Brain-gut axis and mucosal immunity: a perspective on mucosal psychoneuroimmunology

The role of the brain-gut axis has traditionally been investigated in relation to intestinal motility, secretion, and vascularity. More recently, the concept of brain-gut dialogue has extended to the relationship between the nervous system and mucosal immune function. There is compelling evidence for a reciprocal or bi-directional communication between the immune system and the neuroendocrine system. This is mediated, in part, by shared ligands (chemical messengers) and receptors that are common to the immune and nervous systems. Although the concept of psychoneuroimmunology and neuroimmune cross-talk has been studied primarily in the context of the systemic immune system, it is likely to have special significance in the gut. The mucosal immune system is anatomically, functionally, and operationally distinct from the systemic immune system and is subject to independent regulatory signals. Furthermore, the intestinal mucosal immune system operates in a local milieu that depends on a dense innervation for its integrity, with juxtaposition of neuroendocrine cells and mucosal immune cells. An overview of evidence for the biologic plausibility of a brain-gut-immune axis is presented and its potential relevance to mucosal inflammatory disorders is discussed.