LL-37 (or CAP-18 for cathelicidin antimicrobial peptide, 18 kDa) is a gene encoding for the only member of the human cathelicidin family. Cathelicidin-related antimicrobial peptides are a family of polypeptides found in lysosomes of macrophages and polymorphonuclear leukocytes (PMNs), and keratinocytes. Cathelicidins serve a critical role in mammalian innate immune defense against invasive bacterial infection.
NOTE: This article appears to be split into two parts; more on cathelicidin's clinical significance can be found on the cathelicidin page.
Patients with rosacea have elevated levels of cathelicidin. Cathelicidin is cleaved into the antimicrobial peptide LL-37 by both kallikrein 5 and kallikrein 7 serine proteases. Excessive production of LL-37 is suspected to be a contributing cause in all subtypes of Rosacea.
Higher plasma levels of LL-37, which are up-regulated by vitamin D, appear to significantly reduce the risk of death from infection in dialysis patients. Patients with a high level of LL-37 were 3.7 times more likely to survive kidney dialysis for a year without a fatal infection. Vitamin D up-regulates genetic expression of cathelicidin, which exhibits broad-spectrum microbicidal activity against bacteria, fungi, and viruses.
SAAP-148 (a synthetic antimicrobial and antibiofilm peptide) is a modified version of LL-37 that has enhanced antimicrobial activities compared to LL-37. In particular, SAAP-148 was more efficient in killing bacteria under physiological conditions.