The CD71 Antibody recognizes a 95-kDa disulfide-bonded homodimeric type-II transmembrane glycoprotein called transferring receptor (TfR). CD71 antigen is expressed typically at high level on all proliferating cell, activated cells and erythroblasts or reticulocytes that require iron, but not on resting peripheral blood leucocytes and mature erythrocytes. CD71 antigen is also expressed at high level on cells of most neoplastic cell lines and 29-32% of bone marrow cells. A soluble form of CD71 in serum (plasma) exists besides a membrane form. Monitoring the soluble form of CD71 antigen in plasma is a diagnostic marker of anemia besides assaying plasma ferritin.