LL-37 is the active fragment of human cathelicidin studied in preclinical innate immunity research for its role in antimicrobial peptide activity and immunomodulatory signaling pathway analysis.
LL-37 is a 37-amino acid cationic peptide that represents the active C-terminal fragment of hCAP18 (human cationic antimicrobial protein of 18 kDa). Named for the two leucine residues at its N-terminus and its 37-residue length, LL-37 is released when the precursor protein is proteolytically cleaved, separating the conserved cathelin-like domain from the variable antimicrobial region. It is studied in preclinical innate immunity research as a reference compound for host defense peptide biology.
Cathelicidins are a family of host defense peptides characterized by a highly conserved N-terminal cathelin-like domain and a structurally diverse C-terminal antimicrobial domain. Cathelicidins have been identified across many mammalian species, with considerable variation in the length and sequence of the mature peptide. hCAP18 is the only cathelicidin precursor identified in humans, which makes LL-37 a frequently referenced model peptide in comparative studies of cathelicidin structure, processing, and activity across species. Comparative work on processing enzymes, including proteinase 3 in neutrophil models and kallikreins in epithelial cell systems, has also examined how alternative cleavage of hCAP18 can generate shorter fragments with distinct activity profiles.
In solution, LL-37 adopts an amphipathic alpha-helical conformation, with cationic and hydrophobic residues arranged on opposing faces of the helix. This structure is studied for its electrostatic interaction with negatively charged microbial membranes. In vitro research has examined LL-37's membrane-permeabilizing activity against a range of bacterial and fungal cultures, as well as its effects on biofilm formation in controlled laboratory assays.
Beyond its direct antimicrobial profile, LL-37 is studied for its role in immunomodulatory signaling. In cultured cell models, LL-37 has been investigated for its interaction with formyl peptide receptor 2 (FPR2), purinergic P2X7 receptors, and Toll-like receptor (TLR) signaling pathways. Researchers have examined its effects on chemokine and cytokine expression in macrophage, monocyte, and epithelial cell cultures, as well as its influence on dendritic cell differentiation in vitro. These findings have positioned LL-37 as a tool compound for studying the interface between antimicrobial activity and innate immune signaling.
For in-vitro research use only. Not for human or veterinary use.