Neutrophil Extracellular Traps in Bacterial Meningitis: A novel therapeutic target for treatment.

• Autor(a) principal: Cardoso, José Francisco Pereira
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10348/8523
• topic: Neutrophil extracellular Traps; meningite bacteriana

Streptococcus pneumoniae bacterial meningitis is currently a high impact disease with a mortality rate of 30% and survivors are highly prone to sequelae. Bacterial meningitis is a bacterial infection of the central nervous system (CNS) that results in inflammation of the protective fluid-filled layer, called the meninges, that envelops the brain and spinal cord. The diagnosis of acute bacterial meningitis (ABM) is a major problem due to the difficulty to discern it from viral meningitis (VM) at disease onset. Neutrophils are the first immune cells to react to an infection and they play a primary role in the organism’s response to invading pathogens. Neutrophil extracellular trap (NET) formation, or NETosis, is a process in which neutrophils release a web-like structure to the extracellular space, composed of a DNA backbone and antimicrobial proteins in order to ensnare and kill pathogens. Previous research in our group found that NETs are present specifically in bacterial meningitis patient samples but not in other forms of meningitis or trauma. Since NETs are known to trap and kill bacteria we therefore hypothesize in this study that NETs in the cerebrospinal fluid (CSF) influence bacterial killing during meningitis. In order to inspect the role of NETosis in vivo, we developed a rat model of bacterial meningitis using a clinical isolate of S. pneumoniae. Rats with S. pneumoniae meningitis showed a significant increase of NETosis compared to the saline vehicle controls. To determine whether NETs affect bacterial killing in vitro DNase I, an enzyme that dissolves the DNA backbone of NETs, was infused into the meninges of infected rats. DNase I was able to clear NETs from the CSF and also resulted in a significantly decreased bacterial load in the brain. This effect was observed even if DNase I was administered 10 hours after the infection and even if it was administered intravenously. To study the mechanism of this bacterial killing by DNase, we used an in vitro model of NETosis in isolated human neutrophils. First, to determine whether the formation of NETs can be generalized to other types of bacterial meningitis we analyzed the ability of different meningeal pathogen strains to induce NETosis in vitro and determined that most clinically isolated meningeal pathogens were able to induce NETosis. To test whether innate neutrophil killing mechanisms play a role in DNase-mediated bacterial killing, we inhibited neutrophil phagocytosis and oxidative burst using specific inhibitors and found that this almost completely prevented bacterial killing. Assays measuring neutrophil oxidative burst and phagocytosis also indicated that these processes are increased in the presence of DNase. Our results indicate that NET formation hinders the clearance of bacterial infection. Treatment with DNase I promotes other innate neutrophil bacterial killing mechanisms. DNase I as well as other NET disrupting compounds might be a potential target for therapeutic treatment of bacterial meningitis. In the future detection of NETosis could be a good way to diagnose early bacterial meningitis discerning it from viral meningites.