The IRE1 Stress Signaling Axis Is a Key Regulator of Neutrophil Antimicrobial Effector Function

Activation of the endoplasmic reticulum stress sensor, IRE1 alpha, is required for effective immune responses against bacterial infection and is associated with human inflammatory diseases in which neutrophils are a key immune component. However, the specific role of IRE1 alpha in regulating neutrophil effector function has not been studied. In this study, we show that infection-induced IRE1 alpha activation licenses neutrophil antimicrobial capacity, including IL-1 beta production, formation of neutrophil extracellular traps (NETs), and methicillin-resistant Staphylococcus aureus (MRSA) killing. Inhibition of IRE1 alpha diminished production of mitochondrial reactive oxygen species and decreased CASPASE-2 activation, which both contributed to neutrophil antimicrobial activity. Mice deficient in CASPASE-2 or neutrophil IRE1a were highly susceptible to MRSA infection and failed to effectively form NETs in the s.c. abscess. IRE1 alpha activation enhanced calcium influx and citrullination of histone H3 independently of mitochondrial reactive oxygen species production, suggesting that IRE1 alpha coordinates multiple pathways required for NET formation. Our data demonstrate that the IRE1 alpha-CASPASE-2 axis is a major driver of neutrophil activity against MRSA infection and highlight the importance of IRE1 alpha in neutrophil antibacterial function.