FIG. 3.
Iron recycling by macrophages. Almost 20–30 mg of Iron is recycled by the macrophages and reused for erythropoiesis daily. Macrophages phagocytize senescent red blood cells, and the heme-associated iron released by HO-1 activity is exported out by Fpn for loading to Tf. Macrophages also acquire heme by endocytosis of haptoglobin and hemopexin. In addition, these cells possess the capability of acquiring iron by the Tf/TfR pathway and exporting heme through the FLVCR receptor. CD173 (marker of early hematopoiesis) and CD91 (low density lipoprotein receptor 1 or α-2-macroglobulin receptor). Cp, ceruloplasmin; Fe2+, ferrous iron; Fe3+, ferric iron; FLVCR, feline leukemia virus subgroup C receptor; Fpn, ferroportin; HO-1, heme-oxygenase-1; Hp, hephaestin; TfR, transferrin receptor.