Is There a Primary Defect in the Host Defense Mechanism in IBD?

Abstract

There have been many theories over the years as to the etiology of inflammatory bowel disease, but the main theories revolve around an infectious versus immune etiology. The two are not entirely mutually exclusive however, because even the proponents of an infectious etiology acknowledge that the immune system must be involved in the pathogenesis. However, they see the immune system as responding appropriately to rid the body of whatever the infectious agent might be and causing tissue destruction only secondarily. The immune hypothesis holds that there is no single infectious agent responsible for either ulcerative colitis or Crohn’s disease, although immune reactions toward microorganisms commonly present in the lumen of the bowel may well play a role in the disease. The immune reaction in this hypothesis is seen as inappropriate and excessive. I believe the weight of evidence greatly favors an immune etiology over an infectious one. This does not imply that genetic and environmental factors do not play a role because epidemiologic data indicates that they do. However, these factors most likely exert their effects through the immune system.