Lactoferrin-mediated transfer of iron to intracellular ferritin in human monocytes

Interactions of 125I-59Fe-lactoferrin with human monocytes were studied. After 4 hours of incubation, the uptake of 59Fe exceeded that of 125I. In dissociation studies the cellular 59Fe-activity was only partly dissociable during 16 h, whereas the 125I-activity could be released nearly completely. Disruption of the cells and studies on the cytosolic phase were performed employing gel-filtration and affinity chromatography. An appreciable amount of lactoferrin was found in the cytosolic phase. About 50% of the cytosolic 59Fe-activity was bound to ferritin. The results suggest that lactoferrin is internalized into monocytes and that iron is transferred to ferritin. These cellular events may contribute to an understanding of the accumulation of iron in the monocyte/macrophage system observed during inflammatory conditions.