Purpose: To investigate the role of endothelial Nox2 in sepsis-induced systemic inflammatory response and hypotension. Methods: All experiments were conduced in accordance with the Scientific Procedures Act. 1986 (UK Home Office). Mice with endothelial-target deletion of Nox2 were generated by crossing Nox2fl/fl mice with Tie2Cre transgenic animals. We compared Nox2fl/fl Tie2Cre+/− mice (Knockout,KO) with matched littermate Nox2fl/fl Tie2Cre-/- (Control) animals on a C57BL/6 background. Mice received an iv injection of lipopolysaccharide (LPS, 10mg/kg) or saline. Systolic and diastolic blood pressures were determined by tail-cuff plethysmography. A clinical severity score comprising signs of lethargy, piloerection, tremor, periorbital exudates, respiratory distress and diarrhoea was determined 2-hourly after LPS injection. After 12 hours sepsis, animals were euthanized and neutrophil sequestration in lungs was evaluated by myeloperoxidase assay. ROS production in mesenteric vessels was assessed by dihydroethidium- image assay and 3-nitrotyrosine staining was used as a readout of nitrosative stress. Levels of tumor necrosis factor alpha (TNF-alpha) were determined by enzymatic linked immunoabsorbent assay. Results: KO mice had lower ROS production in mesenteric vessels than controls after LPS injection. Despite similar basal values (94.46±2.1 vs 96.43±2.50mmHg for systolic blood pressure and 68.19±1.74 vs 69.26±2.56mmHg for diastolic pressure), KO mice had lower blood pressure than control mice, 6 hours after LPS injection (63.04±2.56 vs 76.70±1.38mmHg for systolic blood pressure and 48.24±2.77 vs 59.14±1.89 mmHg for diastolic pressure; p<0.05; n=9). The clinical severity scores were also more aggravate in KO mice compared to controls (p=0.0003, n=9). Mice with endothelial-target Nox2 deletion had higher number of neutrophils trapped in lungs (12480±207.4 vs 6489±75.09 cells/mg lung, p=0.0004, n=6), and increased levels of TNF-alpha in plasma (95.70±13.51 vs 33.69±11.59 pg/ml, p=0.0207, n=5) compared to controls. Interestingly, 3-nitrotyrosine staining in mesenteric vessels was higher in KO mice compared to controls. Conclusions: Endothelial cell Nox2 appears to be protective during sepsis by reducing the extent of hypotension, neutrophil sequestration in lungs and levels of TNF-alpha in plasma. The severe hypotension in KO mice during sepsis could be associated with evidence of greater nitrosative stress in mesenteric vessels than controls. The cellular mechanisms underlying the Nox2 protective effect are currently being investigated.