LL-37: Your Body's Only Cathelicidin Does Much More Than Kill Bacteria

LL-37 — the only human cathelicidin antimicrobial peptide — does far more than kill bacteria. This review catalogs its many roles: it kills a broad range of microorganisms, neutralizes bacterial toxins (LPS) to prevent septic shock, attracts immune cells to infection sites, prevents neutrophil death, stimulates new blood vessel growth, promotes tissue repair, and triggers cytokine release. Its production is regulated by vitamin D (which explains the sun exposure-immunity connection), bacterial products, and oxygen levels. However, at inflamed sites, DNA and proteins from dead cells can neutralize LL-37, limiting its effectiveness.

This is a comprehensive review paper synthesizing published research on LL-37's antimicrobial activity, immunomodulatory functions, gene regulation, and potential therapeutic applications.

LL-37 is the only cathelicidin peptide humans produce, making it uniquely important in our innate immune defense. Understanding its multiple functions — from direct microbial killing to wound healing to immune signaling — is essential for developing it as a therapeutic agent. The vitamin D connection also has public health implications, as vitamin D deficiency may impair LL-37 production and compromise immune defense.

LL-37 sits at the center of innate immune defense and has become one of the most studied antimicrobial peptides in the world. Its connection to vitamin D has influenced public health recommendations, and synthetic versions are being explored as new antibiotics for drug-resistant infections. Understanding how LL-37's many functions work together — and what limits them — is key to developing peptide-based immunotherapies.

As a review paper, no new experimental data are presented. The therapeutic applications of LL-37 discussed were largely theoretical at the time of publication. The review may not capture more recent discoveries about LL-37's roles in autoimmune conditions and cancer.