Reactive oxygen species (ROS) produced by NADPH phagocyte oxidase isoform (NOX2) are critical for the elimination of intracellular pathogens in many infections. Despite their importance, the role of ROS following infection with the eukaryotic pathogen Leishmania has not been fully elucidated. We addressed the role of ROS in C57BL/6 mice following intradermal infection with Leishmania amazonensis. Despite equivalent parasite loads compared with wild-type (WT) mice, mice deficient in ROS production by NOX2 due to the absence of the gp91 subunit (gp91^phox-/-) had significantly more severe pathology in the later stages of infection. Pathology in gp91^phox-/- mice was not associated with alterations in CD4⁺ T cell-mediated immunity but was preceded by enhanced neutrophil accumulation at the dermal infection site. Ex vivo analysis of infected versus uninfected neutrophils revealed a deficiency in infection-driven apoptosis in gp91^phox-/- mice versus WT mice. gp91^phox-/- mice presented with higher percentages of healthy or necrotic neutrophils but lower percentages of apoptotic neutrophils at early and chronic time points. In vitro infection of gp91^phox-/- versus WT neutrophils also revealed reduced apoptosis and CD95 expression but increased necrosis in infected cells at 10 h postinfection. Provision of exogenous ROS in the form of H₂O₂ reversed the necrotic phenotype and restored CD95 expression on infected gp91^phox-/- neutrophils. Although ROS production is typically viewed as a proinflammatory event, our observations identify the importance of ROS in mediating appropriate neutrophil apoptosis and the importance of apoptosis in inflammation and pathology during chronic infection.

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