Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF) enhances neutrophil regulation of gut bacteria. Crohn’s Disease (CD) patients with reduced neutrophil GM-CSF signaling are more likely to experience stricturing complications requiring surgery. We aimed to determine whether bacterial killing by GM-CSF primed neutrophils is enhanced by physiologic hypoxia and suppressed by lipid peroxidation products including 4-hydroxynonenal (4-HNE).