LL-37 is the only cathelicidin peptide humans make. It’s kept inactive inside neutrophils and becomes active after release, where it kills microbes and also helps attract immune cells, neutralize toxins, promote new blood vessels, and heal wounds, acting as a bridge between the body’s first‑line and later immune defenses.

Neutrophil granules contain several antimicrobial peptides (AMPs) that are important effector molecules of innate immunity. In mammals, the main families of these peptides are the cathelicidins and defensins. Several defensins have been characterized in humans, while there is only one human cathelicidin, designated LL-37. This peptide is stored in specific granules of neutrophils in an inactive proform, which is processed extracellularly to the mature active peptide LL-37 and the propart cathelin after neutrophil degranulation. Apart from exhibiting a broad antimicrobial spectra, it is now evident that LL-37 possesses several additional functions that are related to host defense. Examples of such functions are chemotactic, endotoxin neutralizing, angiogenic and wound healing activities. These effects of LL-37 reveal a role as a mediator between innate and adaptive immunity. This review is giving an overview of the different immunological effects exerted by LL-37 and the physiological significance of these functions in immunity.