Mucosal immunity of the gastrointestinal tract and oral tolerance

To guard against disease, mucosal surfaces of the intestinal, respiratory and urogenital tracts are protected by a carefully regulated system of defenses known as the mucosal immune system. The hallmark of mucosal immunity is secretory IgA which can prevent infection and remove antigen crossing the mucosal barrier. IgE responses are also associated with mucosal immunity. In addition, a lymphocyte population resides within the mucosal epithelium, possibly forming a 'first line of defense' against infections. Oral administration of antigen can also induce antigen-specific peripheral immune tolerance, known as oral tolerance. Oral tolerance may prevent allergies, inflammation and other problems due to responses against food antigens or gut flora. It also has a tremendous potential in treating autoimmune and inflammatory diseases. The aim of this article is to present an overview of mucosal immunity. Specifically, the focus is on immunity along the gastrointestinal tract; however, similar principles are active in other mucosal tissues.