The gastrointestinal tract as an immunologic organ--state of the art

Mucosal as well as systemic immune responses are extensively influenced by the external environment. The maintenance of the physiologic integrity of the mucosa is complex and depends largely on local immune responses. The physiologic processes of the body are integrated and carefully regulated so that no single event can be considered in the absence of consideration of its interaction with its environment. These principles are perhaps best demonstrated by the models and concepts emerging to explain the apparent idiosyncrasies of the mucosal immune system. How these can be harnessed to promote protection and how they may be manipulated to prevent disease is the subject of extensive current investigation which we have attempted to summarize in this brief review.