Date of Award
Master of Science in Medical Sciences (MSMS)
Maria J. Fernandez-Cabezudo
Inflammation is a crucial defence mechanism that protects the body from the effect of invading pathogens. However, the inflammatory response needs to be controlled in order to avoid systemic manifestations with serious consequences to the host. Accumulating evidence indicates that the inflammatory response is tightly regulated through immunological and neural pathways. Previously, it has been demonstrated that cholinergic stimulation by paraoxon, a specific and irreversible inhibitor of acetylcholinesterase (AChE), improved survival in mice following oral infection with virulent Salmonella enterica serovar Typhimurium (S. Typhimurium). However, paraoxon is an organophosphorus compound unsuited for human use. In this study, the main objective is to investigate the efficiency of rivastigmine, an FDA-approved inhibitor of AChE, on murine mucosal defences in the gastrointestinal (GI) tract against Salmonella infections. Results show that cholinergic stimulation with rivastigmine enhanced host survival following an oral-route infection, and this correlated with lower bacterial load in systemic organs, including the liver and spleen. Interestingly, while bacterial loads in systemic organs were decreased, bacterial loads were higher in intestinal content and feces compared to the saline control group, suggesting enhanced bacterial shedding in the GI tract. Morphological analysis of the small intestine (ileum) showed that rivastigmine induced the degranulation of goblet cells and Paneth cells, two specialized secretory cells involved in innate immunity, and demonstrated a significant increase in the thickness of the mucin layer in these mice. An immunohistochemical study of the immune population present in the intestinal mucosa revealed that rivastigmine treatment resulted in minor changes in the lymphoid population in the epithelium (intraepithelial lymphocytes or IELs) and lamina propria (LP). A comparative flow cytometric analysis of the different leukocytic populations present in the two isolated compartments of the intestinal mucosa (IEL and LP) following either paraoxon or rivastigmine treatment, demonstrated that only paraoxon induced an increase in the CD8⁺ population in the LP. Moreover, the intestinal epithelium of rivastigmine-treated mice presented a decrease in CD8⁺γδTCR⁺ cells. These findings indicate that rivastigmine-mediated cholinergic modulation increases the innate defence mechanisms at the level of the intestinal lumen, delaying the bacterial translocation from the intestine to LP and systemic organs, ultimately leading to enhanced
initial protection against a lethal bacterial infection. However, complete protection in this model appears to require the recruitment of professional T cells to the LP, which was only observed after treatment with irreversible AChE inhibitors, like paraoxon. The data highlight the crucial interactions between neural and immune systems that act at the GI mucosal interface to protect the host against invading pathogens.
Al-Mansori, Alreem Abdulaziz Al-Dhalali, "MODULATION OF ANTI-MICROBICAL DEFENSES IN THE GASROINTESTINAL TRACT BY ACETYLCHOLINESTERASE INHIBITORS." (2020). Theses. 901.