LL-37: immune function, wound healing and the research
Clinical review pending
LL-37 is part of innate immunity. What its natural functions and wound-healing research suggest about possible therapeutic uses.
What is LL-37?
LL-37 is the active fragment of the only human cathelicidin. It consists of 37 amino acids and is produced by immune and skin cells. This antimicrobial peptide is part of the well-studied innate immune system. In wellness settings and as a “research peptide,” it is offered for immune support and its antimicrobial activity. It is not an approved medicine.
How does it work?
LL-37 acts in several ways. Its positively charged structure can directly damage microbial membranes. It also influences immunity, helping regulate immune-cell recruitment, inflammatory responses and wound healing, and binding certain microbial components. These functions have been described in numerous laboratory and animal studies. Its effects depend on the biological context, however. The peptide can both promote and suppress inflammation and is involved in certain inflammatory skin diseases. These biological functions do not yet establish a benefit from therapeutic administration.
Is it FDA-approved?
No. There is no FDA-approved medicine for administering LL-37. Products sold through unofficial channels are not approved either. The peptide was not among the substances receiving a favorable assessment during the FDA’s 2026 compounding deliberations.
What does the research show?
For injected use in wellness settings, evidence is limited to preclinical work. LL-37’s role in innate immunity, wound healing and skin disease, by contrast, has been studied in humans and extensively in laboratory research. This includes work on how it damages microorganisms and binds microbial components 1.
Controlled human studies establishing the efficacy or safety of self-administered LL-37 for antimicrobial, immune-supporting or healing-related wellness uses are lacking. Its context-dependent and sometimes pro-inflammatory effects argue against broad promises of benefit.
Frequently asked questions
Is LL-37 FDA-approved?
No. LL-37 has no FDA approval for any indication. Under the September 2026 status cited in the source article, it is also not eligible for compounding under Section 503A: the FDA removed it from Category 2 in April 2026 2 after its nomination was withdrawn. However, it appears on neither the 503A list of permitted bulk drug substances nor the FDA’s Category 1 list 3. The agency has announced an advisory committee meeting 4 to take place before the end of February 2027 and consider LL-37.
What natural role does LL-37 play in the body?
LL-37 is an antimicrobial peptide produced by the body, including by neutrophils and various epithelial cells such as skin cells 5. In neutrophils, it initially exists as the precursor protein hCAP-18. After release from the cell, proteinase 3 cleaves this protein to release the active peptide 6. By damaging membranes, it acts directly against bacteria, viruses and fungi. Through the FPRL1 receptor, it helps attract neutrophils, monocytes and T cells to infection sites. It also supports wound healing through regeneration of the skin surface 7 and the formation of blood vessels 8.
How does vitamin D influence LL-37 levels?
When 1,25-dihydroxyvitamin D activates the vitamin D receptor, it promotes transcription of the CAMP gene 9. This gene encodes hCAP-18, the precursor of LL-37. In laboratory studies of human immune cells, serum with low 25-hydroxyvitamin D levels supported cathelicidin production less effectively 10.
Could LL-37 worsen autoimmune disease?
That is biologically possible. LL-37 has been identified as a T-cell autoantigen in psoriasis 11. It can bind the body’s own DNA and thereby activate plasmacytoid dendritic cells through TLR9 12. The resulting interferon response could promote autoimmune processes in psoriasis. The peptide is also thought to act as an inflammatory mediator in rosacea when increased serine protease activity alters its processing 13.
How does LL-37 differ from defensins?
LL-37 belongs to the cathelicidins. Defensins form a structurally different family of antimicrobial peptides 14. In a membrane-like environment, LL-37 adopts a helical structure. Its water-attracting and fat-attracting regions enable membrane damage. Defensins, by contrast, contain six cysteine residues connected by three disulfide bridges into a beta-sheet structure. Both belong to human innate immunity.
What has been investigated in human clinical trials?
The most advanced clinical research on LL-37 concerns local wound treatment. In a multicenter randomized phase IIb trial involving 148 people with hard-to-heal venous leg ulcers, topical LL-37 showed no significant benefit in the overall group 15. A post-hoc analysis suggested a possible signal in larger ulcers. A 2023 randomized trial in diabetic foot ulcers consistently reported more granulation tissue in the LL-37 group 16. This use accounts for most human studies. The evidence has not, however, led to FDA approval.
Who faces particular concerns with LL-37?
LL-37’s varied biological effects raise particular concerns for several groups: people with active or previous psoriasis, because LL-37 can act as an autoantigen and, together with the body’s own DNA, activate plasmacytoid dendritic cells through TLR9; people with rosacea or rosacea-prone skin, in whom altered cathelicidin processing is involved; and people with active cancers. Increased LL-37 expression has been described in ovarian, breast and lung tumors 8. The FDA also points to preclinical findings of tumor-promoting effects in certain tissues 2. Further concerns involve systemic autoimmune diseases with dysregulated innate immunity, pregnancy and breastfeeding because safety data are lacking, and known hypersensitivity to LL-37. These are examples of mechanistically grounded concerns, not a formal list of contraindications.
References provided in the source article
Sources: laboratory work on LL-37’s antimicrobial and immune actions (Zsila and Beke-Somfai, Biochemical and Biophysical Research Communications, 2020, DOI: 10.1016/j.bbrc.2020.03.162 1 ), indexed on PubMed.
Provenance and editorial review status
Adapted for Nutrient Desk from the source article. The claims and source attributions in the original text still require clinical review. This draft has not been cleared for indexing.