LL-37

LL-37 is the only human cathelicidin antimicrobial peptide, a 37-amino-acid peptide cleaved from the precursor protein hCAP-18. It is produced by immune cells (neutrophils, macrophages), epithelial cells, and keratinocytes as part of the innate immune response. It has broad-spectrum antimicrobial activity against bacteria, viruses, and fungi, and plays a role in wound healing and immune modulation.

LL-37 has a helical amphipathic structure that allows it to insert into and disrupt microbial cell membranes, creating pores and causing lysis. Beyond direct antimicrobial action, it modulates the immune response by recruiting immune cells (chemotaxis), promoting wound healing, inhibiting biofilm formation, neutralizing bacterial endotoxins (LPS), and modulating TLR signaling. Vitamin D regulates LL-37 expression, linking vitamin D deficiency to increased infection susceptibility.

Extensive research on innate immunity. Studies show broad-spectrum activity against MRSA, E. coli, Pseudomonas, Candida, and enveloped viruses including influenza and HIV. Anti-biofilm activity demonstrated against surgical implant infections. Wound healing promotion through angiogenesis and re-epithelialization. Phase I/II clinical trials for chronic leg ulcers showed improved healing. Vitamin D supplementation increases LL-37 levels — a key finding linking vitamin D to immune function.

Peptides commonly paired with LL-37 for synergistic effects.