IGHG3 and hemochromatosis type 1: We have previously developed a mouse/human chimeric IgG3 antibody specific for TfR1 (ch128.1/IgG3) that does not cross-react with TfR2, nor does it interfere with the binding of the TfR1 ligands transferrin or the hemochromatosis protein (HFE) to the receptor [20,21,22].