Changes in the gut microbiome have long been linked with Crohn's disease and other forms of inflammatory bowel disease, but the biology behind those links has remained murky. Researchers at the Broad Institute, Massachusetts General Hospital, and Harvard Medical School have now found that one bacterium, Ruminococcus gnavus, which is associated with Crohn’s disease, releases a certain type of polysaccharide (or a chain of sugar molecules) that triggers an immune response. 

Link to full Broad Institute release on study co-authored by MGH physician Ramnik Xavier.