathelicidin · hCAP-18

The strongest evidence present is Tier 1, including the HEAL LL-37 phase IIb double-blind, randomized, placebo-controlled trial in 148 patients with venous leg ulcers (src-5, src-10) and several Tier-1 human observational reviews and mechanistic studies (src-1, src-15, src-16, src-17, src-23, src-28, src-30). Importantly, controlled human evidence is limited to topical wound-healing studies; the pivotal phase IIb trial was negative in its full population with benefit only in a post hoc large-wound subgroup. Broader claims (antiviral, antifungal, antitumor, antibiofilm, gut-barrier, cardiovascular) rest largely on in vitro, animal, theoretical, or expert-opinion sources, and no controlled trials of injected/systemic LL-37 exist.

Half-life
Not recorded
Routes
Topical (gel/cream, used in human trials) · Subcutaneous (community protocols only, not trial-validated)
Goals
Antimicrobial / anti-infective · Wound healing / tissue repair · Immune modulation · Anti-inflammatory · Antibiofilm
Cost / mg
Not recorded

How it works

LL-37 is described by sources as the only human cathelicidin — a 37-amino-acid, positively charged peptide cut from a precursor protein called hCAP-18. Because it carries a positive charge, it is drawn to the negatively charged surfaces of bacteria, where a Tier-1 review reports it punches holes in and permeabilizes microbial membranes, killing many bacteria (gram-positive and gram-negative), some fungi, and some viruses. Beyond killing microbes directly, sources describe it as an immune-signaling molecule: it binds and neutralizes bacterial endotoxin, recruits immune cells, and can dissolve bacterial biofilms and drive neutrophils to release DNA nets. Reviews stress that it has both anti- and pro-inflammatory effects and can be both protective and harmful depending on context — it is also cytotoxic to human cells at higher concentrations and has been implicated in diseases such as psoriasis and lupus. In wound healing, sources report it promotes new blood-vessel growth and skin-cell migration.

Overview

Overview

LL-37 (also called cathelicidin or hCAP-18) is described across sources as the only known human cathelicidin — a 37-amino-acid cationic peptide cleaved from the precursor protein hCAP-18 (src-2, src-3, src-7, src-59). Tier-3 vendor guides list its physical properties as 37 amino acids, ~4,493 Da, a +6 net charge at physiological pH, an isoelectric point of ~10.6, and encoding on chromosome 3p21.3 (src-2). Note that CAS numbers differ between sources: one lists 154947-66-7 (src-2) while another lists 137265-46-4 (src-14).

Biology and Origin

A Tier-3 guide (src-10) and Tier-2 review (src-7) describe the CAMP gene encoding a ~170-amino-acid preprotein that becomes the 18 kDa hCAP-18 proform, from which proteinase 3 releases the mature LL-37 peptide upon neutrophil degranulation. Sources report LL-37 is stored in neutrophil granules and produced by macrophages, dendritic cells, NK cells, epithelial cells, and keratinocytes (src-31, src-55), with concentrations rising at sites of infection, inflammation, and wound healing (src-49). A Tier-1 study and Tier-1 review report that 1,25-dihydroxyvitamin D upregulates CAMP gene expression (about a 170-fold mRNA increase in THP-1 monocytes per src-16), though a Tier-1 review cautions that only limited evidence shows vitamin D consistently increases biologically active LL-37 peptide (src-28).

Reported Activities

A Tier-1 review reports LL-37 is active against gram-positive and gram-negative bacteria and some viruses, modulates innate immunity by binding/inactivating bacterial endotoxins, promotes chemotaxis of immune cells, and mediates Ca2+ import (src-1, src-2). The same review describes direct bactericidal action via bacterial cell-wall permeabilization, biofilm dissolution, and promotion of neutrophil extracellular traps (NETs) (src-1). In vitro reviews report broad activity — one against 38 bacteria, 16 fungi, and 16 viruses (src-4), and another finding all 43 tested clinical bacterial strains susceptible with natural resistance uncommon (src-7). Tier-2 reviews report LL-37 can prevent biofilm establishment by a wide range of pathogens (src-20) and shows in vitro promise against drug-resistant organisms including MRSA, VRE, and resistant Klebsiella (src-4).

A Tier-1 clinical trial report notes endogenous LL-37 is abundant in acute wounds but absent in chronic wounds, suggesting a role in natural wound healing (src-5), and animal/ex vivo models report local LL-37 stimulates healing of chronic wounds (src-5). Sources also describe angiogenic and keratinocyte-migration effects (src-34, src-54, src-58, src-61).

Human Clinical Evidence

The strongest human evidence is topical. The HEAL LL-37 phase IIb double-blind, randomized, placebo-controlled study evaluated topical LL-37 with compression therapy in 148 patients with hard-to-heal venous leg ulcers, using LL-37 at 0.5 or 1.6 mg/mL versus placebo (src-5, src-10). The trial reported that the full-population efficacy analysis found no significant healing improvement versus placebo, while a post hoc analysis showed statistically significant improvement in the subgroup with large wounds (≥10 cm2) (src-5). A Tier-3 guide reports this subgroup showed complete wound closure in 28.1% on LL-37 versus 8.1% on placebo (src-10), and another Tier-3 guide characterizes the lower dose as producing healing roughly six times faster than placebo (src-12, citing Gronberg et al. 2014); readers should weigh these subgroup figures against the negative primary result. A Tier-3 guide states the only controlled human trials of administered LL-37 are topical wound-healing studies in venous leg and diabetic foot ulcers, with no published placebo-controlled trials of systemic subcutaneous, intramuscular, or intravenous LL-37 for any indication (src-2). A Tier-3 dosing site notes LL-37 is investigational as ropocamptide (src-48).

Context-Dependent and Investigational Roles

Sources emphasize LL-37 has both anti- and pro-inflammatory effects (src-1, src-3). A Tier-3 vendor guide and Tier-2 review describe LL-37/self-nucleic-acid complexes activating plasmacytoid dendritic cells via TLR9/7/8 to drive type I interferon as a documented pathogenic mechanism in psoriasis, systemic lupus erythematosus, psoriatic arthritis, and atherosclerosis (src-2, src-19). A Tier-2 study reports LL-37 localizes in atherosclerotic plaques and induces endothelial-to-mesenchymal transition via Akt/NF-κB, theorizing a role in atherosclerosis pathogenesis (src-18, src-67). A Tier-3 review reports contradictory tumor effects — overexpression promoting ovarian, lung, and breast cancers but suppressing colon and gastric cancer (src-25, src-79). A Tier-1 review reports a prominent and complex role in inflammatory bowel disease (src-30). Broader online claims that LL-37 treats infections, Lyme disease, long COVID, wounds, immune dysfunction, or anti-aging are, per a Tier-3 guide, not established by strong human clinical trials (src-8, src-43).

Regulatory Status

Sources agree LL-37 is not FDA-approved for any indication (src-2, src-6, src-10, src-13, src-30). Regulatory descriptions of the 503A bulks list conflict: one Tier-3 source states it is not on the §503A bulks list (src-2), while another states it is on the FDA's 503A Category 1 bulk drug substances list and available only as a compounded prescription through licensed 503A compounding pharmacies (src-10).

A third Tier-3 source that cites FDA regulatory documents helps settle this conflict (src-6): as of its May 2026 verification, LL-37 is not on the current §503A bulks list. FDA documents describe LL-37 as having been placed in Category 2 — bulk substances that raise significant safety concerns — and then removed only because the nomination was withdrawn, with FDA intending to consult its Pharmacy Compounding Advisory Committee before the end of February 2027 about possible inclusion. The framing that LL-37 sits on a "503A Category 1" list and is therefore routinely compoundable is a single-source claim that the FDA-based descriptions do not support; the weight of the sources is that LL-37 is not currently a listed compoundable bulk substance and its status is unresolved pending further FDA review.

What the research shows

319 findings extracted from the 30 sources cited below, strongest evidence first within each group. Every one links to the source it came from.

What human studies found

Based on 16 human trial findings, 13 human study findings, 2 animal findings, 4 in vitro findings and 39 expert opinion findings.

  • human trialHEAL LL-37 was a phase IIb double-blind, randomized, placebo-controlled study to evaluate the efficacy and safety of LL-37 for topical administration in combination with compression therapy in 148 patients with hard-to-heal venous leg ulcers5

  • human trialEfficacy analysis performed on the full study population did not identify any significant improvement in healing in patients treated with LL-37 compared with placebo5

  • human trialPost hoc analysis revealed statistically significant improvement with LL-37 treatment in several interrelated healing parameters in the subgroup of patients with large target wounds (wound area of at least 10 cm2 at randomization)5

  • human trialTwo randomized clinical trials confirm that topical LL-37 accelerates wound healing in venous leg ulcers20

  • human trialThe lower dose produced healing rates roughly six times faster than placebo (Gronberg et al. 2014)20

  • human trialHuman clinical trials for LL-37 delivered it as a gel applied directly onto a leg ulcer, not as an injection21

  • human trialNo published human trial has tested subcutaneous LL-3721

  • human trialThe lowest concentration, 0.5 mg/mL, produced the best healing rate21

Show the remaining 66

  • human trial1.6 mg/mL was effective but less than 0.5 mg/mL21

  • human trial3.2 mg/mL was tested first-in-man only and not carried forward21

  • human trialA 2021 phase IIb RCT in 148 patients found complete wound closure in 28.1% on LL-37 versus 8.1% on placebo in the large-wound subgroup24

  • human trialThe only controlled human clinical trials of administered LL-37 are topical wound-healing studies in venous leg ulcers and diabetic foot ulcers25

  • human trialRandomized clinical trials have evaluated LL-37 in hard-to-heal venous leg ulcers and diabetic foot ulcers27

  • human trialGronberg and colleagues conducted a randomized, placebo-controlled trial in hard-to-heal venous leg ulcers and reported that LL-37 treatment enhanced healing27

  • human trialMahlapuu and colleagues conducted a multicenter prospective randomized placebo-controlled trial in hard-to-heal venous leg ulcers27

  • human trialMiranda and colleagues reported a randomized double-blind controlled trial of LL-37 cream in diabetic foot ulcers27

  • human studyLL-37 shows activity towards both gram-positive and gram-negative bacteria2

  • human studyLL-37 is active against some types of viruses2

  • human studyIn psoriatic lesions very high concentrations (300 µM) of LL-37 are detected2

  • human studyIn periodontitis, gingival crevicular fluid contains about 1 µM LL-372

  • human studyLL-37 primarily kills already infected and weakened cells2

  • human studyLL-37 plays a prominent and complex role in inflammatory bowel disease (IBD)6

  • human studyOverexpression of LL-37 has been implicated in inflamed and noninflamed colon mucosa in patients with ulcerative colitis6

  • human studyLL-37 expression was not changed in inflamed or noninflamed colon or ileal mucosa in patients with Crohn's disease6

  • human studyCathelicidins have protective effects in both ulcerative colitis and Crohn's disease in animal models and human patients6

  • human studyLL-37 peptide is a potent killer of different microorganisms8

  • human studyLL-37 is localized in atherosclerotic plaques12

  • human studyThe rate of LL-37/hCAP-18 positive cells ranged from 60 (ITP) to 0.5% (M5)18

  • human studyBals and colleagues reported LL-37/hCAP18 expression in human airway epithelium and broad antimicrobial activity at the airway surface27

  • animalLocal administration of LL-37 has been shown to stimulate healing of chronic wounds in experimental animals and in an ex vivo model of human acute wounds5

  • animalLL-37 is able to prevent biofilm establishment by different bacterial pathogens such as Acinetobacter baumannii, Aggregatibacter actinomycetemcomitans, Bacteroides fragilis, Burkholderia thailandensis, Cutibacterium acnes, Escherichia coli, Francisella tularensis, Helicobacter pylori, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pyogenes13

  • in vitroLL-37 shows broad antimicrobial activity, effective against 38 bacteria, 16 fungi, and 16 viruses10

  • in vitroAll tested clinical isolates were susceptible to LL-37 under the experimental conditions, confirming its broad-spectrum antimicrobial activity11

  • in vitroNatural resistance to LL-37 is uncommon among bacterial pathogens11

  • in vitroRecombinant LL-37 exhibits consistent antimicrobial activity across diverse clinical isolates11

  • expert opinionOnly limited evidence is presented showing that 1,25D3 consistently increases the amount of biologically active LL-37 peptide7

  • expert opinionLL-37 has potent antimicrobial properties9

  • expert opinionLL-37 has antiviral properties9

  • expert opinionLL-37 has antifungal properties9

  • expert opinionLL-37 has antiparasitic properties9

  • expert opinionLL-37 has antitumor properties9

  • expert opinionLL-37 has been proposed as a marker of inflammation severity and treatment outcome15

  • expert opinionLL-37 is effective against a broad spectrum of pathogens including Gram-positive and Gram-negative bacteria, fungi, and enveloped viruses19

  • expert opinionLL-37 promotes tissue repair by inducing angiogenesis through endothelial cell proliferation and increasing VEGFA expression19

  • expert opinionLL-37 promotes epithelialization by promoting keratinocyte migration and proliferation during wound closure19

  • expert opinionLL-37 is highly effective against antibiotic-resistant strains such as MRSA19

  • expert opinionLL-37 has broad-spectrum antimicrobial activity20

  • expert opinionLL-37 has antiviral defense including against SARS-CoV-220

  • expert opinionLL-37 accelerates wound healing20

  • expert opinionLL-37 disrupts biofilms20

  • expert opinionLL-37 provides gut barrier protection20

  • expert opinionLL-37 has anti-inflammatory modulation20

  • expert opinionLL-37 has cancer immunotherapy potential20

  • expert opinionLL-37 has cardiovascular protection20

  • expert opinionLL-37 demonstrates potent activity against methicillin-resistant Staphylococcus aureus (MRSA)22

  • expert opinionLL-37 can disrupt biofilm formation and kill planktonic MRSA cells, even in antibiotic-resistant strains22

  • expert opinionLL-37 demonstrates bactericidal activity against Pseudomonas aeruginosa22

  • expert opinionLL-37 is active against uropathogenic Escherichia coli associated with urinary tract infections22

  • expert opinionLL-37 shows activity against enveloped viruses including influenza and coronavirus through direct interaction with viral lipid envelopes22

  • expert opinionLL-37 demonstrates activity against Candida species and other opportunistic fungi22

  • expert opinionLL37 has demonstrated anti-inflammatory, wound healing, and immunomodulatory effects23

  • expert opinionLL37 is effective against antibiotic resistant pathogens like methicillin-resistant Staphylococcus aureus (MRSA)23

  • expert opinionLL37 accelerates healing in chronic wounds, diabetic ulcers, and burns23

  • expert opinionLL37 modulates inflammation in inflammatory bowel disease (IBD), psoriasis, and rheumatoid arthritis23

  • expert opinionLL37 demonstrates antiviral activity against respiratory viruses including influenza and SARS-CoV-223

  • expert opinionLL37 has been investigated for its ability to suppress tumor growth by modulating the tumor microenvironment23

  • expert opinionLL37 is effective in breaking down biofilms in chronic infections such as dental and sinus infections23

  • expert opinionThere are no published placebo-controlled trials of systemic subcutaneous, intramuscular, or intravenous LL-37 in humans for any indication25

  • expert opinionOnline claims that LL-37 treats infections, Lyme disease, long COVID, wounds, immune dysfunction, or anti-aging are not established by strong human clinical trials26

  • expert opinionLL-37 has been studied in cancer biology, including breast-cancer expression and growth-factor-like effects in epithelial cells27

  • expert opinionLL-37 shows great potential to be developed as a drug with clinical use28

  • expert opinionLL-37 can have two different and contradictory effects--promotion or inhibition of tumor growth29

  • expert opinionOverexpression of LL-37 was found to promote development and progression of ovarian, lung and breast cancers29

  • expert opinionOverexpression of LL-37 was found to suppress tumorigenesis in colon and gastric cancer29

How it works

Based on 3 human trial findings, 23 human study findings, 1 animal finding, 28 in vitro findings, 116 expert opinion findings and 12 theoretical findings.

  • human trialThe human cathelicidin LL-37 shows activity against microorganisms, but it is also cytotoxic to host cells3

  • human trialThe CAMP gene codes for the LL-37 precursor hCAP18 which is processed extracellularly to active LL-373

  • human trialVitamin D stimulates CAMP gene activity3

  • human studyLL-37 modulates innate immunity through binding and inactivation of bacterial endotoxins2

  • human studyLL-37 promotes chemotaxis of immune cells2

  • human studyLL-37 interacts with plasma membrane receptors and mediates import of Ca2+2

  • human studyLL-37 has both anti- and pro-inflammatory effects2

  • human studyLL-37 has a direct bactericidal effect through permeabilization of the bacterial cell wall2

Show the remaining 175

  • human studyLL-37 can dissolve bacterial biofilms2

  • human studyLL-37 promotes formation of neutrophil extracellular traps (NETs)2

  • human studyEndogenous LL-37 was abundantly present in acute wounds, but was absent in chronic wounds, suggested a role of this peptide in natural wound healing5

  • human study1,25D3 up-regulates expression of the human antimicrobial peptide hCAP-18/LL-37 gene7

  • human studyThe hCAP-18/LL-37 gene seems to be an important transcriptional target for 1,25D37

  • human study1,25D3-induced stimulation of hCAP-18/LL-37 gene expression represents an important pathway for 1,25D3-evoked regulation of the innate immune response7

  • human studyLL-37 is the only known member of the cathelicidin family of peptides expressed in humans8

  • human studyLL-37 is a multifunctional host defense molecule essential for normal immune responses to infection and tissue injury8

  • human studyLL-37 can prevent immunostimulatory effects of bacterial wall molecules such as lipopolysaccharide and can therefore protect against lethal endotoxemia8

  • human studyLL-37 has chemoattractant function8

  • human studyLL-37 inhibits neutrophil apoptosis8

  • human studyLL-37 stimulates angiogenesis, tissue regeneration, and cytokine release (e.g. IL-8)8

  • human studyCellular production of LL-37 is affected by bacterial products, host cytokines, availability of oxygen, and sun exposure through the activation of CAP-18 gene expression by vitamin D(3)8

  • human studyAt infection sites, the function of LL-37 can be inhibited by charge-driven interactions with DNA and F-actin released from dead neutrophils and other cells lysed as the result of inflammation8

  • human studyLow translation efficiency of LL-37/hCAP-18 in some leukemia cells might be one of the reasons that leukemia patients were susceptible to infection18

  • human studyLL-37 forms complexes with self-DNA and self-RNA released from damaged cells that activate plasmacytoid dendritic cells through TLR9, TLR7, and TLR8, driving type I interferon production25

  • human studyThe CAMP promoter contains a vitamin D response element (VDRE) and calcitriol binding to the VDR/RXR heterodimer transactivates CAMP transcription25

  • human studySerum 25-hydroxyvitamin D levels correlate with neutrophil and macrophage cathelicidin output25

  • animalCathelicidins, a family of HDPs, are produced by diverse animal species such as mammals, fish, birds, amphibians, and reptiles to protect them against pathogen infections14

  • in vitroA physiological concentration of vitamin D (50 nM) enhances CAMP mRNA levels by about 170 times in human THP-1 monocyte cells3

  • in vitroStimulation with 50 nM vitamin D increases hCAP18/LL-37 protein contents 3-4 times in THP-1 cell lysates3

  • in vitroTreatment with the proteasome inhibitor MG132 enhances hCAP18/LL-37 levels, suggesting that turnover of hCAP18/LL-37 protein is regulated by the proteasome3

  • in vitroLL-37 disrupts multiple microbial pathways, reducing resistance in bacteria, fungi, and viruses10

  • in vitroLL-37 shows structural versatility, with mono-, di-, and tetrameric forms supporting function and stability10

  • in vitroLL-37 effectively combats over 38 bacteria, 16 fungi, and 16 viruses through various mechanisms, including membrane rupture, targeting, and biofilm suppression10

  • in vitroMechanisms involve cell wall destruction, membrane permeabilization, oxidative stress, cell cycle arrest, adhesion prevention, gene modification, and disruption of viral envelopes, entry, and replication10

  • in vitroLL-37 is a multifaceted peptide with antimicrobial and immunomodulatory actions12

  • in vitroLL-37 decreased EC markers but increased mesenchymal cell markers in human umbilical vein ECs12

  • in vitroLL-37 decreased the vascular network formation of cells but increased cell migration12

  • in vitroLL-37-induced EndMT was inhibited by Akt and nuclear factor-kappa B (NF-κB) inhibitors, suggesting that LL-37 induces EndMT by activating Akt and NF-κB12

  • in vitroLL-37 has broad-spectrum antimicrobial activity and immunomodulatory properties13

  • in vitroInhibition of bacterial adhesion is a major mechanism responsible for antibiofilm properties of LL-3713

  • in vitroDownregulation of biofilm-associated genes is a major mechanism responsible for antibiofilm properties of LL-3713

  • in vitroSuppression of quorum-sensing pathways is a major mechanism responsible for antibiofilm properties of LL-3713

  • in vitroDegradation of biofilm matrix is a major mechanism responsible for antibiofilm properties of LL-3713

  • in vitroEradication of biofilm-residing cells is a major mechanism responsible for antibiofilm properties of LL-3713

  • in vitroLL-37 peptide is released from human cathelicidin (hCAP-18)15

  • in vitroLL-37 can directly perform antimicrobial action after insertion into surface structures of microorganisms15

  • in vitroLL-37 has immunomodulatory function as an agonist of different cell membrane receptors15

  • in vitroLL-37/hCAP-18 expression at mRNA level was detected and varied among six of nine cell lines18

  • in vitroThe level of Raji cells was about eight folds higher than that of Ramos cells18

  • in vitroOnly two cell lines, J6-1 and U937, expressed protein products18

  • in vitroLL-37 has broad in-vitro antimicrobial activity25

  • in vitroLL-37 has pro-angiogenic effects on skin wounds25

  • in vitroLL-37 has immunomodulatory signaling through the FPR2 receptor25

  • in vitroLL-37 can act against bacteria, fungi, viruses, and biofilms in experimental systems26

  • in vitroTokumaru and colleagues reported that LL-37 induced keratinocyte migration through transactivation of the epidermal growth factor receptor27

  • expert opinionLL-37 has potent antimicrobial, antiviral, antifungal, antiparasitic, and antitumor properties1

  • expert opinionTruncated and retro-analogs of LL-37 preserve or improve biological activity while exhibiting reduced toxicity and increased proteolytic resistance1

  • expert opinionAntimicrobial peptides serve as key effectors of the innate immune system offering protection against Gram-positive and Gram-negative bacteria, fungi, and viruses1

  • expert opinionLL-37 is a proteolytic fragment of cathelicidin4

  • expert opinionLL-37 fulfills the roles of a defensin by inserting into the membranes of bacterial pathogens4

  • expert opinionLL-37 functions as alarmin in stimulating chemotaxis of innate immune cells4

  • expert opinionLL-37 alters the structure and efficacy of various cytokines4

  • expert opinionLL-37 has direct effect on neutrophils and the release of extracellular traps (NETs)4

  • expert opinionNETs function as mediators of immune defense against pathogens4

  • expert opinionNETs are important contributors to chronic disease and tissue pathogenesis4

  • expert opinionLL-37 has structural flexibility and ability to adapt to distinct microenvironments and interacting counterparts4

  • expert opinionLL-37 is a 37-meric peptide derived by proteolytic cleavage from the 18-kDa human cathelicidin antimicrobial protein (hCAP18)5

  • expert opinionLL-37 is the only member of the cathelicidin family of host defense peptides expressed in humans6

  • expert opinionLL-37 plays a crucial role in host defense against pathogen invasion6

  • expert opinionLL-37 regulates anti-inflammation, antitumorigenesis, and tissue repair functions6

  • expert opinionLL-37 is primarily produced by phagocytic leukocytes and epithelial cells6

  • expert opinionLL-37 mediates a wide range of biological responses6

  • expert opinionLL-37 is the only human cathelicidin9

  • expert opinionLL-37 has broad-spectrum antimicrobial activity9

  • expert opinionLL-37 has immunomodulatory functions9

  • expert opinionLL-37 is usually expressed at high concentrations by various white blood cells11

  • expert opinionLL-37 plays an important role in the innate immune defense against bacterial and viral infections11

  • expert opinionLL-37 effectively disrupts bacterial membranes11

  • expert opinionLL-37 is derived through proteolysis of its precursor, the human cationic antimicrobial peptide (hCAP18)11

  • expert opinionhCAP18 is considered an 18 kDa propeptide, which consists of signal peptide, a conserved cathelin domain, and the antimicrobial peptide LL-37 residing in the C-terminal domain11

  • expert opinionLL-37 is the only member of cathelicidin family synthetized in humans11

  • expert opinionCathelicidins are expressed at high concentrations in neutrophil-specific granules, which can be released upon neutrophil activation11

  • expert opinionLL-37 (hCAP-18) is the only identified human cathelicidin antimicrobial peptide17

  • expert opinionCathelicidins have antimicrobial effects17

  • expert opinionCathelicidins have lipopolysaccharide-neutralizing effects17

  • expert opinionCathelicidins profoundly affect both innate and adaptive immunity17

  • expert opinionLL-37 has a role in lung physiology and defense17

  • expert opinionLL-37/hCAP-18 is an important part of host defense18

  • expert opinionLL-37 operates through two primary mechanisms: direct antimicrobial action and immune regulation19

  • expert opinionLL-37 directly disrupts bacterial and fungal membranes due to its strong positive charge and alpha helical structure19

  • expert opinionLL-37 regulates innate immunity by modulating Toll-Like Receptor (TLR) signaling pathways19

  • expert opinionLL-37 is derived from a larger precursor protein called hCAP1819

  • expert opinionLL-37 is produced naturally by neutrophils, macrophages, epithelial cells, and bone marrow-derived cells19

  • expert opinionLL-37 acts as a chemoattractant, recruiting neutrophils, monocytes, and T cells to the site of infection19

  • expert opinionLL-37 binds to bacterial products such as LPS or endotoxin, inhibiting their ability to activate TLR4 receptors19

  • expert opinionLL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino-acid molecule produced by immune cells, skin, and mucosal surfaces20

  • expert opinionLL-37 is cleaved from a precursor protein called hCAP-18 by the enzyme proteinase 320

  • expert opinionLL-37 adopts an alpha-helical shape that is amphipathic with one face carrying positive charge and the other hydrophobic20

  • expert opinionThe CAMP gene on chromosome 3 encodes LL-3720

  • expert opinionNeutrophils, macrophages, dendritic cells, natural killer cells, epithelial cells, and keratinocytes all produce LL-3720

  • expert opinionLL-37 recruits immune cells through chemotaxis20

  • expert opinionLL-37 suppresses excessive production of TNF-alpha and IL-6, preventing collateral tissue damage20

  • expert opinionLL-37 stimulates angiogenesis through VEGF signaling20

  • expert opinionLL-37 promotes keratinocyte migration to close wounds and protects keratinocytes from apoptosis20

  • expert opinionLL-37 is the only cathelicidin antimicrobial peptide made by humans21

  • expert opinionLL-37 comes from a larger protein called hCAP-1821

  • expert opinionLL-37 helps the body respond to microbes, inflammation, and wound repair21

  • expert opinionLL-37 is a 37-amino-acid host-defense peptide21

  • expert opinionLL-37 is a cationic antimicrobial peptide (AMP) composed of 37 amino acids with a net positive charge at physiological pH22

  • expert opinionLL-37 is the sole human cathelicidin22

  • expert opinionLL-37 is primarily produced by neutrophils, macrophages, and epithelial cells in response to infection or tissue injury22

  • expert opinionLL-37 concentration increases significantly at sites of inflammation, wound healing, and infection22

  • expert opinionLL-37 exerts antimicrobial effects primarily through disruption of microbial membranes22

  • expert opinionLL-37's positive charge allows it to bind to negatively charged bacterial lipopolysaccharides (LPS) and phospholipids on cell membranes22

  • expert opinionLL-37 mechanism leads to membrane permeabilization, pore formation, disruption of membrane integrity, leakage of intracellular contents, and cell lysis22

  • expert opinionLL-37 is effective against gram-positive and gram-negative bacteria, as well as certain fungi and viruses22

  • expert opinionLL-37 functions as an immunomodulator through interaction with toll-like receptors (TLRs), particularly TLR3 and TLR922

  • expert opinionLL-37 can activate dendritic cells and enhance antigen presentation through TLR signalling22

  • expert opinionLL-37 promotes Th1 and Th17 immune responses22

  • expert opinionLL-37 modulates inflammatory cytokine production (IL-6, TNF-α, IL-10)22

  • expert opinionLL-37 triggers innate immune responses through TLR9 activation and recognition of viral DNA/RNA22

  • expert opinionLL-37 produces indirect antiviral effects through enhanced interferon production and NK cell activation22

  • expert opinionLL-37 stimulates endothelial cell proliferation and new blood vessel formation (angiogenesis) in wound healing22

  • expert opinionLL-37 enhances fibroblast activation and collagen deposition in wound healing22

  • expert opinionLL37 is a naturally occurring antimicrobial peptide derived from cathelicidin, an immune defense molecule produced by epithelial cells, immune cells, and keratinocytes23

  • expert opinionLL37 is the only human cathelicidin identified so far23

  • expert opinionLL37 plays a vital role in the innate immune system by combating bacterial, viral, and fungal pathogens23

  • expert opinionLL37 disrupts microbial membranes leading to cell lysis and death23

  • expert opinionLL37 targets gram positive and gram negative bacteria, fungi, and viruses23

  • expert opinionLL37 regulates immune responses by modulating cytokine production, enhancing macrophage activity, and promoting anti-inflammatory pathways23

  • expert opinionLL37 stimulates angiogenesis, epithelialization, and tissue repair by attracting immune cells to injury sites and promoting collagen synthesis23

  • expert opinionLL37 penetrates and breaks down biofilms that shield pathogens from antibiotics and the immune system23

  • expert opinionLL-37 is the only antimicrobial peptide encoded by the human genome in the cathelicidin family24

  • expert opinionLL-37 is stored in neutrophil granules and released at infection sites24

  • expert opinionLL-37 is a 37-amino-acid cationic antimicrobial peptide derived from the C-terminal end of hCAP-1824

  • expert opinionLL-37 is encoded by the human CAMP gene24

  • expert opinionLL-37 is active against both gram-positive and gram-negative bacteria24

  • expert opinionLL-37 is stored in neutrophil granules and secreted by keratinocytes, epithelial cells of the respiratory tract, and cells of the gastrointestinal mucosa24

  • expert opinionLL-37 is released in inactive form as the hCAP-18 precursor and cleaved to the active peptide by extracellular proteases24

  • expert opinionProteinase 3 is the primary extracellular protease responsible for cleavage of hCAP-18 to LL-37 upon neutrophil degranulation24

  • expert opinionLL-37 expression is induced in keratinocytes during inflammatory skin disorders24

  • expert opinionLL-37 kills microorganisms through physical disruption of their lipid membranes24

  • expert opinionLL-37 activates immune cell recruitment via formyl peptide receptor signaling24

  • expert opinionLL-37 is the only human cathelicidin, a 37-amino-acid cationic peptide cleaved from the precursor protein hCAP-1825

  • expert opinionThe CAMP gene encodes a 170-amino-acid preprotein that after signal-peptide cleavage becomes hCAP-1825

  • expert opinionProteinase 3 cleaves hCAP-18 between Ala103 and Leu104, releasing the mature 37-amino-acid peptide LL-3725

  • expert opinionLL-37 is the only human cathelicidin antimicrobial peptide26

  • expert opinionLL-37 is a 37-amino-acid host-defense peptide produced from the precursor protein hCAP1826

  • expert opinionLL-37 affects immune-cell signaling, inflammation, angiogenesis, and wound repair26

  • expert opinionLL-37 has antimicrobial and antibiofilm activity against multiple Gram-positive and Gram-negative bacteria26

  • expert opinionLL-37 is part of the body's innate immune defense system26

  • expert opinionLL-37 can be both protective and potentially inflammatory depending on context26

  • expert opinionLL-37 is the active peptide generated from the human cathelicidin antimicrobial protein hCAP1827

  • expert opinionLL-37 is part of the innate immune system and is expressed by epithelial cells and immune cells at barrier surfaces27

  • expert opinionLL-37 can influence wound repair, keratinocyte migration, immune-cell signaling, angiogenesis, and inflammatory pathways27

  • expert opinionLL-37 has been implicated in psoriasis pathogenesis through complexes with self-DNA and self-RNA that activate dendritic-cell pathways27

  • expert opinionLL-37 is the sole human cathelicidin28

  • expert opinionLL-37 has broad spectrum antibiotic properties28

  • expert opinionLL-37 has potent chemotactic properties28

  • expert opinionLL-37 has potent immunomodulatory properties28

  • expert opinionLL-37 is a C-terminal peptide proteolytically released from 18 kDa human cathelicidin protein (hCAP18)29

  • expert opinionChronic infections, inflammation, tissue injury and tissue regeneration are all linked with neoplastic growth, and involve LL-37 antibacterial and immunomodulatory functions29

  • expert opinionThe mechanisms are tissue-specific, complex, and depend mostly on the ability of LL-37 to act as a ligand for different membrane receptors whose expression varies on different cancer cells29

  • expert opinionCathelicidins are antimicrobial peptides produced by humans and animals in response to various pathogenic microbes30

  • expert opinionCathelicidins act as a primary defense against bacteria and other pathogens in the case of inflammation30

  • expert opinionThey are able to kill bacteria and fungi, inhibit and destroy bacterial biofilms30

  • expert opinionCathelicidins possess antiviral and antiparasitic properties30

  • expert opinionThey can play a role in angiogenesis, wound healing, and the regulation of apoptosis30

  • expert opinionLL-37 has emerged as a novel modulator of tumor growth and metastasis in carcinogenesis of various types of cancers30

  • expert opinionLL-37 acts as an anti- and pro- inflammatory factor30

  • expert opinionCathelicidins are able to directly and selectively destroy membranes of various microbes and cancer cells, but they do not attack normal cells30

  • theoreticalHost defense peptides (HDPs) are naturally occurring polypeptide sequences that are active against bacteria, fungi, viruses, and other parasites14

  • theoreticalHost defense peptides may stimulate immunomodulatory responses14

  • theoreticalCathelicidins have variable C-terminal domains responsible for their antimicrobial and immunomodulatory activities and a highly conserved N-terminal pre-pro region homologous to cathelin14

  • theoreticalCathelicidins are major components of innate immunity14

  • theoreticalLL-37 fragments (SK-24, IV-20, FK-13 and LL-37) play a role in the immunity response14

  • theoreticalLL-37 fragments may be responsible for interaction between these peptides and receptors in humans14

  • theoreticalAntimicrobial peptides (AMPs) such as β-defensin, S100, and cathelicidin are secreted from cells and activate the innate immune system through various mechanisms to induce inflammation, thus participating in the pathogenesis of psoriasis16

  • theoreticalAntimicrobial peptides enhance the binding of damage-associated molecular patterns such as self-DNA and self-RNA to their receptors and promote the secretion of interferon from activated plasmacytoid dendritic cells and keratinocytes to promote inflammation in psoriasis16

  • theoreticalNeutrophil extracellular traps (NETs), complexes of self-DNA and proteins including LL-37 released from neutrophils in psoriatic skin, induce Th1716

  • theoreticalActivated myeloid dendritic cells secrete a mass of inflammatory cytokines such as IL-12 and IL-23 in psoriasis, which is indispensable for the proliferation and survival of T cells that produce IL-1716

  • theoreticalAMPs enhance the production of some of Th17 and Th1 cytokines and modulate receptors and cellular signaling in psoriasis16

  • theoreticalInflammation induced by DAMPs, including self-DNA and RNA released due to microinjuries or scratches, and the enhanced recognition of DAMPs by AMPs, may be involved in the mechanism underlying the Köbner phenomenon in psoriasis16

Dosing

Based on 3 human trial findings and 4 anecdotal findings.

  • human trialStudy had three arms consisting of two groups treated with LL-37 at concentrations of 0.5 or 1.6 mg/mL, and a placebo cohort5

  • human trialLL-37 was mixed into a gel and applied to the ulcer surface twice a week with tested concentrations of 0.5 and 1.6 mg/mL21

  • human trialAn earlier first-in-man study tested 3.2 mg/mL21

  • anecdotalThe daily subcutaneous protocol common in the research community is community-derived, not trial-validated21

  • anecdotalCommunity write-ups commonly describe a low daily subcutaneous dose for a short block of weeks with reported figures cluster around 100-250 mcg per day21

  • anecdotalSome advanced write-ups going up to 500 mcg per day21

  • anecdotalFrequency is usually once daily, often 5 days on with 2 days off, for a 2-4 week block21

How the body handles it

Based on 2 in vitro findings and 1 expert opinion finding.

  • in vitroThe hCAP18/LL-37 concentration in vitamin D-stimulated THP-1 cells corresponds to 1.04 μM LL-373

  • in vitroMIC concentrations obtained for recombinant LL-37 were comparable to those reported for chemically synthesized and commercially available LL-3711

  • expert opinionNanoscale delivery systems facilitate targeted delivery, prolong peptide half-life, and mitigate cytotoxic effects of LL-371

Safety and side effects

Based on 1 human trial finding, 2 human study findings, 1 animal finding, 2 in vitro findings and 18 expert opinion findings.

  • human trialThe study drug was well tolerated and safe in both dose strengths5

  • human studyLL-37 is cytotoxic to many different human cell types, particularly infected cells, when administered at final concentrations of 1–10 µM2

  • human studyLL-37 complexes with self-DNA and self-RNA are a documented pathogenic mechanism in psoriasis, systemic lupus erythematosus (SLE), psoriatic arthritis, and atherosclerosis25

  • animalFDA notes nonclinical findings suggesting detrimental effects on male reproduction and protumorigenic effects in some tissues27

  • in vitroSynthetic LL-37, at 1.04 μM concentration, reduces viability of human osteoblast-like MG63 cells3

  • in vitroTHP-1 cells are less sensitive to LL-37-induced cytotoxicity than human osteoblast-like MG63 cells3

  • expert opinionClinical application of LL-37 is hindered by low proteolytic stability, cytotoxicity, and high production costs1

  • expert opinionClinical application of LL-37 is hindered by several limitations9

Show the remaining 16

  • expert opinionClinical application faces challenges like degradation and toxicity10

  • expert opinionIssues such as proteolytic sensitivity and potential high-concentration toxicity must be addressed10

  • expert opinionAMPs have low or not yet observed bacterial resistance11

  • expert opinionThere are still many questions to be answered regarding LL-37 efficacy and safety in vivo13

  • expert opinionLL-37 is not FDA-approved for therapeutic use20

  • expert opinionHigher doses are linked in the literature to stronger inflammatory and mast-cell effects21

  • expert opinionBacteria resistance to conventional antibiotics has not been observed to extend to LL-37's membrane-disruption mechanism22

  • expert opinionLL37 is not FDA approved23

  • expert opinionLL-37 is not FDA-approved for any indication as of April 202624

  • expert opinionLL-37 is on the FDA's 503A Category 1 bulk drug substances list24

  • expert opinionNot FDA approved and not on the §503A bulks list25

  • expert opinionLL-37 is not FDA-approved for human therapeutic use26

  • expert opinionFDA says compounded drugs containing cathelicidin LL-37 may pose immunogenicity risk and peptide-characterization concerns26

  • expert opinionAbnormal LL-37 activity has been discussed in inflammatory skin conditions, autoimmunity, and tissue-damage contexts26

  • expert opinionLL-37 is not FDA-approved in the United States for infection prevention, wound healing, diabetic foot ulcers, venous leg ulcers, immune support, Lyme disease, biofilm treatment, dermatology, or any other indication27

  • expert opinionFDA states that compounded drugs containing cathelicidin LL-37 may pose immunogenicity risk for certain routes and peptide-related impurity/API-characterization concerns27

What people use it for

Based on 1 human study finding, 1 in vitro finding, 21 expert opinion findings and 1 theoretical finding.

  • human studySeveral diseases in human are characterized by impairment in the function of LL-37/hCAP-18 peptide18

  • in vitroLL-37 shows therapeutic promise against drug-resistant infections like MRSA, VRE, and resistant Klebsiella10

  • expert opinionLL-37-based analogs represent promising candidates for the development of next-generation antimicrobial and immunomodulatory therapies1

  • expert opinionLL-37 promotes wound healing11

  • expert opinionOral LL-37 expression is an important factor in maintaining physiological microbiota in oral homeostasis15

  • expert opinionLL-37 is involved in the development of oral dysbiosis15

  • expert opinionLL-37 is involved in the development of infectious diseases including viral, bacterial, and fungal infections15

  • expert opinionLL-37 is involved in the development of autoimmune diseases and oral carcinomas15

Show the remaining 16

  • expert opinionAntimicrobial peptides including LL-37 are being evaluated as therapeutic drugs in oral mucositis, cystic fibrosis, and septic shock17

  • expert opinionLL-37 is not FDA-approved; investigational as ropocamptide21

  • expert opinionLL-37 may be relevant in Mycobacterium tuberculosis research contexts22

  • expert opinionLL37 is useful in managing chronic sinusitis, urinary tract infections, and respiratory infections23

  • expert opinionLL-37 is available only as a compounded prescription through licensed providers and licensed 503A compounding pharmacies24

  • expert opinionCommunity subcutaneous protocols are extrapolations from preclinical work, not validated by controlled trials25

  • expert opinionLL-37 is studied for antimicrobial activity, antibiofilm effects, immune modulation, inflammation, wound healing, epithelial barrier defense, and tissue repair26

  • expert opinionLL-37 shows potential as a therapeutic agent in immunological systems28

  • expert opinionLL-37 shows potential as a therapeutic agent in respiratory systems28

  • expert opinionLL-37 shows potential as a therapeutic agent in gastrointestinal systems28

  • expert opinionLL-37 shows potential as a therapeutic agent in skin systems28

  • expert opinionLL-37 may be a therapeutic agent against a variety of bacterial and viral diseases, cancers, and hard-to-heal wounds30

  • expert opinionLL-37 could be applied in pharmacotherapy due to its activity spectrum30

  • expert opinionCathelicidin peptides could serve as a template for the development of modern anti-microbial and anti-viral drugs30

  • expert opinionLL-37 is an excellent candidate to develop into therapeutics for infected wounds30

  • theoreticalLL-37 may play a role in the pathogenesis of atherosclerosis as an EndMT inducer12

Other findings

Based on 4 expert opinion findings.

  • expert opinionLL-37 is the only human cathelicidin1

  • expert opinionFuture studies should focus on creating stable analogs, optimizing delivery mechanisms, and exploring synergistic combinations with existing antibiotics10

  • expert opinionHuman cathelicidin LL-37 is one of the best studied antimicrobial peptides11

  • expert opinionLL-37 is the only known cathelicidin antimicrobial peptide (AMP) expressed in humans19

Points of contention

Where the evidence is unsettled, thin, or says less than the popular claim — worth knowing before you draw conclusions.

Limited evidence

No controlled human trials of injected/systemic LL-37 exist; only topical wound trials.

Multiple sources state the only controlled human trials of administered LL-37 are topical wound-healing studies in venous leg ulcers and diabetic foot ulcers, with no published placebo-controlled trials of subcutaneous, intramuscular, or intravenous LL-37 for any indication. Community subcutaneous protocols (100-250 mcg/day, up to 500 mcg/day) are extrapolations from preclinical work, not trial-validated.

Contested

The pivotal phase IIb wound trial was negative overall; benefit came only from a post hoc subgroup.

The HEAL LL-37 trial in 148 patients found no significant healing improvement versus placebo in the full population; a statistically significant benefit appeared only in a post hoc analysis of patients with large wounds (≥10 cm2). Tier-3 guides emphasize the subgroup finding (28.1% vs 8.1% closure; 'six times faster') without foregrounding the negative primary result.

Contested

LL-37 is both protective and pathogenic depending on context.

Sources describe LL-37 as having both anti- and pro-inflammatory effects. While antimicrobial and wound-healing roles are highlighted, LL-37/self-nucleic-acid complexes are a documented pathogenic mechanism in psoriasis, SLE, psoriatic arthritis, and atherosclerosis, and LL-37 can both promote (ovarian, lung, breast) and suppress (colon, gastric) tumor growth.

Limited evidence

Cytotoxicity to human cells is a recognized limitation.

LL-37 is cytotoxic to many human cell types at 1–10 µM (reducing osteoblast-like MG63 cell viability at 1.04 µM), and clinical application is hindered by low proteolytic stability, cytotoxicity, and high production costs. The FDA also notes nonclinical findings of possible detrimental effects on male reproduction and protumorigenic effects.

Contested

CAS numbers differ between sources.

One tier-3 source lists CAS number 154947-66-7, while another tier-3 source lists CAS number 137265-46-4 for LL-37.

Single source

Conflicting CAMP/vitamin D 'consistency' of active peptide increase.

A tier-1 review notes only limited evidence shows 1,25D3 consistently increases biologically active LL-37 peptide, even though vitamin D robustly upregulates CAMP gene expression (about 170-fold mRNA increase in THP-1 cells per one study).

Limited evidence

Many broad efficacy claims rest on in vitro, animal, or expert-opinion sources, not human trials.

Claims of antiviral (SARS-CoV-2, influenza), antifungal, antitumor, antibiofilm, gut-barrier, and cardiovascular effects come largely from in vitro, theoretical, or expert-opinion tiers; one tier-3 source explicitly states online claims that LL-37 treats infections, Lyme disease, long COVID, wounds, immune dysfunction, or anti-aging are not established by strong human clinical trials.

Using it with other compounds

Check a stack
  • TB-500Complementary

    May be complementary

    Both promote wound healing, new blood-vessel growth (VEGF), and reduced inflammation, but through distinct mechanisms — LL-37 drives keratinocyte migration and angiogenesis via EGFR/FPR2, while TB-500 regulates actin/cytoskeletal dynamics and cell migration. This makes them a strong complementary tissue-repair pairing.

    Tier 4Theoretical — not established

    What the research doesn't fully establish

    Both peptides' mechanisms clearly establish the four shared dimensions claimed. LL-37 explicitly targets EGFR, FPR2, and TLR pathways leading to angiogenesis, wound healing, and keratinocyte migration with VEGF/VEGFA signaling noted. TB-500 explicitly targets integrins and G-actin for cell migration, angiogenesis via VEGF, and tissue remodeling. Both show anti-inflammatory effects (LL-37 via NF-κB/TLR signaling; TB-500 via NF-κB suppression and reduced TNF-α/IL-1β/IL-6). Both list tissue_repair, angiogenesis, anti_inflammatory, and VEGF_upregulation in approved tags. The explanation correctly identifies distinct mechanistic pathways (LL-37: EGFR/FPR2/keratinocyte-driven; TB-500: actin/cytoskeletal/integrin-driven) that would complement rather than duplicate each other. The relationship type 'complementary' is well-justified by the mechanism material.

    Shares tissue repair · angiogenesis · anti inflammatory · VEGF upregulation

  • SemaxComplementary

    No documented conflict

    Both support angiogenesis, tissue repair, and anti-inflammatory signaling, though Semax is oriented toward neuroprotection via BDNF/NGF-TrkB pathways and LL-37 toward peripheral wound healing via VEGF/EGFR. Overlap is modest and context-dependent rather than a targeted combination.

    Tier 4Theoretical — not established

    What the research doesn't fully establish

    Both peptides' mechanisms support the three claimed shared dimensions: (1) tissue_repair: LL-37 explicitly promotes angiogenesis, wound healing, and keratinocyte migration; Semax shows BDNF/NGF upregulation and neuroprotection, both tissue-repair mechanisms. (2) angiogenesis: LL-37 directly targets VEGF/VEGFA signaling and angiogenesis; Semax is tagged with angiogenesis in approved tags. (3) anti_inflammatory: LL-37 shows immunomodulation and NF-κB signaling; Semax shows anti-inflammatory/immune modulation and NF-κB modulation. The explanation accurately characterizes the relationship as complementary rather than synergistic—different tissue contexts (peripheral vs. neural) and different primary pathways (VEGF/EGFR vs. BDNF/TrkB) but overlapping functional outcomes. The modest, context-dependent overlap described is consistent with the mechanisms provided.

    Shares tissue repair · angiogenesis · anti inflammatory

  • TeduglutideComplementary

    No documented conflict

    Both support repair of epithelial/mucosal surfaces by different means: teduglutide promotes intestinal epithelial proliferation, while LL-37 drives keratinocyte/epithelial migration, wound closure and antimicrobial defense at mucosal barriers. They can reinforce barrier healing from separate pathways, though LL-37 can be cytotoxic at higher concentrations, so this is more speculative.

    Tier 4Theoretical — not established

    What the research doesn't fully establish

    Both peptides' mechanisms clearly support tissue_repair through distinct but complementary pathways affecting epithelial/mucosal surfaces. Teduglutide explicitly promotes intestinal epithelial growth, proliferation, and mucosal repair via GLP-2 receptor signaling. LL-37 explicitly supports keratinocyte migration, wound healing, and angiogenesis via multiple pathways (FPR2, TLRs, EGFR transactivation, VEGF signaling). The proposed relationship correctly identifies that they work through different mechanisms (proliferation/growth vs. migration/wound closure/antimicrobial defense) on epithelial barriers. Both are tagged with tissue_repair. The caveat about LL-37's cytotoxicity at higher concentrations is appropriately noted in the explanation and does not contradict the complementary relationship at therapeutic concentrations. The mechanisms justify this as a supported complementary relationship.

    Shares tissue repair

  • PidotimodComplementary

    No documented conflict

    Both modulate Toll-like receptor signaling and support innate immunity, but pidotimod primarily drives dendritic-cell maturation and adaptive (Th1/antibody) responses while LL-37 provides direct antimicrobial and TLR-modulating actions. This gives coverage across innate and adaptive immune defense.

    Tier 4Theoretical — not established

    What the research doesn't fully establish

    Both peptides' mechanisms clearly support the proposed complementary relationship. LL-37 targets multiple TLRs (TLR3, TLR7, TLR8, TLR9, TLR4) and FPR2, providing direct antimicrobial effects and broad-spectrum pathogen neutralization. Pidotimod targets TLR2 and TLR7, stimulating dendritic cell maturation and adaptive immunity (Th1 differentiation, T-lymphocyte proliferation, immunoglobulin production). All three shared dimensions are explicitly supported: (1) innate_immune—both activate TLR signaling and immune cell responses; (2) anti_inflammatory—both are tagged with this and modulate immune balance; (3) antimicrobial—LL-37 has direct antimicrobial activity while pidotimod reduces recurrent infections through immune enhancement. The explanation accurately characterizes their distinct but complementary mechanisms: LL-37 provides direct pathogen killing and TLR modulation, while pidotimod bridges innate to adaptive immunity via dendritic cell maturation. This division of labor across innate and adaptive defense is well-justified by the provided mechanisms.

    Shares innate immune · anti inflammatory · antimicrobial

  • ThymulinComplementary

    No documented conflict

    Thymulin normalizes T-cell balance and dampens excess pro-inflammatory cytokines via NF-κB/p38 modulation, while LL-37 provides antimicrobial and TLR/FPR2-based innate immune actions. Their different immune targets can complement each other in immune support.

    Tier 4Theoretical — not established

    What the research doesn't fully establish

    Both peptides' mechanisms clearly establish the claimed shared dimensions. LL-37 is explicitly tagged with innate_immune and anti_inflammatory, with documented effects including immunomodulation (both anti- and pro-inflammatory), TLR/FPR2 signaling, and NF-κB pathway activation. Thymulin is also explicitly tagged innate_immune and anti_inflammatory, with documented T-cell maturation/differentiation, NF-κB inhibition, and suppression of excessive proinflammatory cytokines. The proposed relationship correctly identifies that they operate through distinct but compatible mechanisms: LL-37 acts primarily through pattern recognition receptors (TLRs, FPR2) and direct antimicrobial effects, while thymulin acts through T-cell regulation and cytokine modulation. These different mechanistic approaches to immune support are genuinely complementary rather than redundant, justifying the relationship type and both shared dimensions.

    Shares innate immune · anti inflammatory

  • VilonComplementary

    Worth caution

    LL-37 is a human cathelicidin providing frontline antimicrobial and innate-immune signaling; Vilon supports adaptive/T-cell immunity via gene reactivation. They cover different arms of immunity, so they are complementary rather than redundant, though LL-37's context-dependent pro-inflammatory effects warrant monitoring.

    Tier 4Theoretical — not established

    What the research doesn't fully establish

    The mechanisms clearly establish complementary roles in immunity. Vilon targets adaptive immunity (T-cell regulation, CD4/CD8 ratio improvement, thymus stimulation, age-silenced gene reactivation in lymphocytes) via receptor-independent chromatin remodeling and gene expression modulation. LL-37 targets innate immunity (antimicrobial activity, TLR/FPR2 signaling, neutrophil chemotaxis, NET promotion) via multiple cell-surface receptors. Both peptides modulate anti-inflammatory pathways (Vilon: IL-1β/IL-6/TNF-α suppression; LL-37: NF-κB and TLR signaling with documented anti-inflammatory effects), but through distinct mechanisms and immune arms. The shared tags (innate_immune, anti_inflammatory) are justified by their respective mechanisms, and the explanation accurately captures their non-redundant, complementary positioning—Vilon reactivates adaptive immunity while LL-37 provides frontline innate defense. The caveat about LL-37's context-dependent pro-inflammatory effects is supported by the mechanism description noting 'both anti- and pro-inflammatory' immunomodulation.

    Shares innate immune · anti inflammatory

  • BPC-157Complementary

    Worth caution

    Both promote angiogenesis and wound epithelialization, but LL-37 adds broad-spectrum antimicrobial and endotoxin-neutralizing activity that BPC-157 lacks. In a contaminated or infected wound context the two are complementary — LL-37 clears microbes/biofilm while BPC-157 drives vascular and connective-tissue repair. Note LL-37 has context-dependent pro-inflammatory effects, so monitoring is reasonable.

    Tier 4Theoretical — not established
  • GHK-CuComplementary

    May be complementary

    GHK-Cu stimulates collagen/elastin synthesis, angiogenesis and antioxidant defenses while suppressing NF-κB, and LL-37 contributes antimicrobial defense plus angiogenic and epithelializing wound-healing effects. Their distinct mechanisms both support skin remodeling and tissue repair, making them a reasonable complementary combination for wound/skin contexts.

    Tier 4Theoretical — not established
  • KPVComplementary

    Worth caution

    Both have reported antimicrobial and immune-modulating activity but by different means: LL-37 is a cathelicidin that directly disrupts microbial membranes and neutralises endotoxin, while KPV calms the downstream inflammatory response via NF-κB. Together they cover microbial killing plus inflammation control, though LL-37 can be pro-inflammatory and cytotoxic at higher concentrations, so this is a nuanced pairing.

    Tier 4Theoretical — not established

    What the research doesn't fully establish

    Both peptides' mechanisms clearly establish the claimed shared dimensions. KPV demonstrates anti-inflammatory effects via NF-κB suppression (IκBα stabilisation, IKK inhibition, p65RelA nuclear import blocking) and antimicrobial activity (S. aureus, C. albicans in vitro). LL-37 demonstrates innate immune activation through multiple TLR and FPR2 pathways, antimicrobial activity (broad-spectrum bacteria, fungi, viruses), and NF-κB signaling, while also showing anti-inflammatory capacity (endotoxin neutralization). The proposed relationship correctly identifies mechanistic complementarity: KPV acts primarily on downstream inflammatory resolution (NF-κB modulation), while LL-37 combines direct antimicrobial disruption with immune cell recruitment and endotoxin neutralization. The caveat about LL-37's pro-inflammatory and cytotoxic effects at higher concentrations is explicitly supported by the mechanism description ('pro- and anti-inflammatory', 'cytotoxicity to human cells at higher concentrations'). The explanation accurately reflects the distinct pathways and their potential synergy without overstating the relationship.

    Shares innate immune · anti inflammatory

  • HumaninSame mechanism

    Worth caution

    Both LL-37 and humanin act on the formyl peptide receptor FPR2 and share anti-inflammatory, cytoprotective signaling. Because they engage the same receptor, combining them is more likely to be redundant (competing for the same target) than additive, so it makes more sense to choose one FPR2-directed agent rather than stack the two.

    Tier 4Theoretical — not established

    What the research doesn't fully establish

    The mechanism descriptions clearly establish that both LL-37 and humanin target FPR2 (formyl peptide receptor 2). LL-37 is described as targeting 'FPR2 (formyl peptide receptor 2)' and humanin targets 'Formyl peptide receptors FPR2/FPR3 (FPRL1)'. Both peptides are also documented to have anti-inflammatory effects: LL-37 shows 'Immunomodulation (both anti- and pro-inflammatory)' with anti_inflammatory tag, and humanin shows 'Anti-inflammatory / reduced pro-inflammatory cytokines (reported)' with anti_inflammatory tag. The shared dimension of anti-inflammatory activity combined with the documented shared FPR2 receptor target justifies the 'same_mechanism' relationship type and the reasoning that they may compete for the same receptor, making them potentially redundant rather than additive.

    Shares anti inflammatory

  • ImunofanComplementary

    No documented conflict

    Imunofan bidirectionally normalizes immune function, boosts phagocytosis/NK activity and antioxidant defenses, and supports tissue repair, while LL-37 adds direct antimicrobial and TLR-based innate actions. Different mechanisms converging on immune balance and repair.

    Tier 4Theoretical — not established

    What the research doesn't fully establish

    Both peptides' mechanisms clearly support the three claimed shared dimensions. (1) Innate_immune: LL-37 targets FPR2, TLRs, and promotes NETs/chemotaxis; Imunofan enhances phagocytic/bactericidal activity and NK cytotoxicity. (2) Anti_inflammatory: LL-37 shows immunomodulation with both pro- and anti-inflammatory effects; Imunofan explicitly modulates anti-inflammatory cytokines (reduced TNF, IL-6). (3) Tissue_repair: LL-37 promotes angiogenesis, wound healing, and keratinocyte migration; Imunofan stimulates fibroblast and keratinocyte proliferation. The explanation accurately characterizes their complementary nature—LL-37 provides direct antimicrobial/TLR signaling while Imunofan provides bidirectional immune normalization and antioxidant support—with both converging on innate immunity, inflammation control, and tissue repair. The mechanisms justify this relationship type and all three shared dimensions.

    Shares innate immune · anti inflammatory · tissue repair

  • LactoferrinComplementary

    May be complementary

    Both are frontline innate-immune defence peptides but attack microbes by different routes: LL-37 is a cationic peptide that punches holes in bacterial membranes, while lactoferrin starves microbes of iron and also binds their surfaces. Because the mechanisms differ, they can broaden antimicrobial coverage and both help calm inflammation — a classic complementary innate-immunity pairing seen naturally in neutrophils and mucosal fluids.

    Tier 3Largely anecdotal — commonly discussed

    What the research doesn't fully establish

    The mechanisms clearly establish both peptides as innate-immune antimicrobial agents with distinct modes of action. Lactoferrin targets iron binding and microbial cell-surface binding via cationic sequences, while LL-37 acts as a cationic peptide with membrane-disrupting capacity (implied by FPR2/TLR signaling and broad-spectrum antimicrobial effects). Both demonstrate anti-inflammatory activity (lactoferrin via PI3K/Akt/mTOR and immune modulation; LL-37 via NF-κB and TLR signaling). The proposed relationship correctly identifies mechanistically distinct but complementary antimicrobial pathways—iron starvation vs. membrane disruption—and both are documented to modulate inflammatory responses. The claim that they represent a natural pairing in neutrophils and mucosal fluids is consistent with their described roles in innate immunity. The three shared dimensions (antimicrobial, innate_immune, anti_inflammatory) are all supported by the provided mechanisms.

    Shares antimicrobial · innate immune · anti inflammatory

  • Alpha-MSHComplementary

    Worth caution

    Both peptides fight microbes and modulate inflammation, but by different routes: alpha-MSH works through melanocortin receptors and NF-κB suppression, while LL-37 is a cationic cathelicidin that directly disrupts microbial membranes and signals through TLR/FPR2 pathways. Their distinct mechanisms converge on innate defense and tissue protection, so they are conceptually complementary rather than redundant.

    Tier 4Theoretical — not established

    What the research doesn't fully establish

    Both peptides' mechanisms clearly establish the two shared dimensions. (1) Antimicrobial: Alpha-MSH has 'Antimicrobial' listed as a direct effect; LL-37 has 'Broad-spectrum antimicrobial' as a primary effect. (2) Anti-inflammatory: Alpha-MSH explicitly shows 'Anti-inflammatory / immunomodulatory' and 'NF-κB suppression'; LL-37 shows 'Immunomodulation (both anti- and pro-inflammatory)' and 'NF-κB signaling'. The explanation correctly identifies distinct mechanistic routes (melanocortin/NF-κB suppression vs. cationic membrane disruption/TLR-FPR2 signaling) that converge on overlapping functional outcomes. This is a valid characterization of complementarity—different pathways achieving related defensive and immunomodulatory effects without redundancy.

    Shares anti inflammatory · antimicrobial

  • ElafinComplementary

    May be complementary

    Both are human host-defense molecules but hit different targets: LL-37 is a cathelicidin that directly punctures microbial membranes, while elafin blocks the destructive enzymes (elastase, proteinase 3) that neutrophils release. Together they cover both direct killing and protection of the tissue from friendly-fire enzyme damage, converging on mucosal defense and repair.

    Tier 3Largely anecdotal — commonly discussed

    What the research doesn't fully establish

    The proposed relationship is well-justified by the mechanism material. Both peptides share the four claimed dimensions: (1) innate_immune—both are explicitly tagged and described as host-defense molecules with immune modulation roles; (2) antimicrobial—both have broad-spectrum antimicrobial activity documented; (3) anti_inflammatory—both are tagged and show anti-inflammatory effects; (4) tissue_repair—both are tagged with tissue repair/mucosal protection roles. The 'complementary' relationship type is strongly supported: the mechanisms show distinct but synergistic modes of action—LL-37 targets membrane receptors (FPR2, TLRs) and directly kills microbes, while elafin inhibits neutrophil serine proteases (elastase, proteinase 3) to prevent tissue damage. The explanation accurately reflects that they converge on mucosal defense through different mechanisms: direct antimicrobial activity versus protection from collateral enzyme damage. This is a textbook complementary relationship where both peptides address the same biological problem (mucosal defense) via non-overlapping mechanisms.

    Shares innate immune · antimicrobial · anti inflammatory · tissue repair

Safety and side effects

Safety and Side Effects

Cytotoxicity. A Tier-1 review reports LL-37 is cytotoxic to many human cell types — particularly infected and weakened cells — at final concentrations of 1–10 µM, and describes it as primarily killing already infected and weakened cells (src-1). A Tier-1 study reports synthetic LL-37 at 1.04 µM reduces viability of human osteoblast-like MG63 cells, with THP-1 monocytes less sensitive than MG63 cells (src-16). Tier-1 and Tier-2 reviews list cytotoxicity, low proteolytic stability, degradation, potential high-concentration toxicity, and high production costs as limitations to clinical application (src-15, src-17, src-4, src-23).

Concentration context. A Tier-1 review reports very high concentrations (~300 µM) are detected in psoriatic lesions, while gingival crevicular fluid in periodontitis contains about 1 µM (src-1). A Tier-3 dosing site notes higher doses are linked in the literature to stronger inflammatory and mast-cell effects (src-9).

Pro-inflammatory / autoimmune mechanism. A Tier-3 vendor guide and Tier-2 review describe LL-37 forming complexes with self-DNA and self-RNA released from damaged cells that activate plasmacytoid dendritic cells through TLR9, TLR7, and TLR8, driving type I interferon production — described as a documented pathogenic mechanism in psoriasis, systemic lupus erythematosus, psoriatic arthritis, and atherosclerosis (src-2, src-19, src-35).

Regulatory safety notes. A Tier-3 guide states the FDA notes that compounded LL-37 may pose immunogenicity risk for certain routes and raises peptide-related impurity/characterization concerns (src-6, src-8), and reports nonclinical findings suggesting detrimental effects on male reproduction and protumorigenic effects in some tissues (src-6, src-37). A Tier-3 review reports tissue-dependent, contradictory tumor effects (promoting ovarian/lung/breast, suppressing colon/gastric) (src-25, src-79).

Trial tolerability. In the HEAL LL-37 phase IIb trial, the topical study drug was reported to be well tolerated and safe at both dose strengths (0.5 and 1.6 mg/mL) (src-5).

Overall caveat. No controlled human trials of injected or systemic LL-37 exist; safety data outside topical wound use are absent, and community subcutaneous protocols are extrapolations from preclinical work rather than trial-validated (src-2, src-12).

Reconstitution and handling

Dosing

No dose has been established for this compound. No regulatory label exists for LL-37 — sources agree it is not FDA-approved for any indication (src-2, src-6, src-10). The figures below are what sources report, not guidance.

What human trials actually used (topical only)

  • The HEAL LL-37 phase IIb randomized, placebo-controlled trial applied LL-37 as a gel to the venous leg ulcer surface, at tested concentrations of 0.5 or 1.6 mg/mL versus placebo (src-5, src-10). A Tier-3 dosing site reports gel was applied twice a week, an earlier first-in-man study tested 3.2 mg/mL, and that the lowest concentration (0.5 mg/mL) produced the best healing rate, 1.6 mg/mL was effective but less so, and 3.2 mg/mL was not carried forward (src-9, src-47).
  • A Tier-3 dosing site emphasizes that human trials delivered LL-37 as a gel onto a leg ulcer — not as an injection — and that no published human trial has tested subcutaneous LL-37 (src-9, src-44).

Community (non-trial) subcutaneous protocols

  • A Tier-3 dosing site reports a community-derived daily subcutaneous protocol — explicitly not trial-validated — clustering around 100–250 mcg per day, with some advanced write-ups up to 500 mcg per day, usually once daily, often 5 days on with 2 days off, for a 2–4 week block (src-9, src-45).
  • A Tier-3 vendor guide states these community subcutaneous protocols are extrapolations from preclinical work and are not validated by controlled trials (src-2, src-12). The same source notes higher doses are linked in the literature to stronger inflammatory and mast-cell effects (src-9).

Preparation notes

The claims provided do not specify a reconstitution diluent volume or resulting concentration for research vials. Note that LL-37 is described as having low proteolytic stability (src-15), and a Tier-3 guide states it is available only as a compounded prescription through licensed providers and 503A compounding pharmacies (src-10); its 503A bulks-list status is described inconsistently across sources (src-2 vs src-10).

Sources

Ordered by evidence quality — the strongest first.

  1. Antimicrobial Peptides of the Cathelicidin Family: Focus on LL-37 and Its Modifications(opens in a new tab)
    Tier 1Web · pmc.ncbi.nlm.nih.gov
  2. Human antimicrobial/host defense peptide LL-37 may prevent the spread of a local infection through multiple mechanisms: an update | Inflammation Research | Springer Nature Link(opens in a new tab)
    Tier 1Web · link.springer.com · 2025
  3. Vitamin D triggers hCAP18/LL-37 production: Implications for LL-37-induced human osteoblast cytotoxicity.(opens in a new tab)
    Tier 1PubMed · pubmed.ncbi.nlm.nih.gov · 2024
  4. LL-37, a Multi-Faceted Amphipathic Peptide Involved in NETosis.(opens in a new tab)
    Tier 1PubMed · pubmed.ncbi.nlm.nih.gov · 2022
  5. Evaluation of LL‐37 in healing of hard‐to‐heal venous leg ulcers: A multicentric prospective randomized placebo‐controlled clinical trial(opens in a new tab)
    Tier 1Web · doi.org · 2021
  6. The Roles of Cathelicidin LL-37 in Inflammatory Bowel Disease.(opens in a new tab)
    Tier 1PubMed · pubmed.ncbi.nlm.nih.gov · 2016
  7. Vitamin D3 modulates the innate immune response through regulation of the hCAP-18/LL-37 gene expression and cytokine production.(opens in a new tab)
    Tier 1PubMed · pubmed.ncbi.nlm.nih.gov · 2016
  8. Cathelicidin LL-37: a multitask antimicrobial peptide.(opens in a new tab)
    Tier 1PubMed · pubmed.ncbi.nlm.nih.gov · 2010
  9. Antimicrobial Peptides of the Cathelicidin Family - PMC - NIH(opens in a new tab)
    Tier 2Web · pmc.ncbi.nlm.nih.gov
  10. Decoding LL-37: Structure and antimicrobial mechanisms against microbial threats(opens in a new tab)
    Tier 2Web · sciencedirect.com
  11. The Potential of Human Recombinant Cathelicidin LL-37 in the Treatment of Infections | International Journal of Peptide Research and Therapeutics | Springer Nature Link(opens in a new tab)
    Tier 2Web · link.springer.com · 2025
  12. Human cathelicidin peptide LL-37 induces endothelial-to-mesenchymal transition.(opens in a new tab)
    Tier 2PubMed · pubmed.ncbi.nlm.nih.gov · 2025
  13. Antibiofilm properties of cathelicidin LL-37: an in-depth review.(opens in a new tab)
    Tier 2PubMed · pubmed.ncbi.nlm.nih.gov · 2023
  14. The LL-37 domain: A clue to cathelicidin immunomodulatory response?(opens in a new tab)
    Tier 2PubMed · pubmed.ncbi.nlm.nih.gov · 2023
  15. Cathelicidin LL-37 in Health and Diseases of the Oral Cavity.(opens in a new tab)
    Tier 2PubMed · pubmed.ncbi.nlm.nih.gov · 2022
  16. Psoriasis and Antimicrobial Peptides.(opens in a new tab)
    Tier 2PubMed · pubmed.ncbi.nlm.nih.gov · 2020
  17. Pulmonary defense and the human cathelicidin hCAP-18/LL-37.(opens in a new tab)
    Tier 2PubMed · pubmed.ncbi.nlm.nih.gov · 2005
  18. Expression of LL-37/hCAP-18 gene in human leukemia cells.(opens in a new tab)
    Tier 2PubMed · pubmed.ncbi.nlm.nih.gov · 2003
  19. LL-37(opens in a new tab)
    Tier 3Web · thepreptide.com
  20. LL-37 Peptide Benefits: 8 Key Uses | PeptidesExplorer(opens in a new tab)
    Tier 3Web · peptidesexplorer.com
  21. LL-37 Peptide Protocol Guide | Peptide Dosing Protocols(opens in a new tab)
    Tier 3Web · peptidedosingprotocols.com
  22. LL-37 UK: Complete Research Guide (2026) - Peptides Lab UK(opens in a new tab)
    Tier 3Web · peptideslabuk.com
  23. LL37: Revolutionizing Antimicrobial Therapy for Infections, Wound Healing, and Immunity(opens in a new tab)
    Tier 3Web · youtube.com
  24. Superpower(opens in a new tab)
    Tier 3Web · superpower.com
  25. LL-37 Peptide Guide 2026: Cathelicidin Antimicrobial Review(opens in a new tab)
    Tier 3Web · thepeptidetoolkit.com · 2026
  26. What Is LL-37? Uses, Benefits, Safety, FDA Status, and Evidence | Peptide Portal(opens in a new tab)
    Tier 3Web · peptideportal.org · 2026
  27. LL-37 — ProPeptideGuide(opens in a new tab)
    Tier 3Web · propeptideguide.com · 2026
  28. LL-37: Cathelicidin-related antimicrobial peptide with pleiotropic activity.(opens in a new tab)
    Tier 3PubMed · pubmed.ncbi.nlm.nih.gov · 2016
  29. The Role of Cathelicidin LL-37 in Cancer Development.(opens in a new tab)
    Tier 3PubMed · pubmed.ncbi.nlm.nih.gov · 2016
  30. Unique features of human cathelicidin LL-37.(opens in a new tab)
    Tier 3PubMed · pubmed.ncbi.nlm.nih.gov · 2015