Interferon regulatory factor 8 induces intrinsic functional changes in mature neutrophils

Neutrophils are the first line of host defense. Neutrophils target invading pathogens by phagocytosis, generation of reactive oxygen species (ROS), neutrophil extracellular trap formation (NETosis), and cytokine production. Interferon regulatory factor 8 (IRF8) plays a central role in the regulation of myeloid cells fate, promoting monocyte and dendritic cell development while inhibiting neutrophil production. The global IRF8 deficiency leads to an accumulation of immature myeloid cells, mostly neutrophils, while IRF8 deficiency restricted to myeloid cells has no effect on myeloid cell differentiation. However, the role of IRF8 in regulating neutrophil function remains to be fully elucidated, especially due to the fact that IRF8 is not expressed in mature neutrophils. This study aims to investigate the impact of IRF8 on effector functions of neutrophils. The absence of IRF8 resulted in a diminished response of neutrophils to inflammatory challenge by lipopolysaccharide (LPS), as evidenced by reduced expression of inflammatory cytokines. This effect was intrinsic to IRF8-/- neutrophils and not driven by extrinsic factors, as assessed comparing bone marrow-derived and estrogen receptor-regulated homeobox B8-derived IRF8-/- neutrophils and was accompanied by reduced p38, extracellular signal-regulated kinase 1/2, and mitogen-activated protein kinase-activated protein kinase 2 activation. It is noteworthy that not all effector functions were affected by IRF8 deficiency. The mechanisms of pathogen elimination, such as phagocytosis and ROS production, were impaired in IRF8-/- neutrophils, whereas processes like NETosis remained entirely intact. In conclusion, our findings suggest that IRF8 shapes the neutrophil response to LPS and modulates neutrophil function, and this process is independent of external factors.