LL-37

Research-Grade

LL-37 is the only cathelicidin-derived antimicrobial peptide expressed in humans. Produced by neutrophils, macrophages, and epithelial cells, it is the active C-terminal fragment of the precursor protein hCAP18. Its amphipathic alpha-helical structure allows it to disrupt microbial membranes directly — it inserts into lipid bilayers at concentrations above 1–5 μM, forming pores that lyse bacteria, fungi, and enveloped viruses. Beyond direct antimicrobial activity, LL-37 functions as an immune alarm signal. It chemoattracts neutrophils, monocytes, and T cells via the formyl peptide receptor-like 1 (FPRL1). It promotes angiogenesis through VEGF upregulation and accelerates wound closure by stimulating keratinocyte migration and proliferation. In biofilm contexts — particularly relevant to chronic wound infections and implant-associated infections — LL-37 has demonstrated the ability to penetrate established Pseudomonas aeruginosa and Staphylococcus aureus biofilms at concentrations that conventional antibiotics cannot match. Clinical interest centers on chronic wound healing, antimicrobial-resistant infections, and immunodeficiency states where endogenous LL-37 production is suppressed (vitamin D deficiency correlates with low LL-37, which partly explains the vitamin D–infection link). A Phase I/IIa trial for hard-to-heal leg ulcers demonstrated safety and accelerated healing at the highest dose group. Research into topical and injectable formulations is ongoing.