T cell immunity to oral allergens

Considerable light has been thrown on the mechanisms of oral tolerance (or, more correctly, orally-induced systemic tolerance) in the past 12-18 month s. While it is very clear that T cell anergy and apoptosis can occur after being fed antigen, a major pathway that has been described in different mod els is the induction of regulatory T cells which secrete transforming growt h factor beta. These cells have been designated Th3 cells but their relatio n to the in-vitro-generated Tr cells, which inhibit tissue-damaging T cell responses in the gut mucosa, is not known. An important discovery is that f ood antigens have major systemic effects on T cells, similar in many ways t o those seen following intravenous injection of soluble antigens. This conc eptually moves us away from the notion that there is something special abou t mucosal (compared to systemic) lymphoid tissue to the notion that ii is t he type of antigens seen in the gut (i.e, digested, soluble polypeptides) w hich dictates the types of response seen there. After initial excitement, c linical trials using oral tolerance to treat autoimmune disease have been s omewhat disappointing.