LL-37 is the only cathelicidin your body makes — a small natural peptide (a short chain of amino acids, the building blocks of proteins) that your skin and immune cells release to fight infection. It does two things at once: it kills microbes directly, and it acts as a signal that summons and steers immune cells1. It is genuinely part of human biology, not a foreign drug — but as an *injected* research peptide it has essentially no controlled human evidence, and it carries a real double edge.
In plain terms: a natural human "antibiotic-plus-immune-messenger" peptide with deep basic science behind it — and almost no evidence as an injected product.
What it is
"Cathelicidins" are a family of antimicrobial peptides found across many animals. Humans have exactly one, and LL-37 is it1. The name is literal: the active peptide is 37 amino acids long, and its first two residues are both leucine (the letter "L") — hence LL-37.
It does not start out active. Cells first make a larger precursor protein called hCAP-18. An enzyme then snips off the business end — those final 37 amino acids — to release LL-372. It is produced by neutrophils (a type of white blood cell), and by the cells lining skin, gut, and airways — the body's front-line barriers.
How it works
LL-37 is amphipathic: one side of the folded peptide likes water, the other likes fat. That structure lets it slot into and disrupt the fatty membranes of bacteria, punching holes that kill the microbe1. In plain terms: it behaves like a tiny natural antibiotic that ruptures bacterial walls.
But killing microbes is only half the story. LL-37 is also an immune-signalling molecule ("host defence peptide")2:
- Chemotaxis — it acts as a chemical beacon that draws immune cells (neutrophils, monocytes, T cells) toward a site of infection.
- Wound and vessel signalling — in cell and animal studies it promotes cell migration and angiogenesis (the growth of new blood vessels), steps involved in healing.
- Bridging innate and adaptive immunity — it influences how immune cells mature and respond.
In plain terms: it is both a weapon and a walkie-talkie — it damages microbes and it tells the immune system where to go.
The honest catch: a double edge
Here is what vendor pages leave out. LL-37 is not simply "good." When it binds the body's own DNA and RNA released from dying cells, those complexes can over-stimulate the immune system. In psoriasis research, LL-37 becomes a self-antigen — a target the immune system attacks as if it were foreign — and roughly two-thirds of patients with moderate-to-severe plaque psoriasis carry T cells that react to it3. It has been implicated the same way in lupus and rosacea research.
In plain terms: the same peptide that fights infection can, in the wrong setting, help drive chronic inflammatory disease. That matters for anyone imagining it as a clean "immune booster."
Pharmacology at a glance
| Property | LL-37 |
|---|---|
| Class | Human cathelicidin / host-defence peptide |
| Length | 37 amino acids (cleaved from hCAP-18) |
| Made by | Neutrophils; skin, gut and airway lining cells |
| Actions | Direct microbe killing + immune signalling (chemotaxis, angiogenesis) |
| Evidence base | Cell + animal studies; human data centres on natural disease biology |
| Injectable human trials | None established for muscle/healing/anti-ageing |
| Status | Research compound; not an approved medicine |
A note on half-life: LL-37 is regulated tightly by the body and broken down by enzymes; there is no well-established plasma half-life for it as an injected therapeutic, because it has not been developed as one. Treat any specific "half-life" number for injectable LL-37 as unsupported.
What the studies actually found
The literature is deep on *biology* and thin on *therapy*. Note the model in every row — these are cell and animal findings plus human disease observations, not injectable human efficacy trials:
| Study | Model / level | What it showed | Year |
|---|---|---|---|
| Dürr et al. — review1 | Review (biophysics + cell) | Characterised LL-37 as the sole human cathelicidin: membrane-disrupting antimicrobial with immune-modulating roles | 2006 |
| Vandamme et al. — review2 | Review (cell + animal) | Summarised its "factotum" range — antimicrobial, chemotactic, angiogenic, wound-related actions | 2012 |
| Lande et al.3 | Human (psoriasis patients) | LL-37 acts as a T-cell autoantigen; ~2/3 of moderate-severe plaque psoriasis patients had LL-37-reactive T cells | 2014 |
The pattern: strong, consistent basic-science and disease-biology evidence — and a clear absence of the injectable human efficacy trials that would justify the uses it is marketed for.
Latest research
- Its natural biology remains the active frontier, not injectable use: work continues on LL-37 in wound infection, its role in autoimmune skin disease, and even cancer-cell studies (where results cut both ways depending on tumour type)2.
- The autoimmunity angle keeps growing. Since the 2014 psoriasis finding, LL-37 has been studied as a self-target in lupus and other inflammatory conditions3 — reinforcing that "more LL-37" is not automatically good.
- Controlled human trials of injected LL-37 for performance, healing, or anti-ageing are still absent. That gap is the headline for anyone treating it as a therapy.
The short version
LL-37 is the single cathelicidin peptide humans produce — a natural antimicrobial that also signals the immune system, with genuinely deep basic science behind it. But its evidence is cell-and-animal biology plus human disease observation, not injectable human efficacy data, and it carries a real double edge in autoimmune inflammation. It is a research compound, not an approved medicine. Educational overview only, not medical advice. For context, see what are research peptides.