Cell surface polysaccharides of induce the generation of Foxp3 regulatory T cells.

Dysregulation of intestinal microflora is linked to inflammatory disorders associated with compromised immunosuppressive functions of Foxp3 T regulatory (T) cells. Although mucosa-associated commensal microbiota has been implicated in T generation, molecular identities of the "effector" components controlling this process remain largely unknown. Here, we have defined as a potent inducer of Foxp3 T cells with diverse T cell receptor specificity to dietary antigens, commensal bacteria, and itself. Cell surface β-glucan/galactan (CSGG) polysaccharides of were identified as key components responsible for T induction. CSGG efficiently recapitulated the activity of whole bacteria and acted via regulatory dendritic cells through a partially Toll-like receptor 2-mediated mechanism. T cells induced by or purified CSGG display stable and robust suppressive capacity toward experimental colitis. By identifying CSGG as a functional component of T-inducing bacteria, our studies highlight the immunomodulatory potential of CSGG and CSGG-producing microbes.