CD71, also known as transferrin receptor 1 (TfR1), is a type II transmembrane glycoprotein that exists as a disulfide-linked homodimer on the cell surface. It plays a crucial role in cellular iron uptake by binding to iron-bound transferrin and mediating its internalization through receptor-mediated endocytosis. CD71 is widely expressed on proliferating cells, including erythroid precursors, activated immune cells, and various cancer cells. It is also a preferred entry receptor for several viruses, such as arenaviruses and hepatitis C virus. In addition, CD71 has been identified as a marker for cell proliferation and activation, and its expression is often used in the diagnosis and prognosis of hematological diseases.