An Ultrastructural Study of the Red Pulp of the Spleen in Malaria

An ultrastructural study was undertaken of the spleen of a rhesus monkey infected with Plasmodium knowlesi to determine whether the spleen is able to pit malaria parasites from red cells. It was found that in the spleen parasitized cells are: (1) phagocytized in toto by cordal macrophages, (2) pitted of parasites, and (3) hemolyzed in the splenic microvasculature. Phagocytosis of the entire parasitized red cell appears to occur most frequently of the three mechanisms and probably accounts for most of the anemia. Pitting of parasitized red cells may account in part for the hemolysis in excess of the number of parasitized red cells seen in malaria. The red cells that have had their parasites removed would become spherocytic and hence, would be more susceptible to removal from the circulation during subsequent passages through the spleen.