New and emerging therapies for inflammatory bowel disease.

SD One of the major discoveries in Crohn’s disease over the past few years has been the realization that the innate immune system plays a key role in the disease mechanism. Following an initial defect in the innate immune system, there is overreaction of the adaptive immune system, which leads to the classical inflammatory response that has been described in these patients. Ulcerative colitis has classically been described as a disease involving T helper 2 cells and increased levels of interleukin (IL)-13, which seems to be a key cytokine, but the pathophysiology of ulcerative colitis has not been studied as much as that of Crohn’s disease. Finally, another concept that is very relevant is that most diseases are dependent not only on T cells but also on nonimmune cells. While a primary defect in epithelial cells seems to be a key step in the disease process, the development of inflammatory bowel disease (IBD) also depends on the immune response and on nonimmune cells such as fibroblasts and endothelial cells.