-, comprising green tea leaves fermented with , increases regulatory T cell production in mice and humans.

Green tea leaves fermented with (-) are a health food containing live . In this study, we examined the effects of - on the immune system and the enteric environment. First, we designed a clinical trial; after ingesting - daily for 28 days, blood parameters and the fecal composition of the participants were analyzed. Similarly, mice were administered (oral administration) with - suspension or its vehicle for 14 days. Thereafter, both humans and mice were examined by analyzing their immune cell phenotypes and intestinal microbiota. Regulatory T cell (Treg) numbers were significantly increased after administering -. An increase of subcluster XIVa, that were known to be rich in butyrate-producing bacterium, was observed in human feces, but not in mice. These results suggest that - has the ability to increase Treg production in both humans and mice, irrespective of the presence of enteric butyrate.