good bacteria & immune system functioning………
“A mounting body of evidence indicates that diverse microbial metabolites profoundly regulate the immune system via host receptors and other target molecules.”
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“Immune cells express metabolite‐specific receptors such as P2X7, GPR41, GPR43, GPR109A, aryl hydrocarbon receptor precursor (AhR), pregnane X receptor (PXR), farnesoid X receptor (FXR), TGR5 and other molecular targets.”
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“Microbial metabolites and their receptors form an extensive array of signals to respond to changes in nutrition, health and immunological status. As a consequence, microbial metabolite signals contribute to nutrient harvest from diet, and regulate host metabolism and the immune system.”
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“Importantly, microbial metabolites bidirectionally function to promote both tolerance and immunity to effectively fight infection without developing inflammatory diseases. In pathogenic conditions, adverse effects of microbial metabolites have been observed as well. Key immune‐regulatory functions of the metabolites, generated from carbohydrates, proteins and bile acids, are reviewed in this article.”
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CH.Kim
Immune regulation by microbiome metabolites
Immunology — Volume 154 #2 — June 2018 — page 220

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good bacteria -vs- multiple sclerosis…………
“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.”
“Recent studies in experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis, 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.”
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“Conversely, some commensal bacteria and their antigenic products can protect against inflammation within the central nervous system.”
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“Specific components of the gut microbiome have been implicated in the production of pro‐inflammatory cytokines and subsequent generation of Th17 cells. Similarly, commensal bacteria and their metabolites can also promote the generation of regulatory T‐cells, contributing to immune suppression.”
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“Short‐chain fatty acids may induce Treg either by G‐protein‐coupled receptors or inhibition of histone deacetylases. Tryptophan metabolites may suppress inflammatory responses by acting on the aryl hydrocarbon receptor in T‐cells or astrocytes.”
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“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.”
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“This review discusses new aspects of host–microbiota interaction and the immune system with a special focus on multiple sclerosis as a prototype T‐cell‐mediated autoimmune disease of the central nervous system.”
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S.H.Aiden, et al
Impacts of microbiome metabolites on immune regulation and autoimmunity
Immunology — Volume 154 #2 — June 2018 — page 230