Pathogenic T cell subsets in allergic and chronic inflammatory bowel disorders

Homeostasis in the gastrointestinal tract relies on a sensitive equilibrium between permissive and protective functions. This is closely reflected in the regulation of the intestinal immune system and especially T cells in the gut. This balance, however, is susceptible to disturbances as demonstrated by pathological conditions like food allergy, celiac disease, or inflammatory bowel disease. In these allergic and chronic inflammatory bowel disorders, luminal antigens get access to the lamina propria where they trigger a dysregulated immune response with crucial involvement of different T cell subsets. We will begin this review with some comprehensive remarks on current concepts on the pathogenesis of these diseases before taking a closer look at the life cycle of intestinal T cells consisting of priming, homing, differentiation and proliferation and apoptosis respectively. Subsequently we will discuss the specific implication of distinct T cell subsets in allergic and chronic inflammatory conditions of the gastrointestinal tract in detail and comment on current and future approaches to targeted therapy in this context.