Capsular polysaccharide correlates with immune response to the human gut microbe Ruminococcus gnavus

Proc Natl Acad Sci U S A. 2021 May 18;118(20):e2007595118. doi: 10.1073/pnas.2007595118.


Active inflammatory bowel disease (IBD) often coincides with increases of Ruminococcus gnavus, a gut microbe found in nearly everyone. It was not known how, or if, this correlation contributed to disease. We investigated clinical isolates of R. gnavus to identify molecular mechanisms that would link R. gnavus to inflammation. Here, we show that only some isolates of R. gnavus produce a capsular polysaccharide that promotes a tolerogenic immune response, whereas isolates lacking functional capsule biosynthetic genes elicit robust proinflammatory responses in vitro. Germ-free mice colonized with an isolate of R. gnavus lacking a capsule show increased measures of gut inflammation compared to those colonized with an encapsulated isolate in vivo. These observations in the context of our earlier identification of an inflammatory cell-wall polysaccharide reveal how some strains of R. gnavus could drive the inflammatory responses that characterize IBD.

Keywords: Ruminococcus gnavus; capsular polysaccharide; capsule; dendritic cell; inflammation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adult
  • Animals
  • Anti-Bacterial Agents / pharmacology
  • Bacterial Capsules / chemistry
  • Bacterial Capsules / immunology*
  • Bacterial Capsules / ultrastructure
  • Cells, Cultured
  • Child
  • Clostridiales / classification
  • Clostridiales / genetics
  • Clostridiales / immunology*
  • Cytokines / immunology
  • Cytokines / metabolism
  • Female
  • Gastrointestinal Microbiome / drug effects
  • Gastrointestinal Microbiome / genetics
  • Gastrointestinal Microbiome / immunology*
  • Humans
  • Ileum / immunology
  • Ileum / metabolism
  • Ileum / microbiology
  • Immunity / immunology*
  • Inflammatory Bowel Diseases / immunology*
  • Inflammatory Bowel Diseases / microbiology
  • Mice, Inbred C57BL
  • Multigene Family / genetics
  • Phylogeny
  • Polysaccharides / immunology*


  • Anti-Bacterial Agents
  • Cytokines
  • Polysaccharides

Supplementary concepts

  • Ruminococcus gnavus