Extracellular Superoxide Dismutase Hinders Effective Containment of Listeria monocytogenes by Neutrophils

dc.contributor.authorBerg, Rance E.
dc.creatorOkunnu, Busola
dc.description.abstractPurpose: Increased activity of Extracellular Superoxide Dismutase (ecSOD), an enzyme widely regarded as having protective functions during ROS induced inflammation, has been shown to be detrimental to host survival during infection with the intracellular bacteria, Listeria monocytogenes (Lm). Although, we have also demonstrated that neutrophils are essential for protection during Lm infection, a higher percentage of neutrophils are present in mice with high ecSOD activity during Lm infection. However, these mice are still more susceptible to infection in comparison to mice that lack ecSOD activity. These paradoxical findings led to the objective to better understand how ecSOD activity modulates the protective functions of neutrophils during Lm infection. Materials and Methods: For these studies, ecSOD congenic mice: ecSOD HI mice with high ecSOD activity, ecSOD WT mice with normal ecSOD activity, and ecSOD KO mice with no ecSOD activity were utilized. To determine phagosomal containment, we made use of flow cytometry and a strain of Lm, actA:LMGFP, which only fluoresces GFP when the bacteria escapes out of the phagosome into the cytosol. Results: A higher percentage of neutrophils from the ecSOD KO mice took up Lm in comparison to the HI neutrophils. Correlated with this was also a higher percentage of ecSOD KO neutrophils allowing for phagosomal escape in comparison to the ecSOD HI neutrophils. Analysis of the mean fluorescence intensity (MFI) showed that although there were more bacteria present in the ecSOD KO neutrophils, the amount of escaped bacteria was comparable to that in the ecSOD HI neutrophils. Treatment of the ecSOD KO neutrophils with IFN-g, an activator of neutrophils, also led to better phagosomal containment. Though the IFN-g treated neutrophils took up more bacteria, there was no difference in the amount of escaped bacteria in comparison to the non-treated cells. Conclusion: EcSOD activity hinders the ability of neutrophils to keep Lm contained in the phagosome which prevents effective bacterial killing. Additionally, neutrophil activation with IFN-g also makes the cells more effective at bacterial containment. However, the effect of ecSOD activity in conjunction with IFN-g is yet to be determined. Future studies on how ecSOD affects bacterial killing and other functions downstream of phagosomal escape will aid in a better understanding of how ROS can modulate neutrophil function during intracellular bacterial infections.
dc.titleExtracellular Superoxide Dismutase Hinders Effective Containment of Listeria monocytogenes by Neutrophils