Macrophages in inflammatory bowel disease.

Blood monocytes which differentiate into tissue macrophages, are unique in that they can not only initiate immune responses but can also be effector cells which contribute to the resolution of these responses. There is no single activation phenotype, and macrophages can be induced to differentiate into cells that either exacerbate or inhibit acute inflammation. Similarly, these cells can promote, deviate or suppress adaptive immune responses. This review focuses on the mechanisms that have been implicated in the recruitment, activation and differentiation of inflammatory monocytes/macrophages in chronic inflammatory bowel diseases, i.e. ulcerative colitis and Crohn's disease. These mechanisms might provide attractive targets for novel therapies.