Neuroimmune mechanisms in functional bowel disorders

The enteric nervous system regulates diverse functions including gastrointestinal motility and nociception. The sensory neurons detect mechanical and chemical stimuli while motor neurons control peristalsis and secretion. In addition to this extensive neuronal network, the gut also houses a highly specialised immune system which plays an important role in the induction and maintenance of tolerance to food and other luminal antigens and in the protection of the epithelial barrier against pathogenic invasion. It is now increasingly recognised that the gastrointestinal immune system and the enteric nervous system closely interact. This review will focus on two common functional gastrointestinal disorders in which neuroimmune interaction is involved in the pathophysiology: i.e. postoperative ileus and irritable bowel syndrome. Postoperative ileus arises after almost every abdominal surgical procedure. Handling of the bowel results in local inflammation and activation of inhibitory neuronal pathways resulting in a generalised impairment of gastrointestinal motor function or ileus. On the other hand, postinfectious irritable bowel syndrome (PI-IBS) occurs in 10 to 30% of patients who suffer from infectious gastroenteritis. PI -IBS patients develop abnormal gastrointestinal sensitivity, motility and secretion which contribute to abdominal pain and discomfort, bloating and abnormal bowel function (diarrhoea and/or constipation). Biopsy studies revealed persistent low-grade inflammation and altered immunological function which may lead to abnormal pain perception and motor activity within the gastrointestinal tract.