Establishing Epithelial-Immune Cell Co-Cultures: Effects on Epithelial Ion Transport and Permeability

The epithelial lining of the gastrointestinal tract is constantly exposed to a vast array of antigenic and potentially disease-evoking material derived from the diet and gut microflora. Thus, this single cell thick layer of cells (mainly transporting enterocytes, but also mucin-secreting goblet cells, enteroendocrine cells, and defensin-producing Paneth cells) stands as sentinel at the boundary between the external world and the body proper, where it must restrict the entry of potentially noxious substances while simultaneously absorbing nutrients. While regulation of the homeostatic role of the enteric epithelium has been traditionally considered the remit of the neuroendocrine system, it has become increasingly apparent that immune cells can directly, and indirectly, affect many aspects of epithelial function, including electrolyte transport, nutrient absorption, permeability, and the synthesis and release of messenger molecules (1 ). Much of our current knowledge of immunomodulation of epithelial function has been obtained from in vitro co-culture studies, where model epithelia are juxtaposed to different immune cell types or immune mediators (2 -5 ).