Laboratory for Gut Homeostasis
The gut microbiota intimately interacts with the host immune system and influences pathogenesis of several immune disorders. CD4+Foxp3+ Treg cells are the most prominent regulatory cells. They are indispensable for maintaining immune tolerance and are also an emerging therapeutic target for inflammatory bowel diseases (IBD). Treg cells are most abundant in the intestinal mucosa at steady state. In germ-free (GF) or antibiotic-treated mice, the frequency of colonic Treg cells is significantly reduced and interleukin (IL)-10, an immune suppressive cytokine, expression by Treg cells is markedly decreased. We aimed to identify Treg-inducing bacterial strains derived from the human microbiota and test their potential to attenuate diseases such as colitis and allergy, thus enabling clinical translation of our previous findings. Starting from a complete human fecal sample from a healthy Japanese volunteer, which can typically include several hundred strains, a sequence of selection steps was applied to isolate Treg inducing strains. These steps included chloroform treatment, 20,000-fold dilution, and serial transplantation to GF mice using gnotobiotic techniques. These steps allowed us to narrow the number of bacterial strains down to 17 without sacrificing Treg-inducing potency. All 17 strains were successfully isolated, cultured, and stored in frozen stocks. All strains are members of Clostridia clusters IV, XIVa, and XVIII. When these 17 strains were mixed and inoculated into GF mice, they robustly induced Tregs in the colonic LP and displayed full Treg-inducing capacity, comparable to that of a complete fecal microbiome. The 17 strains act as a community to both provide bacterial antigens to T cells and to help polarize the T cells to become Tregs by inducing the generation of a TGF-b-rich environment. Furthermore, oral administration of the cocktail of 17 strains to adult mice attenuated disease in models of colitis and allergic diarrhea.
We published these results in Nature.
Figure: Treg-inducing 17 strains of Clostridia
The image is scanning electron micrograph showing the proximal colon of germ-free mice colonized with the regulatory T cell-inducing human Clostridia strains that we have isolated (magnification ~5,000x). The community of Clostridia strains induces regulatory T cells and contributes to suppression of unfavorable inflammation and allergic responses.