Freeze‐Fracture Study of Malaria Sporozoites: Antibody‐Induced Changes of the Pellicular Membrane*

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Abstract
Plasmodium cynomolgi, P. knowlesi and P. berghei sporozoites, before and after incubation with immune serum [from Alumice and from Macaca mulatta] were studied after freeze-fracture by EM. There were evenly distributed numerous intramembranous particles (IMP) on the P face of the outer membrane. The E face of the plasma membrane had fewer IMP than its P face. The E face of the intermediate membrane had few IMP and also linear arrays of slightly raised ridges running the length of the parasite. The P face of the intermediate membrane had many IMP aligned along the long axis of the sporozoite. On the P face of the inner membrane, IMP were arranged in very distinct rows conforming to the long axis of the parasite; the E face of this membrane had a few randomly distributed IMP. A prominent change in the sporozoite incubated in immune serum was the appearance of a layer of aggregated particles around the parasite. The P face of the plasma membrane had several clear areas devoid of IMP and IMP aggregates. No changes were seen in the other fractured faces of the pellicle. Immune serum may act only on the P face of the plasma membrane.