Hematopoietic tissue in malaria: facilitation of erythrocytic recycling by bone marrow in Plasmodium berghei-infected mice.

In P. berghei murine malaria, parasitized erythrocytes and nonparasitized reticulocytes were concentrated in the lumen of venous sinuses of bone marrow, adherent to endothelium and to one another. Merozoites maturing in erythrocytes contained in venous sinuses are so positioned against adherent reticulocytes that when they break out they can penetrate adherent reticulocytes without significant extracellular exposure. Merozoites from cells not adjacent to reticulocytes would spill into the plasma and be opsonized and phagocytized. The vascular sinuses of bone marrow therefore appear to be sites where erythrocytic parasitization is secured and where the severity and chronicity of the erythrocytic phase of the disease is regulated in P. berghei and, perhaps, other reticulocyte-prone malarias. In P. chabaudi, where fully mature erythrocytes rather than reticulocytes are preferentially parasitized, parasitized erythrocytes show far less predilection for bone marrow.