FAM19A4 Enhances Neutrophil Respiratory Burst via p38 MAPK in Lethal Sepsis

Sepsis causes high mortality and resource strain, with neutrophil-derived reactive oxygen species (ROS) contributing to excessive inflammation. The secretory protein FAM19A4 modulates ROS release, but its role in sepsis was unclear. We measured elevated FAM19A4 levels in septic patients and cecal ligation and puncture (CLP) mice, correlating with increased mortality. Fam19a4 ^−/− mice subjected to CLP showed significantly improved survival and attenuated multiorgan injury without impaired peritoneal bacterial clearance or altered circulating neutrophil counts. Deficiency reduced the cell counts of neutrophil (Ly6G ⁺ ) and macrophage (F4/80 ⁺ ) in lungs and liver, diminished systemic ROS production tracked by bioluminescence, and decreased neutrophil extracellular trap (NET) formation in serum and lung tissue. In vitro, FAM19A4 enhanced neutrophil phagocytosis and ROS generation but did not affect lipopolysaccharide-induced chemotaxis. Mechanistically, bulk RNA sequencing, western blotting, and the p38 inhibitor SB203580 demonstrated that FAM19A4 drives neutrophil ROS release specifically through p38 MAPK signaling activation. These results indicate that FAM19A4 is upregulated during sepsis and exacerbates outcomes by enhancing neutrophil ROS production via p38 MAPK, representing a promising therapeutic target for this condition.