The biology of oral tolerance and issues related to oral vaccine design.

Intestinal tissues are continuously exposed to tremendous amount of foreign material, either beneficial or harmful. Although strong protective immune responses are required to clear harmful pathogen infections, similar responses against food antigen can lead to harmful inflammation. Therefore, oral tolerance or unresponsiveness against dietary and commensal bacteria is also important to maintain tissue integrity by preventing harmful inflammatory responses in the intestine. While oral tolerance is an important phenomenon to protect unnecessary inflammatory responses, it presents an obstacle in the development of oral vaccines. Therefore an understanding of the gut immune system and the induction of oral tolerance is important. This review will focus on important aspects of the intestinal immune system and how immune responses in the intestine maintain homeostasis via oral tolerance. Also it will provide new insights in the development of oral vaccines.