Regulation of T cells in the intestinal mucosa

It is intuitively apparent that the mucosal immune system protecting the gastrointestinal tract is unique. The lymphocytes lining the gut must be able to defend against bacterial infection as well as permit the absorption of antigenic food particles. Parenteral administration of antigens results in activation of lymphocytes, whereas oral administration of the same antigens results in active suppression of a systemic immune response. Failure to downregulate intestinal immune responses to ubiquitous lumenal antigens results in chronic inflammation. At the regulatory core of intestinal immune responses are T cells residing in the epithelium, lamina propria, and Peyer's patches. This review highlights exciting progress in our understanding of the regulation of intestinal immune responses. Of particular interest is the extrathymic development of intraepithelial lymphocytes and the characterization of novel class l-like molecules on intestinal epithelial cells. Animal models of inflammatory bowel disease have also elucidated critical cytokine interactions necessary for the regulation of lamina propria lymphocytes.