Figure 9. Iron uptake by T lymphocytes and hepatocytes.

Transferrin-bound iron is internalized by TFR1-mediated endocytosis in hepatocytes [47] and T-lymphocytes [48]. Non-transferrin-bound iron (NTBI) is taken up by hepatocytes via Zrt- and Irt-like Protein 14 (ZIP14, Slc39A14; after ferric reductase-mediated reduction of Fe³⁺ to Fe²⁺) [49], [50]. Divalent metal transporter 1 (DMT1) was the first described NTBI (Fe²⁺) transporter [51], although recent data suggests it may not be important for the iron loading of the hepatocyte [52]. We hypothesize that ZIP14 and DMT1 are not involved in the uptake of ferric citrate by T lymphocytes (red×symbols). Clathrin-mediated endocytosis of ferric citrate does not occur in hepatocytes and T lymphocytes (red×symbols). T lymphocytes and hepatocytes selectively take up the oligomer Fe₃Cit₃, which suggests the existence of a specific transporter (green symbols).