Genes and environment: how will our concepts on the pathophysiology of IBD develop in the future?

Inflammatory bowel disease (IBD) has long been known to arise from the interplay between host and environmental factors. From this, a picture is currently emerging in which IBD is likely the result of a continuum of diseases that range from mono- and oligogenically inherited familial forms at one extreme to sporadic forms at the other extreme, which are polygenic in origin and strongly influenced by environmental factors and especially those of infectious origin. The recent expansion of knowledge on the genetic underpinning of IBD has revealed several converging and inter-related functional host pathways that are central to the pathogenesis of these disorders. These include pathways such as autophagy, intracellular bacterial sensing and the unfolded protein response, which play specific roles at the interface between the host and the highly complex microbial communities within the intestines. As such they focus on the functional relationship between the intestinal epithelium and the unique microbial and immune environments along its luminal and abluminal surfaces. Thus, the genetic and environmental factors which are relevant to IBD seem to have the common property of influencing disease by virtue of their specific impact upon the functional relationship between these microbial communities and the intestinal immune system.