What it is

LL-37 is named for its first two amino acids, two leucines, and its length of 37. It is the active piece of hCAP-18, cut free by proteinase 3 in neutrophils and by kallikreins in the skin. It is made in white blood cells, skin, the gut, the airways and the bladder lining. It is part of the innate immune system, the defence that works before antibodies are made.