ABSTRACT
The nature of the immune system in the intestinal tract is unique by virtue of its requirement to co-exist intimately with the external environment. The emphasis, therefore, is on rigorous control of immunologic responses in the GI tract, to dietary antigens, luminal bacteria and viruses. When control mechanisms are disrupted, the result is a series of chronic inflammatory diseases of the bowel, specifically ulcerative colitis (UC) and Crohn’s disease (CD). These diseases affect over 2 million Americans and are quite prevalent in Europe and Scandinavia. While there is no clear-cut inheritance pattern, the high incidence of disease segregation within families suggests a genetic predisposition (1-7). A number of etiologies have been proposed for these diseases yet, as with many chronic inflammatory diseases, no specific pathogenic mechanism has been clearly defined. In this chapter, we will describe the unique features of each disease and discuss some of the immune and non-immune theories of disease development. The bulk of the chapter will be devoted to the current controversies in the etiopathogenesis of IBD: a directed autoimmune response against elements within the mucosa-associated lymphoid tissue versus immune dysregulation resulting in chronic inflammation and secondary nonspecific tissue injury.
