title: Ultrastructural study of erythrophagocytosis in the rat bone marrow. I. Red cell engulfment by reticulum cells.
abstract: Previous light microscopic studies have revealed the erythroclastic potential of the rat bone marrow reticulum cells, and call for ultrastructural study of the finer details of this process. Electron microscopy of rat bone marrow which had been stimulated to increase its erythrophagic activity, either by splenectomy or by transfusion of heat denatured erythrocytes, confirmed the central reticulum cell of erythroblastic islands as the main phagocytic cell in bone marrow erythroclasia. The early digestive vacuoles, which are formed by the fusion of erythrophagic vacuoles with lysosomes, correspond to the acidophilic, globular structures which characterize erythrophagocytosis as observed by light microscopy. By forming intrasinusoidal protrusions, the bone marrow reticulum cells engulf circulating effete red cells. The engulfed red cells are then transported intracellularly across the sinusoidal wall for final disintegration in the intraparenchymal part of the reticulum cell. This transmural mode of erythrophagocytosis by reticulum cells most probably demonstrates the fundamental phagocytic mechanism of the bone marrow part of the reticulo-endothelial system. Transmural transport of reticulocytes adherent to reticulum cells during the formation of protrusions illustrates a possible mechanism for liberation of red cells from the bone marrow.
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000648:ultrastructure*; D001854:Bone Marrow Cells; D002465:Cell Movement; D002467:Cell Nucleus / Q000648:ultrastructure; D003593:Cytoplasm / Q000648:ultrastructure; D004900:Erythroblasts / Q000648:ultrastructure; D017707:Erythrocyte Transfusion; D004912:Erythrocytes / Q000648:ultrastructure*; D005260:Female; D006358:Hot Temperature; D008247:Lysosomes / Q000648:ultrastructure; D010587:Phagocytosis; D051381:Rats; D012156:Reticulocytes / Q000648:ultrastructure; D013154:Spleen / Q000502:physiology; D013156:Splenectomy; D014184:Transplantation, Homologous