LL-37

LL-37 is the only cathelicidin-type antimicrobial peptide found in humans. It is a 37-amino-acid peptide (beginning with two leucine residues, hence "LL") cleaved from its precursor protein hCAP18. LL-37 is produced by neutrophils, macrophages, and epithelial cells as a first-line defense against invading pathogens. It demonstrates broad-spectrum antimicrobial activity against gram-positive and gram-negative bacteria, enveloped viruses, and fungi.

Beyond direct antimicrobial killing, LL-37 serves as a critical immunomodulator — it recruits immune cells to sites of infection, promotes wound healing, modulates inflammatory responses, and can neutralize bacterial endotoxins (LPS). LL-37 kills microbes primarily by disrupting their cell membranes through electrostatic interactions with negatively charged microbial surfaces. In the health optimization community, LL-37 is used to support immune defense, particularly against chronic or biofilm-forming infections that are resistant to conventional antibiotics. It has shown particular promise against Lyme disease-associated Borrelia burgdorferi biofilms and chronic staph infections.