These interleukin 17 (IL-17)-producing T cells have a yin and yang effect on gut inflammation: on one hand, in their absence or in the absence of IL-17 signaling, gut dysbiosis is increased, but on the other hand, Th17 cells are associated with inflammatory bowel disease (IBD) and can exacerbate arthritis in mice (55, 56). This evidence concerns the gene IL17A and arthritic joint disease.