LL-37: Mechanism of Action in Published Studies

From precursor to active peptide

LL-37 doesn't exist as a free peptide inside the cell. It is generated by cleavage of a larger precursor protein, hCAP-18, which is stored in neutrophil secondary granules and produced by epithelial cells at barrier tissues. Research comparing three serine proteases found in neutrophil azurophil granules found that proteinase 3 was solely responsible for converting hCAP-18 into LL-37 following exocytosis, even though other enzymes could cleave the precursor in a test tube.

Structure drives antimicrobial activity

LL-37's antimicrobial activity is tied directly to its three-dimensional shape. Structural research reported that LL-37 is largely disordered in pure water at low concentrations, but transitions into an alpha-helical conformation in the presence of specific anions or as peptide concentration increases. Antibacterial potency against both Gram-positive and Gram-negative bacteria tracked directly with the degree of helicity, and the peptide adopts its active helical form in solutions mimicking physiological plasma and interstitial fluid.

Angiogenesis via FPRL1

A study combining chorioallantoic membrane assays and a rabbit hind-limb ischemia model reported that LL-37 promotes new blood vessel formation by activating endothelial cells through the formyl peptide receptor-like 1 (FPRL1), triggering calcium mobilization, NF-kB activation, and MAPK signaling downstream. Mice deficient in CRAMP, the murine cathelicidin, showed impaired wound vascularization in the same research.

Self-DNA sensing and immune activation

Research published in Nature reported that LL-37 binds self-DNA released from damaged or dying cells, forming aggregated complexes that accumulate in the endocytic compartments of plasmacytoid dendritic cells. This activates Toll-like receptor 9 (TLR9), converting DNA that would normally be immunologically inert into a potent trigger of interferon production. The authors proposed this mechanism as a driver of the aberrant immune activation seen in psoriasis.

Vitamin D-dependent expression

Research has identified the human cathelicidin (CAMP) gene as a direct transcriptional target of the vitamin D receptor, with 1,25-dihydroxyvitamin D3 exposure strongly increasing cathelicidin expression in myeloid cells in laboratory models.

How to read this

These findings span structural biology, cell-based receptor studies, animal-model angiogenesis and immunology work, and direct human-tissue sampling. That breadth is part of why LL-37 is studied across such different fields, but through different, specific, well-defined mechanisms rather than one general effect.