Immune-epithelial interactions in host defense

Over the past 15 years, it has become very clear that the immune system can have profound effects on epithelial function. Acute immune-mediated change s in epithelial physiology are beneficial to host defense against enteric p athogens. For example, ion secretion washes out noxious luminal contents an d increased permeability allows phagocytic cells and antibodies to enter th e gut lumen. However, ongoing immune activation results in chronic effects that may be pathophysiologic. Responses are mediated by soluble immune medi ators that act directly on the epithelium, or indirectly via nerves that al so serve to amplify the epithelial response. Here, we will review some of t he recent advances that have been made in the field of immunophysiology. Th e effect of mast cells on transport functions of the epithelium will be rev iewed, with emphasis on the consequence of interactions between mast cells and nerves. The use of in vitro coculture systems has recently provided con siderable information on the effects of neutrophils, eosinophils, monocytes , and lymphocytes on epithelial functions; the contribution of each immunoc yte will be highlighted. Finally, we will describe evidence for the active participation of the epithelium in mucosal immune activation, including pat hogen or cytokine induced epithelial cytokine synthesis or secretion and ad hesion molecule expression.