Fig. 1.

Development and functions of resident intestinal macrophages. In the healthy gut, Ly6C^hi monocytes are constantly recruited from the blood into the gut to replenish the resident macrophage pool. Ly6C^hi monocytes transit through a series of phenotypically defined stages to eventually become mature CX3CR1^hiMHCII^hiLy6C^low macrophages in the lamina propria and muscularis. These macrophages are hyporesponsive to bacterial ligands, constitutively produce IL-10 and have multiple crucial functions in gut homeostasis including Treg expansion, epithelial maintenance, luminal sampling and bacterial killing