Browsing by Subject "Neutrophils"
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Item EXTRACELLULAR SUPEROXIDE DISMUTASE ENHANCES NEUTROPHIL RECRUITMENT TO THE LIVER BY MODULATING THE EXTRACELLULAR ENVIRONMENT(2014-03) Witter, Alexandra R.; Break, Timothy J.; Indramohan, Mohanalaxmi; Berg, Rance E.Listeria monocytogenes (LM) infection represents one of the leading causes of death from foodborne infection, especially in immunocompromised individuals, and can cause spontaneous abortion in pregnant women; however, it is commonly used as a model to study the host immune response against infection. Our lab utilizes three groups of mice with varying levels of extracellular superoxide dismutase (ecSOD) activity (high, wild-type, and none) to determine the impact that this antioxidant enzyme has on the host immune response during LM infection. We have previously shown that ecSOD activity leads to decreased innate immune response against LM. Our current data shows that ecSOD activity protects the extracellular matrix from degradation, and leads to increased neutrophil recruitment; however, these neutrophils display inhibited function and therefore do not provide adequate protection against LM. This research is relevant due to the potential use of ecSOD inhibitors to enhance immune responses during bacterial infection. In addition, these findings help clarify the impact of the oxidative environment on the immune response and how antioxidants contribute to this dynamic. Purpose (a): Listeria monocytogenes (LM) is an intracellular foodborne pathogen that causes severe disease in immunocompromised individuals, spontaneous abortion in pregnant women, and results in ~25% mortality rate in infected individuals. Extracellular superoxide dismutase (ecSOD) converts superoxide into hydrogen peroxide in the extracellular milieu and protects against oxidative stress. We have previously shown that ecSOD activity inhibits innate immune responses during LM infection leading to increased bacterial burden; however, it is unclear whether ecSOD activity affects neutrophil recruitment and function in a cell-intrinsic manner or by modulating the extracellular environment. Methods (b): Congenic mice with high ecSOD activity (ecSOD HI), wild type ecSOD activity (ecSOD WT), or lacking ecSOD (ecSOD KO), on the C57Bl/6 background were used to perform adoptive transfer experiments after intravenous infection with ~10,000 wild-type LM (WTLM). Either isolated neutrophils or labeled whole bone marrow cells were transferred from ecSOD HI or ecSOD KO mice into ecSOD WT mice and then flow cytometry analysis was performed and colony forming units (CFUs) were calculated. Concentrations of hyaluronan and lymphotoxin alpha were determined by ELISA. Results (c): Whole bone marrow cell transfers indicated that there was no difference in recruitment of neutrophils transferred from ecSOD HI or ecSOD KO mice to the liver when the neutrophils were all in the same environment (ecSOD WT mice). In addition, neutrophils isolated from ecSOD HI or ecSOD KO mice showed no difference in their ability to protect against LM infection, as shown by equivalent CFUs, when in comparable environments (ecSOD WT mice). Analysis of hyaluronan concentrations – a component of the extracellular matrix (ECM) – indicated that ecSOD activity protects the ECM from degradation. Conclusions (d): We observed from adoptive transfer experiments that ecSOD activity does not affect neutrophil recruitment or function in a cell-intrinsic manner. Additionally, we determined that ecSOD activity protects the ECM, which is important for neutrophil trafficking. Overall, we concluded that ecSOD activity enhances neutrophil recruitment yet decreases their function by modulating the extracellular environment.Item The Divergent Roles of Neutrophils and Monocytes During Infection with the Bacterium, Listeria monocytogenes(2020-05) Okunnu, Busola; Berg, Rance E.; Hodge, Lisa M.; Su, Dong-Ming; Fudala, Rafal; Uteshev, Victor V.Neutrophils are polymorphonuclear phagocytic cells that can play both protective and damaging roles during innate immune responses to infection and disease. Therefore, gaining a complete understanding of the functions and capabilities of neutrophils is vital. Our studies on neutrophil function were focused on their role during bacterial infections and were conducted using a Listeria monocytogenes (Lm) mouse infection model. Lm is an intracellular bacterium that causes diseases such as gastroenteritis, spontaneous abortion and meningitis. Lm infection in mice is commonly used as a model to study cell mediated immune responses and previous studies have demonstrated that neutrophils are essential for host protection against the bacteria. A major function attributed to neutrophils is the killing of pathogens via the generation of Reactive Oxygen Species (ROS). The unintentional damage to host cells by ROS is mitigated by antioxidants such as superoxide dismutases (SODs) which convert superoxide into hydrogen peroxide. Our studies focused on how one of the SODs, extracellular superoxide dismutase (ecSOD), modulates the function of neutrophils during Lm infection. Congenic mice with differing activities of ecSOD: high (ecSOD HI), normal (ecSOD WT), and no activity (ecSOD KO) were used for these studies. Previous studies from our lab have shown that the ecSOD HI mice are more susceptible to Lm infection in comparison to ecSOD KO mice, though the ecSOD HI mice have a higher percentage of neutrophils recruited to the sites of infection. Therefore, the purpose of these studies was to determine how ecSOD activity modifies functions such as phagocytosis, phagosomal containment and killing of Lm by neutrophils. EcSOD activity correlated with increased presence of extracellular bacteria in the spleen after three days of infection. High activity of ecSOD was also observed to decrease neutrophil phagocytosis of Lm. However, surprisingly, ecSOD activity had no effect on phagosomal containment or killing of Lm by neutrophils. As a result, ecSOD activity appears to primarily modify Lm uptake by neutrophils during infection. Another class of innate immune phagocytes that have also been demonstrated to be necessary for protection during Lm infection are monocytes. Previous studies also indicate that monocytes play important roles during infection and disease, similarly to neutrophils. Although specific functions have generally been assigned to each of the cells, similarities and differences in functions necessary for Lm clearance have not previously been investigated. In the present study, phagocytosis, phagosomal containment, bacterial killing and cytokine production by neutrophils and monocytes during Lm infection were studied. Data obtained via in vitro studies show that neutrophils are more effective at Lm uptake, phagosomal containment, and killing than monocytes. However, monocytes were found to be more effective at cytokine production during Lm infection, in vivo. Additionally, the data demonstrated that neutrophils and monocytes are also capable of producing IL-1α, a cytokine that does not yet have a clearly defined role during infection with Lm. Furthermore, a population of monocytes capable of producing both TNF-α and IL-1α, concurrently, were identified. Collectively, these studies highlight the impact of ecSOD activity on neutrophils, as well as the multi-functional capabilities of neutrophils and monocytes, further adding to our knowledge of these innate immune cells.