Extracellular RNA Activates Neutrophils via Toll-like Receptor 7

Objective:We have recently reported that extracellular RNA (exRNA) released from necrotic cells induces cytokines production in cardiomyocytes (CM) and may play a role in a mouse model of myocardial ischemia-reperfusion injury. However, whether exRNA has any effect on neutrophils (NE) and how it works is unclear. Methods: Mouse peritoneal NEs were treated with RNA (2.5 – 10 µg/ml) purified from mouse heart or rat CM. Cytokine mRNA at 3 h and proteins at 18 h were measured by qRT-PCR and ELISA, respectively. WT mice were injected i.p. with 50 µg of the purified RNA. Six h later, the peritoneal lavage was harvested and centrifuged. The supernatants were measured for cytokines production. The peritoneal cells were counted and NE gated with Ly-6G. ROS generation and CD11b expression in NE were measured by flow cytometry. Results: exRNA induced MIP-2 production in a dose-dependent manner. The effect was completely diminished by RNase, but not DNase. Moreover, the exRNA-induced cytokine production in NE was nea...