ABSTRACT
The intestine has an effective defence mechanism that purges the bowel of foreign threats through an integrated system of mast cells, the enteric nervous system (ENS) and effectors made-up of the musculature, secretory epithelium and blood vasculature. Enteric mast cells acquire and retain memory of antigenic threats as they appear and reappear in the digestive tract throughout a lifetime. Antibody-based memory enables mast cells to detect and respond to forbidden antigens whenever they appear. Insofar as mast cells send signals to the enteric nervous system, their function is analogous to sensory neurons. Like sensory neurons, mast cells detect and signal. They release chemical signals (e.g. histamine) that alert the ENS to the presence within the lumen of a potential threat. The ENS responds by calling-up from its library of programs a coordinated cascade of events that quickly purges the threat. The program starts by stimulating the secretion of H2O, electrolytes and mucous to flush the antigen from the cryptic depths of the mucosa and suspend it in solution in the lumen. This is followed by initiation of powerful propulsive motility that rapidly moves the secretions and suspended antigen toward the anal outlet. These defensive events are accompanied by the side effects of abdominal distress, urgency and diarrhoea.
