LL-37 (CAP-18) 5mg

LL-37's antimicrobial mechanism involves direct insertion into and disruption of bacterial cell membranes via its amphipathic alpha-helical structure, a mechanism studied using model lipid bilayer and liposome leakage assays. Separately, LL-37 engages host cell surface receptors — including FPR2, P2X7, and EGFR transactivation pathways — to modulate immune cell chemotaxis, cytokine release, and cell migration, representing a receptor-mediated signalling mechanism distinct from its direct membrane-disrupting antimicrobial action. Research distinguishing these two activities typically uses peptide fragments or receptor antagonists to isolate which mechanism drives a given experimental endpoint.

Standard approaches include transwell migration assays to quantify LL-37-induced chemotaxis of neutrophils, monocytes, or mast cells, alongside cytokine/chemokine release assays (ELISA, multiplex) following LL-37 exposure in immune cell culture models. FPR2-specific signalling is often confirmed using selective FPR2 antagonists or receptor-knockdown approaches to establish receptor dependence of the observed chemotactic or signalling response.

Model lipid bilayer systems — including liposome dye-leakage assays, planar lipid bilayer electrophysiology, and circular dichroism spectroscopy to monitor peptide secondary structure upon membrane association — are standard biophysical methods for characterising LL-37's membrane interaction and permeabilisation kinetics. These methods allow researchers to correlate peptide concentration, lipid composition (mimicking bacterial versus mammalian membranes), and resulting membrane disruption, providing mechanistic insight into the peptide's selectivity for bacterial over host cell membranes.