Fig. 2.

Ferritin in RBC iron homeostasis. Macrophages phagocytize senescent RBCs directly, as well as taking up circulating hemoglobin–haptoglobin complexes (Hgb–Hp) via CD163 receptor-mediated endocytosis. This allows the macrophage to recycle iron via HMOX1, where hemoglobin is broken down into biliverdin, carbon monoxide and the free iron of the labile iron pool. It can then be incorporated into intracellular ferritin, preventing the formation of toxic free radicals. Once complexed, it is then stable for storage or transport into the plasma circulation.