Project description:The gastrointestinal tract of mammals is inhabited by hundreds of distinct species of commensal microorganisms that exist in a mutualistic relationship with the host. The process by which the commensal microbiota influence the host immune system is poorly understood. We show here that colonization of the small intestine of mice with a single commensal microbe, segmented filamentous bacterium (SFB), is sufficient to induce the appearance of CD4+ T helper cells that produce IL-17 and IL-22 (Th17 cells) in the lamina propria. SFB adhere tightly to the surface of epithelial cells in the terminal ileum of mice with Th17 cells but are absent from mice that have few Th17 cells. Colonization with SFB was correlated with increased expression of genes associated with inflammation, anti-microbial defenses, and tissue repair, and resulted in enhanced resistance to the intestinal pathogen Citrobacter rodentium. Control of Th17 cell differentiation by SFB may thus establish a balance between optimal host defense preparedness and potentially damaging T cell responses. Manipulation of this commensal-regulated pathway may provide new opportunities for enhancing mucosal immunity and treating autoimmune disease.
Project description:Vertebrates typically harbor a rich gastrointestinal microbiota, which has co-evolved with the host over millennia and is essential for several of its physiological functions, in particular maturation of the immune system. Recent studies have highlighted the importance of a single bacterial species, segmented filamentous bacteria (SFB), in inducing a robust T helper (Th)17 population in the small intestinal lamina propria (SI-LP) of the mouse gut. Consequently, SFB can promote IL-17-dependent immune and autoimmune responses, gut-associated as well as systemic, including inflammatory arthritis and experimental autoimmune encephalomyelitis. Here, we exploit the incomplete penetrance of SFB colonization of NOD mice in our animal facility to explore its impact on the incidence and course of type-1 diabetes in this prototypical, spontaneous model. There was a strong co-segregation of SFB-positivity and diabetes protection in females, but not in males, which remained relatively disease-free regardless of the SFB status. In contrast, insulitis did not depend on SFB colonization. SFB-positive, but not SFB-negative, females had a substantial population of Th17 cells in the SI-LP, which was the only significant, repeatable difference in the examined T cell compartments of the gut, pancreas or systemic lymphoid tissues. Th17 signature transcripts dominated the very limited SFB-induced molecular changes detected in SI-LP CD4+ T cells. Thus, a single bacterium, and the gut immune system alterations associated with it, can either promote or protect from autoimmunity in predisposed mouse models, likely reflecting their variable dependence on different Th subsets.
Project description:H3K27Ac enrichment in intestinal epithelial cells from intestine of germ-free and segmented filamentous bacteria (SFB)-monoassociated mice. Intestinal epithelial cells were harvested from the terminal ileum of germ-free or SFB mice. Chromatin immunoprecipitation was performed with anti-H3K27Ac. Sequencing was performed using the Illumina HiSeq2500. Reads were mapped to the mm10 genome using Bowtie.