The intestinal cholinergic anti-inflammatory pathway.

The main task of the immune system is to distinguish and respond accordingly to 'danger' or 'non-danger' signals. This is of critical importance in the gastrointestinal tract in which immune cells are constantly in contact with food antigens, symbiotic microflora and potential pathogens. This complex mixture of food antigens and symbionts are essential for providing vital nutrients, so they must be tolerated by the intestinal immune system to prevent aberrant inflammation. Therefore, in the gut the balance between immune activation and tolerance should be tightly regulated to maintain intestinal homeostasis and to prevent hypersensitivity to harmless luminal antigens. Loss of this delicate equilibrium can lead to abnormal activation of the intestinal immune system resulting in devastating gastrointestinal disorders such as inflammatory bowel disease (IBD). Recent evidence supports the idea that the central nervous system interacts dynamically via the vagus nerve with the intestinal immune system to modulate inflammation through humoral and neural pathways, using a mechanism also referred to as the intestinal cholinergic anti-inflammatory pathway. In this review, we will focus on the current understanding of the mechanisms and neuronal circuits involved in the intestinal cholinergic anti-inflammatory pathway. Further investigation on the crosstalk between the nervous and intestinal immune system will hopefully provide new insights leading to the identification of innovative therapeutic approaches to treat intestinal inflammatory diseases.