The broad repertoire of functions within the gastrointestinal tract demands close co-ordination between various tissues and regions of the gut. It is no longer reasonable to consider the gut as a compartmentalized organ, in which secretion, motor function, sensory perception and immune function operate independently. In health, recruitment and co-ordination of these systems is largely accomplished through the nervous system but also through the mucosal immune system. Interactions between the immune system and neuroendocrine system are evident in the innervation of immune organs, the effects of neurocrine factors on immune cells and neuroendocrine responses to cytokines derived from immunological cells. 1, 2 The mucosal immune system may even become more important in certain disease states as illustrated by the trophic effect of inflammation on smooth muscle cells. 3

The pivotal role of the enteric nervous system (ENS) in co-ordinating and integrating various components of gut function is reflected in its complex circuitry that receives inputs from the cephalic brain and the autonomic nervous system as well as in its ability to respond to signals from the immune system of the gut. 4 The mucosal immune system is responsible for discriminating between useful and harmful components of lumenal content, and for neutralizing noxious agents by humoral or cell-mediated immune responses. The immune system may also recruit other tissues in