gnavus comprises at least two clades, one of which is enriched in CD patients and produces inflammatory polysaccharides, which induce the production of TNF-α by dendritic cells via TLR4.28,29 Although the immunostimulatory effects of R. gnavus 131A1 isolated herein were weak, R. gnavus may facilitate the colonization of other bacteria associated with CD pathogenesis. Here, TLR4 is linked to Cowden disease.