The gut mucosa as a site for induction of regulatory T-cells

Regulatory T lymphocytes (Tregs) are specialized for immune suppression and are important regulators of the immune response in various settings. Tregs actively suppress enteroantigen-reactive cells and contribute to the maintenance of intestinal immune homeostasis. Distinct Treg subsets coexist in the intestinal mucosa and mesenteric lymph nodes. Disturbances in Treg number and function are associated with immune-mediated disorders. Therefore, Tregs are potential targets for immunotherapies. The gut mucosal immune system is the largest lymphoid organ in the body. This site has continuous antigenic challenges from food antigens, antigens of the abundant normal bacterial flora, and pathogens. Despite this constant antigenic stimulation, controlled inflammatory responses and suppression of inflammation appear to be the rule. The gut immune system differentiates the antigenic signals from the high background noise of food and bacterial antigens. This tight regulation required to maintain homeostasis is achieved through multiple non-immune and immune factors. Oral tolerance is a mechanism in which the gastrointestinal immune system inhibits or promotes its reaction toward an orally administered antigen. Mucosal tolerance is attractive as an approach to the treatment of autoimmune and inflammatory diseases; the benefits of using an oral tolerance approach are: lack of toxicity, ease of administration over time, and antigen-specific mechanisms of action. Multiple mechanisms of tolerance are induced by oral antigen administration. Recent data suggest that oral antigen administration of antigens may promote activation of different types of regulatory T lymphocytes, enabling treatment of immune mediated disorders. This review summarizes the recent data on induction of regulatory T-cells by oral antigen administration as a possible mechanism of oral tolerance.