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The intestinal epithelium acts as a barrier to the external environment contained within the gut lumen. (1) The barrier is not complete, with the intestine allowing sampling of macromolecules (2) and active absorption of nutrients. It has become increasingly apparent that the enterocyte itself acts as an immune cell, as evidenced by the existence of receptors for bacterial products (3) and its ability to express a wide variety of molecules on its surface that contain immunoglobulin domains. The epithelial cell also expresses proteins that may interact with immunocytes within the intestine. These include surface molecules such as class II major histocompatibility complex (MHC) and cytokines that are released from the epithelium such as chemokines or interleukin (IL)-6.

These signaling proteins enable the epithelial cell to orchestrate events in the intestine. We have hypothesized that changes...

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