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      Commensal microbiota affects ischemic stroke outcome by regulating intestinal γδT cells

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          Abstract

          Commensal gut bacteria impact the host immune system and can influence disease processes in several organs, including the brain. However, it remains unclear whether the microbiota has an impact on the outcome of acute brain injury. Here we show that antibiotic-induced alterations in the intestinal flora reduces ischemic brain injury in mice, an effect transmissible by fecal transplants. Intestinal dysbiosis alters immune homeostasis in the small intestine leading to an increase in regulatory T cells and a reduction in IL-17 + γδ T cells, through altered dendritic cell activity. Dysbiosis suppresses trafficking of effector T cells from the gut to the leptomeninges after stroke. Interleukin-10 (IL-10) and IL-17 are required for the neuroprotection afforded by intestinal dysbiosis. The findings reveal a previously unrecognized gut-brain axis and the impact of the intestinal flora and meningeal IL-17 + γδ T cells on ischemic injury.

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          Most cited references45

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          An immunomodulatory molecule of symbiotic bacteria directs maturation of the host immune system.

          The mammalian gastrointestinal tract harbors a complex ecosystem consisting of countless bacteria in homeostasis with the host immune system. Shaped by evolution, this partnership has potential for symbiotic benefit. However, the identities of bacterial molecules mediating symbiosis remain undefined. Here we show that, during colonization of animals with the ubiquitous gut microorganism Bacteroides fragilis, a bacterial polysaccharide (PSA) directs the cellular and physical maturation of the developing immune system. Comparison with germ-free animals reveals that the immunomodulatory activities of PSA during B. fragilis colonization include correcting systemic T cell deficiencies and T(H)1/T(H)2 imbalances and directing lymphoid organogenesis. A PSA mutant of B. fragilis does not restore these immunologic functions. PSA presented by intestinal dendritic cells activates CD4+ T cells and elicits appropriate cytokine production. These findings provide a molecular basis for host-bacterial symbiosis and reveal the archetypal molecule of commensal bacteria that mediates development of the host immune system.
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            Individuality in gut microbiota composition is a complex polygenic trait shaped by multiple environmental and host genetic factors.

            In vertebrates, including humans, individuals harbor gut microbial communities whose species composition and relative proportions of dominant microbial groups are tremendously varied. Although external and stochastic factors clearly contribute to the individuality of the microbiota, the fundamental principles dictating how environmental factors and host genetic factors combine to shape this complex ecosystem are largely unknown and require systematic study. Here we examined factors that affect microbiota composition in a large (n = 645) mouse advanced intercross line originating from a cross between C57BL/6J and an ICR-derived outbred line (HR). Quantitative pyrosequencing of the microbiota defined a core measurable microbiota (CMM) of 64 conserved taxonomic groups that varied quantitatively across most animals in the population. Although some of this variation can be explained by litter and cohort effects, individual host genotype had a measurable contribution. Testing of the CMM abundances for cosegregation with 530 fully informative SNP markers identified 18 host quantitative trait loci (QTL) that show significant or suggestive genome-wide linkage with relative abundances of specific microbial taxa. These QTL affect microbiota composition in three ways; some loci control individual microbial species, some control groups of related taxa, and some have putative pleiotropic effects on groups of distantly related organisms. These data provide clear evidence for the importance of host genetic control in shaping individual microbiome diversity in mammals, a key step toward understanding the factors that govern the assemblages of gut microbiota associated with complex diseases.
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              Pivotal role of cerebral interleukin-17-producing gammadeltaT cells in the delayed phase of ischemic brain injury.

              Lymphocyte recruitment and activation have been implicated in the progression of cerebral ischemia-reperfusion (I/R) injury, but the roles of specific lymphocyte subpopulations and cytokines during stroke remain to be clarified. Here we demonstrate that the infiltration of T cells into the brain, as well as the cytokines interleukin-23 (IL-23) and IL-17, have pivotal roles in the evolution of brain infarction and accompanying neurological deficits. Blockade of T cell infiltration into the brain by the immunosuppressant FTY720 reduced I/R-induced brain damage. The expression of IL-23, which was derived mostly from infiltrated macrophages, increased on day 1 after I/R, whereas IL-17 levels were elevated after day 3, and this induction of IL-17 was dependent on IL-23. These data, together with analysis of mice genetically disrupted for IL-17 and IL-23, suggest that IL-23 functions in the immediate stage of I/R brain injury, whereas IL-17 has an important role in the delayed phase of I/R injury during which apoptotic neuronal death occurs in the penumbra. Intracellular cytokine staining revealed that gammadeltaT lymphocytes, but not CD4(+) helper T cells, were a major source of IL-17. Moreover, depletion of gammadeltaT lymphocytes ameliorated the I/R injury. We propose that T lymphocytes, including gammadeltaT lymphocytes, could be a therapeutic target for mitigating the inflammatory events that amplify the initial damage in cerebral ischemia.
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                Author and article information

                Journal
                9502015
                8791
                Nat Med
                Nat. Med.
                Nature medicine
                1078-8956
                1546-170X
                2 March 2016
                28 March 2016
                May 2016
                28 September 2016
                : 22
                : 5
                : 516-523
                Affiliations
                [1 ]Feil Family Brain and Mind Research Institute, Weill Cornell Medical College, New York, NY, USA
                [2 ]Immunology Program and Infectious Disease Service, Memorial Sloan-Kettering Cancer Center, New York, NY, USA
                [3 ]Immunology and Microbial Pathogenesis Program, Weill Cornell Graduate School of Medical Sciences, New York, NY, USA
                [4 ]Lucille Castori Center for Microbes, Inflammation and Cancer, Memorial Sloan Kettering Cancer Center, New York, NY, USA
                [5 ]Infectious Diseases Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, NY, USA
                Author notes
                Correspondence should be addressed to J.A. ( joa2006@ 123456med.cornell.edu )
                [6]

                These authors contributed equally to this work.

                Article
                NIHMS761041
                10.1038/nm.4068
                4860105
                27019327
                95247c60-0347-4f52-89d3-f2a2b057f98a

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