ABSTRACT
The mucosal surfaces are the first portals of entry for numerous infectious agents. Therefore, mucosal tissues contain the largest immune cell population in the body, tasked with preparing for, or reacting to, a broad range of infectious threats. Treg cells were initially discovered as the T-cell subsets existing in healthy animals that play essential roles in constitutively preventing the development of autoimmune disease and inflammatory bowel disease. The gut microbiota affects the number, function, and T-cell receptor repertoire of intestinal Treg cells. Having adapted to the barrier sites, mucosal Treg cells are phenotypically distinct from those found in other organs. Induced mucosal Treg cells then contribute to the constitutive suppression and prevention of aberrant immune reactions to innocuous environmental factors, such as commensal bacteria and dietary components. Treg cells play a nonredundant role in the maintenance of mucosal immune homeostasis, as illustrated by the fact that defects in the development and/or functional maturation of Treg cells lead to mucosal inflammation.
