Neutrophils release microvesicles (ectosomes) upon stimulation. Interestingly, ectosome level is elevated in sepsis survivors. Previously, we revealed that LL-37, a human cathelicidin antimicrobial peptide, improves the survival of a murine cecal ligation and puncture (CLP) sepsis model. Thus, in this study, we elucidated the action of LL-37 on sepsis, by focusing on the effect of LL-37 on ectosome release in the CLP model. The results demonstrated that the ectosome level was elevated in CLP mice, and the level was further enhanced by the administration of LL-37, accompanied by reduced bacterial load. More importantly, ectosome-containing microvesicles isolated from LL-37-injected CLP mice contained a higher amount of antimicrobial proteins/peptides (such as lactoferrin and murine cathelicidin-related antimicrobial peptide), and exhibited higher antibacterial activity, compared with those from PBS-injected CLP mice, suggesting that LL-37 induces the release of ectosomes with antibacterial potential in vivo. In fact, LL-37 stimulated mouse bone marrow neutrophils to release ectosomes ex vivo, and the LL-37-induced ectosomes possessed antibacterial activity. Furthermore, the administration of LL-37-induced ectosomes reduced the bacterial load and improved the survival of CLP mice. These observations suggest that LL- 37 induces the release of ectosome-containing antimicrobial microvesicles in CLP mice, thereby reducing the bacterial load and protecting the mice from lethal septic
conditions.