PB0778 - Impact of Biological Sex on the Host Response to Sepsis in PAD4-deficient Mice

Background: Neutrophil extracellular traps (NETs) are important in innate immunity. The process of NET formation (NETosis) requires PAD4, an enzyme that catalyzes histone citrullination. NETs trap and kill pathogens, but excessive NETosis also promotes microvascular thrombosis. In mice, the impact of PAD4 deficiency on the host response to sepsis remains unclear. Some studies have reported that PAD4 deficiency improves outcome, whereas others reported that it has no effect. To investigate whether this discrepancy may reflect sepsis model and/or biological sex, we included both sexes of mice in a mouse model of fecal-induced peritonitis (FIP).

Aims: Investigate the impact of biological sex and sepsis model on sepsis response in PAD4-deficient mice.

Methods: Neutrophils from 8–13-week-old C57Bl/6 wild-type or PAD4-/- mice were stimulated with lipopolysaccharide (LPS) to induce NETosis, then visualized by fluorescent microscopy via Sytox staining. Sepsis was induced in mice using intraperitoneal injections of rat fecal slurry (0.4 mg/g) and monitored over 48h. Data collected included bacterial counts in the blood and peritoneal cavity, physiological illness signs, temperature, blood glucose, and immunothrombosis biomarkers.

Results: Neutrophils from wild-type mice exhibited LPS-dependent NET formation whereas neutrophils isolated from PAD4-/- mice did not. In the FIP model, the survival rate of PAD4-/- mice was similar to that of wild-type mice (p=0.23). Interestingly, when stratified by sex, male PAD-/- mice exhibited worse survival compared to male wild-type mice (p=0.03) and female PAD4-/- mice (p=0.008). Low body temperatures, increased bacterial loads, increased coagulation biomarkers, and a sustained increase in IL-6 levels were associated with poor survival in male PAD4-/- mice.

Conclusion(s): Biological sex as well as sepsis model impact host response to infection. Specifically, male PAD4-/- mice have worse outcomes compared to wild-type mice and female PAD4-/- mice in FIP. Poor survival in male PAD4-/- mice is associated with low temperatures, increased bacterial loads, and elevations in inflammation/coagulation biomarkers.