Abstract
Salmonella enterica serovar Typhimurium (S. Typhimurium) is a major cause of acute gastroenteritis in humans. During infection, reactive oxygen species (ROS), generated from NADPH oxidase (a multisubunit enzyme complex), are required for pathogen killing upon phagocytosis and for regulating pro-inflammatory signaling in phagocytic cells. Mutations in subunits forming the NADPH complex may lead to enhanced susceptibility to infection and inflammatory disease. Compared to other NADPH oxidase subunits, the function of p40phox is relatively understudied, particularly in the context of intestinal bacterial infection. In this study, we utilized genetically engineered mice to determine the role of p40phox in the response to S. Typhimurium infection. We show that mice lacking p40phox are more susceptible to oral infection with S. Typhimurium, as demonstrated by significantly enhanced bacterial dissemination to spleen and liver, and development of exacerbated bacterial colitis. Moreover, we demonstrate that the increased infection and disease severity are correlated with markedly increased F4/80+ macrophage and Ly6G+ neutrophil infiltration in the infected tissues, coincident with significantly elevated pro-inflammatory cytokines (IL-1β and TNF-α) and chemoattractant molecules in the infected tissues. Functional analysis of macrophages and neutrophils further shows that p40phox deficiency impairs bacteria- or PMA-induced intracellular ROS production as well as intracellular killing of Salmonella. These observations indicate that the p40phox subunit of NADPH oxidase plays an essential role in suppressing intracellular multiplication of Salmonella in macrophages and in the regulation of both systemic and mucosal inflammatory responses to bacterial infection.
Highlights
Salmonella infection is a major cause of human food-borne gastroenteritis worldwide
To effectively control the infection, molecules that can enhance the microbicidal capacity of phagocytes, such as phagocyte NADPH oxidase, are required
Functional analysis of macrophages revealed that, in addition to the anticipated reduced reactive oxygen species (ROS) generation, the bacterial killing capacity of macrophages was significantly impaired in p40phox-deficient mice and that p40phox-deficient macrophages produced significantly more IL-1β and TNF-α
Summary
Typhimurium in lamina propria monocytic phagocytes/macrophages plays an important role in the development of colitis [6] It is less clear whether/how host mucosal defenses are affected by NADPH oxidase. The importance of ROS production in host defense is demonstrated by the enhanced susceptibility to infection of individuals who have inherited deficiencies of NADPH oxidase and develop chronic granulomatous disease (CGD) [16]. Macrophages and neutrophils contribute significantly to the effector phase of the immune response, i.e., elimination of bacteria, and are thought to be critical mediators of many chronic inflammatory diseases These phagocytic cells have evolved a repertoire of antimicrobial mechanisms based on the formation of toxic radicals, including NADPH phagocytic oxidase and inducible nitric oxide synthase.
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