The role of the immune system in inflammatory bowel disease

Although the etiologic agents for Crohn's disease and ulcerative colitis remain unknown, there is increasing evidence that immunologic and inflammatory mechanisms are important in the pathogenesis of these diseases. The most striking and most relevant immunologic changes are found in the inflamed portions of the intestine rather than in the peripheral blood. Among the immunologic changes seen in the affected intestine are both a generalized increase in spontaneous immunoglobulin production and specific increases in certain immunoglobulin subclasses. The major clinical and histologic changes seen in the intestine in inflammatory bowel disease appear to be primarily products of a nonspecific inflammatory activation. This inflammatory response is mediated by soluble mediators of inflammation; in particular, leukotriene B₄ appears to play a major role in neutrophil recruitment in inflammatory bowel disease.