Stat4 Promotes Critical Neutrophil Functions And Is Required For Antimicrobial Immunity In Mice

Signal transducer and activator of transcription 4 (STAT4) is a transcription factor mainly associated with Th1 development, yet its role in neutrophil biology is unknown. We are the first to demonstrate that in vitro murine neutrophils stimulated with IL-12 directly activate STAT4 in a JAK2-dependent manner resulting in distinct transcriptional changes in antimicrobial response genes. STAT4-deficiency also impairs several neutrophil functions in vitro. Interestingly, IL-12 directly induces STAT4-dependent ROS formation at 14 hours, which is not due to cell death. Neutrophil extracellular trap (NET) formation in response to either LPS or heat-killed Pseudomonas aeruginosa results in decreased nuclear translocation of myeloperoxidase, decreased neutrophil elastase release, and decreased DNA release in STAT4-deficient neutrophils. In vivo neutrophil migration to the peritoneal cavity is blunted in Stat4−/− mice following either thioglycollate, CXCL1, or GM-CSF injections. Finally, we have generated Stat4floxLysMCre and Stat4floxS100A8Cre mice which are deficient in STAT4 in either myeloid cells or specifically neutrophils, respectively. Following in vivo infection with methicillin-resistant S. aureus, bacterial burden is increased in the blood and peritoneal cavity of Stat4floxLysMCre and Stat4floxS100A8Cre mice. Gene expression analysis of peritoneal exudate cells from infected mice show decreased expression of Ly6G/CD11b, further highlighting defective homing of Stat4−/− neutrophils in vivo. All together these data reveal an undiscovered role of STAT4 in neutrophil functions and a subsequent role of STAT4 in innate immunity and antimicrobial defense mechanisms.