Ferritin Localization on the Erythroblast Cell Membrane and Ropheocytosis in Hypersiderotic Human Bone Marrows

1. Preferential ferritin localization on specialized areas of the plasma membrane of erythroblasts with subsequent invagination into ropheocytotic vesicles, and the occurrence of ropheocytosis without ferritin being present in the vesicles, has been previously described.

2. In a study of bone marrows from patients with hypersiderosis we have confirmed the previous observations, but we frequently found nonferritin ropheocytosis in erythroblasts adjacent to ferritin laden reticulum cells. In addition, ferritin localization along the outer surface of erythroblasts was noted, particularly between continuous surfaces of two adjacent erythroblasts. Such intercellular accumulations of ferritin were not necessarily associated with a high ferritin content of adjacent cells.

3. These observations did not favor the hypothesis that ferritin iron was being transferred directly from reticulum cells to adjacent erythroblasts. It is suggested that the accumulation of ferritin along extended stretches of the erythroblast surface may signify that iron which is detached from siderophilin but not immediately transported across the cell membrane is incorporated into apoferritin produced on the cell membrane.