Immunology
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The importance of the gut microbiome in the regulation of non-infectious diseases has earned unprecedented interest from biomedical researchers. Widespread use of next-generation sequencing techniques has prepared a foundation for further research by correlating the presence of specific bacterial species with the onset or severity of a disease state, heralding paradigm-shifting results. ⋯ This review focuses on the immunoregulatory functionality of microbial metabolites, which can cross the BBB and mediate their effects directly on immune cells within the CNS and/or indirectly through modulating the response of peripheral T cells to stimulate or inhibit pro-inflammatory chemokines and cytokines, which in turn regulate the autoimmune response in the CNS. Although more research is clearly needed to directly link the changes in gut microbiome with neuroinflammation, focusing research on microbiota that produce beneficial metabolites with the ability to attenuate chronic inflammation systemically as well as in the CNS, can offer novel preventive and therapeutic modalities against a wide array of inflammatory and autoimmune diseases.
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A vast number of studies have demonstrated a remarkable role for the gut microbiota and their metabolites in the pathogenesis of inflammatory diseases, including multiple sclerosis (MS). Recent studies in experimental autoimmune encephalomyelitis, an animal model of MS, have revealed that modifying certain intestinal bacterial populations may influence immune cell priming in the periphery, resulting in dysregulation of immune responses and neuroinflammatory processes in the central nervous system (CNS). Conversely, some commensal bacteria and their antigenic products can protect against inflammation within the CNS. ⋯ Tryptophan metabolites may suppress inflammatory responses by acting on the aryl hydrocarbon receptor in T-cells or astrocytes. Interestingly, secretion of these metabolites can be impaired by excess consumption of dietary components, such as long-chain fatty acids or salt, indicating that the diet represents an environmental factor affecting the complex crosstalk between the gut microbiota and the immune system. This review discusses new aspects of host-microbiota interaction and the immune system with a special focus on MS as a prototype T-cell-mediated autoimmune disease of the CNS.