Interaction of bacteria and bacterial toxins with intestinal epithelial cells.

The epithelium of the intestinal tract is a key barrier between the external environment and the internal body environment. Intestinal epithelial cells are targets for luminal bacteria and viruses and must discriminate between pathogenic and nonpathogenic commensal organisms. Pathogenic bacteria and their secreted products influence epithelial cell function and induce diarrhea by numerous mechanisms that range from an effect on epithelial cell-cell associations to intracellular signal transduction pathways. These effects lead to an inflammatory response and an influx of neutrophils into the epithelium. Infiltrating neutrophils, in turn, signal to epithelial cells, induce a secretory response, and perpetuate the diarrhea. Conversely, commensal bacteria have the ability to suppress inflammatory responses by inhibiting specific intracellular signal transduction pathways. Some of these diverse host pathogenic responses are addressed in this review.