Reactive-Oxygen-Species-Mediated P. aeruginosa Killing Is Functional in Human Cystic Fibrosis Macrophages

Abstract

Pseudomonas aeruginosa is the most common pathogen for chronic lung infection in cystic fibrosis (CF) patients. About 80% of adult CF patients have chronic P. aeruginosa infection, which accounts for much of the morbidity and most of the mortality. Both bacterial genetic adaptations and defective innate immune responses contribute to the bacteria persistence. It is well accepted that CF transmembrane conductance regulator (CFTR) dysfunction impairs the airways-epithelium-mediated lung defence; however, other innate immune cells also appear to be affected, such as neutrophils and macrophages, which thus contribute to this infectious pathology in the CF lung. In macrophages, the absence of CFTR has been linked to defective P. aeruginosa killing, increased pro-inflammatory cytokine secretion, and reduced reactive oxygen species (ROS) production. To learn more about macrophage dysfunction in CF patients, we investigated the generation of the oxidative burst and its impact on bacterial killing in CF macrophages isolated from peripheral blood or lung parenchyma of CF patients, after P. aeruginosa infection. Our data demonstrate that CF macrophages show an oxidative response of similar intensity to that of non-CF macrophages. Intracellular ROS are recognized as one of the earliest microbicidal mechanisms against engulfed pathogens that are activated by macrophages. Accordingly, NADPH inhibition resulted in a significant increase in the intracellular bacteria survival in CF and non-CF macrophages, both as monocyte-derived macrophages and as lung macrophages. These data strongly suggest that the contribution of ROS to P. aeruginosa killing is not affected by CFTR mutations.

Human Cystic Fibrosis Macrophages Have Defective Calcium-Dependent Protein Kinase C Activation of the NADPH Oxidase, an Effect Augmented by Burkholderia cenocepacia

“…It is unclear if CF macrophages have basal deficits in oxidative killing since some studies have suggested functional ROS responses to pathogens such as P. aeruginosa (36), while others have demonstrated deficient ROS production (37). Importantly, a comprehensive assessment of human CF macrophage oxidase assembly has not been performed.…”

“…Finally, we examined the oxidative burst in response to another common CF pathogen, P. aeruginosa , which has been previously shown to not affect the respiratory burst in CF macrophages (36). There was no difference in ROS production in response to P. aeruginosa between CF and non-CF MDMs (Figures 8E, F), confirming previous findings.…”

Melatonin: an ancient molecule that makes oxygen metabolically tolerable

“…In aerobes, oxidative stress is inevitable and, perhaps fortunately, cannot be completely prevented. Some free radicals escape detoxification and have essential functions in organisms, for example, the killing of invading bacteria by leukocytes and macrophages . Clearly, quenching all radicals with direct scavengers or enzymatic antioxidants would be detrimental.…”

TRPC6 channel translocation into phagosomal membrane augments phagosomal function

“…We have previously shown that murine cftr −/− AMs are not defective in ROS production but are defective in microbicidal function (3), strongly suggesting that other microbicidal enzymatic effectors contributed by lysosomal fusion and activated in the acidic environment of the phagosome play a significant role in bacterial killing. Although both human and murine CF lung macrophages seem to be intrinsically defective in bacterial killing, there is disagreement in the literature as to whether CFTR dysfunction impairs the contribution of ROS production to P. aeruginosa killing (44,45) and may well be a function of species and tissue source.…”