Oral tolerance for treatment of GI inflammation

Tolerance is defined as a mechanism by which a potentially injurious immune response is prevented, suppressed, or shifted to a non-injurious type of response. Immune tolerance was traditionally divided into two categories: central tolerance, whereby tolerance is inducedviapresentation of foreign antigens in the thymus; and peripheral tolerance where tolerance is induced outside the thymus [1]. Tolerance can also be divided into “dominant” and “passive” types of tolerance based on the mechanisms of tolerance induction. A “dominant” type of tolerance involves production of suppressor cells that suppress the anti-foreign antigen immune response, and which can be transferred. A “passive” type of immune tolerance involves immune ignorance or clonal deletion and is non-transferable [1]. Tolerance is today viewed as an active process. The current understanding of immunological tolerance does not simply distinguish between self and non-self, but also reacts to danger signals that confront the immune system [2, 3]. Auto reactive cells, present in all individuals and reacting with brain antigens, thyroglobulin, serum albumin, collagen and other auto-antigens, are not deleted. These cells, under normal conditions, remain harmless. Cells reactive with self may have an important function in maintaining tissue homeostasis. Thus, immunological tolerance, requiring an active process that functions during the entire life of the organism, cannot rely solely on neonatal deletion.