Gut-primed neutrophils activate Kupffer cells to promote hepatic injury in mouse sepsis

Sepsis-induced liver injury is common, but the underlying mechanisms remain poorly understood. Given the critical role of gut-liver crosstalk in sepsis, we hypothesize that gut-trained neutrophils, migrating via the portal vein, release neutrophil extracellular traps (NETs) to activate Kupffer cells, thereby exacerbating hepatic injury during sepsis. Here we show that iNOS expression in Kupffer cells increases in septic wild type mice but decreases in PAD4^-/- mice. In vitro, NETs stimulate Kupffer cell IL-6 and TNF release, while conditioned media from NET-treated Kupffer cells induces hepatocyte death. Inhibition of neutrophil elastase and protease-activated receptor-1 (PAR-1) mitigates IL-6 and TNF secretion by Kupffer cells. Ex vivo, portal vein neutrophils from septic mice produce more NETs and induce greater Kupffer cell activation than systemic neutrophils, with this effect attenuated in PAD4^-/- neutrophils. Furthermore, gut intraepithelial lymphocytes (IELs) interact with neutrophils during sepsis and facilitate NETosis, and IEL-primed neutrophils also induce Kupffer cell activation in vitro and in vivo. Our data thus suggest that IEL-facilitated, gut-derived neutrophil NETs activate Kupffer cells to contribute to sepsis-induced liver injury.