Studies on transferrin receptor of macrophages in iron metabolism Part 2. Regulation of tranferrin receptors on alveolar macorophages in iron-overloaded and iron-deficient conditions

Transferrin receptors (TfR) are involved in the first step of iron uptake into cells. To clarify the changes in TfR under various conditions, radiobinding assay of (125)I-labeled iron-saturated transferrin was performed in alveolar macrophages from 2 patients with idiopathic hemo-chromatosis and iron-overloaded or iron-deficient guinea pigs. Patients with idiopathic hemochromatosis showed a reduction in the Fe-TfR count on alveolar macrophages (5.0×10(4)/cell) as compared to that in healthy individuals (19.88±8.19×10(4)/cell). Concerning the Fe-TfR binding constant, no differnce was observed between patients with idiopathic hemochromatosis and healthy controls. The Fe-TfR count on alveolar macrophages was significantly lower in iron-overloaded guined pigs than in normal cntrols. The count was significantly elevated in iron-deficient guinea pigs. Concerning the Fe-TfR binding constant, none of the iron-overloaded and iron-deficient groups showed any significant difference from the normal controls. These findings suggest that experimentally-induced iron overload and iron deficiency may be autoregulated by intracellular iron levels.