Basic and clinical overview of the mucosal immune system.

What is clearly evolving today is the concept of mucosal immunity as a discrete system that performs novel immunologic tasks and is uniquely regulated. Although many of the same factors exist in both the systemic and the mucosal immune systems, their structural and functional properties are tailored to different microenvironments. Because it is persistently flooded by a massive antigen load from the environment, the gut-associated lymphoid tissue must continually maintain a delicate balance between active immunity, tolerance, and suppression of immune responses. Homeostasis is essential. Dysfunction of the mucosa's complex immunoregulatory mechanisms may give rise to a diverse panoply of illnesses, including inflammatory bowel disease and celiac sprue. Current research on mucosal interactions at the molecular and cellular level is revolutionizing our understanding of the underlying pathophysiology of these diseases, and may guide their future diagnosis, therapy, and prevention. Indeed, the current wave of investigation has carried the field beyond the realm of mucosal disease, allowing for the harnessing of special mucosal phenomena in the development of new therapeutic modalities and in the treatment of an even wider array of systemic disorders.