Acute and chronic inflammation cause many changes in total body iron metabolism including the sequestration of iron in phagocytic cells of the reticuloendothelial system. This change in iron metabolism contributes to the development of the anemia of inflammation. MTP1, the duodenal enterocyte basolateral iron exporter, is also expressed in the cells of the reticuloendothelial system (RES) and is likely to be involved in iron recycling of these cells. In this study, we use a lipopolysaccharide model of the acute inflammation in the mouse and demonstrate that MTP1 expression in RES cells of the spleen, liver, and bone marrow is down-regulated by inflammation. The down-regulation of splenic expression of MTP1 by inflammation was also observed in a Leishmania donovani model of chronic infection. The response of MTP1 to lipopolysaccharide (LPS) requires signaling through the LPS receptor, Toll-like receptor 4 (TLR4). In mice lacking TLR4, MTP1 expression is not altered in response to LPS. In addition, mice lacking tumor necrosis factor-receptor 1a respond appropriately to LPS with down-regulation of MTP1, despite hyporesponsiveness to tumor necrosis factor-␣ signaling, suggesting that this cytokine may not be required for the LPS effect. We hypothesize that the iron sequestration in the RES system that accompanies inflammation is because of down-regulation of MTP1.Iron is an essential nutrient for growth and development of eucaryotes and most prokaryote species. A normal individual will absorb ϳ1 mg of elemental iron a day through the duodenum, to match an equivalent daily physiologic loss. The plasma turnover of iron is ϳ10 -20 mg a day and one source of this pool is iron released from the reticuloendothelial system (RES).