AUTHOR=Patterson Angela M. , Mulder Imke E. , Travis Anthony J. , Lan Annaig , Cerf-Bensussan Nadine , Gaboriau-Routhiau Valerie , Garden Karen , Logan Elizabeth , Delday Margaret I. , Coutts Alistair G. P. , Monnais Edouard , Ferraria Vanessa C. , Inoue Ryo , Grant George , Aminov Rustam I. 

TITLE=Human Gut Symbiont Roseburia hominis Promotes and Regulates Innate Immunity

JOURNAL=Frontiers in Immunology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2017.01166

DOI=10.3389/fimmu.2017.01166

ISSN=1664-3224

ABSTRACT=<sec id="ST1"><title>Objective</title><p><italic>Roseburia hominis</italic> is a flagellated gut anaerobic bacterium belonging to the <italic>Lachnospiraceae</italic> family within the Firmicutes phylum. A significant decrease of <italic>R. hominis</italic> colonization in the gut of ulcerative colitis patients has recently been demonstrated. In this work, we have investigated the mechanisms of <italic>R. hominis</italic>–host cross talk using both murine and <italic>in vitro</italic> models.</p></sec><sec id="ST2"><title>Design</title><p>The complete genome sequence of <italic>R. hominis</italic> A2-183 was determined. C3H/HeN germ-free mice were mono-colonized with <italic>R. hominis</italic>, and the host–microbe interaction was studied using histology, transcriptome analyses and FACS. Further investigations were performed <italic>in vitro</italic> and using the TLR5KO and DSS-colitis murine models.</p></sec><sec id="ST3"><title>Results</title><p>In the bacterium, <italic>R. hominis</italic>, host gut colonization upregulated genes involved in conjugation/mobilization, metabolism, motility, and chemotaxis. In the host cells, bacterial colonization upregulated genes related to antimicrobial peptides, gut barrier function, toll-like receptors (TLR) signaling, and T cell biology. CD4<sup>+</sup>CD25<sup>+</sup>FoxP3<sup>+</sup> T cell numbers increased in the <italic>lamina propria</italic> of both mono-associated and conventional mice treated with <italic>R. hominis</italic>. Treatment with the <italic>R. hominis</italic> bacterium provided protection against DSS-induced colitis. The role of flagellin in host–bacterium interaction was also investigated.</p></sec><sec id="ST4"><title>Conclusion</title><p>Mono-association of mice with <italic>R. hominis</italic> bacteria results in specific bidirectional gene expression patterns. A set of genes thought to be important for host colonization are induced in <italic>R. hominis</italic>, while the host cells respond by strengthening gut barrier function and enhancing Treg population expansion, possibly <italic>via</italic> TLR5-flagellin signaling. Our data reveal the immunomodulatory properties of <italic>R. hominis</italic> that could be useful for the control and treatment of gut inflammation.</p></sec>