CD71, also known as the transferrin receptor (TfR1), is a transmembrane glycoprotein whose primary function is to mediate cellular uptake of iron from a plasma glycoprotein, transferrin. CD71 is a widely used marker for cell activation or proliferation of lymphocytes as transferrin receptor expression is undetectable in resting T and B lymphocytes, but increases significantly upon lymphocyte antigen activation (Galbraith, R.M., et al 1981). Rapidly proliferating cells and energy-requiring cells, like cancer cells, osteoclasts (Roodman, G.D., 2009), and activated lymphocytes (Wieland, E., et al, 2016) express high levels of CD71 due to increased iron demand. TfR1 is seen as an efficient drug delivery system for cancer patients as it can mediate extracellular transferrin conjugated molecules for treatment (Luria-Perez, R., et al, 2016).
