Plasmodium falciparum: immune pressure in Saimiri sciureus monkeys can select for a parasite population inducing a protective immunity that is not controlled by antibody

Rosetting is associated with increased Plasmodium falciparum in vivo multiplication rate in the Saimiri sciureus monkey

Severe Plasmodium falciparum malaria in African children is associated with high peripheral parasite densities and high rate of rosette-forming parasites. To explore the relationship between rosette formation and parasite density in vivo, we compared the multiplication rate of a rosette-forming variant (varO) of the Palo Alto line with a sibling non-rosetting variant (varR) in splenectomized Saimiri monkeys. The multiplication rate of varO parasites was 1.5-fold higher than that of the varR variant. This indicates that rosetting is indeed associated with high parasite multiplication efficiency in vivo and, as such, may contribute to the high parasite densities observed in severe malaria.

Blood typing in Saimiri sciureus monkeys: influence of anti-red blood cell alloantibodies on Plasmodium falciparum parasitaemia in vivo

The Saimiri sciureus monkey is a well-established host for experimental studies with human malaria parasites. During the course of iterative inoculations with Plasmodium falciparum parasitised red blood cells (RBC), anti-RBC alloantibodies were detected in the sera of two of eight Saimiri monkeys. These anti-RBC antibodies were further used to investigate RBC phenotypes in 35 colony-reared Saimiri monkeys by flow cytometry. Three RBC phenotypes (named I-III) were observed. Their distribution was I (86%), II (11%) and III (3%). Using the Palo Alto FUP-2 strain, a variant P. falciparum line insensitive to hyperimmune serum and the passive transfer of anti-RBC alloantibodies, a dramatic drop in parasite growth was documented in an incompatible monkey.

Pfsbp1, a Maurer's cleft Plasmodium falciparum protein, is associated with the erythrocyte skeleton

Antibodies from hyperimmune monkey sera, selected by absorption to Plasmodium falciparum-infected erythrocytes, and elution at acidic pH, allowed us to characterize a novel parasite protein, Pfsbp1 (P. falciparum skeleton binding protein 1). Pfsbp1 is an integral membrane protein of parasite-induced membranous structures associated with the erythrocyte plasma membrane and referred to as Maurer's clefts. The carboxy-terminal domain of Pfsbp1, exposed within the cytoplasm of the host cell, interacts with a 35 kDa erythrocyte skeletal protein and might participate in the binding of the Maurer's clefts to the erythrocyte submembrane skeleton. Antibodies to the carboxy- and amino-terminal domains of Pfsbp1 labelled similar vesicular structures in the cytoplasm of Plasmodium chabaudi and Plasmodium berghei-infected murine erythrocytes, suggesting that the protein is conserved among malaria species, consistent with an important role of Maurer's cleft-like structures in the intraerythrocytic development of malaria parasites.