ABSTRACT
Most body iron is utilized for production of erythrocytes: about 20 mg per day. This is much more than the amount of approximately 1 mg iron that needs to be absorbed from the gut to compensate for normal daily iron losses. After release from the bone marrow erythrocytes circulate for 100-120 days. During this period, they show physiological aging and are finally selected by macrophages of the mononuclear phagocyte system (MPS) for destruction. Iron is removed from hemoglobin (Hb) and either released to the plasma for
redistribution and production of heme-, and other iron proteins, or stored in ferritin and hemosiderin. In conditions of hemolysis, erythrocyte life span is shortened and erythrophagocytosis is accelerated, leading to increased iron processing and iron overload. Erythrophagocytosis and MPS iron release are also modified in inflammation and hemochromatosis. Our understanding of iron handling by macrophages has increased considerably in recent years due to the discovery of several new genes involved in iron transport, and quantitative analysis of macrophage iron transport. The impact of acute and chronic changes in erythrophagocytosis and macrophage iron release on iron kinetics and internal iron distribution are much more important than changes in iron absorption, due to the vast amount of iron that is handled by the MPS each day.
