Transferrin (TF) is a circulating iron-transport protein that safely delivers iron to cells throughout the body 1. Primary function: TF binds ferric iron in plasma and delivers it to cells via transferrin receptor 1 (TfR1)-mediated endocytosis, which internalizes the TF-iron complex through clathrin-coated pits into early endosomes 1. Mechanism: Upon acidification in endosomes, iron dissociates from TF, which is then recycled back to the cell surface for reuse. TfR2, a second TF receptor predominantly in hepatocytes and erythroid precursors, functions in iron sensing by forming a complex with the hemochromatosis protein HFE and regulating hepcidin expression 1. In erythroid cells, TfR2 also partners with the erythropoietin receptor to regulate red blood cell production. Disease relevance: Defects in TfR2 cause hereditary hemochromatosis through dysregulated hepcidin and systemic iron overload 1. Atransferrinemia, caused by TF deficiency, represents a rare but severe iron metabolism disorder. Clinical significance: Apo-transferrin (iron-free TF) has therapeutic potential for atransferrinemia, iron overload conditions, and β-thalassemia anemia in animal models 1. Additionally, pathogenic organisms including Plasmodium vivax and New World arenaviruses exploit TfR1 for cellular entry, highlighting TF's role in host-pathogen interactions.