Vagus nerve-mediated intestinal immune regulation: therapeutic implications of inflammatory bowel diseases

The pathophysiology of inflammatory bowel diseases (IBDs) involves immunological, genetic and environmental factors. Through its ability to sense environmental stimuli, the autonomic nervous system plays a key role in the development and persistence of IBDs. The vagus nerve (VN), which contains sensory and motor neurons, travels throughout the body to innervate the gut and other visceral organs in the thoracic and abdominopelvic cavities. Recent studies show that the VN has anti-inflammatory effects via the release of acetylcholine, in what is known as the cholinergic anti-inflammatory pathway (CAIP). In the gut immune system, the CAIP is proposed to be activated directly by signals from the gut and indirectly by signals from the liver, which receives gut-derived bioactive substances via the portal vein and senses the status of the gut. The gut-brain axis and liver-brain-gut reflex arc regulate a wide variety of peripheral immune cells to maintain homeostasis in the gut. Therefore, targeting the neural reflex by methods such as VN stimulation is now under investigation for suppressing intestinal inflammation associated with IBDs. In this review, we describe the role of the VN in the regulation of intestinal immunity, and we discuss novel therapeutic approaches for IBDs that target neuroimmune interactions.