# What is LL-37? The human cathelicidin peptide explained Updated 2026-10-16. LL-37 is a peptide, a short chain of 37 amino acids. The body cuts it from a bigger protein called hCAP18. A 2000 study described hCAP18 as the only human member identified of a protein family called cathelicidins. Neutrophils (a type of white blood cell) and epithelial cells (the cells that line skin and organs) make LL-37. It is a natural part of the immune system. | | | | --- | --- | | Common name | LL-37 | | Length | 37 amino acids (De Yang et al., 2000) | | Comes from | hCAP18, human cationic antimicrobial protein, 18 kilodaltons | | Family | Cathelicidins; hCAP18 is the only human member identified in the 2000 paper | | Made by | Neutrophils and epithelial cells | | Developer name | Ropocamptide (Promore Pharma) | | Amino-acid sequence | Not reproduced here; not taken from a primary paper for this hub | | Half-life in people | Not established in the sources opened | | Records checked | 16 October 2026 | Scrape your knee and your body starts a clean-up job straight away. Your skin and some of your white blood cells make tiny defence molecules. LL-37 is one of them, and it is the subject of [the LL-37 hub](/learn/ll-37). This page answers the first plain questions: what LL-37 is, where it comes from, what its names mean and what is still unknown. The papers checked here do not say how soon after a scrape LL-37 is released. Next, read [how LL-37 works](/learn/ll-37/how-ll-37-works) and [what the human trials found](/learn/ll-37/ll-37-study-findings). ## What is LL-37? LL-37 is a short chain of 37 amino acids. Amino acids are the small building blocks that proteins are made from. Scientists call each link in the chain a residue, so 37 residues means 37 amino acids. LL-37 is the piece cut from the carboxyl end (the COOH-terminal end, or tail end) of a bigger protein called hCAP18. The 2000 paper by De Yang and colleagues calls it antimicrobial, which means it acts against germs. The same paper says hCAP18 is the only member of the cathelicidin family identified in humans. So LL-37 is part of a human protein, not a stand-alone invention. The name tells you two things. The number 37 is the length of the chain. The letters LL stand for the two leucines, a kind of amino acid, at the starting end of the chain. The 2000 paper sits in PubMed, the biomedical library run by the US National Institutes of Health, under PMID 11015447. Whether LL-37 also acts on other cells is a separate question. [The page on how LL-37 works](/learn/ll-37/how-ll-37-works) sets out what that paper measured. ## What is hCAP18, and how does LL-37 relate to it? hCAP18 is the bigger protein that LL-37 comes from. The name is short for human cationic antimicrobial protein, 18 kilodaltons. Cationic means it carries a positive electric charge. A kilodalton is a unit for the weight of a molecule, so 18 kilodaltons gives its size. When hCAP18 is cut, the piece at its carboxyl end, or tail end, is set free. That piece is LL-37. The 2000 paper says neutrophils and various epithelial cells make both forms. It gives no half-life for either form. A half-life is the time it takes for half of a substance to be cleared. This hub found none. Think of hCAP18 as a folded-up package and LL-37 as the part that is unwrapped when it is needed. This picture is only a teaching aid for the cut the paper describes. It does not say how often or where the cut happens in a living person. This hub did not check which enzymes, the body's cutting tools, cut hCAP18. It also did not check how much LL-37 is in each tissue. ![Diagram of a long folded protein chain with a short piece snipped free from its tail end, labelled larger protein, cut point and 37 amino acids.](/assets/content/edu-defence-piece-cut-from-larger-protein.png) LL-37 is the piece of 37 amino acids cut from the tail end of the larger protein hCAP18. Source: De Yang et al., Journal of Experimental Medicine, 2000. ## Which cells make LL-37? Two kinds of cells make LL-37: neutrophils and epithelial cells. Neutrophils are a common type of white blood cell. Inside them are granules, which are small storage pouches. Epithelial cells line the skin, the airways and the gut. The title and summary of the 2000 paper by De Yang and colleagues describe LL-37 as coming from neutrophil granules and epithelial cells. The paper reports this as the source of the natural peptide in the body. It does not describe the effect of any material supplied from outside the body. Where the peptide comes from and what extra material does are two separate questions. Your skin and your airways meet germs every day. So a defence peptide made by their own lining cells fits the picture the paper draws. The paper also links LL-37 to calling white blood cells to a site, which scientists call leukocyte recruitment. [The page on how LL-37 works](/learn/ll-37/how-ll-37-works) explains this. ## Is LL-37 the same as ropocamptide? Ropocamptide is the name Promore Pharma uses for its development of LL-37. It is a non-proprietary name, which means a generic drug name rather than a brand name. This fact comes from the conflict-of-interest statement in a 2021 trial paper by Mahlapuu and colleagues. A conflict-of-interest statement lists the ties that authors have to companies. The paper does not say that the two names describe the exact same preparation. This hub did not open a document that does. The company-linked trials are described on [the study findings page](/learn/ll-37/ll-37-study-findings). Three of the paper's authors worked for Promore Pharma at the time of the study. One reported a minority shareholding, which means owning a small part of the company. A company-run trial can still be sound. The ties are a reason to read the design closely, not a reason to dismiss the result. ## What is not established about LL-37? Several basic facts about LL-37 are missing from the sources opened for this hub. The full amino-acid order was not taken from a primary paper, so this page does not print it. No plasma half-life was found for LL-37 supplied from outside the body. Plasma is the liquid part of blood. The papers checked on 16 October 2026 do not establish that LL-37 is an approved medicine. The ARTG, Australia's register of approved medicines, was not searched. The human trials known to this hub are two small-to-mid-sized studies in one kind of wound. They say little about anything else. A missing number stays missing, and this page does not guess one. [The legal and regulatory page](/learn/ll-37/is-ll-37-legal-in-australia) records what regulators have written. [The side effects page](/learn/ll-37/ll-37-side-effects) records what the trials and the FDA reported about safety. ## Comparison Three names you will meet when reading about LL-37, compared by what each one means, who uses it and what is not established. Taken from the 2000 and 2021 papers in the citations, read on 16 October 2026. | Name | What it is | Who uses the name | What is not established | | --- | --- | --- | --- | | LL-37 | The 37-amino-acid piece cut from the tail end of hCAP18 | Researchers, including De Yang and colleagues (2000) | A plasma half-life for LL-37 supplied from outside the body | | hCAP18 | The larger human cationic antimicrobial protein, 18 kilodaltons; the only human cathelicidin identified in the 2000 paper | Researchers, including De Yang and colleagues (2000) | Which enzymes cut it, and how much LL-37 each tissue holds (not checked by this hub) | | Ropocamptide | The non-proprietary name Promore Pharma uses for its development of LL-37 | Promore Pharma, in the 2021 trial paper by Mahlapuu and colleagues | Whether it is the exact same preparation as any other LL-37 | ## Frequently asked questions ### Is LL-37 a peptide or a protein? LL-37 is a peptide of 37 amino acids that is cut from a larger protein, hCAP18. Where a peptide ends and a protein begins is a matter of custom. A chain of 37 units is usually called a peptide. ### Is LL-37 made naturally in the body? Yes. The 2000 paper by De Yang and colleagues describes LL-37 as coming from neutrophil granules and epithelial cells. That means the human body makes it. ### How long does LL-37 last in the body? No half-life for LL-37 was found in the sources opened for this hub, so none is given here. The 2000 paper and the two trial papers in the citations do not report one in the abstracts (summaries) read on 16 October 2026. ### Is LL-37 an approved medicine? The sources checked on 16 October 2026 do not establish an approval status for LL-37. The ARTG was not searched. [The regulatory page](/learn/ll-37/is-ll-37-legal-in-australia) explains how the TGA, FDA and WADA records differ. ## Citations - De Yang, Chen Q, Schmidt AP, et al.. Journal of Experimental Medicine. 2000;192(7):1069-1074. DOI: 10.1084/jem.192.7.1069 - Grönberg A, Mahlapuu M, Ståhle M, Whately-Smith C, Rollman O. Wound Repair and Regeneration. 2014;22(5):613-621. DOI: 10.1111/wrr.12211 - Mahlapuu M, Sidorowicz A, Mikosinski J, et al.. Wound Repair and Regeneration. 2021;29(6):938-950. DOI: 10.1111/wrr.12977 --- Canonical page: https://www.formlaboratories.com/learn/ll-37/what-is-ll-37 Form Laboratories - Perth-based research-use-only peptide supplier, shipping Australia-wide. - Site guide for agents: https://www.formlaboratories.com/llms.txt - Sitemap: https://www.formlaboratories.com/sitemap.xml - Full catalogue: https://www.formlaboratories.com/shop - Contact: hello@formlaboratories.com All materials are supplied for laboratory research use only - not for human or veterinary use, and nothing on this site is medical advice.