Neutrophil secondary necrosis is induced by LL-37 derived from cathelicidin

Zhifang Zhang, Gregory Cherryholmes and John E. Shively¹

Division of Immunology, Beckman Research Institute of the City of Hope, Duarte, California, USA

¹ Correspondence: Division of Immunology, Beckman Research Institute of the City of Hope, 1500E Duarte Rd., Duarte, CA 91010, USA. E-mail: jshively{at}coh.org

Neutrophils represent the most common granulocyte subtype presentin blood. The short half-life of circulating neutrophils isregulated by spontaneous apoptosis, and tissue infiltratingneutrophils die by apoptosis and secondary necrosis. The mechanismof neutrophil apoptosis has been the subject of many studies;however, the mechanism of neutrophil secondary necrosis is lessclear. Human cathelicidin cationic peptide 18, proteolyticallyprocessed to its active form, LL-37, is secreted by neutrophilsand epithelial cells and shown to have effects in addition tobacterial lysis. We demonstrate here that LL-37 affects neutrophillifespan by the pathway of secondary necrosis, rapidly convertingannexin V-positive (AV⁺), propidium iodide-negative (PI^–;apoptotic) cells into PI⁺ (necrotic) cells with the releaseof IL-8, IL-1R antagonist, ATP, and intact granules. The effectsof LL-37 on apoptotic neutrophils are neither energy-dependentnor affected by pretreatment with G-CSF, GM-CSF, TNF- ${alpha}$ , and LPSand are partially inhibited by human serum. Moreover, LL-37decreases CXCR2 expression of AV^–PI^– (live) neutrophils,suggesting an effect on the neutrophil response to its chemotacticfactors, including IL-8. Thus, the lifespan and inflammatoryfunctions of neutrophils are directly affected by LL-37.

Key Words: apoptosis • CXCR2 • IL-8 • IL-1Ra