The group around Hiroshi Ohno demonstrated in germ-free mice that butyrate, a by-product of dietary fiber digestion by gut microbes, acted on naive T-cells promoting their differentiation into Treg cellse via epigenetic changes.
Yukihiro FURUSAWA et al., Nature doi:10.1038/nature12721
RIKEN team: butyrate formed in the gut to act as an epigenetic switch to boost immune system