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are referred elsewhere [14] for a comprehensive review of regulation of the epithelial barrier function. Below the epithelium lies the mucosa, which is densely populated by resident immune cells, including CD4+ and CD8+ T effector and regulatory T cells, antibodysecreting B cells, and mononuclear phagocytes (macrophages and dendritic cells (DCs). Eosinophils are also resident cells in the normal intestinal mucosa